diff --git a/Cargo.lock b/Cargo.lock
index d1afe5944ee9..46d8b3de806f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3052,7 +3052,6 @@ dependencies = [
  "rustc 0.0.0",
  "rustc_data_structures 0.0.0",
  "rustc_errors 0.0.0",
- "rustc_mir 0.0.0",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
 ]
diff --git a/src/librustc_interface/passes.rs b/src/librustc_interface/passes.rs
index c7be6276f4ac..3c7d854b36b1 100644
--- a/src/librustc_interface/passes.rs
+++ b/src/librustc_interface/passes.rs
@@ -461,7 +461,7 @@ fn configure_and_expand_inner<'a>(
     sess.profiler(|p| p.end_activity("macro expansion"));
 
     time(sess, "maybe building test harness", || {
-        syntax_ext::test_harness::modify_for_testing(
+        syntax_ext::test_harness::inject(
             &sess.parse_sess,
             &mut resolver,
             sess.opts.test,
@@ -490,7 +490,7 @@ fn configure_and_expand_inner<'a>(
             let num_crate_types = crate_types.len();
             let is_proc_macro_crate = crate_types.contains(&config::CrateType::ProcMacro);
             let is_test_crate = sess.opts.test;
-            syntax_ext::proc_macro_decls::modify(
+            syntax_ext::proc_macro_harness::inject(
                 &sess.parse_sess,
                 &mut resolver,
                 krate,
diff --git a/src/librustc_passes/Cargo.toml b/src/librustc_passes/Cargo.toml
index 5f378dacd25a..596ec6c19bcb 100644
--- a/src/librustc_passes/Cargo.toml
+++ b/src/librustc_passes/Cargo.toml
@@ -11,7 +11,6 @@ path = "lib.rs"
 [dependencies]
 log = "0.4"
 rustc = { path = "../librustc" }
-rustc_mir = { path = "../librustc_mir"}
 rustc_data_structures = { path = "../librustc_data_structures" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index e53757dce3d3..bb7834a133f0 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -1,6 +1,6 @@
 use crate::ast::{self, Attribute, Name, PatKind};
 use crate::attr::{HasAttrs, Stability, Deprecation};
-use crate::source_map::{SourceMap, Spanned, FileName, respan};
+use crate::source_map::{SourceMap, Spanned, respan};
 use crate::edition::Edition;
 use crate::ext::expand::{self, AstFragment, Invocation};
 use crate::ext::hygiene::{ExpnId, SyntaxContext, Transparency};
diff --git a/src/libsyntax/ext/proc_macro.rs b/src/libsyntax/ext/proc_macro.rs
index 4b4ac57207ef..425b9813f590 100644
--- a/src/libsyntax/ext/proc_macro.rs
+++ b/src/libsyntax/ext/proc_macro.rs
@@ -231,7 +231,7 @@ crate fn add_derived_markers<T: HasAttrs>(
         names.insert(unwrap_or!(path.segments.get(0), continue).ident.name);
     }
 
-    let span = span.fresh_expansion(cx.current_expansion.mark, ExpnInfo::allow_unstable(
+    let span = span.fresh_expansion(cx.current_expansion.id, ExpnInfo::allow_unstable(
         ExpnKind::Macro(MacroKind::Derive, Symbol::intern(&pretty_name)), span,
         cx.parse_sess.edition, cx.allow_derive_markers.clone(),
     ));
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 52f65e1b4747..3cd5464f3571 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -794,7 +794,7 @@ mod tests {
     use std::path::PathBuf;
     use syntax_pos::{BytePos, Span, NO_EXPANSION, edition::Edition};
     use rustc_data_structures::fx::{FxHashSet, FxHashMap};
-    use rustc_data_structures::sync::Lock;
+    use rustc_data_structures::sync::{Lock, Once};
 
     fn mk_sess(sm: Lrc<SourceMap>) -> ParseSess {
         let emitter = errors::emitter::EmitterWriter::new(Box::new(io::sink()),
@@ -817,6 +817,7 @@ mod tests {
             param_attr_spans: Lock::new(Vec::new()),
             let_chains_spans: Lock::new(Vec::new()),
             async_closure_spans: Lock::new(Vec::new()),
+            injected_crate_name: Once::new(),
         }
     }
 
diff --git a/src/libsyntax_ext/lib.rs b/src/libsyntax_ext/lib.rs
index f49c75d7424d..fae884860ed5 100644
--- a/src/libsyntax_ext/lib.rs
+++ b/src/libsyntax_ext/lib.rs
@@ -1,4 +1,5 @@
-//! Syntax extensions in the Rust compiler.
+//! This crate contains implementations of built-in macros and other code generating facilities
+//! injecting code into the crate before it is lowered to HIR.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 
@@ -10,16 +11,12 @@
 #![feature(mem_take)]
 #![feature(nll)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(unicode_internals)]
-
-extern crate proc_macro;
 
 use crate::deriving::*;
 
 use syntax::ast::Ident;
 use syntax::edition::Edition;
 use syntax::ext::base::{SyntaxExtension, SyntaxExtensionKind, MacroExpanderFn};
-use syntax::ext::source_util;
 use syntax::symbol::sym;
 
 mod error_codes;
@@ -42,7 +39,7 @@ mod test;
 mod trace_macros;
 
 pub mod plugin_macro_defs;
-pub mod proc_macro_decls;
+pub mod proc_macro_harness;
 pub mod standard_library_imports;
 pub mod test_harness;
 
diff --git a/src/libsyntax_ext/proc_macro_decls.rs b/src/libsyntax_ext/proc_macro_harness.rs
similarity index 99%
rename from src/libsyntax_ext/proc_macro_decls.rs
rename to src/libsyntax_ext/proc_macro_harness.rs
index 357da6ba3c3a..fc6cd5dc94cd 100644
--- a/src/libsyntax_ext/proc_macro_decls.rs
+++ b/src/libsyntax_ext/proc_macro_harness.rs
@@ -38,7 +38,7 @@ struct CollectProcMacros<'a> {
     is_test_crate: bool,
 }
 
-pub fn modify(sess: &ParseSess,
+pub fn inject(sess: &ParseSess,
               resolver: &mut dyn (::syntax::ext::base::Resolver),
               mut krate: ast::Crate,
               is_proc_macro_crate: bool,
diff --git a/src/libsyntax_ext/test.rs b/src/libsyntax_ext/test.rs
index 36aeb3065ff2..a2d93d01cec5 100644
--- a/src/libsyntax_ext/test.rs
+++ b/src/libsyntax_ext/test.rs
@@ -30,7 +30,7 @@ pub fn expand_test_case(
 
     if !ecx.ecfg.should_test { return vec![]; }
 
-    let sp = attr_sp.with_ctxt(SyntaxContext::empty().apply_mark(ecx.current_expansion.mark));
+    let sp = attr_sp.with_ctxt(SyntaxContext::empty().apply_mark(ecx.current_expansion.id));
     let mut item = anno_item.expect_item();
     item = item.map(|mut item| {
         item.vis = respan(item.vis.span, ast::VisibilityKind::Public);
diff --git a/src/libsyntax_ext/test_harness.rs b/src/libsyntax_ext/test_harness.rs
index 061f5c3408b3..848c797856ea 100644
--- a/src/libsyntax_ext/test_harness.rs
+++ b/src/libsyntax_ext/test_harness.rs
@@ -37,12 +37,14 @@ struct TestCtxt<'a> {
 
 // Traverse the crate, collecting all the test functions, eliding any
 // existing main functions, and synthesizing a main test harness
-pub fn modify_for_testing(sess: &ParseSess,
-                          resolver: &mut dyn Resolver,
-                          should_test: bool,
-                          krate: &mut ast::Crate,
-                          span_diagnostic: &errors::Handler,
-                          features: &Features) {
+pub fn inject(
+    sess: &ParseSess,
+    resolver: &mut dyn Resolver,
+    should_test: bool,
+    krate: &mut ast::Crate,
+    span_diagnostic: &errors::Handler,
+    features: &Features,
+) {
     // Check for #[reexport_test_harness_main = "some_name"] which
     // creates a `use __test::main as some_name;`. This needs to be
     // unconditional, so that the attribute is still marked as used in