diff --git a/src/tools/rust-analyzer/crates/hir-def/src/expr_store/lower.rs b/src/tools/rust-analyzer/crates/hir-def/src/expr_store/lower.rs
index 29871f5e04db..b7a482a85dbb 100644
--- a/src/tools/rust-analyzer/crates/hir-def/src/expr_store/lower.rs
+++ b/src/tools/rust-analyzer/crates/hir-def/src/expr_store/lower.rs
@@ -2141,26 +2141,10 @@ impl ExprCollector<'_> {
         block: ast::BlockExpr,
         mk_block: impl FnOnce(Option<BlockId>, Box<[Statement]>, Option<ExprId>) -> Expr,
     ) -> ExprId {
-        let block_has_items = {
-            let statement_has_item = block.statements().any(|stmt| match stmt {
-                ast::Stmt::Item(_) => true,
-                // Macro calls can be both items and expressions. The syntax library always treats
-                // them as expressions here, so we undo that.
-                ast::Stmt::ExprStmt(es) => matches!(es.expr(), Some(ast::Expr::MacroExpr(_))),
-                _ => false,
-            });
-            statement_has_item
-                || matches!(block.tail_expr(), Some(ast::Expr::MacroExpr(_)))
-                || (block.may_carry_attributes() && block.attrs().next().is_some())
-        };
-
-        let block_id = if block_has_items {
-            let file_local_id = self.expander.ast_id_map().ast_id(&block);
+        let block_id = self.expander.ast_id_map().ast_id_for_block(&block).map(|file_local_id| {
             let ast_id = self.expander.in_file(file_local_id);
-            Some(self.db.intern_block(BlockLoc { ast_id, module: self.module }))
-        } else {
-            None
-        };
+            self.db.intern_block(BlockLoc { ast_id, module: self.module })
+        });
 
         let (module, def_map) =
             match block_id.map(|block_id| (block_def_map(self.db, block_id), block_id)) {
diff --git a/src/tools/rust-analyzer/crates/hir-def/src/item_tree/pretty.rs b/src/tools/rust-analyzer/crates/hir-def/src/item_tree/pretty.rs
index 47c6eb13293f..51172c0a1ee3 100644
--- a/src/tools/rust-analyzer/crates/hir-def/src/item_tree/pretty.rs
+++ b/src/tools/rust-analyzer/crates/hir-def/src/item_tree/pretty.rs
@@ -353,8 +353,8 @@ impl Printer<'_> {
                 let MacroCall { path, ast_id, expand_to, ctxt } = &self.tree[it];
                 let _ = writeln!(
                     self,
-                    "// AstId: {:?}, SyntaxContextId: {}, ExpandTo: {:?}",
-                    ast_id.erase().into_raw(),
+                    "// AstId: {:#?}, SyntaxContextId: {}, ExpandTo: {:?}",
+                    ast_id.erase(),
                     ctxt,
                     expand_to
                 );
@@ -377,7 +377,7 @@ impl Printer<'_> {
     }
 
     fn print_ast_id(&mut self, ast_id: ErasedFileAstId) {
-        wln!(self, "// AstId: {:?}", ast_id.into_raw());
+        wln!(self, "// AstId: {ast_id:#?}");
     }
 }
 
diff --git a/src/tools/rust-analyzer/crates/hir-def/src/item_tree/tests.rs b/src/tools/rust-analyzer/crates/hir-def/src/item_tree/tests.rs
index 824fbfa5921a..abfff283ef64 100644
--- a/src/tools/rust-analyzer/crates/hir-def/src/item_tree/tests.rs
+++ b/src/tools/rust-analyzer/crates/hir-def/src/item_tree/tests.rs
@@ -35,23 +35,23 @@ use a::{c, d::{e}};
             #![no_std]
             #![doc = " another file comment"]
 
-            // AstId: 1
+            // AstId: ExternCrate[5A82, 0]
             pub(self) extern crate self as renamed;
 
-            // AstId: 2
+            // AstId: ExternCrate[7E1C, 0]
             pub(super) extern crate bli;
 
-            // AstId: 3
+            // AstId: Use[0000, 0]
             pub use crate::path::{nested, items as renamed, Trait as _};
 
-            // AstId: 4
+            // AstId: Use[0000, 1]
             pub(self) use globs::*;
 
             #[doc = " docs on import"]
-            // AstId: 5
+            // AstId: Use[0000, 2]
             pub(self) use crate::{A, B};
 
-            // AstId: 6
+            // AstId: Use[0000, 3]
             pub(self) use a::{c, d::{e}};
         "##]],
     );
@@ -75,18 +75,18 @@ extern "C" {
         "#,
         expect![[r##"
             #[on_extern_block]
-            // AstId: 1
+            // AstId: ExternBlock[0000, 0]
             extern "C" {
                 #[on_extern_type]
-                // AstId: 2
+                // AstId: TypeAlias[9FDF, 0]
                 pub(self) type ExType;
 
                 #[on_extern_static]
-                // AstId: 3
+                // AstId: Static[43C1, 0]
                 pub(self) static EX_STATIC = _;
 
                 #[on_extern_fn]
-                // AstId: 4
+                // AstId: Fn[452D, 0]
                 pub(self) fn ex_fn;
             }
         "##]],
@@ -124,39 +124,39 @@ enum E {
 }
         "#,
         expect![[r#"
-            // AstId: 1
+            // AstId: Struct[DFF3, 0]
             pub(self) struct Unit;
 
             #[derive(Debug)]
-            // AstId: 2
+            // AstId: Struct[C7A1, 0]
             pub(self) struct Struct {
                 #[doc = " fld docs"]
                 pub(self) fld,
             }
 
-            // AstId: 3
+            // AstId: Struct[DAC2, 0]
             pub(self) struct Tuple(
                 #[attr]
                 pub(self) 0,
             );
 
-            // AstId: 4
+            // AstId: Union[2DBB, 0]
             pub(self) union Ize {
                 pub(self) a,
                 pub(self) b,
             }
 
-            // AstId: 5
+            // AstId: Enum[7FF8, 0]
             pub(self) enum E
-                // AstId: 6
+                // AstId: Variant[C717, 0]
                 #[doc = " comment on Unit"]
                 Unit,
-                // AstId: 7
+                // AstId: Variant[AEAB, 0]
                 #[doc = " comment on Tuple"]
                 Tuple(
                     pub(self) 0,
                 ),
-                // AstId: 8
+                // AstId: Variant[4B1B, 0]
                 Struct {
                     #[doc = " comment on a: u8"]
                     pub(self) a,
@@ -185,23 +185,23 @@ trait Tr: SuperTrait + 'lifetime {
 }
         "#,
         expect![[r#"
-            // AstId: 1
+            // AstId: Static[B393, 0]
             pub static ST = _;
 
-            // AstId: 2
+            // AstId: Const[B309, 0]
             pub(self) const _ = _;
 
             #[attr]
             #[inner_attr_in_fn]
-            // AstId: 3
+            // AstId: Fn[75E3, 0]
             pub(self) fn f;
 
-            // AstId: 4
+            // AstId: Trait[2998, 0]
             pub(self) trait Tr {
-                // AstId: 6
+                // AstId: TypeAlias[9F08, 0]
                 pub(self) type Assoc;
 
-                // AstId: 7
+                // AstId: Fn[6C0C, 0]
                 pub(self) fn method;
             }
         "#]],
@@ -226,16 +226,16 @@ mod outline;
         expect![[r##"
             #[doc = " outer"]
             #[doc = " inner"]
-            // AstId: 1
+            // AstId: Module[CF93, 0]
             pub(self) mod inline {
-                // AstId: 3
+                // AstId: Use[0000, 0]
                 pub(self) use super::*;
 
-                // AstId: 4
+                // AstId: Fn[1B26, 0]
                 pub(self) fn fn_in_module;
             }
 
-            // AstId: 2
+            // AstId: Module[8994, 0]
             pub(self) mod outline;
         "##]],
     );
@@ -254,13 +254,13 @@ pub macro m2() {}
 m!();
         "#,
         expect![[r#"
-            // AstId: 1
+            // AstId: MacroRules[88CE, 0]
             macro_rules! m { ... }
 
-            // AstId: 2
+            // AstId: MacroDef[DC34, 0]
             pub macro m2 { ... }
 
-            // AstId: 3, SyntaxContextId: ROOT2024, ExpandTo: Items
+            // AstId: MacroCall[612F, 0], SyntaxContextId: ROOT2024, ExpandTo: Items
             m!(...);
         "#]],
     );
@@ -273,7 +273,7 @@ fn pub_self() {
 pub(self) struct S;
         "#,
         expect![[r#"
-            // AstId: 1
+            // AstId: Struct[42E2, 0]
             pub(self) struct S;
         "#]],
     )
diff --git a/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/mbe.rs b/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/mbe.rs
index 38fc4b3d118a..eea50d16f5a0 100644
--- a/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/mbe.rs
+++ b/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/mbe.rs
@@ -35,9 +35,9 @@ macro_rules! f {
     };
 }
 
-struct#0:1@58..64#14336# MyTraitMap2#0:2@31..42#ROOT2024# {#0:1@72..73#14336#
-    map#0:1@86..89#14336#:#0:1@89..90#14336# #0:1@89..90#14336#::#0:1@91..93#14336#std#0:1@93..96#14336#::#0:1@96..98#14336#collections#0:1@98..109#14336#::#0:1@109..111#14336#HashSet#0:1@111..118#14336#<#0:1@118..119#14336#(#0:1@119..120#14336#)#0:1@120..121#14336#>#0:1@121..122#14336#,#0:1@122..123#14336#
-}#0:1@132..133#14336#
+struct#0:MacroRules[8C8E, 0]@58..64#14336# MyTraitMap2#0:MacroCall[D499, 0]@31..42#ROOT2024# {#0:MacroRules[8C8E, 0]@72..73#14336#
+    map#0:MacroRules[8C8E, 0]@86..89#14336#:#0:MacroRules[8C8E, 0]@89..90#14336# #0:MacroRules[8C8E, 0]@89..90#14336#::#0:MacroRules[8C8E, 0]@91..93#14336#std#0:MacroRules[8C8E, 0]@93..96#14336#::#0:MacroRules[8C8E, 0]@96..98#14336#collections#0:MacroRules[8C8E, 0]@98..109#14336#::#0:MacroRules[8C8E, 0]@109..111#14336#HashSet#0:MacroRules[8C8E, 0]@111..118#14336#<#0:MacroRules[8C8E, 0]@118..119#14336#(#0:MacroRules[8C8E, 0]@119..120#14336#)#0:MacroRules[8C8E, 0]@120..121#14336#>#0:MacroRules[8C8E, 0]@121..122#14336#,#0:MacroRules[8C8E, 0]@122..123#14336#
+}#0:MacroRules[8C8E, 0]@132..133#14336#
 "#]],
     );
 }
@@ -75,12 +75,12 @@ macro_rules! f {
     };
 }
 
-fn#0:2@30..32#ROOT2024# main#0:2@33..37#ROOT2024#(#0:2@37..38#ROOT2024#)#0:2@38..39#ROOT2024# {#0:2@40..41#ROOT2024#
-    1#0:2@50..51#ROOT2024#;#0:2@51..52#ROOT2024#
-    1.0#0:2@61..64#ROOT2024#;#0:2@64..65#ROOT2024#
-    (#0:2@74..75#ROOT2024#(#0:2@75..76#ROOT2024#1#0:2@76..77#ROOT2024#,#0:2@77..78#ROOT2024# )#0:2@78..79#ROOT2024#,#0:2@79..80#ROOT2024# )#0:2@80..81#ROOT2024#.#0:2@81..82#ROOT2024#0#0:2@82..85#ROOT2024#.#0:2@82..85#ROOT2024#0#0:2@82..85#ROOT2024#;#0:2@85..86#ROOT2024#
-    let#0:2@95..98#ROOT2024# x#0:2@99..100#ROOT2024# =#0:2@101..102#ROOT2024# 1#0:2@103..104#ROOT2024#;#0:2@104..105#ROOT2024#
-}#0:2@110..111#ROOT2024#
+fn#0:MacroCall[D499, 0]@30..32#ROOT2024# main#0:MacroCall[D499, 0]@33..37#ROOT2024#(#0:MacroCall[D499, 0]@37..38#ROOT2024#)#0:MacroCall[D499, 0]@38..39#ROOT2024# {#0:MacroCall[D499, 0]@40..41#ROOT2024#
+    1#0:MacroCall[D499, 0]@50..51#ROOT2024#;#0:MacroCall[D499, 0]@51..52#ROOT2024#
+    1.0#0:MacroCall[D499, 0]@61..64#ROOT2024#;#0:MacroCall[D499, 0]@64..65#ROOT2024#
+    (#0:MacroCall[D499, 0]@74..75#ROOT2024#(#0:MacroCall[D499, 0]@75..76#ROOT2024#1#0:MacroCall[D499, 0]@76..77#ROOT2024#,#0:MacroCall[D499, 0]@77..78#ROOT2024# )#0:MacroCall[D499, 0]@78..79#ROOT2024#,#0:MacroCall[D499, 0]@79..80#ROOT2024# )#0:MacroCall[D499, 0]@80..81#ROOT2024#.#0:MacroCall[D499, 0]@81..82#ROOT2024#0#0:MacroCall[D499, 0]@82..85#ROOT2024#.#0:MacroCall[D499, 0]@82..85#ROOT2024#0#0:MacroCall[D499, 0]@82..85#ROOT2024#;#0:MacroCall[D499, 0]@85..86#ROOT2024#
+    let#0:MacroCall[D499, 0]@95..98#ROOT2024# x#0:MacroCall[D499, 0]@99..100#ROOT2024# =#0:MacroCall[D499, 0]@101..102#ROOT2024# 1#0:MacroCall[D499, 0]@103..104#ROOT2024#;#0:MacroCall[D499, 0]@104..105#ROOT2024#
+}#0:MacroCall[D499, 0]@110..111#ROOT2024#
 
 
 "#]],
@@ -171,7 +171,7 @@ fn main(foo: ()) {
     }
 
     fn main(foo: ()) {
-        /* error: unresolved macro unresolved */"helloworld!"#0:3@236..321#ROOT2024#;
+        /* error: unresolved macro unresolved */"helloworld!"#0:Fn[B9C7, 0]@236..321#ROOT2024#;
     }
 }
 
@@ -197,7 +197,7 @@ macro_rules! mk_struct {
 #[macro_use]
 mod foo;
 
-struct#1:1@59..65#14336# Foo#0:2@32..35#ROOT2024#(#1:1@70..71#14336#u32#0:2@41..44#ROOT2024#)#1:1@74..75#14336#;#1:1@75..76#14336#
+struct#1:MacroRules[E572, 0]@59..65#14336# Foo#0:MacroCall[BDD3, 0]@32..35#ROOT2024#(#1:MacroRules[E572, 0]@70..71#14336#u32#0:MacroCall[BDD3, 0]@41..44#ROOT2024#)#1:MacroRules[E572, 0]@74..75#14336#;#1:MacroRules[E572, 0]@75..76#14336#
 "#]],
     );
 }
diff --git a/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/proc_macros.rs b/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/proc_macros.rs
index b2e1adc3650d..d5ae6f8d885d 100644
--- a/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/proc_macros.rs
+++ b/src/tools/rust-analyzer/crates/hir-def/src/macro_expansion_tests/proc_macros.rs
@@ -181,9 +181,9 @@ fn foo(&self) {
     self.0. 1;
 }
 
-fn#0:1@45..47#ROOT2024# foo#0:1@48..51#ROOT2024#(#0:1@51..52#ROOT2024#&#0:1@52..53#ROOT2024#self#0:1@53..57#ROOT2024# )#0:1@57..58#ROOT2024# {#0:1@59..60#ROOT2024#
-    self#0:1@65..69#ROOT2024# .#0:1@69..70#ROOT2024#0#0:1@70..71#ROOT2024#.#0:1@71..72#ROOT2024#1#0:1@73..74#ROOT2024#;#0:1@74..75#ROOT2024#
-}#0:1@76..77#ROOT2024#"#]],
+fn#0:Fn[4D85, 0]@45..47#ROOT2024# foo#0:Fn[4D85, 0]@48..51#ROOT2024#(#0:Fn[4D85, 0]@51..52#ROOT2024#&#0:Fn[4D85, 0]@52..53#ROOT2024#self#0:Fn[4D85, 0]@53..57#ROOT2024# )#0:Fn[4D85, 0]@57..58#ROOT2024# {#0:Fn[4D85, 0]@59..60#ROOT2024#
+    self#0:Fn[4D85, 0]@65..69#ROOT2024# .#0:Fn[4D85, 0]@69..70#ROOT2024#0#0:Fn[4D85, 0]@70..71#ROOT2024#.#0:Fn[4D85, 0]@71..72#ROOT2024#1#0:Fn[4D85, 0]@73..74#ROOT2024#;#0:Fn[4D85, 0]@74..75#ROOT2024#
+}#0:Fn[4D85, 0]@76..77#ROOT2024#"#]],
     );
 }
 
diff --git a/src/tools/rust-analyzer/crates/hir-expand/src/builtin/quote.rs b/src/tools/rust-analyzer/crates/hir-expand/src/builtin/quote.rs
index 62b7b638e7b6..d5874f829ba5 100644
--- a/src/tools/rust-analyzer/crates/hir-expand/src/builtin/quote.rs
+++ b/src/tools/rust-analyzer/crates/hir-expand/src/builtin/quote.rs
@@ -277,8 +277,8 @@ mod tests {
         assert_eq!(quoted.to_string(), "hello");
         let t = format!("{quoted:#?}");
         expect![[r#"
-            SUBTREE $$ 937550:0@0..0#ROOT2024 937550:0@0..0#ROOT2024
-              IDENT   hello 937550:0@0..0#ROOT2024"#]]
+            SUBTREE $$ 937550:Root[0000, 0]@0..0#ROOT2024 937550:Root[0000, 0]@0..0#ROOT2024
+              IDENT   hello 937550:Root[0000, 0]@0..0#ROOT2024"#]]
         .assert_eq(&t);
     }
 
diff --git a/src/tools/rust-analyzer/crates/hir-expand/src/files.rs b/src/tools/rust-analyzer/crates/hir-expand/src/files.rs
index 8024823cbc5c..e8f6b82434ee 100644
--- a/src/tools/rust-analyzer/crates/hir-expand/src/files.rs
+++ b/src/tools/rust-analyzer/crates/hir-expand/src/files.rs
@@ -2,7 +2,7 @@
 use std::borrow::Borrow;
 
 use either::Either;
-use span::{AstIdNode, ErasedFileAstId, FileAstId, FileId, SyntaxContext};
+use span::{ErasedFileAstId, FileAstId, FileId, SyntaxContext};
 use syntax::{AstNode, AstPtr, SyntaxNode, SyntaxNodePtr, SyntaxToken, TextRange, TextSize};
 
 use crate::{
@@ -106,7 +106,7 @@ impl FileRange {
 /// It is stable across reparses, and can be used as salsa key/value.
 pub type AstId<N> = crate::InFile<FileAstId<N>>;
 
-impl<N: AstIdNode> AstId<N> {
+impl<N: AstNode> AstId<N> {
     pub fn to_node(&self, db: &dyn ExpandDatabase) -> N {
         self.to_ptr(db).to_node(&db.parse_or_expand(self.file_id))
     }
diff --git a/src/tools/rust-analyzer/crates/mbe/src/tests.rs b/src/tools/rust-analyzer/crates/mbe/src/tests.rs
index 769455faac04..56034516ef3b 100644
--- a/src/tools/rust-analyzer/crates/mbe/src/tests.rs
+++ b/src/tools/rust-analyzer/crates/mbe/src/tests.rs
@@ -3,7 +3,9 @@
 // FIXME: Move more of the nameres independent tests from
 // crates\hir-def\src\macro_expansion_tests\mod.rs to this
 use expect_test::expect;
-use span::{Edition, EditionedFileId, ErasedFileAstId, FileId, Span, SpanAnchor, SyntaxContext};
+use span::{
+    Edition, EditionedFileId, FileId, ROOT_ERASED_FILE_AST_ID, Span, SpanAnchor, SyntaxContext,
+};
 use stdx::format_to;
 use tt::{TextRange, TextSize};
 
@@ -24,7 +26,7 @@ fn check_(
         def_edition,
         SpanAnchor {
             file_id: EditionedFileId::new(FileId::from_raw(0), def_edition),
-            ast_id: ErasedFileAstId::from_raw(0),
+            ast_id: ROOT_ERASED_FILE_AST_ID,
         },
         SyntaxContext::root(Edition::CURRENT),
         decl,
@@ -37,7 +39,7 @@ fn check_(
     };
     let call_anchor = SpanAnchor {
         file_id: EditionedFileId::new(FileId::from_raw(1), call_edition),
-        ast_id: ErasedFileAstId::from_raw(0),
+        ast_id: ROOT_ERASED_FILE_AST_ID,
     };
     let arg_tt = syntax_bridge::parse_to_token_tree(
         call_edition,
@@ -110,8 +112,8 @@ fn unbalanced_brace() {
 "#,
         r#""#,
         expect![[r#"
-            SUBTREE $$ 1:0@0..0#ROOT2024 1:0@0..0#ROOT2024
-              SUBTREE {} 0:0@9..10#ROOT2024 0:0@11..12#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..0#ROOT2024 1:Root[0000, 0]@0..0#ROOT2024
+              SUBTREE {} 0:Root[0000, 0]@9..10#ROOT2024 0:Root[0000, 0]@11..12#ROOT2024
 
             {}"#]],
     );
@@ -133,25 +135,25 @@ fn token_mapping_smoke_test() {
 struct MyTraitMap2
 "#,
         expect![[r#"
-            SUBTREE $$ 1:0@0..20#ROOT2024 1:0@0..20#ROOT2024
-              IDENT   struct 0:0@34..40#ROOT2024
-              IDENT   MyTraitMap2 1:0@8..19#ROOT2024
-              SUBTREE {} 0:0@48..49#ROOT2024 0:0@100..101#ROOT2024
-                IDENT   map 0:0@58..61#ROOT2024
-                PUNCH   : [alone] 0:0@61..62#ROOT2024
-                PUNCH   : [joint] 0:0@63..64#ROOT2024
-                PUNCH   : [alone] 0:0@64..65#ROOT2024
-                IDENT   std 0:0@65..68#ROOT2024
-                PUNCH   : [joint] 0:0@68..69#ROOT2024
-                PUNCH   : [alone] 0:0@69..70#ROOT2024
-                IDENT   collections 0:0@70..81#ROOT2024
-                PUNCH   : [joint] 0:0@81..82#ROOT2024
-                PUNCH   : [alone] 0:0@82..83#ROOT2024
-                IDENT   HashSet 0:0@83..90#ROOT2024
-                PUNCH   < [alone] 0:0@90..91#ROOT2024
-                SUBTREE () 0:0@91..92#ROOT2024 0:0@92..93#ROOT2024
-                PUNCH   > [joint] 0:0@93..94#ROOT2024
-                PUNCH   , [alone] 0:0@94..95#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..20#ROOT2024 1:Root[0000, 0]@0..20#ROOT2024
+              IDENT   struct 0:Root[0000, 0]@34..40#ROOT2024
+              IDENT   MyTraitMap2 1:Root[0000, 0]@8..19#ROOT2024
+              SUBTREE {} 0:Root[0000, 0]@48..49#ROOT2024 0:Root[0000, 0]@100..101#ROOT2024
+                IDENT   map 0:Root[0000, 0]@58..61#ROOT2024
+                PUNCH   : [alone] 0:Root[0000, 0]@61..62#ROOT2024
+                PUNCH   : [joint] 0:Root[0000, 0]@63..64#ROOT2024
+                PUNCH   : [alone] 0:Root[0000, 0]@64..65#ROOT2024
+                IDENT   std 0:Root[0000, 0]@65..68#ROOT2024
+                PUNCH   : [joint] 0:Root[0000, 0]@68..69#ROOT2024
+                PUNCH   : [alone] 0:Root[0000, 0]@69..70#ROOT2024
+                IDENT   collections 0:Root[0000, 0]@70..81#ROOT2024
+                PUNCH   : [joint] 0:Root[0000, 0]@81..82#ROOT2024
+                PUNCH   : [alone] 0:Root[0000, 0]@82..83#ROOT2024
+                IDENT   HashSet 0:Root[0000, 0]@83..90#ROOT2024
+                PUNCH   < [alone] 0:Root[0000, 0]@90..91#ROOT2024
+                SUBTREE () 0:Root[0000, 0]@91..92#ROOT2024 0:Root[0000, 0]@92..93#ROOT2024
+                PUNCH   > [joint] 0:Root[0000, 0]@93..94#ROOT2024
+                PUNCH   , [alone] 0:Root[0000, 0]@94..95#ROOT2024
 
             struct MyTraitMap2 {
                 map: ::std::collections::HashSet<()>,
@@ -180,28 +182,28 @@ fn main() {
 }
 "#,
         expect![[r#"
-            SUBTREE $$ 1:0@0..63#ROOT2024 1:0@0..63#ROOT2024
-              IDENT   fn 1:0@1..3#ROOT2024
-              IDENT   main 1:0@4..8#ROOT2024
-              SUBTREE () 1:0@8..9#ROOT2024 1:0@9..10#ROOT2024
-              SUBTREE {} 1:0@11..12#ROOT2024 1:0@61..62#ROOT2024
-                LITERAL Integer 1 1:0@17..18#ROOT2024
-                PUNCH   ; [alone] 1:0@18..19#ROOT2024
-                LITERAL Float 1.0 1:0@24..27#ROOT2024
-                PUNCH   ; [alone] 1:0@27..28#ROOT2024
-                SUBTREE () 1:0@33..34#ROOT2024 1:0@39..40#ROOT2024
-                  SUBTREE () 1:0@34..35#ROOT2024 1:0@37..38#ROOT2024
-                    LITERAL Integer 1 1:0@35..36#ROOT2024
-                    PUNCH   , [alone] 1:0@36..37#ROOT2024
-                  PUNCH   , [alone] 1:0@38..39#ROOT2024
-                PUNCH   . [alone] 1:0@40..41#ROOT2024
-                LITERAL Float 0.0 1:0@41..44#ROOT2024
-                PUNCH   ; [alone] 1:0@44..45#ROOT2024
-                IDENT   let 1:0@50..53#ROOT2024
-                IDENT   x 1:0@54..55#ROOT2024
-                PUNCH   = [alone] 1:0@56..57#ROOT2024
-                LITERAL Integer 1 1:0@58..59#ROOT2024
-                PUNCH   ; [alone] 1:0@59..60#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..63#ROOT2024 1:Root[0000, 0]@0..63#ROOT2024
+              IDENT   fn 1:Root[0000, 0]@1..3#ROOT2024
+              IDENT   main 1:Root[0000, 0]@4..8#ROOT2024
+              SUBTREE () 1:Root[0000, 0]@8..9#ROOT2024 1:Root[0000, 0]@9..10#ROOT2024
+              SUBTREE {} 1:Root[0000, 0]@11..12#ROOT2024 1:Root[0000, 0]@61..62#ROOT2024
+                LITERAL Integer 1 1:Root[0000, 0]@17..18#ROOT2024
+                PUNCH   ; [alone] 1:Root[0000, 0]@18..19#ROOT2024
+                LITERAL Float 1.0 1:Root[0000, 0]@24..27#ROOT2024
+                PUNCH   ; [alone] 1:Root[0000, 0]@27..28#ROOT2024
+                SUBTREE () 1:Root[0000, 0]@33..34#ROOT2024 1:Root[0000, 0]@39..40#ROOT2024
+                  SUBTREE () 1:Root[0000, 0]@34..35#ROOT2024 1:Root[0000, 0]@37..38#ROOT2024
+                    LITERAL Integer 1 1:Root[0000, 0]@35..36#ROOT2024
+                    PUNCH   , [alone] 1:Root[0000, 0]@36..37#ROOT2024
+                  PUNCH   , [alone] 1:Root[0000, 0]@38..39#ROOT2024
+                PUNCH   . [alone] 1:Root[0000, 0]@40..41#ROOT2024
+                LITERAL Float 0.0 1:Root[0000, 0]@41..44#ROOT2024
+                PUNCH   ; [alone] 1:Root[0000, 0]@44..45#ROOT2024
+                IDENT   let 1:Root[0000, 0]@50..53#ROOT2024
+                IDENT   x 1:Root[0000, 0]@54..55#ROOT2024
+                PUNCH   = [alone] 1:Root[0000, 0]@56..57#ROOT2024
+                LITERAL Integer 1 1:Root[0000, 0]@58..59#ROOT2024
+                PUNCH   ; [alone] 1:Root[0000, 0]@59..60#ROOT2024
 
             fn main(){
                 1;
@@ -227,14 +229,14 @@ fn expr_2021() {
     const { 1 },
 "#,
         expect![[r#"
-            SUBTREE $$ 1:0@0..25#ROOT2024 1:0@0..25#ROOT2024
-              IDENT   _ 1:0@5..6#ROOT2024
-              PUNCH   ; [joint] 0:0@36..37#ROOT2024
-              SUBTREE () 0:0@34..35#ROOT2024 0:0@34..35#ROOT2024
-                IDENT   const 1:0@12..17#ROOT2024
-                SUBTREE {} 1:0@18..19#ROOT2024 1:0@22..23#ROOT2024
-                  LITERAL Integer 1 1:0@20..21#ROOT2024
-              PUNCH   ; [alone] 0:0@39..40#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..25#ROOT2024 1:Root[0000, 0]@0..25#ROOT2024
+              IDENT   _ 1:Root[0000, 0]@5..6#ROOT2024
+              PUNCH   ; [joint] 0:Root[0000, 0]@36..37#ROOT2024
+              SUBTREE () 0:Root[0000, 0]@34..35#ROOT2024 0:Root[0000, 0]@34..35#ROOT2024
+                IDENT   const 1:Root[0000, 0]@12..17#ROOT2024
+                SUBTREE {} 1:Root[0000, 0]@18..19#ROOT2024 1:Root[0000, 0]@22..23#ROOT2024
+                  LITERAL Integer 1 1:Root[0000, 0]@20..21#ROOT2024
+              PUNCH   ; [alone] 0:Root[0000, 0]@39..40#ROOT2024
 
             _;
             (const  {
@@ -255,13 +257,13 @@ fn expr_2021() {
         expect![[r#"
             ExpandError {
                 inner: (
-                    1:0@5..6#ROOT2024,
+                    1:Root[0000, 0]@5..6#ROOT2024,
                     NoMatchingRule,
                 ),
             }
 
-            SUBTREE $$ 1:0@0..8#ROOT2024 1:0@0..8#ROOT2024
-              PUNCH   ; [alone] 0:0@39..40#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..8#ROOT2024 1:Root[0000, 0]@0..8#ROOT2024
+              PUNCH   ; [alone] 0:Root[0000, 0]@39..40#ROOT2024
 
             ;"#]],
     );
@@ -279,13 +281,13 @@ fn expr_2021() {
         expect![[r#"
             ExpandError {
                 inner: (
-                    1:0@5..10#ROOT2024,
+                    1:Root[0000, 0]@5..10#ROOT2024,
                     NoMatchingRule,
                 ),
             }
 
-            SUBTREE $$ 1:0@0..18#ROOT2024 1:0@0..18#ROOT2024
-              PUNCH   ; [alone] 0:0@39..40#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..18#ROOT2024 1:Root[0000, 0]@0..18#ROOT2024
+              PUNCH   ; [alone] 0:Root[0000, 0]@39..40#ROOT2024
 
             ;"#]],
     );
@@ -305,26 +307,26 @@ fn expr_2021() {
     break 'foo bar,
 "#,
         expect![[r#"
-            SUBTREE $$ 1:0@0..76#ROOT2024 1:0@0..76#ROOT2024
-              LITERAL Integer 4 1:0@5..6#ROOT2024
-              PUNCH   ; [joint] 0:0@41..42#ROOT2024
-              LITERAL Str literal 1:0@12..21#ROOT2024
-              PUNCH   ; [joint] 0:0@41..42#ROOT2024
-              SUBTREE () 0:0@39..40#ROOT2024 0:0@39..40#ROOT2024
-                IDENT   funcall 1:0@27..34#ROOT2024
-                SUBTREE () 1:0@34..35#ROOT2024 1:0@35..36#ROOT2024
-              PUNCH   ; [joint] 0:0@41..42#ROOT2024
-              SUBTREE () 0:0@39..40#ROOT2024 0:0@39..40#ROOT2024
-                IDENT   future 1:0@42..48#ROOT2024
-                PUNCH   . [alone] 1:0@48..49#ROOT2024
-                IDENT   await 1:0@49..54#ROOT2024
-              PUNCH   ; [joint] 0:0@41..42#ROOT2024
-              SUBTREE () 0:0@39..40#ROOT2024 0:0@39..40#ROOT2024
-                IDENT   break 1:0@60..65#ROOT2024
-                PUNCH   ' [joint] 1:0@66..67#ROOT2024
-                IDENT   foo 1:0@67..70#ROOT2024
-                IDENT   bar 1:0@71..74#ROOT2024
-              PUNCH   ; [alone] 0:0@44..45#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..76#ROOT2024 1:Root[0000, 0]@0..76#ROOT2024
+              LITERAL Integer 4 1:Root[0000, 0]@5..6#ROOT2024
+              PUNCH   ; [joint] 0:Root[0000, 0]@41..42#ROOT2024
+              LITERAL Str literal 1:Root[0000, 0]@12..21#ROOT2024
+              PUNCH   ; [joint] 0:Root[0000, 0]@41..42#ROOT2024
+              SUBTREE () 0:Root[0000, 0]@39..40#ROOT2024 0:Root[0000, 0]@39..40#ROOT2024
+                IDENT   funcall 1:Root[0000, 0]@27..34#ROOT2024
+                SUBTREE () 1:Root[0000, 0]@34..35#ROOT2024 1:Root[0000, 0]@35..36#ROOT2024
+              PUNCH   ; [joint] 0:Root[0000, 0]@41..42#ROOT2024
+              SUBTREE () 0:Root[0000, 0]@39..40#ROOT2024 0:Root[0000, 0]@39..40#ROOT2024
+                IDENT   future 1:Root[0000, 0]@42..48#ROOT2024
+                PUNCH   . [alone] 1:Root[0000, 0]@48..49#ROOT2024
+                IDENT   await 1:Root[0000, 0]@49..54#ROOT2024
+              PUNCH   ; [joint] 0:Root[0000, 0]@41..42#ROOT2024
+              SUBTREE () 0:Root[0000, 0]@39..40#ROOT2024 0:Root[0000, 0]@39..40#ROOT2024
+                IDENT   break 1:Root[0000, 0]@60..65#ROOT2024
+                PUNCH   ' [joint] 1:Root[0000, 0]@66..67#ROOT2024
+                IDENT   foo 1:Root[0000, 0]@67..70#ROOT2024
+                IDENT   bar 1:Root[0000, 0]@71..74#ROOT2024
+              PUNCH   ; [alone] 0:Root[0000, 0]@44..45#ROOT2024
 
             4;
             "literal";
@@ -346,13 +348,13 @@ fn expr_2021() {
         expect![[r#"
             ExpandError {
                 inner: (
-                    1:0@5..6#ROOT2024,
+                    1:Root[0000, 0]@5..6#ROOT2024,
                     NoMatchingRule,
                 ),
             }
 
-            SUBTREE $$ 1:0@0..8#ROOT2024 1:0@0..8#ROOT2024
-              PUNCH   ; [alone] 0:0@44..45#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..8#ROOT2024 1:Root[0000, 0]@0..8#ROOT2024
+              PUNCH   ; [alone] 0:Root[0000, 0]@44..45#ROOT2024
 
             ;"#]],
     );
@@ -370,88 +372,88 @@ fn minus_belongs_to_literal() {
     check(
         "-1",
         expect![[r#"
-            SUBTREE $$ 1:0@0..2#ROOT2024 1:0@0..2#ROOT2024
-              PUNCH   - [alone] 0:0@10..11#ROOT2024
-              LITERAL Integer 1 0:0@11..12#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..2#ROOT2024 1:Root[0000, 0]@0..2#ROOT2024
+              PUNCH   - [alone] 0:Root[0000, 0]@10..11#ROOT2024
+              LITERAL Integer 1 0:Root[0000, 0]@11..12#ROOT2024
 
             -1"#]],
     );
     check(
         "- 1",
         expect![[r#"
-            SUBTREE $$ 1:0@0..3#ROOT2024 1:0@0..3#ROOT2024
-              PUNCH   - [alone] 0:0@10..11#ROOT2024
-              LITERAL Integer 1 0:0@11..12#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..3#ROOT2024 1:Root[0000, 0]@0..3#ROOT2024
+              PUNCH   - [alone] 0:Root[0000, 0]@10..11#ROOT2024
+              LITERAL Integer 1 0:Root[0000, 0]@11..12#ROOT2024
 
             -1"#]],
     );
     check(
         "-2",
         expect![[r#"
-            SUBTREE $$ 1:0@0..2#ROOT2024 1:0@0..2#ROOT2024
-              PUNCH   - [alone] 0:0@25..26#ROOT2024
-              LITERAL Integer 2 0:0@27..28#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..2#ROOT2024 1:Root[0000, 0]@0..2#ROOT2024
+              PUNCH   - [alone] 0:Root[0000, 0]@25..26#ROOT2024
+              LITERAL Integer 2 0:Root[0000, 0]@27..28#ROOT2024
 
             -2"#]],
     );
     check(
         "- 2",
         expect![[r#"
-            SUBTREE $$ 1:0@0..3#ROOT2024 1:0@0..3#ROOT2024
-              PUNCH   - [alone] 0:0@25..26#ROOT2024
-              LITERAL Integer 2 0:0@27..28#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..3#ROOT2024 1:Root[0000, 0]@0..3#ROOT2024
+              PUNCH   - [alone] 0:Root[0000, 0]@25..26#ROOT2024
+              LITERAL Integer 2 0:Root[0000, 0]@27..28#ROOT2024
 
             -2"#]],
     );
     check(
         "-3.0",
         expect![[r#"
-            SUBTREE $$ 1:0@0..4#ROOT2024 1:0@0..4#ROOT2024
-              PUNCH   - [alone] 0:0@43..44#ROOT2024
-              LITERAL Float 3.0 0:0@45..48#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..4#ROOT2024 1:Root[0000, 0]@0..4#ROOT2024
+              PUNCH   - [alone] 0:Root[0000, 0]@43..44#ROOT2024
+              LITERAL Float 3.0 0:Root[0000, 0]@45..48#ROOT2024
 
             -3.0"#]],
     );
     check(
         "- 3.0",
         expect![[r#"
-            SUBTREE $$ 1:0@0..5#ROOT2024 1:0@0..5#ROOT2024
-              PUNCH   - [alone] 0:0@43..44#ROOT2024
-              LITERAL Float 3.0 0:0@45..48#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..5#ROOT2024 1:Root[0000, 0]@0..5#ROOT2024
+              PUNCH   - [alone] 0:Root[0000, 0]@43..44#ROOT2024
+              LITERAL Float 3.0 0:Root[0000, 0]@45..48#ROOT2024
 
             -3.0"#]],
     );
     check(
         "@1",
         expect![[r#"
-            SUBTREE $$ 1:0@0..2#ROOT2024 1:0@0..2#ROOT2024
-              LITERAL Integer 1 1:0@1..2#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..2#ROOT2024 1:Root[0000, 0]@0..2#ROOT2024
+              LITERAL Integer 1 1:Root[0000, 0]@1..2#ROOT2024
 
             1"#]],
     );
     check(
         "@-1",
         expect![[r#"
-            SUBTREE $$ 1:0@0..3#ROOT2024 1:0@0..3#ROOT2024
-              PUNCH   - [alone] 1:0@1..2#ROOT2024
-              LITERAL Integer 1 1:0@2..3#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..3#ROOT2024 1:Root[0000, 0]@0..3#ROOT2024
+              PUNCH   - [alone] 1:Root[0000, 0]@1..2#ROOT2024
+              LITERAL Integer 1 1:Root[0000, 0]@2..3#ROOT2024
 
             -1"#]],
     );
     check(
         "@1.0",
         expect![[r#"
-            SUBTREE $$ 1:0@0..4#ROOT2024 1:0@0..4#ROOT2024
-              LITERAL Float 1.0 1:0@1..4#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..4#ROOT2024 1:Root[0000, 0]@0..4#ROOT2024
+              LITERAL Float 1.0 1:Root[0000, 0]@1..4#ROOT2024
 
             1.0"#]],
     );
     check(
         "@-1.0",
         expect![[r#"
-            SUBTREE $$ 1:0@0..5#ROOT2024 1:0@0..5#ROOT2024
-              PUNCH   - [alone] 1:0@1..2#ROOT2024
-              LITERAL Float 1.0 1:0@2..5#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..5#ROOT2024 1:Root[0000, 0]@0..5#ROOT2024
+              PUNCH   - [alone] 1:Root[0000, 0]@1..2#ROOT2024
+              LITERAL Float 1.0 1:Root[0000, 0]@2..5#ROOT2024
 
             -1.0"#]],
     );
@@ -460,16 +462,16 @@ fn minus_belongs_to_literal() {
         expect![[r#"
             ExpandError {
                 inner: (
-                    1:0@1..2#ROOT2024,
+                    1:Root[0000, 0]@1..2#ROOT2024,
                     BindingError(
                         "expected literal",
                     ),
                 ),
             }
 
-            SUBTREE $$ 1:0@0..6#ROOT2024 1:0@0..6#ROOT2024
-              PUNCH   - [joint] 1:0@1..2#ROOT2024
-              PUNCH   - [alone] 1:0@2..3#ROOT2024
+            SUBTREE $$ 1:Root[0000, 0]@0..6#ROOT2024 1:Root[0000, 0]@0..6#ROOT2024
+              PUNCH   - [joint] 1:Root[0000, 0]@1..2#ROOT2024
+              PUNCH   - [alone] 1:Root[0000, 0]@2..3#ROOT2024
 
             --"#]],
     );
diff --git a/src/tools/rust-analyzer/crates/proc-macro-api/src/legacy_protocol/msg.rs b/src/tools/rust-analyzer/crates/proc-macro-api/src/legacy_protocol/msg.rs
index 55185aa492de..4e1526fe48bd 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-api/src/legacy_protocol/msg.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-api/src/legacy_protocol/msg.rs
@@ -22,9 +22,10 @@ pub const HAS_GLOBAL_SPANS: u32 = 3;
 pub const RUST_ANALYZER_SPAN_SUPPORT: u32 = 4;
 /// Whether literals encode their kind as an additional u32 field and idents their rawness as a u32 field.
 pub const EXTENDED_LEAF_DATA: u32 = 5;
+pub const HASHED_AST_ID: u32 = 6;
 
 /// Current API version of the proc-macro protocol.
-pub const CURRENT_API_VERSION: u32 = EXTENDED_LEAF_DATA;
+pub const CURRENT_API_VERSION: u32 = HASHED_AST_ID;
 
 /// Represents requests sent from the client to the proc-macro-srv.
 #[derive(Debug, Serialize, Deserialize)]
@@ -54,7 +55,7 @@ pub enum SpanMode {
     Id,
 
     /// Rust Analyzer-specific span handling mode.
-    RustAnalyzer,
+    RustAnalyzer { fixup_ast_id: u32 },
 }
 
 /// Represents responses sent from the proc-macro-srv to the client.
@@ -201,7 +202,9 @@ type ProtocolWrite<W: Write> = for<'o, 'msg> fn(out: &'o mut W, msg: &'msg str)
 #[cfg(test)]
 mod tests {
     use intern::{Symbol, sym};
-    use span::{Edition, ErasedFileAstId, Span, SpanAnchor, SyntaxContext, TextRange, TextSize};
+    use span::{
+        Edition, ROOT_ERASED_FILE_AST_ID, Span, SpanAnchor, SyntaxContext, TextRange, TextSize,
+    };
     use tt::{
         Delimiter, DelimiterKind, Ident, Leaf, Literal, Punct, Spacing, TopSubtree,
         TopSubtreeBuilder,
@@ -215,7 +218,7 @@ mod tests {
                 span::FileId::from_raw(0xe4e4e),
                 span::Edition::CURRENT,
             ),
-            ast_id: ErasedFileAstId::from_raw(0),
+            ast_id: ROOT_ERASED_FILE_AST_ID,
         };
 
         let mut builder = TopSubtreeBuilder::new(Delimiter {
@@ -305,7 +308,7 @@ mod tests {
     #[test]
     fn test_proc_macro_rpc_works() {
         let tt = fixture_token_tree();
-        for v in RUST_ANALYZER_SPAN_SUPPORT..=CURRENT_API_VERSION {
+        for v in HASHED_AST_ID..=CURRENT_API_VERSION {
             let mut span_data_table = Default::default();
             let task = ExpandMacro {
                 data: ExpandMacroData {
diff --git a/src/tools/rust-analyzer/crates/proc-macro-api/src/process.rs b/src/tools/rust-analyzer/crates/proc-macro-api/src/process.rs
index fcea75ef672a..e3b0614546de 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-api/src/process.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-api/src/process.rs
@@ -8,6 +8,7 @@ use std::{
 };
 
 use paths::AbsPath;
+use span::FIXUP_ERASED_FILE_AST_ID_MARKER;
 use stdx::JodChild;
 
 use crate::{
@@ -15,8 +16,7 @@ use crate::{
     legacy_protocol::{
         json::{read_json, write_json},
         msg::{
-            CURRENT_API_VERSION, Message, RUST_ANALYZER_SPAN_SUPPORT, Request, Response,
-            ServerConfig, SpanMode,
+            CURRENT_API_VERSION, HASHED_AST_ID, Message, Request, Response, ServerConfig, SpanMode,
         },
     },
 };
@@ -71,7 +71,9 @@ impl ProcMacroServerProcess {
             Ok(v) => {
                 tracing::info!("Proc-macro server version: {v}");
                 srv.version = v;
-                if srv.version >= RUST_ANALYZER_SPAN_SUPPORT {
+                if srv.version >= HASHED_AST_ID {
+                    // We don't enable spans on versions prior to `HASHED_AST_ID`, because their ast id layout
+                    // is different.
                     if let Ok(mode) = srv.enable_rust_analyzer_spans() {
                         srv.mode = mode;
                     }
@@ -111,7 +113,11 @@ impl ProcMacroServerProcess {
 
     /// Enable support for rust-analyzer span mode if the server supports it.
     fn enable_rust_analyzer_spans(&self) -> Result<SpanMode, ServerError> {
-        let request = Request::SetConfig(ServerConfig { span_mode: SpanMode::RustAnalyzer });
+        let request = Request::SetConfig(ServerConfig {
+            span_mode: SpanMode::RustAnalyzer {
+                fixup_ast_id: FIXUP_ERASED_FILE_AST_ID_MARKER.into_raw(),
+            },
+        });
         let response = self.send_task(request)?;
 
         match response {
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv-cli/src/main_loop.rs b/src/tools/rust-analyzer/crates/proc-macro-srv-cli/src/main_loop.rs
index f54dff1f2d82..25a49fbff9fd 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-srv-cli/src/main_loop.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-srv-cli/src/main_loop.rs
@@ -26,7 +26,7 @@ pub(crate) fn run() -> io::Result<()> {
     let write_response = |msg: msg::Response| msg.write(write_json, &mut io::stdout().lock());
 
     let env = EnvSnapshot::default();
-    let srv = proc_macro_srv::ProcMacroSrv::new(&env);
+    let mut srv = proc_macro_srv::ProcMacroSrv::new(&env);
 
     let mut span_mode = SpanMode::Id;
 
@@ -78,7 +78,7 @@ pub(crate) fn run() -> io::Result<()> {
                         })
                         .map_err(msg::PanicMessage)
                     }),
-                    SpanMode::RustAnalyzer => msg::Response::ExpandMacroExtended({
+                    SpanMode::RustAnalyzer { .. } => msg::Response::ExpandMacroExtended({
                         let mut span_data_table = deserialize_span_data_index_map(&span_data_table);
 
                         let def_site = span_data_table[def_site];
@@ -122,6 +122,9 @@ pub(crate) fn run() -> io::Result<()> {
             msg::Request::ApiVersionCheck {} => msg::Response::ApiVersionCheck(CURRENT_API_VERSION),
             msg::Request::SetConfig(config) => {
                 span_mode = config.span_mode;
+                if let SpanMode::RustAnalyzer { fixup_ast_id } = span_mode {
+                    srv.set_fixup_ast_id(fixup_ast_id);
+                }
                 msg::Response::SetConfig(config)
             }
         };
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv/src/dylib.rs b/src/tools/rust-analyzer/crates/proc-macro-srv/src/dylib.rs
index c49159df9916..c64a9833e3ff 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-srv/src/dylib.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-srv/src/dylib.rs
@@ -3,6 +3,7 @@
 mod version;
 
 use proc_macro::bridge;
+use span::ErasedFileAstId;
 use std::{fmt, fs, io, time::SystemTime};
 
 use libloading::Library;
@@ -161,14 +162,20 @@ impl Expander {
         def_site: S,
         call_site: S,
         mixed_site: S,
+        fixup_ast_id: ErasedFileAstId,
     ) -> Result<TopSubtree<S>, String>
     where
         <S::Server as bridge::server::Types>::TokenStream: Default,
     {
-        let result = self
-            .inner
-            .proc_macros
-            .expand(macro_name, macro_body, attributes, def_site, call_site, mixed_site);
+        let result = self.inner.proc_macros.expand(
+            macro_name,
+            macro_body,
+            attributes,
+            def_site,
+            call_site,
+            mixed_site,
+            fixup_ast_id,
+        );
         result.map_err(|e| e.into_string().unwrap_or_default())
     }
 
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv/src/lib.rs b/src/tools/rust-analyzer/crates/proc-macro-srv/src/lib.rs
index 223c5a54b703..22afa018de01 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-srv/src/lib.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-srv/src/lib.rs
@@ -41,7 +41,7 @@ use std::{
 };
 
 use paths::{Utf8Path, Utf8PathBuf};
-use span::{Span, TokenId};
+use span::{ErasedFileAstId, FIXUP_ERASED_FILE_AST_ID_MARKER, Span, TokenId};
 
 use crate::server_impl::TokenStream;
 
@@ -57,11 +57,16 @@ pub const RUSTC_VERSION_STRING: &str = env!("RUSTC_VERSION");
 pub struct ProcMacroSrv<'env> {
     expanders: Mutex<HashMap<Utf8PathBuf, Arc<dylib::Expander>>>,
     env: &'env EnvSnapshot,
+    fixup_ast_id: ErasedFileAstId,
 }
 
 impl<'env> ProcMacroSrv<'env> {
     pub fn new(env: &'env EnvSnapshot) -> Self {
-        Self { expanders: Default::default(), env }
+        Self { expanders: Default::default(), env, fixup_ast_id: FIXUP_ERASED_FILE_AST_ID_MARKER }
+    }
+
+    pub fn set_fixup_ast_id(&mut self, fixup_ast_id: u32) {
+        self.fixup_ast_id = ErasedFileAstId::from_raw(fixup_ast_id);
     }
 }
 
@@ -101,6 +106,7 @@ impl ProcMacroSrv<'_> {
                             def_site,
                             call_site,
                             mixed_site,
+                            self.fixup_ast_id,
                         )
                         .map(|tt| tt.0)
                 });
@@ -156,25 +162,41 @@ impl ProcMacroSrv<'_> {
 
 pub trait ProcMacroSrvSpan: Copy + Send {
     type Server: proc_macro::bridge::server::Server<TokenStream = TokenStream<Self>>;
-    fn make_server(call_site: Self, def_site: Self, mixed_site: Self) -> Self::Server;
+    fn make_server(
+        call_site: Self,
+        def_site: Self,
+        mixed_site: Self,
+        fixup_ast_id: ErasedFileAstId,
+    ) -> Self::Server;
 }
 
 impl ProcMacroSrvSpan for TokenId {
     type Server = server_impl::token_id::TokenIdServer;
 
-    fn make_server(call_site: Self, def_site: Self, mixed_site: Self) -> Self::Server {
+    fn make_server(
+        call_site: Self,
+        def_site: Self,
+        mixed_site: Self,
+        _fixup_ast_id: ErasedFileAstId,
+    ) -> Self::Server {
         Self::Server { call_site, def_site, mixed_site }
     }
 }
 impl ProcMacroSrvSpan for Span {
     type Server = server_impl::rust_analyzer_span::RaSpanServer;
-    fn make_server(call_site: Self, def_site: Self, mixed_site: Self) -> Self::Server {
+    fn make_server(
+        call_site: Self,
+        def_site: Self,
+        mixed_site: Self,
+        fixup_ast_id: ErasedFileAstId,
+    ) -> Self::Server {
         Self::Server {
             call_site,
             def_site,
             mixed_site,
             tracked_env_vars: Default::default(),
             tracked_paths: Default::default(),
+            fixup_ast_id,
         }
     }
 }
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv/src/proc_macros.rs b/src/tools/rust-analyzer/crates/proc-macro-srv/src/proc_macros.rs
index 18532706c4aa..3b9c45894c60 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-srv/src/proc_macros.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-srv/src/proc_macros.rs
@@ -1,6 +1,7 @@
 //! Proc macro ABI
 
 use proc_macro::bridge;
+use span::ErasedFileAstId;
 
 use crate::{ProcMacroKind, ProcMacroSrvSpan, server_impl::TopSubtree};
 
@@ -22,6 +23,7 @@ impl ProcMacros {
         def_site: S,
         call_site: S,
         mixed_site: S,
+        fixup_ast_id: ErasedFileAstId,
     ) -> Result<TopSubtree<S>, crate::PanicMessage> {
         let parsed_body = crate::server_impl::TokenStream::with_subtree(macro_body);
 
@@ -37,7 +39,7 @@ impl ProcMacros {
                 {
                     let res = client.run(
                         &bridge::server::SameThread,
-                        S::make_server(call_site, def_site, mixed_site),
+                        S::make_server(call_site, def_site, mixed_site, fixup_ast_id),
                         parsed_body,
                         cfg!(debug_assertions),
                     );
@@ -48,7 +50,7 @@ impl ProcMacros {
                 bridge::client::ProcMacro::Bang { name, client } if *name == macro_name => {
                     let res = client.run(
                         &bridge::server::SameThread,
-                        S::make_server(call_site, def_site, mixed_site),
+                        S::make_server(call_site, def_site, mixed_site, fixup_ast_id),
                         parsed_body,
                         cfg!(debug_assertions),
                     );
@@ -59,7 +61,7 @@ impl ProcMacros {
                 bridge::client::ProcMacro::Attr { name, client } if *name == macro_name => {
                     let res = client.run(
                         &bridge::server::SameThread,
-                        S::make_server(call_site, def_site, mixed_site),
+                        S::make_server(call_site, def_site, mixed_site, fixup_ast_id),
                         parsed_attributes,
                         parsed_body,
                         cfg!(debug_assertions),
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv/src/server_impl/rust_analyzer_span.rs b/src/tools/rust-analyzer/crates/proc-macro-srv/src/server_impl/rust_analyzer_span.rs
index 5d1271ba81e1..b071ad80f5b6 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-srv/src/server_impl/rust_analyzer_span.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-srv/src/server_impl/rust_analyzer_span.rs
@@ -11,7 +11,7 @@ use std::{
 
 use intern::Symbol;
 use proc_macro::bridge::{self, server};
-use span::{FIXUP_ERASED_FILE_AST_ID_MARKER, Span};
+use span::{ErasedFileAstId, Span};
 use tt::{TextRange, TextSize};
 
 use crate::server_impl::{from_token_tree, literal_from_str, token_stream::TokenStreamBuilder};
@@ -28,6 +28,7 @@ pub struct RaSpanServer {
     pub call_site: Span,
     pub def_site: Span,
     pub mixed_site: Span,
+    pub fixup_ast_id: ErasedFileAstId,
 }
 
 impl server::Types for RaSpanServer {
@@ -181,10 +182,10 @@ impl server::Span for RaSpanServer {
     fn join(&mut self, first: Self::Span, second: Self::Span) -> Option<Self::Span> {
         // We can't modify the span range for fixup spans, those are meaningful to fixup, so just
         // prefer the non-fixup span.
-        if first.anchor.ast_id == FIXUP_ERASED_FILE_AST_ID_MARKER {
+        if first.anchor.ast_id == self.fixup_ast_id {
             return Some(second);
         }
-        if second.anchor.ast_id == FIXUP_ERASED_FILE_AST_ID_MARKER {
+        if second.anchor.ast_id == self.fixup_ast_id {
             return Some(first);
         }
         // FIXME: Once we can talk back to the client, implement a "long join" request for anchors
@@ -213,7 +214,7 @@ impl server::Span for RaSpanServer {
         end: Bound<usize>,
     ) -> Option<Self::Span> {
         // We can't modify the span range for fixup spans, those are meaningful to fixup.
-        if span.anchor.ast_id == FIXUP_ERASED_FILE_AST_ID_MARKER {
+        if span.anchor.ast_id == self.fixup_ast_id {
             return Some(span);
         }
         let length = span.range.len().into();
@@ -256,7 +257,7 @@ impl server::Span for RaSpanServer {
 
     fn end(&mut self, span: Self::Span) -> Self::Span {
         // We can't modify the span range for fixup spans, those are meaningful to fixup.
-        if span.anchor.ast_id == FIXUP_ERASED_FILE_AST_ID_MARKER {
+        if span.anchor.ast_id == self.fixup_ast_id {
             return span;
         }
         Span { range: TextRange::empty(span.range.end()), ..span }
@@ -264,7 +265,7 @@ impl server::Span for RaSpanServer {
 
     fn start(&mut self, span: Self::Span) -> Self::Span {
         // We can't modify the span range for fixup spans, those are meaningful to fixup.
-        if span.anchor.ast_id == FIXUP_ERASED_FILE_AST_ID_MARKER {
+        if span.anchor.ast_id == self.fixup_ast_id {
             return span;
         }
         Span { range: TextRange::empty(span.range.start()), ..span }
@@ -318,7 +319,7 @@ mod tests {
             range: TextRange::empty(TextSize::new(0)),
             anchor: span::SpanAnchor {
                 file_id: EditionedFileId::current_edition(FileId::from_raw(0)),
-                ast_id: span::ErasedFileAstId::from_raw(0),
+                ast_id: span::ROOT_ERASED_FILE_AST_ID,
             },
             ctx: SyntaxContext::root(span::Edition::CURRENT),
         };
@@ -360,7 +361,7 @@ mod tests {
             range: TextRange::empty(TextSize::new(0)),
             anchor: span::SpanAnchor {
                 file_id: EditionedFileId::current_edition(FileId::from_raw(0)),
-                ast_id: span::ErasedFileAstId::from_raw(0),
+                ast_id: span::ROOT_ERASED_FILE_AST_ID,
             },
             ctx: SyntaxContext::root(span::Edition::CURRENT),
         };
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/mod.rs b/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/mod.rs
index d1ea89d2dcaf..08495f50bff4 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/mod.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/mod.rs
@@ -21,14 +21,14 @@ fn test_derive_empty() {
 
             SUBTREE $$ 1 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   struct 42:2@0..6#ROOT2024
-              IDENT   S 42:2@7..8#ROOT2024
-              PUNCH   ; [alone] 42:2@8..9#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   struct 42:Root[0000, 0]@0..6#ROOT2024
+              IDENT   S 42:Root[0000, 0]@7..8#ROOT2024
+              PUNCH   ; [alone] 42:Root[0000, 0]@8..9#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024"#]],
     );
 }
 
@@ -52,19 +52,19 @@ fn test_derive_error() {
                 LITERAL Str #[derive(DeriveError)] struct S ; 1
               PUNCH   ; [alone] 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   struct 42:2@0..6#ROOT2024
-              IDENT   S 42:2@7..8#ROOT2024
-              PUNCH   ; [alone] 42:2@8..9#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   struct 42:Root[0000, 0]@0..6#ROOT2024
+              IDENT   S 42:Root[0000, 0]@7..8#ROOT2024
+              PUNCH   ; [alone] 42:Root[0000, 0]@8..9#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   compile_error 42:2@0..100#ROOT2024
-              PUNCH   ! [alone] 42:2@0..100#ROOT2024
-              SUBTREE () 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-                LITERAL Str #[derive(DeriveError)] struct S ; 42:2@0..100#ROOT2024
-              PUNCH   ; [alone] 42:2@0..100#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   compile_error 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   ! [alone] 42:Root[0000, 0]@0..100#ROOT2024
+              SUBTREE () 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+                LITERAL Str #[derive(DeriveError)] struct S ; 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   ; [alone] 42:Root[0000, 0]@0..100#ROOT2024"#]],
     );
 }
 
@@ -94,25 +94,25 @@ fn test_fn_like_macro_noop() {
               PUNCH   , [alone] 1
               SUBTREE [] 1 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   ident 42:2@0..5#ROOT2024
-              PUNCH   , [alone] 42:2@5..6#ROOT2024
-              LITERAL Integer 0 42:2@7..8#ROOT2024
-              PUNCH   , [alone] 42:2@8..9#ROOT2024
-              LITERAL Integer 1 42:2@10..11#ROOT2024
-              PUNCH   , [alone] 42:2@11..12#ROOT2024
-              SUBTREE [] 42:2@13..14#ROOT2024 42:2@14..15#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   ident 42:Root[0000, 0]@0..5#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@5..6#ROOT2024
+              LITERAL Integer 0 42:Root[0000, 0]@7..8#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@8..9#ROOT2024
+              LITERAL Integer 1 42:Root[0000, 0]@10..11#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@11..12#ROOT2024
+              SUBTREE [] 42:Root[0000, 0]@13..14#ROOT2024 42:Root[0000, 0]@14..15#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   ident 42:2@0..5#ROOT2024
-              PUNCH   , [alone] 42:2@5..6#ROOT2024
-              LITERAL Integer 0 42:2@7..8#ROOT2024
-              PUNCH   , [alone] 42:2@8..9#ROOT2024
-              LITERAL Integer 1 42:2@10..11#ROOT2024
-              PUNCH   , [alone] 42:2@11..12#ROOT2024
-              SUBTREE [] 42:2@13..14#ROOT2024 42:2@14..15#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   ident 42:Root[0000, 0]@0..5#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@5..6#ROOT2024
+              LITERAL Integer 0 42:Root[0000, 0]@7..8#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@8..9#ROOT2024
+              LITERAL Integer 1 42:Root[0000, 0]@10..11#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@11..12#ROOT2024
+              SUBTREE [] 42:Root[0000, 0]@13..14#ROOT2024 42:Root[0000, 0]@14..15#ROOT2024"#]],
     );
 }
 
@@ -134,17 +134,17 @@ fn test_fn_like_macro_clone_ident_subtree() {
               PUNCH   , [alone] 1
               SUBTREE [] 1 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   ident 42:2@0..5#ROOT2024
-              PUNCH   , [alone] 42:2@5..6#ROOT2024
-              SUBTREE [] 42:2@7..8#ROOT2024 42:2@8..9#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   ident 42:Root[0000, 0]@0..5#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@5..6#ROOT2024
+              SUBTREE [] 42:Root[0000, 0]@7..8#ROOT2024 42:Root[0000, 0]@8..9#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   ident 42:2@0..5#ROOT2024
-              PUNCH   , [alone] 42:2@5..6#ROOT2024
-              SUBTREE [] 42:2@7..9#ROOT2024 42:2@7..9#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   ident 42:Root[0000, 0]@0..5#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@5..6#ROOT2024
+              SUBTREE [] 42:Root[0000, 0]@7..9#ROOT2024 42:Root[0000, 0]@7..9#ROOT2024"#]],
     );
 }
 
@@ -162,13 +162,13 @@ fn test_fn_like_macro_clone_raw_ident() {
             SUBTREE $$ 1 1
               IDENT   r#async 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   r#async 42:2@0..7#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   r#async 42:Root[0000, 0]@0..7#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   r#async 42:2@0..7#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   r#async 42:Root[0000, 0]@0..7#ROOT2024"#]],
     );
 }
 
@@ -187,14 +187,14 @@ fn test_fn_like_fn_like_span_join() {
             SUBTREE $$ 1 1
               IDENT   r#joined 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   foo 42:2@0..3#ROOT2024
-              IDENT   bar 42:2@8..11#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   foo 42:Root[0000, 0]@0..3#ROOT2024
+              IDENT   bar 42:Root[0000, 0]@8..11#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   r#joined 42:2@0..11#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   r#joined 42:Root[0000, 0]@0..11#ROOT2024"#]],
     );
 }
 
@@ -216,17 +216,17 @@ fn test_fn_like_fn_like_span_ops() {
               IDENT   resolved_at_def_site 1
               IDENT   start_span 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   set_def_site 42:2@0..12#ROOT2024
-              IDENT   resolved_at_def_site 42:2@13..33#ROOT2024
-              IDENT   start_span 42:2@34..44#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   set_def_site 42:Root[0000, 0]@0..12#ROOT2024
+              IDENT   resolved_at_def_site 42:Root[0000, 0]@13..33#ROOT2024
+              IDENT   start_span 42:Root[0000, 0]@34..44#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   set_def_site 41:1@0..150#ROOT2024
-              IDENT   resolved_at_def_site 42:2@13..33#ROOT2024
-              IDENT   start_span 42:2@34..34#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   set_def_site 41:Root[0000, 0]@0..150#ROOT2024
+              IDENT   resolved_at_def_site 42:Root[0000, 0]@13..33#ROOT2024
+              IDENT   start_span 42:Root[0000, 0]@34..34#ROOT2024"#]],
     );
 }
 
@@ -259,28 +259,28 @@ fn test_fn_like_mk_literals() {
               PUNCH   - [alone] 1
               LITERAL Integer 123 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              LITERAL ByteStr byte_string 42:2@0..100#ROOT2024
-              LITERAL Char c 42:2@0..100#ROOT2024
-              LITERAL Str string 42:2@0..100#ROOT2024
-              LITERAL Str -string 42:2@0..100#ROOT2024
-              LITERAL CStr cstring 42:2@0..100#ROOT2024
-              LITERAL Float 3.14f64 42:2@0..100#ROOT2024
-              PUNCH   - [alone] 42:2@0..100#ROOT2024
-              LITERAL Float 3.14f64 42:2@0..100#ROOT2024
-              LITERAL Float 3.14 42:2@0..100#ROOT2024
-              PUNCH   - [alone] 42:2@0..100#ROOT2024
-              LITERAL Float 3.14 42:2@0..100#ROOT2024
-              LITERAL Integer 123i64 42:2@0..100#ROOT2024
-              PUNCH   - [alone] 42:2@0..100#ROOT2024
-              LITERAL Integer 123i64 42:2@0..100#ROOT2024
-              LITERAL Integer 123 42:2@0..100#ROOT2024
-              PUNCH   - [alone] 42:2@0..100#ROOT2024
-              LITERAL Integer 123 42:2@0..100#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL ByteStr byte_string 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Char c 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Str string 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Str -string 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL CStr cstring 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Float 3.14f64 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Float 3.14f64 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Float 3.14 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Float 3.14 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Integer 123i64 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Integer 123i64 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Integer 123 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Integer 123 42:Root[0000, 0]@0..100#ROOT2024"#]],
     );
 }
 
@@ -298,13 +298,13 @@ fn test_fn_like_mk_idents() {
               IDENT   standard 1
               IDENT   r#raw 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   standard 42:2@0..100#ROOT2024
-              IDENT   r#raw 42:2@0..100#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   standard 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   r#raw 42:Root[0000, 0]@0..100#ROOT2024"#]],
     );
 }
 
@@ -360,51 +360,51 @@ fn test_fn_like_macro_clone_literals() {
               PUNCH   , [alone] 1
               LITERAL CStr null 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              LITERAL Integer 1u16 42:2@0..4#ROOT2024
-              PUNCH   , [alone] 42:2@4..5#ROOT2024
-              LITERAL Integer 2_u32 42:2@6..11#ROOT2024
-              PUNCH   , [alone] 42:2@11..12#ROOT2024
-              PUNCH   - [alone] 42:2@13..14#ROOT2024
-              LITERAL Integer 4i64 42:2@14..18#ROOT2024
-              PUNCH   , [alone] 42:2@18..19#ROOT2024
-              LITERAL Float 3.14f32 42:2@20..27#ROOT2024
-              PUNCH   , [alone] 42:2@27..28#ROOT2024
-              LITERAL Str hello bridge 42:2@29..43#ROOT2024
-              PUNCH   , [alone] 42:2@43..44#ROOT2024
-              LITERAL Str suffixedsuffix 42:2@45..61#ROOT2024
-              PUNCH   , [alone] 42:2@61..62#ROOT2024
-              LITERAL StrRaw(2) raw 42:2@63..73#ROOT2024
-              PUNCH   , [alone] 42:2@73..74#ROOT2024
-              LITERAL Char a 42:2@75..78#ROOT2024
-              PUNCH   , [alone] 42:2@78..79#ROOT2024
-              LITERAL Byte b 42:2@80..84#ROOT2024
-              PUNCH   , [alone] 42:2@84..85#ROOT2024
-              LITERAL CStr null 42:2@86..93#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Integer 1u16 42:Root[0000, 0]@0..4#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@4..5#ROOT2024
+              LITERAL Integer 2_u32 42:Root[0000, 0]@6..11#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@11..12#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@13..14#ROOT2024
+              LITERAL Integer 4i64 42:Root[0000, 0]@14..18#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@18..19#ROOT2024
+              LITERAL Float 3.14f32 42:Root[0000, 0]@20..27#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@27..28#ROOT2024
+              LITERAL Str hello bridge 42:Root[0000, 0]@29..43#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@43..44#ROOT2024
+              LITERAL Str suffixedsuffix 42:Root[0000, 0]@45..61#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@61..62#ROOT2024
+              LITERAL StrRaw(2) raw 42:Root[0000, 0]@63..73#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@73..74#ROOT2024
+              LITERAL Char a 42:Root[0000, 0]@75..78#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@78..79#ROOT2024
+              LITERAL Byte b 42:Root[0000, 0]@80..84#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@84..85#ROOT2024
+              LITERAL CStr null 42:Root[0000, 0]@86..93#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              LITERAL Integer 1u16 42:2@0..4#ROOT2024
-              PUNCH   , [alone] 42:2@4..5#ROOT2024
-              LITERAL Integer 2_u32 42:2@6..11#ROOT2024
-              PUNCH   , [alone] 42:2@11..12#ROOT2024
-              PUNCH   - [alone] 42:2@13..14#ROOT2024
-              LITERAL Integer 4i64 42:2@14..18#ROOT2024
-              PUNCH   , [alone] 42:2@18..19#ROOT2024
-              LITERAL Float 3.14f32 42:2@20..27#ROOT2024
-              PUNCH   , [alone] 42:2@27..28#ROOT2024
-              LITERAL Str hello bridge 42:2@29..43#ROOT2024
-              PUNCH   , [alone] 42:2@43..44#ROOT2024
-              LITERAL Str suffixedsuffix 42:2@45..61#ROOT2024
-              PUNCH   , [alone] 42:2@61..62#ROOT2024
-              LITERAL StrRaw(2) raw 42:2@63..73#ROOT2024
-              PUNCH   , [alone] 42:2@73..74#ROOT2024
-              LITERAL Char a 42:2@75..78#ROOT2024
-              PUNCH   , [alone] 42:2@78..79#ROOT2024
-              LITERAL Byte b 42:2@80..84#ROOT2024
-              PUNCH   , [alone] 42:2@84..85#ROOT2024
-              LITERAL CStr null 42:2@86..93#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              LITERAL Integer 1u16 42:Root[0000, 0]@0..4#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@4..5#ROOT2024
+              LITERAL Integer 2_u32 42:Root[0000, 0]@6..11#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@11..12#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@13..14#ROOT2024
+              LITERAL Integer 4i64 42:Root[0000, 0]@14..18#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@18..19#ROOT2024
+              LITERAL Float 3.14f32 42:Root[0000, 0]@20..27#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@27..28#ROOT2024
+              LITERAL Str hello bridge 42:Root[0000, 0]@29..43#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@43..44#ROOT2024
+              LITERAL Str suffixedsuffix 42:Root[0000, 0]@45..61#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@61..62#ROOT2024
+              LITERAL StrRaw(2) raw 42:Root[0000, 0]@63..73#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@73..74#ROOT2024
+              LITERAL Char a 42:Root[0000, 0]@75..78#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@78..79#ROOT2024
+              LITERAL Byte b 42:Root[0000, 0]@80..84#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@84..85#ROOT2024
+              LITERAL CStr null 42:Root[0000, 0]@86..93#ROOT2024"#]],
     );
 }
 
@@ -442,33 +442,33 @@ fn test_fn_like_macro_negative_literals() {
               PUNCH   - [alone] 1
               LITERAL Float 2.7 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              PUNCH   - [alone] 42:2@0..1#ROOT2024
-              LITERAL Integer 1u16 42:2@1..5#ROOT2024
-              PUNCH   , [alone] 42:2@5..6#ROOT2024
-              PUNCH   - [alone] 42:2@7..8#ROOT2024
-              LITERAL Integer 2_u32 42:2@9..14#ROOT2024
-              PUNCH   , [alone] 42:2@14..15#ROOT2024
-              PUNCH   - [alone] 42:2@16..17#ROOT2024
-              LITERAL Float 3.14f32 42:2@17..24#ROOT2024
-              PUNCH   , [alone] 42:2@24..25#ROOT2024
-              PUNCH   - [alone] 42:2@26..27#ROOT2024
-              LITERAL Float 2.7 42:2@28..31#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@0..1#ROOT2024
+              LITERAL Integer 1u16 42:Root[0000, 0]@1..5#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@5..6#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@7..8#ROOT2024
+              LITERAL Integer 2_u32 42:Root[0000, 0]@9..14#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@14..15#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@16..17#ROOT2024
+              LITERAL Float 3.14f32 42:Root[0000, 0]@17..24#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@24..25#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@26..27#ROOT2024
+              LITERAL Float 2.7 42:Root[0000, 0]@28..31#ROOT2024
 
 
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              PUNCH   - [alone] 42:2@0..1#ROOT2024
-              LITERAL Integer 1u16 42:2@1..5#ROOT2024
-              PUNCH   , [alone] 42:2@5..6#ROOT2024
-              PUNCH   - [alone] 42:2@7..8#ROOT2024
-              LITERAL Integer 2_u32 42:2@9..14#ROOT2024
-              PUNCH   , [alone] 42:2@14..15#ROOT2024
-              PUNCH   - [alone] 42:2@16..17#ROOT2024
-              LITERAL Float 3.14f32 42:2@17..24#ROOT2024
-              PUNCH   , [alone] 42:2@24..25#ROOT2024
-              PUNCH   - [alone] 42:2@26..27#ROOT2024
-              LITERAL Float 2.7 42:2@28..31#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@0..1#ROOT2024
+              LITERAL Integer 1u16 42:Root[0000, 0]@1..5#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@5..6#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@7..8#ROOT2024
+              LITERAL Integer 2_u32 42:Root[0000, 0]@9..14#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@14..15#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@16..17#ROOT2024
+              LITERAL Float 3.14f32 42:Root[0000, 0]@17..24#ROOT2024
+              PUNCH   , [alone] 42:Root[0000, 0]@24..25#ROOT2024
+              PUNCH   - [alone] 42:Root[0000, 0]@26..27#ROOT2024
+              LITERAL Float 2.7 42:Root[0000, 0]@28..31#ROOT2024"#]],
     );
 }
 
@@ -498,21 +498,21 @@ fn test_attr_macro() {
                 LITERAL Str #[attr_error(some arguments)] mod m {} 1
               PUNCH   ; [alone] 1"#]],
         expect![[r#"
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   mod 42:2@0..3#ROOT2024
-              IDENT   m 42:2@4..5#ROOT2024
-              SUBTREE {} 42:2@6..7#ROOT2024 42:2@7..8#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   mod 42:Root[0000, 0]@0..3#ROOT2024
+              IDENT   m 42:Root[0000, 0]@4..5#ROOT2024
+              SUBTREE {} 42:Root[0000, 0]@6..7#ROOT2024 42:Root[0000, 0]@7..8#ROOT2024
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   some 42:2@0..4#ROOT2024
-              IDENT   arguments 42:2@5..14#ROOT2024
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   some 42:Root[0000, 0]@0..4#ROOT2024
+              IDENT   arguments 42:Root[0000, 0]@5..14#ROOT2024
 
-            SUBTREE $$ 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-              IDENT   compile_error 42:2@0..100#ROOT2024
-              PUNCH   ! [alone] 42:2@0..100#ROOT2024
-              SUBTREE () 42:2@0..100#ROOT2024 42:2@0..100#ROOT2024
-                LITERAL Str #[attr_error(some arguments)] mod m {} 42:2@0..100#ROOT2024
-              PUNCH   ; [alone] 42:2@0..100#ROOT2024"#]],
+            SUBTREE $$ 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+              IDENT   compile_error 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   ! [alone] 42:Root[0000, 0]@0..100#ROOT2024
+              SUBTREE () 42:Root[0000, 0]@0..100#ROOT2024 42:Root[0000, 0]@0..100#ROOT2024
+                LITERAL Str #[attr_error(some arguments)] mod m {} 42:Root[0000, 0]@0..100#ROOT2024
+              PUNCH   ; [alone] 42:Root[0000, 0]@0..100#ROOT2024"#]],
     );
 }
 
diff --git a/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/utils.rs b/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/utils.rs
index a0a45b269e4a..e0a69608decd 100644
--- a/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/utils.rs
+++ b/src/tools/rust-analyzer/crates/proc-macro-srv/src/tests/utils.rs
@@ -1,7 +1,10 @@
 //! utils used in proc-macro tests
 
 use expect_test::Expect;
-use span::{EditionedFileId, ErasedFileAstId, FileId, Span, SpanAnchor, SyntaxContext, TokenId};
+use span::{
+    EditionedFileId, FIXUP_ERASED_FILE_AST_ID_MARKER, FileId, ROOT_ERASED_FILE_AST_ID, Span,
+    SpanAnchor, SyntaxContext, TokenId,
+};
 use tt::TextRange;
 
 use crate::{EnvSnapshot, ProcMacroSrv, dylib, proc_macro_test_dylib_path};
@@ -65,8 +68,17 @@ fn assert_expand_impl(
     let input_ts_string = format!("{input_ts:?}");
     let attr_ts_string = attr_ts.as_ref().map(|it| format!("{it:?}"));
 
-    let res =
-        expander.expand(macro_name, input_ts, attr_ts, def_site, call_site, mixed_site).unwrap();
+    let res = expander
+        .expand(
+            macro_name,
+            input_ts,
+            attr_ts,
+            def_site,
+            call_site,
+            mixed_site,
+            FIXUP_ERASED_FILE_AST_ID_MARKER,
+        )
+        .unwrap();
     expect.assert_eq(&format!(
         "{input_ts_string}\n\n{}\n\n{res:?}",
         attr_ts_string.unwrap_or_default()
@@ -76,7 +88,7 @@ fn assert_expand_impl(
         range: TextRange::new(0.into(), 150.into()),
         anchor: SpanAnchor {
             file_id: EditionedFileId::current_edition(FileId::from_raw(41)),
-            ast_id: ErasedFileAstId::from_raw(1),
+            ast_id: ROOT_ERASED_FILE_AST_ID,
         },
         ctx: SyntaxContext::root(span::Edition::CURRENT),
     };
@@ -84,7 +96,7 @@ fn assert_expand_impl(
         range: TextRange::new(0.into(), 100.into()),
         anchor: SpanAnchor {
             file_id: EditionedFileId::current_edition(FileId::from_raw(42)),
-            ast_id: ErasedFileAstId::from_raw(2),
+            ast_id: ROOT_ERASED_FILE_AST_ID,
         },
         ctx: SyntaxContext::root(span::Edition::CURRENT),
     };
@@ -98,7 +110,17 @@ fn assert_expand_impl(
     let fixture_string = format!("{fixture:?}");
     let attr_string = attr.as_ref().map(|it| format!("{it:?}"));
 
-    let res = expander.expand(macro_name, fixture, attr, def_site, call_site, mixed_site).unwrap();
+    let res = expander
+        .expand(
+            macro_name,
+            fixture,
+            attr,
+            def_site,
+            call_site,
+            mixed_site,
+            FIXUP_ERASED_FILE_AST_ID_MARKER,
+        )
+        .unwrap();
     expect_spanned
         .assert_eq(&format!("{fixture_string}\n\n{}\n\n{res:#?}", attr_string.unwrap_or_default()));
 }
diff --git a/src/tools/rust-analyzer/crates/span/Cargo.toml b/src/tools/rust-analyzer/crates/span/Cargo.toml
index b3b401c3db44..966962bab381 100644
--- a/src/tools/rust-analyzer/crates/span/Cargo.toml
+++ b/src/tools/rust-analyzer/crates/span/Cargo.toml
@@ -22,6 +22,9 @@ vfs.workspace = true
 syntax.workspace = true
 stdx.workspace = true
 
+[dev-dependencies]
+syntax.workspace = true
+
 [features]
 default = ["salsa"]
 
diff --git a/src/tools/rust-analyzer/crates/span/src/ast_id.rs b/src/tools/rust-analyzer/crates/span/src/ast_id.rs
index 228fba1fa096..51a693ca011b 100644
--- a/src/tools/rust-analyzer/crates/span/src/ast_id.rs
+++ b/src/tools/rust-analyzer/crates/span/src/ast_id.rs
@@ -4,137 +4,534 @@
 //! Specifically, it enumerates all items in a file and uses position of a an
 //! item as an ID. That way, id's don't change unless the set of items itself
 //! changes.
+//!
+//! These IDs are tricky. If one of them invalidates, its interned ID invalidates,
+//! and this can cause *a lot* to be recomputed. For example, if you invalidate the ID
+//! of a struct, and that struct has an impl (any impl!) this will cause the `Self`
+//! type of the impl to invalidate, which will cause the all impls queries to be
+//! invalidated, which will cause every trait solve query in this crate *and* all
+//! transitive reverse dependencies to be invalidated, which is pretty much the worst
+//! thing that can happen incrementality wise.
+//!
+//! So we want these IDs to stay as stable as possible. For top-level items, we store
+//! their kind and name, which should be unique, but since they can still not be, we
+//! also store an index disambiguator. For nested items, we also store the ID of their
+//! parent. For macro calls, we store the macro name and an index. There aren't usually
+//! a lot of macro calls in item position, and invalidation in bodies is not much of
+//! a problem, so this should be enough.
 
 use std::{
     any::type_name,
     fmt,
-    hash::{BuildHasher, BuildHasherDefault, Hash, Hasher},
+    hash::{BuildHasher, Hash, Hasher},
     marker::PhantomData,
 };
 
 use la_arena::{Arena, Idx, RawIdx};
-use rustc_hash::FxHasher;
-use syntax::{AstNode, AstPtr, SyntaxNode, SyntaxNodePtr, ast};
+use rustc_hash::{FxBuildHasher, FxHashMap};
+use syntax::{
+    AstNode, AstPtr, SyntaxKind, SyntaxNode, SyntaxNodePtr,
+    ast::{self, HasName},
+    match_ast,
+};
+
+// The first index is always the root node's AstId
+/// The root ast id always points to the encompassing file, using this in spans is discouraged as
+/// any range relative to it will be effectively absolute, ruining the entire point of anchored
+/// relative text ranges.
+pub const ROOT_ERASED_FILE_AST_ID: ErasedFileAstId =
+    ErasedFileAstId(pack_hash_index_and_kind(0, 0, ErasedFileAstIdKind::Root as u32));
+
+/// ErasedFileAstId used as the span for syntax node fixups. Any Span containing this file id is to be
+/// considered fake.
+pub const FIXUP_ERASED_FILE_AST_ID_MARKER: ErasedFileAstId =
+    ErasedFileAstId(pack_hash_index_and_kind(0, 0, ErasedFileAstIdKind::Fixup as u32));
 
-/// See crates\hir-expand\src\ast_id_map.rs
 /// This is a type erased FileAstId.
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub struct ErasedFileAstId(u32);
 
-impl ErasedFileAstId {
-    pub const fn into_raw(self) -> u32 {
-        self.0
-    }
-    pub const fn from_raw(u32: u32) -> Self {
-        Self(u32)
-    }
-}
-
-impl fmt::Display for ErasedFileAstId {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.0.fmt(f)
-    }
-}
 impl fmt::Debug for ErasedFileAstId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.0.fmt(f)
+        let kind = self.kind();
+        macro_rules! kind {
+            ($($kind:ident),* $(,)?) => {
+                if false {
+                    // Ensure we covered all variants.
+                    match ErasedFileAstIdKind::Root {
+                        $( ErasedFileAstIdKind::$kind => {} )*
+                    }
+                    unreachable!()
+                }
+                $( else if kind == ErasedFileAstIdKind::$kind as u32 {
+                    stringify!($kind)
+                } )*
+                else {
+                    "Unknown"
+                }
+            };
+        }
+        let kind = kind!(
+            Root,
+            Enum,
+            Struct,
+            Union,
+            ExternCrate,
+            MacroDef,
+            MacroRules,
+            Module,
+            Static,
+            Trait,
+            TraitAlias,
+            Variant,
+            Const,
+            Fn,
+            MacroCall,
+            TypeAlias,
+            ExternBlock,
+            Use,
+            Impl,
+            BlockExpr,
+            Fixup,
+        );
+        if f.alternate() {
+            write!(f, "{kind}[{:04X}, {}]", self.hash_value(), self.index())
+        } else {
+            f.debug_struct("ErasedFileAstId")
+                .field("kind", &format_args!("{kind}"))
+                .field("index", &self.index())
+                .field("hash", &format_args!("{:04X}", self.hash_value()))
+                .finish()
+        }
     }
 }
 
-/// `AstId` points to an AST node in a specific file.
-pub struct FileAstId<N: AstIdNode> {
-    raw: ErasedFileAstId,
-    covariant: PhantomData<fn() -> N>,
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
+enum ErasedFileAstIdKind {
+    Root,
+    // The following are associated with `ErasedHasNameFileAstId`.
+    Enum,
+    Struct,
+    Union,
+    ExternCrate,
+    MacroDef,
+    MacroRules,
+    Module,
+    Static,
+    Trait,
+    TraitAlias,
+    // Until here associated with `ErasedHasNameFileAstId`.
+    // The following are associated with `ErasedAssocItemFileAstId`.
+    Variant,
+    Const,
+    Fn,
+    MacroCall,
+    TypeAlias,
+    // Until here associated with `ErasedAssocItemFileAstId`.
+    // Extern blocks don't really have any identifying property unfortunately.
+    ExternBlock,
+    // FIXME: If we store the final `UseTree` instead of the top-level `Use`, we can store its name,
+    // and be way more granular for incrementality, at the expense of increased memory usage.
+    // Use IDs aren't used a lot. The main thing that stores them is the def map. So everything that
+    // uses the def map will be invalidated. That includes infers, and so is pretty bad, but our
+    // def map incrementality story is pretty bad anyway and needs to be improved (see
+    // https://rust-lang.zulipchat.com/#narrow/channel/185405-t-compiler.2Frust-analyzer/topic/.60infer.60.20queries.20and.20splitting.20.60DefMap.60).
+    // So I left this as-is for now, as the def map improvement should also mitigate this.
+    Use,
+    /// Associated with [`ImplFileAstId`].
+    Impl,
+    /// Associated with [`BlockExprFileAstId`].
+    BlockExpr,
+    /// Keep this last.
+    Fixup,
 }
 
-impl<N: AstIdNode> Clone for FileAstId<N> {
+// First hash, then index, then kind.
+const HASH_BITS: u32 = 16;
+const INDEX_BITS: u32 = 11;
+const KIND_BITS: u32 = 5;
+const _: () = assert!(ErasedFileAstIdKind::Fixup as u32 <= ((1 << KIND_BITS) - 1));
+const _: () = assert!(HASH_BITS + INDEX_BITS + KIND_BITS == u32::BITS);
+
+#[inline]
+const fn u16_hash(hash: u64) -> u16 {
+    // We do basically the same as `FxHasher`. We don't use rustc-hash and truncate because the
+    // higher bits have more entropy, but unlike rustc-hash we don't rotate because it rotates
+    // for hashmaps that just use the low bits, but we compare all bits.
+    const K: u16 = 0xecc5;
+    let (part1, part2, part3, part4) =
+        (hash as u16, (hash >> 16) as u16, (hash >> 32) as u16, (hash >> 48) as u16);
+    part1
+        .wrapping_add(part2)
+        .wrapping_mul(K)
+        .wrapping_add(part3)
+        .wrapping_mul(K)
+        .wrapping_add(part4)
+        .wrapping_mul(K)
+}
+
+#[inline]
+const fn pack_hash_index_and_kind(hash: u16, index: u32, kind: u32) -> u32 {
+    (hash as u32) | (index << HASH_BITS) | (kind << (HASH_BITS + INDEX_BITS))
+}
+
+impl ErasedFileAstId {
+    #[inline]
+    fn hash_value(self) -> u16 {
+        self.0 as u16
+    }
+
+    #[inline]
+    fn index(self) -> u32 {
+        (self.0 << KIND_BITS) >> (HASH_BITS + KIND_BITS)
+    }
+
+    #[inline]
+    fn kind(self) -> u32 {
+        self.0 >> (HASH_BITS + INDEX_BITS)
+    }
+
+    fn ast_id_for(
+        node: &SyntaxNode,
+        index_map: &mut ErasedAstIdNextIndexMap,
+        parent: Option<&ErasedFileAstId>,
+    ) -> Option<ErasedFileAstId> {
+        // Blocks are deliberately not here - we only want to allocate a block if it contains items.
+        has_name_ast_id(node, index_map)
+            .or_else(|| assoc_item_ast_id(node, index_map, parent))
+            .or_else(|| extern_block_ast_id(node, index_map))
+            .or_else(|| use_ast_id(node, index_map))
+            .or_else(|| impl_ast_id(node, index_map))
+    }
+
+    fn should_alloc(node: &SyntaxNode) -> bool {
+        should_alloc_has_name(node)
+            || should_alloc_assoc_item(node)
+            || ast::ExternBlock::can_cast(node.kind())
+            || ast::Use::can_cast(node.kind())
+            || ast::Impl::can_cast(node.kind())
+    }
+
+    #[inline]
+    pub fn into_raw(self) -> u32 {
+        self.0
+    }
+
+    #[inline]
+    pub fn from_raw(v: u32) -> Self {
+        Self(v)
+    }
+}
+
+pub trait AstIdNode: AstNode {}
+
+/// `AstId` points to an AST node in a specific file.
+pub struct FileAstId<N> {
+    raw: ErasedFileAstId,
+    _marker: PhantomData<fn() -> N>,
+}
+
+/// Traits are manually implemented because `derive` adds redundant bounds.
+impl<N> Clone for FileAstId<N> {
+    #[inline]
     fn clone(&self) -> FileAstId<N> {
         *self
     }
 }
-impl<N: AstIdNode> Copy for FileAstId<N> {}
+impl<N> Copy for FileAstId<N> {}
 
-impl<N: AstIdNode> PartialEq for FileAstId<N> {
+impl<N> PartialEq for FileAstId<N> {
     fn eq(&self, other: &Self) -> bool {
         self.raw == other.raw
     }
 }
-impl<N: AstIdNode> Eq for FileAstId<N> {}
-impl<N: AstIdNode> Hash for FileAstId<N> {
+impl<N> Eq for FileAstId<N> {}
+impl<N> Hash for FileAstId<N> {
     fn hash<H: Hasher>(&self, hasher: &mut H) {
         self.raw.hash(hasher);
     }
 }
 
-impl<N: AstIdNode> fmt::Debug for FileAstId<N> {
+impl<N> fmt::Debug for FileAstId<N> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "FileAstId::<{}>({})", type_name::<N>(), self.raw)
+        write!(f, "FileAstId::<{}>({:?})", type_name::<N>(), self.raw)
     }
 }
 
-impl<N: AstIdNode> FileAstId<N> {
+impl<N> FileAstId<N> {
     // Can't make this a From implementation because of coherence
+    #[inline]
     pub fn upcast<M: AstIdNode>(self) -> FileAstId<M>
     where
         N: Into<M>,
     {
-        FileAstId { raw: self.raw, covariant: PhantomData }
+        FileAstId { raw: self.raw, _marker: PhantomData }
     }
 
+    #[inline]
     pub fn erase(self) -> ErasedFileAstId {
         self.raw
     }
 }
 
-pub trait AstIdNode: AstNode {}
-macro_rules! register_ast_id_node {
+#[derive(Hash)]
+struct ErasedHasNameFileAstId<'a> {
+    kind: SyntaxKind,
+    name: &'a str,
+}
+
+/// This holds the ast ID for variants too (they're a kind of assoc item).
+#[derive(Hash)]
+struct ErasedAssocItemFileAstId<'a> {
+    /// Subtle: items in `extern` blocks **do not** store the ID of the extern block here.
+    /// Instead this is left empty. The reason is that `ExternBlockFileAstId` is pretty unstable
+    /// (it contains only an index), and extern blocks don't introduce a new scope, so storing
+    /// the extern block ID will do more harm to incrementality than help.
+    parent: Option<ErasedFileAstId>,
+    properties: ErasedHasNameFileAstId<'a>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+struct ImplFileAstId<'a> {
+    /// This can be `None` if the `Self` type is not a named type, or if it is inside a macro call.
+    self_ty_name: Option<&'a str>,
+    /// This can be `None` if this is an inherent impl, or if the trait name is inside a macro call.
+    trait_name: Option<&'a str>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+struct BlockExprFileAstId {
+    parent: Option<ErasedFileAstId>,
+}
+
+impl AstIdNode for ast::ExternBlock {}
+
+fn extern_block_ast_id(
+    node: &SyntaxNode,
+    index_map: &mut ErasedAstIdNextIndexMap,
+) -> Option<ErasedFileAstId> {
+    if ast::ExternBlock::can_cast(node.kind()) {
+        Some(index_map.new_id(ErasedFileAstIdKind::ExternBlock, ()))
+    } else {
+        None
+    }
+}
+
+impl AstIdNode for ast::Use {}
+
+fn use_ast_id(
+    node: &SyntaxNode,
+    index_map: &mut ErasedAstIdNextIndexMap,
+) -> Option<ErasedFileAstId> {
+    if ast::Use::can_cast(node.kind()) {
+        Some(index_map.new_id(ErasedFileAstIdKind::Use, ()))
+    } else {
+        None
+    }
+}
+
+impl AstIdNode for ast::Impl {}
+
+fn impl_ast_id(
+    node: &SyntaxNode,
+    index_map: &mut ErasedAstIdNextIndexMap,
+) -> Option<ErasedFileAstId> {
+    if let Some(node) = ast::Impl::cast(node.clone()) {
+        let type_as_name = |ty: Option<ast::Type>| match ty? {
+            ast::Type::PathType(it) => Some(it.path()?.segment()?.name_ref()?),
+            _ => None,
+        };
+        let self_ty_name = type_as_name(node.self_ty());
+        let trait_name = type_as_name(node.trait_());
+        let data = ImplFileAstId {
+            self_ty_name: self_ty_name.as_ref().map(|it| it.text_non_mutable()),
+            trait_name: trait_name.as_ref().map(|it| it.text_non_mutable()),
+        };
+        Some(index_map.new_id(ErasedFileAstIdKind::Impl, data))
+    } else {
+        None
+    }
+}
+
+// Blocks aren't `AstIdNode`s deliberately, because unlike other nodes, not all blocks get their own
+// ast id, only if they have items. To account for that we have a different, fallible, API for blocks.
+// impl !AstIdNode for ast::BlockExpr {}
+
+fn block_expr_ast_id(
+    node: &SyntaxNode,
+    index_map: &mut ErasedAstIdNextIndexMap,
+    parent: Option<&ErasedFileAstId>,
+) -> Option<ErasedFileAstId> {
+    if ast::BlockExpr::can_cast(node.kind()) {
+        Some(
+            index_map.new_id(
+                ErasedFileAstIdKind::BlockExpr,
+                BlockExprFileAstId { parent: parent.copied() },
+            ),
+        )
+    } else {
+        None
+    }
+}
+
+#[derive(Default)]
+struct ErasedAstIdNextIndexMap(FxHashMap<(ErasedFileAstIdKind, u16), u32>);
+
+impl ErasedAstIdNextIndexMap {
+    #[inline]
+    fn new_id(&mut self, kind: ErasedFileAstIdKind, data: impl Hash) -> ErasedFileAstId {
+        let hash = FxBuildHasher.hash_one(&data);
+        let initial_hash = u16_hash(hash);
+        // Even though 2^INDEX_BITS=2048 items with the same hash seems like a lot,
+        // it could happen with macro calls or `use`s in macro-generated files. So we want
+        // to handle it gracefully. We just increment the hash.
+        let mut hash = initial_hash;
+        let index = loop {
+            match self.0.entry((kind, hash)) {
+                std::collections::hash_map::Entry::Occupied(mut entry) => {
+                    let i = entry.get_mut();
+                    if *i < ((1 << INDEX_BITS) - 1) {
+                        *i += 1;
+                        break *i;
+                    }
+                }
+                std::collections::hash_map::Entry::Vacant(entry) => {
+                    entry.insert(0);
+                    break 0;
+                }
+            }
+            hash = hash.wrapping_add(1);
+            if hash == initial_hash {
+                // That's 2^27=134,217,728 items!
+                panic!("you have way too many items in the same file!");
+            }
+        };
+        let kind = kind as u32;
+        ErasedFileAstId(pack_hash_index_and_kind(hash, index, kind))
+    }
+}
+
+macro_rules! register_enum_ast_id {
     (impl AstIdNode for $($ident:ident),+ ) => {
         $(
             impl AstIdNode for ast::$ident {}
         )+
-        fn should_alloc_id(kind: syntax::SyntaxKind) -> bool {
-            $(
-                ast::$ident::can_cast(kind)
-            )||+
+    };
+}
+register_enum_ast_id! {
+    impl AstIdNode for
+    Item, AnyHasGenericParams, Adt, Macro,
+    AssocItem
+}
+
+macro_rules! register_has_name_ast_id {
+    (impl AstIdNode for $($ident:ident = $name_method:ident),+ ) => {
+        $(
+            impl AstIdNode for ast::$ident {}
+        )+
+
+        fn has_name_ast_id(node: &SyntaxNode, index_map: &mut ErasedAstIdNextIndexMap) -> Option<ErasedFileAstId> {
+            let kind = node.kind();
+            match_ast! {
+                match node {
+                    $(
+                        ast::$ident(node) => {
+                            let name = node.$name_method();
+                            let name = name.as_ref().map_or("", |it| it.text_non_mutable());
+                            let result = ErasedHasNameFileAstId {
+                                kind,
+                                name,
+                            };
+                            Some(index_map.new_id(ErasedFileAstIdKind::$ident, result))
+                        },
+                    )*
+                    _ => None,
+                }
+            }
+        }
+
+        fn should_alloc_has_name(node: &SyntaxNode) -> bool {
+            let kind = node.kind();
+            false $( || ast::$ident::can_cast(kind) )*
         }
     };
 }
-register_ast_id_node! {
+register_has_name_ast_id! {
     impl AstIdNode for
-    Item, AnyHasGenericParams,
-        Adt,
-            Enum,
-                Variant,
-            Struct,
-            Union,
-        AssocItem,
-            Const,
-            Fn,
-            MacroCall,
-            TypeAlias,
-        ExternBlock,
-        ExternCrate,
-        Impl,
-        Macro,
-            MacroDef,
-            MacroRules,
-        Module,
-        Static,
-        Trait,
-        TraitAlias,
-        Use,
-    BlockExpr, ConstArg
+        Enum = name,
+        Struct = name,
+        Union = name,
+        ExternCrate = name_ref,
+        MacroDef = name,
+        MacroRules = name,
+        Module = name,
+        Static = name,
+        Trait = name,
+        TraitAlias = name
+}
+
+macro_rules! register_assoc_item_ast_id {
+    (impl AstIdNode for $($ident:ident = $name_callback:expr),+ ) => {
+        $(
+            impl AstIdNode for ast::$ident {}
+        )+
+
+        fn assoc_item_ast_id(
+            node: &SyntaxNode,
+            index_map: &mut ErasedAstIdNextIndexMap,
+            parent: Option<&ErasedFileAstId>,
+        ) -> Option<ErasedFileAstId> {
+            let kind = node.kind();
+            match_ast! {
+                match node {
+                    $(
+                        ast::$ident(node) => {
+                            let name = $name_callback(node);
+                            let name = name.as_ref().map_or("", |it| it.text_non_mutable());
+                            let properties = ErasedHasNameFileAstId {
+                                kind,
+                                name,
+                            };
+                            let result = ErasedAssocItemFileAstId {
+                                parent: parent.copied(),
+                                properties,
+                            };
+                            Some(index_map.new_id(ErasedFileAstIdKind::$ident, result))
+                        },
+                    )*
+                    _ => None,
+                }
+            }
+        }
+
+        fn should_alloc_assoc_item(node: &SyntaxNode) -> bool {
+            let kind = node.kind();
+            false $( || ast::$ident::can_cast(kind) )*
+        }
+    };
+}
+register_assoc_item_ast_id! {
+    impl AstIdNode for
+    Variant = |it: ast::Variant| it.name(),
+    Const = |it: ast::Const| it.name(),
+    Fn = |it: ast::Fn| it.name(),
+    MacroCall = |it: ast::MacroCall| it.path().and_then(|path| path.segment()?.name_ref()),
+    TypeAlias = |it: ast::TypeAlias| it.name()
 }
 
 /// Maps items' `SyntaxNode`s to `ErasedFileAstId`s and back.
 #[derive(Default)]
 pub struct AstIdMap {
-    /// Maps stable id to unstable ptr.
-    arena: Arena<SyntaxNodePtr>,
-    /// Reverse: map ptr to id.
-    map: hashbrown::HashTable<Idx<SyntaxNodePtr>>,
+    /// An arena of the ptrs and their associated ID.
+    arena: Arena<(SyntaxNodePtr, ErasedFileAstId)>,
+    /// Map ptr to id.
+    ptr_map: hashbrown::HashTable<ArenaId>,
+    /// Map id to ptr.
+    id_map: hashbrown::HashTable<ArenaId>,
 }
 
+type ArenaId = Idx<(SyntaxNodePtr, ErasedFileAstId)>;
+
 impl fmt::Debug for AstIdMap {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("AstIdMap").field("arena", &self.arena).finish()
@@ -148,31 +545,116 @@ impl PartialEq for AstIdMap {
 }
 impl Eq for AstIdMap {}
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum ContainsItems {
+    Yes,
+    No,
+}
+
 impl AstIdMap {
     pub fn from_source(node: &SyntaxNode) -> AstIdMap {
         assert!(node.parent().is_none());
         let mut res = AstIdMap::default();
+        let mut index_map = ErasedAstIdNextIndexMap::default();
+
+        // Ensure we allocate the root.
+        res.arena.alloc((SyntaxNodePtr::new(node), ROOT_ERASED_FILE_AST_ID));
 
-        // make sure to allocate the root node
-        if !should_alloc_id(node.kind()) {
-            res.alloc(node);
-        }
         // By walking the tree in breadth-first order we make sure that parents
         // get lower ids then children. That is, adding a new child does not
         // change parent's id. This means that, say, adding a new function to a
         // trait does not change ids of top-level items, which helps caching.
-        bdfs(node, |it| {
-            if should_alloc_id(it.kind()) {
-                res.alloc(&it);
-                TreeOrder::BreadthFirst
-            } else {
-                TreeOrder::DepthFirst
+
+        // This contains the stack of the `BlockExpr`s we are under. We do this
+        // so we only allocate `BlockExpr`s if they contain items.
+        // The general idea is: when we enter a block we push `(block, false)` here.
+        // Items inside the block are attributed to the block's container, not the block.
+        // For the first item we find inside a block, we make this `(block, true)`
+        // and create an ast id for the block. When exiting the block we pop it,
+        // whether or not we created an ast id for it.
+        // It may seem that with this setup we will generate an ID for blocks that
+        // have no items directly but have items inside other items inside them.
+        // This is true, but it doesn't matter, because such blocks can't exist.
+        // After all, the block will then contain the *outer* item, so we allocate
+        // an ID for it anyway.
+        let mut blocks = Vec::new();
+        let mut curr_layer = vec![(node.clone(), None)];
+        let mut next_layer = vec![];
+        while !curr_layer.is_empty() {
+            curr_layer.drain(..).for_each(|(node, parent_idx)| {
+                let mut preorder = node.preorder();
+                while let Some(event) = preorder.next() {
+                    match event {
+                        syntax::WalkEvent::Enter(node) => {
+                            if ast::BlockExpr::can_cast(node.kind()) {
+                                blocks.push((node, ContainsItems::No));
+                            } else if ErasedFileAstId::should_alloc(&node) {
+                                // Allocate blocks on-demand, only if they have items.
+                                // We don't associate items with blocks, only with items, since block IDs can be quite unstable.
+                                // FIXME: Is this the correct thing to do? Macro calls might actually be more incremental if
+                                // associated with blocks (not sure). Either way it's not a big deal.
+                                if let Some((
+                                    last_block_node,
+                                    already_allocated @ ContainsItems::No,
+                                )) = blocks.last_mut()
+                                {
+                                    let block_ast_id = block_expr_ast_id(
+                                        last_block_node,
+                                        &mut index_map,
+                                        parent_of(parent_idx, &res),
+                                    )
+                                    .expect("not a BlockExpr");
+                                    res.arena
+                                        .alloc((SyntaxNodePtr::new(last_block_node), block_ast_id));
+                                    *already_allocated = ContainsItems::Yes;
+                                }
+
+                                let parent = parent_of(parent_idx, &res);
+                                let ast_id =
+                                    ErasedFileAstId::ast_id_for(&node, &mut index_map, parent)
+                                        .expect("this node should have an ast id");
+                                let idx = res.arena.alloc((SyntaxNodePtr::new(&node), ast_id));
+
+                                next_layer.extend(node.children().map(|child| (child, Some(idx))));
+                                preorder.skip_subtree();
+                            }
+                        }
+                        syntax::WalkEvent::Leave(node) => {
+                            if ast::BlockExpr::can_cast(node.kind()) {
+                                assert_eq!(
+                                    blocks.pop().map(|it| it.0),
+                                    Some(node),
+                                    "left a BlockExpr we never entered"
+                                );
+                            }
+                        }
+                    }
+                }
+            });
+            std::mem::swap(&mut curr_layer, &mut next_layer);
+            assert!(blocks.is_empty(), "didn't leave all BlockExprs");
+        }
+
+        res.ptr_map = hashbrown::HashTable::with_capacity(res.arena.len());
+        res.id_map = hashbrown::HashTable::with_capacity(res.arena.len());
+        for (idx, (ptr, ast_id)) in res.arena.iter() {
+            let ptr_hash = hash_ptr(ptr);
+            let ast_id_hash = hash_ast_id(ast_id);
+            match res.ptr_map.entry(
+                ptr_hash,
+                |idx2| *idx2 == idx,
+                |&idx| hash_ptr(&res.arena[idx].0),
+            ) {
+                hashbrown::hash_table::Entry::Occupied(_) => unreachable!(),
+                hashbrown::hash_table::Entry::Vacant(entry) => {
+                    entry.insert(idx);
+                }
             }
-        });
-        res.map = hashbrown::HashTable::with_capacity(res.arena.len());
-        for (idx, ptr) in res.arena.iter() {
-            let hash = hash_ptr(ptr);
-            match res.map.entry(hash, |&idx2| idx2 == idx, |&idx| hash_ptr(&res.arena[idx])) {
+            match res.id_map.entry(
+                ast_id_hash,
+                |idx2| *idx2 == idx,
+                |&idx| hash_ast_id(&res.arena[idx].1),
+            ) {
                 hashbrown::hash_table::Entry::Occupied(_) => unreachable!(),
                 hashbrown::hash_table::Entry::Vacant(entry) => {
                     entry.insert(idx);
@@ -180,98 +662,235 @@ impl AstIdMap {
             }
         }
         res.arena.shrink_to_fit();
-        res
+        return res;
+
+        fn parent_of(parent_idx: Option<ArenaId>, res: &AstIdMap) -> Option<&ErasedFileAstId> {
+            let mut parent = parent_idx.map(|parent_idx| &res.arena[parent_idx].1);
+            if parent.is_some_and(|parent| parent.kind() == ErasedFileAstIdKind::ExternBlock as u32)
+            {
+                // See the comment on `ErasedAssocItemFileAstId` for why is this.
+                // FIXME: Technically there could be an extern block inside another item, e.g.:
+                // ```
+                // fn foo() {
+                //     extern "C" {
+                //         fn bar();
+                //     }
+                // }
+                // ```
+                // Here we want to make `foo()` the parent of `bar()`, but we make it `None`.
+                // Shouldn't be a big deal though.
+                parent = None;
+            }
+            parent
+        }
     }
 
     /// The [`AstId`] of the root node
     pub fn root(&self) -> SyntaxNodePtr {
-        self.arena[Idx::from_raw(RawIdx::from_u32(0))]
+        self.arena[Idx::from_raw(RawIdx::from_u32(0))].0
     }
 
     pub fn ast_id<N: AstIdNode>(&self, item: &N) -> FileAstId<N> {
-        let raw = self.erased_ast_id(item.syntax());
-        FileAstId { raw, covariant: PhantomData }
+        self.ast_id_for_ptr(AstPtr::new(item))
+    }
+
+    /// Blocks may not be allocated (if they have no items), so they have a different API.
+    pub fn ast_id_for_block(&self, block: &ast::BlockExpr) -> Option<FileAstId<ast::BlockExpr>> {
+        self.ast_id_for_ptr_for_block(AstPtr::new(block))
     }
 
     pub fn ast_id_for_ptr<N: AstIdNode>(&self, ptr: AstPtr<N>) -> FileAstId<N> {
         let ptr = ptr.syntax_node_ptr();
-        let hash = hash_ptr(&ptr);
-        match self.map.find(hash, |&idx| self.arena[idx] == ptr) {
-            Some(&raw) => FileAstId {
-                raw: ErasedFileAstId(raw.into_raw().into_u32()),
-                covariant: PhantomData,
-            },
-            None => panic!(
-                "Can't find {:?} in AstIdMap:\n{:?}",
-                ptr,
-                self.arena.iter().map(|(_id, i)| i).collect::<Vec<_>>(),
-            ),
-        }
+        FileAstId { raw: self.erased_ast_id(ptr), _marker: PhantomData }
     }
 
-    pub fn get<N: AstIdNode>(&self, id: FileAstId<N>) -> AstPtr<N> {
-        AstPtr::try_from_raw(self.arena[Idx::from_raw(RawIdx::from_u32(id.raw.into_raw()))])
-            .unwrap()
+    /// Blocks may not be allocated (if they have no items), so they have a different API.
+    pub fn ast_id_for_ptr_for_block(
+        &self,
+        ptr: AstPtr<ast::BlockExpr>,
+    ) -> Option<FileAstId<ast::BlockExpr>> {
+        let ptr = ptr.syntax_node_ptr();
+        self.try_erased_ast_id(ptr).map(|raw| FileAstId { raw, _marker: PhantomData })
+    }
+
+    fn erased_ast_id(&self, ptr: SyntaxNodePtr) -> ErasedFileAstId {
+        self.try_erased_ast_id(ptr).unwrap_or_else(|| {
+            panic!(
+                "Can't find SyntaxNodePtr {:?} in AstIdMap:\n{:?}",
+                ptr,
+                self.arena.iter().map(|(_id, i)| i).collect::<Vec<_>>(),
+            )
+        })
+    }
+
+    fn try_erased_ast_id(&self, ptr: SyntaxNodePtr) -> Option<ErasedFileAstId> {
+        let hash = hash_ptr(&ptr);
+        let idx = *self.ptr_map.find(hash, |&idx| self.arena[idx].0 == ptr)?;
+        Some(self.arena[idx].1)
+    }
+
+    // Don't bound on `AstIdNode` here, because `BlockExpr`s are also valid here (`ast::BlockExpr`
+    // doesn't always have a matching `FileAstId`, but a `FileAstId<ast::BlockExpr>` always has
+    // a matching node).
+    pub fn get<N: AstNode>(&self, id: FileAstId<N>) -> AstPtr<N> {
+        let ptr = self.get_erased(id.raw);
+        AstPtr::try_from_raw(ptr)
+            .unwrap_or_else(|| panic!("AstIdMap node mismatch with node `{ptr:?}`"))
     }
 
     pub fn get_erased(&self, id: ErasedFileAstId) -> SyntaxNodePtr {
-        self.arena[Idx::from_raw(RawIdx::from_u32(id.into_raw()))]
-    }
-
-    fn erased_ast_id(&self, item: &SyntaxNode) -> ErasedFileAstId {
-        let ptr = SyntaxNodePtr::new(item);
-        let hash = hash_ptr(&ptr);
-        match self.map.find(hash, |&idx| self.arena[idx] == ptr) {
-            Some(&idx) => ErasedFileAstId(idx.into_raw().into_u32()),
+        let hash = hash_ast_id(&id);
+        match self.id_map.find(hash, |&idx| self.arena[idx].1 == id) {
+            Some(&idx) => self.arena[idx].0,
             None => panic!(
-                "Can't find {:?} in AstIdMap:\n{:?}\n source text: {}",
-                item,
+                "Can't find ast id {:?} in AstIdMap:\n{:?}",
+                id,
                 self.arena.iter().map(|(_id, i)| i).collect::<Vec<_>>(),
-                item
             ),
         }
     }
-
-    fn alloc(&mut self, item: &SyntaxNode) -> ErasedFileAstId {
-        ErasedFileAstId(self.arena.alloc(SyntaxNodePtr::new(item)).into_raw().into_u32())
-    }
 }
 
+#[inline]
 fn hash_ptr(ptr: &SyntaxNodePtr) -> u64 {
-    BuildHasherDefault::<FxHasher>::default().hash_one(ptr)
+    FxBuildHasher.hash_one(ptr)
 }
 
-#[derive(Copy, Clone, PartialEq, Eq)]
-enum TreeOrder {
-    BreadthFirst,
-    DepthFirst,
+#[inline]
+fn hash_ast_id(ptr: &ErasedFileAstId) -> u64 {
+    FxBuildHasher.hash_one(ptr)
 }
 
-/// Walks the subtree in bdfs order, calling `f` for each node. What is bdfs
-/// order? It is a mix of breadth-first and depth first orders. Nodes for which
-/// `f` returns [`TreeOrder::BreadthFirst`] are visited breadth-first, all the other nodes are explored
-/// [`TreeOrder::DepthFirst`].
-///
-/// In other words, the size of the bfs queue is bound by the number of "true"
-/// nodes.
-fn bdfs(node: &SyntaxNode, mut f: impl FnMut(SyntaxNode) -> TreeOrder) {
-    let mut curr_layer = vec![node.clone()];
-    let mut next_layer = vec![];
-    while !curr_layer.is_empty() {
-        curr_layer.drain(..).for_each(|node| {
-            let mut preorder = node.preorder();
-            while let Some(event) = preorder.next() {
-                match event {
-                    syntax::WalkEvent::Enter(node) => {
-                        if f(node.clone()) == TreeOrder::BreadthFirst {
-                            next_layer.extend(node.children());
-                            preorder.skip_subtree();
-                        }
-                    }
-                    syntax::WalkEvent::Leave(_) => {}
-                }
+#[cfg(test)]
+mod tests {
+    use syntax::{AstNode, Edition, SourceFile, SyntaxKind, SyntaxNodePtr, WalkEvent, ast};
+
+    use crate::AstIdMap;
+
+    #[test]
+    fn check_all_nodes() {
+        let syntax = SourceFile::parse(
+            r#"
+extern crate foo;
+fn foo() {
+    union U {}
+}
+struct S;
+macro_rules! m {}
+macro m2() {}
+trait Trait {}
+impl Trait for S {}
+impl S {}
+impl m!() {}
+impl m2!() for m!() {}
+type T = i32;
+enum E {
+    V1(),
+    V2 {},
+    V3,
+}
+struct S; // duplicate
+extern "C" {
+    static S: i32;
+}
+static mut S: i32 = 0;
+const FOO: i32 = 0;
+        "#,
+            Edition::CURRENT,
+        )
+        .syntax_node();
+        let ast_id_map = AstIdMap::from_source(&syntax);
+        for node in syntax.preorder() {
+            let WalkEvent::Enter(node) = node else { continue };
+            if !matches!(
+                node.kind(),
+                SyntaxKind::EXTERN_CRATE
+                    | SyntaxKind::FN
+                    | SyntaxKind::UNION
+                    | SyntaxKind::STRUCT
+                    | SyntaxKind::MACRO_RULES
+                    | SyntaxKind::MACRO_DEF
+                    | SyntaxKind::MACRO_CALL
+                    | SyntaxKind::TRAIT
+                    | SyntaxKind::IMPL
+                    | SyntaxKind::TYPE_ALIAS
+                    | SyntaxKind::ENUM
+                    | SyntaxKind::VARIANT
+                    | SyntaxKind::EXTERN_BLOCK
+                    | SyntaxKind::STATIC
+                    | SyntaxKind::CONST
+            ) {
+                continue;
             }
-        });
-        std::mem::swap(&mut curr_layer, &mut next_layer);
+            let ptr = SyntaxNodePtr::new(&node);
+            let ast_id = ast_id_map.erased_ast_id(ptr);
+            let turn_back = ast_id_map.get_erased(ast_id);
+            assert_eq!(ptr, turn_back);
+        }
+    }
+
+    #[test]
+    fn different_names_get_different_hashes() {
+        let syntax = SourceFile::parse(
+            r#"
+fn foo() {}
+fn bar() {}
+        "#,
+            Edition::CURRENT,
+        )
+        .syntax_node();
+        let ast_id_map = AstIdMap::from_source(&syntax);
+        let fns = syntax.descendants().filter_map(ast::Fn::cast).collect::<Vec<_>>();
+        let [foo_fn, bar_fn] = fns.as_slice() else {
+            panic!("not exactly 2 functions");
+        };
+        let foo_fn_id = ast_id_map.ast_id(foo_fn);
+        let bar_fn_id = ast_id_map.ast_id(bar_fn);
+        assert_ne!(foo_fn_id.raw.hash_value(), bar_fn_id.raw.hash_value(), "hashes are equal");
+    }
+
+    #[test]
+    fn different_parents_get_different_hashes() {
+        let syntax = SourceFile::parse(
+            r#"
+fn foo() {
+    m!();
+}
+fn bar() {
+    m!();
+}
+        "#,
+            Edition::CURRENT,
+        )
+        .syntax_node();
+        let ast_id_map = AstIdMap::from_source(&syntax);
+        let macro_calls = syntax.descendants().filter_map(ast::MacroCall::cast).collect::<Vec<_>>();
+        let [macro_call_foo, macro_call_bar] = macro_calls.as_slice() else {
+            panic!("not exactly 2 macro calls");
+        };
+        let macro_call_foo_id = ast_id_map.ast_id(macro_call_foo);
+        let macro_call_bar_id = ast_id_map.ast_id(macro_call_bar);
+        assert_ne!(
+            macro_call_foo_id.raw.hash_value(),
+            macro_call_bar_id.raw.hash_value(),
+            "hashes are equal"
+        );
+    }
+
+    #[test]
+    fn blocks_with_no_items_have_no_id() {
+        let syntax = SourceFile::parse(
+            r#"
+fn foo() {
+    let foo = 1;
+    bar(foo);
+}
+        "#,
+            Edition::CURRENT,
+        )
+        .syntax_node();
+        let ast_id_map = AstIdMap::from_source(&syntax);
+        let block = syntax.descendants().find_map(ast::BlockExpr::cast).expect("no block");
+        assert!(ast_id_map.ast_id_for_block(&block).is_none());
     }
 }
diff --git a/src/tools/rust-analyzer/crates/span/src/lib.rs b/src/tools/rust-analyzer/crates/span/src/lib.rs
index f81648ac42c5..b81d08eed6d8 100644
--- a/src/tools/rust-analyzer/crates/span/src/lib.rs
+++ b/src/tools/rust-analyzer/crates/span/src/lib.rs
@@ -6,7 +6,10 @@ mod hygiene;
 mod map;
 
 pub use self::{
-    ast_id::{AstIdMap, AstIdNode, ErasedFileAstId, FileAstId},
+    ast_id::{
+        AstIdMap, AstIdNode, ErasedFileAstId, FIXUP_ERASED_FILE_AST_ID_MARKER, FileAstId,
+        ROOT_ERASED_FILE_AST_ID,
+    },
     hygiene::{SyntaxContext, Transparency},
     map::{RealSpanMap, SpanMap},
 };
@@ -15,19 +18,6 @@ pub use syntax::Edition;
 pub use text_size::{TextRange, TextSize};
 pub use vfs::FileId;
 
-// The first index is always the root node's AstId
-/// The root ast id always points to the encompassing file, using this in spans is discouraged as
-/// any range relative to it will be effectively absolute, ruining the entire point of anchored
-/// relative text ranges.
-pub const ROOT_ERASED_FILE_AST_ID: ErasedFileAstId = ErasedFileAstId::from_raw(0);
-
-/// FileId used as the span for syntax node fixups. Any Span containing this file id is to be
-/// considered fake.
-pub const FIXUP_ERASED_FILE_AST_ID_MARKER: ErasedFileAstId =
-    // we pick the second to last for this in case we ever consider making this a NonMaxU32, this
-    // is required to be stable for the proc-macro-server
-    ErasedFileAstId::from_raw(!0 - 1);
-
 pub type Span = SpanData<SyntaxContext>;
 
 impl Span {
@@ -60,7 +50,7 @@ impl<Ctx: fmt::Debug> fmt::Debug for SpanData<Ctx> {
         if f.alternate() {
             fmt::Debug::fmt(&self.anchor.file_id.file_id().index(), f)?;
             f.write_char(':')?;
-            fmt::Debug::fmt(&self.anchor.ast_id.into_raw(), f)?;
+            write!(f, "{:#?}", self.anchor.ast_id)?;
             f.write_char('@')?;
             fmt::Debug::fmt(&self.range, f)?;
             f.write_char('#')?;
@@ -85,7 +75,7 @@ impl fmt::Display for Span {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Debug::fmt(&self.anchor.file_id.file_id().index(), f)?;
         f.write_char(':')?;
-        fmt::Debug::fmt(&self.anchor.ast_id.into_raw(), f)?;
+        write!(f, "{:#?}", self.anchor.ast_id)?;
         f.write_char('@')?;
         fmt::Debug::fmt(&self.range, f)?;
         f.write_char('#')?;
@@ -101,7 +91,7 @@ pub struct SpanAnchor {
 
 impl fmt::Debug for SpanAnchor {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_tuple("SpanAnchor").field(&self.file_id).field(&self.ast_id.into_raw()).finish()
+        f.debug_tuple("SpanAnchor").field(&self.file_id).field(&self.ast_id).finish()
     }
 }
 
diff --git a/src/tools/rust-analyzer/crates/span/src/map.rs b/src/tools/rust-analyzer/crates/span/src/map.rs
index cc7a886643a9..f58201793da2 100644
--- a/src/tools/rust-analyzer/crates/span/src/map.rs
+++ b/src/tools/rust-analyzer/crates/span/src/map.rs
@@ -169,7 +169,7 @@ impl fmt::Display for RealSpanMap {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         writeln!(f, "RealSpanMap({:?}):", self.file_id)?;
         for span in self.pairs.iter() {
-            writeln!(f, "{}: {}", u32::from(span.0), span.1.into_raw())?;
+            writeln!(f, "{}: {:#?}", u32::from(span.0), span.1)?;
         }
         Ok(())
     }
diff --git a/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs b/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs
index dcf853427e53..f5530c5fffd2 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/ast/node_ext.rs
@@ -30,6 +30,16 @@ impl ast::Name {
     pub fn text(&self) -> TokenText<'_> {
         text_of_first_token(self.syntax())
     }
+    pub fn text_non_mutable(&self) -> &str {
+        fn first_token(green_ref: &GreenNodeData) -> &GreenTokenData {
+            green_ref.children().next().and_then(NodeOrToken::into_token).unwrap()
+        }
+
+        match self.syntax().green() {
+            Cow::Borrowed(green_ref) => first_token(green_ref).text(),
+            Cow::Owned(_) => unreachable!(),
+        }
+    }
 }
 
 impl ast::NameRef {