Auto merge of #14752 - ponyii:fix/generate_derive_breaks_indentation, r=Veykril

fix: assists no longer break indentation

Fixes https://github.com/rust-lang/rust-analyzer/issues/14674

These are _ad hoc_ patches for a number of assists that can produce incorrectly indented code, namely:
- generate_derive
- add_missing_impl_members
- add_missing_default_members

Some general solution is required in future, as the same problem arises in many other assists, e.g.
- replace_derive_with...
- generate_default_from_enum...
- generate_default_from_new
- generate_delegate_methods
(the list is incomplete)

crates/ide-assists/src/handlers/add_missing_impl_members.rs

@@ -1346,8 +1346,8 @@ struct SomeStruct {
 }
 impl PartialEq for SomeStruct {
     $0fn ne(&self, other: &Self) -> bool {
-            !self.eq(other)
-        }
+        !self.eq(other)
+    }
 }
 "#,
         );
@@ -1511,11 +1511,175 @@ fn main() {
     struct S;
     impl Tr for S {
         fn method() {
-        ${0:todo!()}
-    }
+            ${0:todo!()}
+        }
     }
 }
 "#,
         );
     }
+
+    #[test]
+    fn test_add_missing_preserves_indentation() {
+        // in different modules
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod m {
+    pub trait Foo {
+        const CONST_MULTILINE: (
+            i32,
+            i32
+        );
+
+        fn foo(&self);
+    }
+}
+struct S;
+impl m::Foo for S { $0 }"#,
+            r#"
+mod m {
+    pub trait Foo {
+        const CONST_MULTILINE: (
+            i32,
+            i32
+        );
+
+        fn foo(&self);
+    }
+}
+struct S;
+impl m::Foo for S {
+    $0const CONST_MULTILINE: (
+        i32,
+        i32
+    );
+
+    fn foo(&self) {
+        todo!()
+    }
+}"#,
+        );
+        // in the same module
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod m {
+    trait Foo {
+        type Output;
+
+        const CONST: usize = 42;
+        const CONST_2: i32;
+        const CONST_MULTILINE: (
+            i32,
+            i32
+        );
+
+        fn foo(&self);
+        fn bar(&self);
+        fn baz(&self);
+    }
+
+    struct S;
+
+    impl Foo for S {
+        fn bar(&self) {}
+$0
+    }
+}"#,
+            r#"
+mod m {
+    trait Foo {
+        type Output;
+
+        const CONST: usize = 42;
+        const CONST_2: i32;
+        const CONST_MULTILINE: (
+            i32,
+            i32
+        );
+
+        fn foo(&self);
+        fn bar(&self);
+        fn baz(&self);
+    }
+
+    struct S;
+
+    impl Foo for S {
+        fn bar(&self) {}
+
+        $0type Output;
+
+        const CONST_2: i32;
+
+        const CONST_MULTILINE: (
+            i32,
+            i32
+        );
+
+        fn foo(&self) {
+            todo!()
+        }
+
+        fn baz(&self) {
+            todo!()
+        }
+
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_add_default_preserves_indentation() {
+        check_assist(
+            add_missing_default_members,
+            r#"
+mod m {
+    pub trait Foo {
+        type Output;
+
+        const CONST: usize = 42;
+        const CONST_2: i32;
+        const CONST_MULTILINE: = (
+            i32,
+            i32,
+        ) = (3, 14);
+
+        fn valid(some: u32) -> bool { false }
+        fn foo(some: u32) -> bool;
+    }
+}
+struct S;
+impl m::Foo for S { $0 }"#,
+            r#"
+mod m {
+    pub trait Foo {
+        type Output;
+
+        const CONST: usize = 42;
+        const CONST_2: i32;
+        const CONST_MULTILINE: = (
+            i32,
+            i32,
+        ) = (3, 14);
+
+        fn valid(some: u32) -> bool { false }
+        fn foo(some: u32) -> bool;
+    }
+}
+struct S;
+impl m::Foo for S {
+    $0const CONST: usize = 42;
+
+    const CONST_MULTILINE: = (
+        i32,
+        i32,
+    ) = (3, 14);
+
+    fn valid(some: u32) -> bool { false }
+}"#,
+        )
+    }
 }

crates/ide-assists/src/handlers/generate_derive.rs

@@ -1,5 +1,5 @@
 use syntax::{
-    ast::{self, AstNode, HasAttrs},
+    ast::{self, edit::IndentLevel, AstNode, HasAttrs},
     SyntaxKind::{COMMENT, WHITESPACE},
     TextSize,
 };
@@ -42,7 +42,12 @@ pub(crate) fn generate_derive(acc: &mut Assists, ctx: &AssistContext<'_>) -> Opt
                 .next();
             match derive_attr {
                 None => {
-                    builder.insert_snippet(cap, node_start, "#[derive($0)]\n");
+                    let indent_level = IndentLevel::from_node(nominal.syntax());
+                    builder.insert_snippet(
+                        cap,
+                        node_start,
+                        format!("#[derive($0)]\n{indent_level}"),
+                    );
                 }
                 Some(tt) => {
                     // Just move the cursor.
@@ -84,6 +89,20 @@ mod tests {
             "struct Foo { $0 a: i32, }",
             "#[derive($0)]\nstruct Foo {  a: i32, }",
         );
+        check_assist(
+            generate_derive,
+            "
+mod m {
+    struct Foo { a: i32,$0 }
+}
+            ",
+            "
+mod m {
+    #[derive($0)]
+    struct Foo { a: i32, }
+}
+            ",
+        );
     }
 
     #[test]
@@ -111,6 +130,24 @@ struct Foo { a: i32$0, }
 struct Foo { a: i32, }
             ",
         );
+        check_assist(
+            generate_derive,
+            "
+mod m {
+    /// `Foo` is a pretty important struct.
+    /// It does stuff.
+    struct Foo { a: i32,$0 }
+}
+            ",
+            "
+mod m {
+    /// `Foo` is a pretty important struct.
+    /// It does stuff.
+    #[derive($0)]
+    struct Foo { a: i32, }
+}
+            ",
+        );
     }
 
     #[test]

crates/ide-assists/src/utils.rs

@@ -9,8 +9,8 @@ use stdx::format_to;
 use syntax::{
     ast::{
         self,
-        edit::{self, AstNodeEdit},
-        edit_in_place::{AttrsOwnerEdit, Removable},
+        edit::{AstNodeEdit, IndentLevel},
+        edit_in_place::{AttrsOwnerEdit, Indent, Removable},
         make, HasArgList, HasAttrs, HasGenericParams, HasName, HasTypeBounds, Whitespace,
     },
     ted, AstNode, AstToken, Direction, SourceFile,
@@ -139,9 +139,11 @@ pub fn add_trait_assoc_items_to_impl(
 
     let transform = PathTransform::trait_impl(&target_scope, &source_scope, trait_, impl_.clone());
 
+    let new_indent_level = IndentLevel::from_node(impl_.syntax()) + 1;
     let items = items.into_iter().map(|assoc_item| {
         transform.apply(assoc_item.syntax());
         assoc_item.remove_attrs_and_docs();
+        assoc_item.reindent_to(new_indent_level);
         assoc_item
     });
 
@@ -153,8 +155,10 @@ pub fn add_trait_assoc_items_to_impl(
         first_item.get_or_insert_with(|| item.clone());
         match &item {
             ast::AssocItem::Fn(fn_) if fn_.body().is_none() => {
-                let body = make::block_expr(None, Some(make::ext::expr_todo()))
-                    .indent(edit::IndentLevel(1));
+                let body = AstNodeEdit::indent(
+                    &make::block_expr(None, Some(make::ext::expr_todo())),
+                    new_indent_level,
+                );
                 ted::replace(fn_.get_or_create_body().syntax(), body.clone_for_update().syntax())
             }
             ast::AssocItem::TypeAlias(type_alias) => {

crates/syntax/src/ast/edit_in_place.rs

@@ -465,6 +465,8 @@ impl ast::Impl {
 }
 
 impl ast::AssocItemList {
+    /// Attention! This function does align the first line of `item` with respect to `self`,
+    /// but it does _not_ change indentation of other lines (if any).
     pub fn add_item(&self, item: ast::AssocItem) {
         let (indent, position, whitespace) = match self.assoc_items().last() {
             Some(last_item) => (