diff --git a/compiler/rustc_ast/src/node_id.rs b/compiler/rustc_ast/src/node_id.rs
index d20bace6088..7f928cb5761 100644
--- a/compiler/rustc_ast/src/node_id.rs
+++ b/compiler/rustc_ast/src/node_id.rs
@@ -1,4 +1,4 @@
-use rustc_span::ExpnId;
+use rustc_span::LocalExpnId;
 use std::fmt;
 
 rustc_index::newtype_index! {
@@ -24,12 +24,12 @@ pub const CRATE_NODE_ID: NodeId = NodeId::from_u32(0);
 pub const DUMMY_NODE_ID: NodeId = NodeId::MAX;
 
 impl NodeId {
-    pub fn placeholder_from_expn_id(expn_id: ExpnId) -> Self {
+    pub fn placeholder_from_expn_id(expn_id: LocalExpnId) -> Self {
         NodeId::from_u32(expn_id.as_u32())
     }
 
-    pub fn placeholder_to_expn_id(self) -> ExpnId {
-        ExpnId::from_u32(self.as_u32())
+    pub fn placeholder_to_expn_id(self) -> LocalExpnId {
+        LocalExpnId::from_u32(self.as_u32())
     }
 }
 
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
index ca1226b445d..90cdd62144d 100644
--- a/compiler/rustc_builtin_macros/src/deriving/clone.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -36,8 +36,9 @@ pub fn expand_deriving_clone(
         Annotatable::Item(ref annitem) => match annitem.kind {
             ItemKind::Struct(_, Generics { ref params, .. })
             | ItemKind::Enum(_, Generics { ref params, .. }) => {
-                let container_id = cx.current_expansion.id.expn_data().parent;
-                if cx.resolver.has_derive_copy(container_id)
+                let container_id = cx.current_expansion.id.expn_data().parent.expect_local();
+                let has_derive_copy = cx.resolver.has_derive_copy(container_id);
+                if has_derive_copy
                     && !params
                         .iter()
                         .any(|param| matches!(param.kind, ast::GenericParamKind::Type { .. }))
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index a3decff3ae7..417dedab60d 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -410,7 +410,7 @@ impl<'a> TraitDef<'a> {
                         .any(|param| matches!(param.kind, ast::GenericParamKind::Type { .. })),
                     _ => unreachable!(),
                 };
-                let container_id = cx.current_expansion.id.expn_data().parent;
+                let container_id = cx.current_expansion.id.expn_data().parent.expect_local();
                 let always_copy = has_no_type_params && cx.resolver.has_derive_copy(container_id);
                 let use_temporaries = is_packed && always_copy;
 
diff --git a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
index a8c61d53346..f83329ecba8 100644
--- a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
+++ b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
@@ -304,7 +304,7 @@ fn mk_decls(
         &[sym::rustc_attrs, sym::proc_macro_internals],
         None,
     );
-    let span = DUMMY_SP.with_def_site_ctxt(expn_id);
+    let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
 
     let proc_macro = Ident::new(sym::proc_macro, span);
     let krate = cx.item(span, proc_macro, Vec::new(), ast::ItemKind::ExternCrate(None));
diff --git a/compiler/rustc_builtin_macros/src/standard_library_imports.rs b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
index fbd8be22a9d..e0d57267525 100644
--- a/compiler/rustc_builtin_macros/src/standard_library_imports.rs
+++ b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
@@ -34,8 +34,8 @@ pub fn inject(
         &[sym::prelude_import],
         None,
     );
-    let span = DUMMY_SP.with_def_site_ctxt(expn_id);
-    let call_site = DUMMY_SP.with_call_site_ctxt(expn_id);
+    let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
+    let call_site = DUMMY_SP.with_call_site_ctxt(expn_id.to_expn_id());
 
     let ecfg = ExpansionConfig::default("std_lib_injection".to_string());
     let cx = ExtCtxt::new(sess, ecfg, resolver, None);
diff --git a/compiler/rustc_builtin_macros/src/test_harness.rs b/compiler/rustc_builtin_macros/src/test_harness.rs
index c8a7ff67b4d..74a97a4058f 100644
--- a/compiler/rustc_builtin_macros/src/test_harness.rs
+++ b/compiler/rustc_builtin_macros/src/test_harness.rs
@@ -126,7 +126,8 @@ impl<'a> MutVisitor for TestHarnessGenerator<'a> {
                 for test in &mut tests {
                     // See the comment on `mk_main` for why we're using
                     // `apply_mark` directly.
-                    test.ident.span = test.ident.span.apply_mark(expn_id, Transparency::Opaque);
+                    test.ident.span =
+                        test.ident.span.apply_mark(expn_id.to_expn_id(), Transparency::Opaque);
                 }
                 self.cx.test_cases.extend(tests);
             }
@@ -223,7 +224,7 @@ fn generate_test_harness(
         &[sym::test, sym::rustc_attrs],
         None,
     );
-    let def_site = DUMMY_SP.with_def_site_ctxt(expn_id);
+    let def_site = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
 
     // Remove the entry points
     let mut cleaner = EntryPointCleaner { sess, depth: 0, def_site };
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 0183add4957..497be2d9318 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -16,7 +16,7 @@ use rustc_parse::{self, nt_to_tokenstream, parser, MACRO_ARGUMENTS};
 use rustc_session::{parse::ParseSess, Limit, Session};
 use rustc_span::def_id::{CrateNum, DefId};
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::{AstPass, ExpnData, ExpnId, ExpnKind};
+use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{FileName, MultiSpan, Span, DUMMY_SP};
@@ -813,7 +813,7 @@ impl SyntaxExtension {
 
     pub fn expn_data(
         &self,
-        parent: ExpnId,
+        parent: LocalExpnId,
         call_site: Span,
         descr: Symbol,
         macro_def_id: Option<DefId>,
@@ -821,7 +821,7 @@ impl SyntaxExtension {
     ) -> ExpnData {
         ExpnData::new(
             ExpnKind::Macro(self.macro_kind(), descr),
-            parent,
+            parent.to_expn_id(),
             call_site,
             self.span,
             self.allow_internal_unstable.clone(),
@@ -843,7 +843,11 @@ pub trait ResolverExpand {
     fn next_node_id(&mut self) -> NodeId;
 
     fn resolve_dollar_crates(&mut self);
-    fn visit_ast_fragment_with_placeholders(&mut self, expn_id: ExpnId, fragment: &AstFragment);
+    fn visit_ast_fragment_with_placeholders(
+        &mut self,
+        expn_id: LocalExpnId,
+        fragment: &AstFragment,
+    );
     fn register_builtin_macro(&mut self, name: Symbol, ext: SyntaxExtensionKind);
 
     fn expansion_for_ast_pass(
@@ -852,37 +856,41 @@ pub trait ResolverExpand {
         pass: AstPass,
         features: &[Symbol],
         parent_module_id: Option<NodeId>,
-    ) -> ExpnId;
+    ) -> LocalExpnId;
 
     fn resolve_imports(&mut self);
 
     fn resolve_macro_invocation(
         &mut self,
         invoc: &Invocation,
-        eager_expansion_root: ExpnId,
+        eager_expansion_root: LocalExpnId,
         force: bool,
     ) -> Result<Lrc<SyntaxExtension>, Indeterminate>;
 
     fn check_unused_macros(&mut self);
 
     /// Some parent node that is close enough to the given macro call.
-    fn lint_node_id(&self, expn_id: ExpnId) -> NodeId;
+    fn lint_node_id(&self, expn_id: LocalExpnId) -> NodeId;
 
     // Resolver interfaces for specific built-in macros.
     /// Does `#[derive(...)]` attribute with the given `ExpnId` have built-in `Copy` inside it?
-    fn has_derive_copy(&self, expn_id: ExpnId) -> bool;
+    fn has_derive_copy(&self, expn_id: LocalExpnId) -> bool;
     /// Resolve paths inside the `#[derive(...)]` attribute with the given `ExpnId`.
     fn resolve_derives(
         &mut self,
-        expn_id: ExpnId,
+        expn_id: LocalExpnId,
         force: bool,
         derive_paths: &dyn Fn() -> DeriveResolutions,
     ) -> Result<(), Indeterminate>;
     /// Take resolutions for paths inside the `#[derive(...)]` attribute with the given `ExpnId`
     /// back from resolver.
-    fn take_derive_resolutions(&mut self, expn_id: ExpnId) -> Option<DeriveResolutions>;
+    fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions>;
     /// Path resolution logic for `#[cfg_accessible(path)]`.
-    fn cfg_accessible(&mut self, expn_id: ExpnId, path: &ast::Path) -> Result<bool, Indeterminate>;
+    fn cfg_accessible(
+        &mut self,
+        expn_id: LocalExpnId,
+        path: &ast::Path,
+    ) -> Result<bool, Indeterminate>;
 
     /// Decodes the proc-macro quoted span in the specified crate, with the specified id.
     /// No caching is performed.
@@ -913,7 +921,7 @@ impl ModuleData {
 
 #[derive(Clone)]
 pub struct ExpansionData {
-    pub id: ExpnId,
+    pub id: LocalExpnId,
     pub depth: usize,
     pub module: Rc<ModuleData>,
     pub dir_ownership: DirOwnership,
@@ -958,7 +966,7 @@ impl<'a> ExtCtxt<'a> {
             extern_mod_loaded,
             root_path: PathBuf::new(),
             current_expansion: ExpansionData {
-                id: ExpnId::root(),
+                id: LocalExpnId::ROOT,
                 depth: 0,
                 module: Default::default(),
                 dir_ownership: DirOwnership::Owned { relative: None },
@@ -995,19 +1003,19 @@ impl<'a> ExtCtxt<'a> {
     /// Equivalent of `Span::def_site` from the proc macro API,
     /// except that the location is taken from the span passed as an argument.
     pub fn with_def_site_ctxt(&self, span: Span) -> Span {
-        span.with_def_site_ctxt(self.current_expansion.id)
+        span.with_def_site_ctxt(self.current_expansion.id.to_expn_id())
     }
 
     /// Equivalent of `Span::call_site` from the proc macro API,
     /// except that the location is taken from the span passed as an argument.
     pub fn with_call_site_ctxt(&self, span: Span) -> Span {
-        span.with_call_site_ctxt(self.current_expansion.id)
+        span.with_call_site_ctxt(self.current_expansion.id.to_expn_id())
     }
 
     /// Equivalent of `Span::mixed_site` from the proc macro API,
     /// except that the location is taken from the span passed as an argument.
     pub fn with_mixed_site_ctxt(&self, span: Span) -> Span {
-        span.with_mixed_site_ctxt(self.current_expansion.id)
+        span.with_mixed_site_ctxt(self.current_expansion.id.to_expn_id())
     }
 
     /// Returns span for the macro which originally caused the current expansion to happen.
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 1ab7e15019e..b9d40962411 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -31,7 +31,7 @@ use rustc_session::lint::BuiltinLintDiagnostics;
 use rustc_session::parse::{feature_err, ParseSess};
 use rustc_session::Limit;
 use rustc_span::symbol::{sym, Ident};
-use rustc_span::{ExpnId, FileName, Span};
+use rustc_span::{FileName, LocalExpnId, Span};
 
 use smallvec::{smallvec, SmallVec};
 use std::ops::DerefMut;
@@ -508,7 +508,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                                 .map(|(path, item, _exts)| {
                                     // FIXME: Consider using the derive resolutions (`_exts`)
                                     // instead of enqueuing the derives to be resolved again later.
-                                    let expn_id = ExpnId::fresh_empty();
+                                    let expn_id = LocalExpnId::fresh_empty();
                                     derive_invocations.push((
                                         Invocation {
                                             kind: InvocationKind::Derive { path, item },
@@ -993,7 +993,7 @@ struct InvocationCollector<'a, 'b> {
 
 impl<'a, 'b> InvocationCollector<'a, 'b> {
     fn collect(&mut self, fragment_kind: AstFragmentKind, kind: InvocationKind) -> AstFragment {
-        let expn_id = ExpnId::fresh_empty();
+        let expn_id = LocalExpnId::fresh_empty();
         let vis = kind.placeholder_visibility();
         self.invocations.push((
             Invocation {
diff --git a/compiler/rustc_expand/src/mbe/transcribe.rs b/compiler/rustc_expand/src/mbe/transcribe.rs
index f9e7c4254bc..9ed5c8b8ffb 100644
--- a/compiler/rustc_expand/src/mbe/transcribe.rs
+++ b/compiler/rustc_expand/src/mbe/transcribe.rs
@@ -8,7 +8,7 @@ use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree, TreeAndSpacing};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{pluralize, PResult};
-use rustc_span::hygiene::{ExpnId, Transparency};
+use rustc_span::hygiene::{LocalExpnId, Transparency};
 use rustc_span::symbol::MacroRulesNormalizedIdent;
 use rustc_span::Span;
 
@@ -16,7 +16,7 @@ use smallvec::{smallvec, SmallVec};
 use std::mem;
 
 // A Marker adds the given mark to the syntax context.
-struct Marker(ExpnId, Transparency);
+struct Marker(LocalExpnId, Transparency);
 
 impl MutVisitor for Marker {
     fn token_visiting_enabled(&self) -> bool {
@@ -24,7 +24,7 @@ impl MutVisitor for Marker {
     }
 
     fn visit_span(&mut self, span: &mut Span) {
-        *span = span.apply_mark(self.0, self.1)
+        *span = span.apply_mark(self.0.to_expn_id(), self.1)
     }
 }
 
diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index d28ebfe107c..8bdd4313de4 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -30,13 +30,12 @@ use rustc_middle::ty::codec::TyDecoder;
 use rustc_middle::ty::{self, Ty, TyCtxt, Visibility};
 use rustc_serialize::{opaque, Decodable, Decoder};
 use rustc_session::Session;
-use rustc_span::hygiene::ExpnDataDecodeMode;
+use rustc_span::hygiene::{ExpnIndex, MacroKind};
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{sym, Ident, Symbol};
-use rustc_span::{self, hygiene::MacroKind, BytePos, ExpnId, Pos, Span, SyntaxContext, DUMMY_SP};
+use rustc_span::{self, BytePos, ExpnId, Pos, Span, SyntaxContext, DUMMY_SP};
 
 use proc_macro::bridge::client::ProcMacro;
-use std::cell::Cell;
 use std::io;
 use std::mem;
 use std::num::NonZeroUsize;
@@ -80,6 +79,8 @@ crate struct CrateMetadata {
     /// `DefIndex`. See `raw_def_id_to_def_id` for more details about how
     /// this is used.
     def_path_hash_map: OnceCell<UnhashMap<DefPathHash, DefIndex>>,
+    /// Likewise for ExpnHash.
+    expn_hash_map: OnceCell<UnhashMap<ExpnHash, ExpnIndex>>,
     /// Used for decoding interpret::AllocIds in a cached & thread-safe manner.
     alloc_decoding_state: AllocDecodingState,
     /// Caches decoded `DefKey`s.
@@ -350,6 +351,12 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for DefIndex {
     }
 }
 
+impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for ExpnIndex {
+    fn decode(d: &mut DecodeContext<'a, 'tcx>) -> Result<ExpnIndex, String> {
+        Ok(ExpnIndex::from_u32(d.read_u32()?))
+    }
+}
+
 impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for SyntaxContext {
     fn decode(decoder: &mut DecodeContext<'a, 'tcx>) -> Result<SyntaxContext, String> {
         let cdata = decoder.cdata();
@@ -371,43 +378,35 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for ExpnId {
     fn decode(decoder: &mut DecodeContext<'a, 'tcx>) -> Result<ExpnId, String> {
         let local_cdata = decoder.cdata();
         let sess = decoder.sess.unwrap();
-        let expn_cnum = Cell::new(None);
-        let get_ctxt = |cnum| {
-            expn_cnum.set(Some(cnum));
-            if cnum == LOCAL_CRATE {
-                &local_cdata.hygiene_context
-            } else {
-                &local_cdata.cstore.get_crate_data(cnum).cdata.hygiene_context
-            }
-        };
 
-        rustc_span::hygiene::decode_expn_id(
-            decoder,
-            ExpnDataDecodeMode::Metadata(get_ctxt),
-            |_this, index| {
-                let cnum = expn_cnum.get().unwrap();
-                // Lookup local `ExpnData`s in our own crate data. Foreign `ExpnData`s
-                // are stored in the owning crate, to avoid duplication.
-                let crate_data = if cnum == LOCAL_CRATE {
-                    local_cdata
-                } else {
-                    local_cdata.cstore.get_crate_data(cnum)
-                };
-                let expn_data = crate_data
-                    .root
-                    .expn_data
-                    .get(&crate_data, index)
-                    .unwrap()
-                    .decode((&crate_data, sess));
-                let expn_hash = crate_data
-                    .root
-                    .expn_hashes
-                    .get(&crate_data, index)
-                    .unwrap()
-                    .decode((&crate_data, sess));
-                Ok((expn_data, expn_hash))
-            },
-        )
+        let cnum = CrateNum::decode(decoder)?;
+        let index = u32::decode(decoder)?;
+
+        let expn_id = rustc_span::hygiene::decode_expn_id(cnum, index, |expn_id| {
+            let ExpnId { krate: cnum, local_id: index } = expn_id;
+            // Lookup local `ExpnData`s in our own crate data. Foreign `ExpnData`s
+            // are stored in the owning crate, to avoid duplication.
+            debug_assert_ne!(cnum, LOCAL_CRATE);
+            let crate_data = if cnum == local_cdata.cnum {
+                local_cdata
+            } else {
+                local_cdata.cstore.get_crate_data(cnum)
+            };
+            let expn_data = crate_data
+                .root
+                .expn_data
+                .get(&crate_data, index)
+                .unwrap()
+                .decode((&crate_data, sess));
+            let expn_hash = crate_data
+                .root
+                .expn_hashes
+                .get(&crate_data, index)
+                .unwrap()
+                .decode((&crate_data, sess));
+            (expn_data, expn_hash)
+        });
+        Ok(expn_id)
     }
 }
 
@@ -1622,6 +1621,41 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         self.def_path_hash_unlocked(index, &mut def_path_hashes)
     }
 
+    fn expn_hash_to_expn_id(&self, index_guess: u32, hash: ExpnHash) -> ExpnId {
+        debug_assert_eq!(ExpnId::from_hash(hash), None);
+        let index_guess = ExpnIndex::from_u32(index_guess);
+        let old_hash = self.root.expn_hashes.get(self, index_guess).map(|lazy| lazy.decode(self));
+
+        let index = if old_hash == Some(hash) {
+            // Fast path: the expn and its index is unchanged from the
+            // previous compilation session. There is no need to decode anything
+            // else.
+            index_guess
+        } else {
+            // Slow path: We need to find out the new `DefIndex` of the provided
+            // `DefPathHash`, if its still exists. This requires decoding every `DefPathHash`
+            // stored in this crate.
+            let map = self.cdata.expn_hash_map.get_or_init(|| {
+                let end_id = self.root.expn_hashes.size() as u32;
+                let mut map =
+                    UnhashMap::with_capacity_and_hasher(end_id as usize, Default::default());
+                for i in 0..end_id {
+                    let i = ExpnIndex::from_u32(i);
+                    if let Some(hash) = self.root.expn_hashes.get(self, i) {
+                        map.insert(hash.decode(self), i);
+                    } else {
+                        panic!("Missing expn_hash entry for {:?}", i);
+                    }
+                }
+                map
+            });
+            map[&hash]
+        };
+
+        let data = self.root.expn_data.get(self, index).unwrap().decode(self);
+        rustc_span::hygiene::register_expn_id(self.cnum, index, data, hash)
+    }
+
     /// Imports the source_map from an external crate into the source_map of the crate
     /// currently being compiled (the "local crate").
     ///
@@ -1860,6 +1894,7 @@ impl CrateMetadata {
             raw_proc_macros,
             source_map_import_info: OnceCell::new(),
             def_path_hash_map: Default::default(),
+            expn_hash_map: Default::default(),
             alloc_decoding_state,
             cnum,
             cnum_map,
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index ce8dfeae076..41839c58021 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -18,11 +18,11 @@ use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, Visibility};
 use rustc_session::utils::NativeLibKind;
 use rustc_session::{Session, StableCrateId};
+use rustc_span::hygiene::{ExpnHash, ExpnId};
 use rustc_span::source_map::{Span, Spanned};
 use rustc_span::symbol::Symbol;
 
 use rustc_data_structures::sync::Lrc;
-use rustc_span::ExpnId;
 use smallvec::SmallVec;
 use std::any::Any;
 
@@ -528,6 +528,10 @@ impl CrateStore for CStore {
         self.get_crate_data(cnum).def_path_hash_to_def_id(cnum, index_guess, hash)
     }
 
+    fn expn_hash_to_expn_id(&self, cnum: CrateNum, index_guess: u32, hash: ExpnHash) -> ExpnId {
+        self.get_crate_data(cnum).expn_hash_to_expn_id(index_guess, hash)
+    }
+
     fn encode_metadata(&self, tcx: TyCtxt<'_>) -> EncodedMetadata {
         encoder::encode_metadata(tcx)
     }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 5c7d84e2bc9..6877d6ef542 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -31,7 +31,7 @@ use rustc_session::config::CrateType;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{self, ExternalSource, FileName, SourceFile, Span, SyntaxContext};
 use rustc_span::{
-    hygiene::{ExpnDataEncodeMode, HygieneEncodeContext, MacroKind},
+    hygiene::{ExpnIndex, HygieneEncodeContext, MacroKind},
     RealFileName,
 };
 use rustc_target::abi::VariantIdx;
@@ -168,6 +168,12 @@ impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for DefIndex {
     }
 }
 
+impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for ExpnIndex {
+    fn encode(&self, s: &mut EncodeContext<'a, 'tcx>) -> opaque::EncodeResult {
+        s.emit_u32(self.as_u32())
+    }
+}
+
 impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for SyntaxContext {
     fn encode(&self, s: &mut EncodeContext<'a, 'tcx>) -> opaque::EncodeResult {
         rustc_span::hygiene::raw_encode_syntax_context(*self, &s.hygiene_ctxt, s)
@@ -176,12 +182,15 @@ impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for SyntaxContext {
 
 impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for ExpnId {
     fn encode(&self, s: &mut EncodeContext<'a, 'tcx>) -> opaque::EncodeResult {
-        rustc_span::hygiene::raw_encode_expn_id(
-            *self,
-            &s.hygiene_ctxt,
-            ExpnDataEncodeMode::Metadata,
-            s,
-        )
+        if self.krate == LOCAL_CRATE {
+            // We will only write details for local expansions.  Non-local expansions will fetch
+            // data from the corresponding crate's metadata.
+            // FIXME(#43047) FIXME(#74731) We may eventually want to avoid relying on external
+            // metadata from proc-macro crates.
+            s.hygiene_ctxt.schedule_expn_data_for_encoding(*self);
+        }
+        self.krate.encode(s)?;
+        self.local_id.encode(s)
     }
 }
 
@@ -1593,8 +1602,10 @@ impl EncodeContext<'a, 'tcx> {
                 Ok(())
             },
             |(this, _, expn_data_table, expn_hash_table), index, expn_data, hash| {
-                expn_data_table.set(index, this.lazy(expn_data));
-                expn_hash_table.set(index, this.lazy(hash));
+                if let Some(index) = index.as_local() {
+                    expn_data_table.set(index.as_raw(), this.lazy(expn_data));
+                    expn_hash_table.set(index.as_raw(), this.lazy(hash));
+                }
                 Ok(())
             },
         );
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index f2ebfb9b725..a487753f462 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -19,7 +19,7 @@ use rustc_middle::ty::{self, ReprOptions, Ty};
 use rustc_serialize::opaque::Encoder;
 use rustc_session::config::SymbolManglingVersion;
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::MacroKind;
+use rustc_span::hygiene::{ExpnIndex, MacroKind};
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::{self, ExpnData, ExpnHash, ExpnId, Span};
 use rustc_target::spec::{PanicStrategy, TargetTriple};
@@ -170,8 +170,8 @@ macro_rules! Lazy {
 }
 
 type SyntaxContextTable = Lazy<Table<u32, Lazy<SyntaxContextData>>>;
-type ExpnDataTable = Lazy<Table<u32, Lazy<ExpnData>>>;
-type ExpnHashTable = Lazy<Table<u32, Lazy<ExpnHash>>>;
+type ExpnDataTable = Lazy<Table<ExpnIndex, Lazy<ExpnData>>>;
+type ExpnHashTable = Lazy<Table<ExpnIndex, Lazy<ExpnHash>>>;
 
 #[derive(MetadataEncodable, MetadataDecodable)]
 crate struct ProcMacroData {
diff --git a/compiler/rustc_middle/src/middle/cstore.rs b/compiler/rustc_middle/src/middle/cstore.rs
index 7efe8e061e8..4c35b49bcef 100644
--- a/compiler/rustc_middle/src/middle/cstore.rs
+++ b/compiler/rustc_middle/src/middle/cstore.rs
@@ -6,12 +6,12 @@ use crate::ty::TyCtxt;
 
 use rustc_ast as ast;
 use rustc_data_structures::sync::{self, MetadataRef};
-use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, StableCrateId, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_macros::HashStable;
 use rustc_session::search_paths::PathKind;
 use rustc_session::utils::NativeLibKind;
-use rustc_session::StableCrateId;
+use rustc_span::hygiene::{ExpnHash, ExpnId};
 use rustc_span::symbol::Symbol;
 use rustc_span::Span;
 use rustc_target::spec::Target;
@@ -207,6 +207,7 @@ pub trait CrateStore: std::fmt::Debug {
         index_guess: u32,
         hash: DefPathHash,
     ) -> Option<DefId>;
+    fn expn_hash_to_expn_id(&self, cnum: CrateNum, index_guess: u32, hash: ExpnHash) -> ExpnId;
 
     // utility functions
     fn encode_metadata(&self, tcx: TyCtxt<'_>) -> EncodedMetadata;
diff --git a/compiler/rustc_middle/src/ty/query/on_disk_cache.rs b/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
index e3db0d2cf30..0ac80ebd636 100644
--- a/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
+++ b/compiler/rustc_middle/src/ty/query/on_disk_cache.rs
@@ -20,8 +20,7 @@ use rustc_serialize::{
 };
 use rustc_session::Session;
 use rustc_span::hygiene::{
-    ExpnDataDecodeMode, ExpnDataEncodeMode, ExpnId, HygieneDecodeContext, HygieneEncodeContext,
-    SyntaxContext, SyntaxContextData,
+    ExpnId, HygieneDecodeContext, HygieneEncodeContext, SyntaxContext, SyntaxContextData,
 };
 use rustc_span::source_map::{SourceMap, StableSourceFileId};
 use rustc_span::CachingSourceMapView;
@@ -84,7 +83,7 @@ pub struct OnDiskCache<'sess> {
     // `ExpnData` (e.g `ExpnData.krate` may not be `LOCAL_CRATE`). Alternatively,
     // we could look up the `ExpnData` from the metadata of foreign crates,
     // but it seemed easier to have `OnDiskCache` be independent of the `CStore`.
-    expn_data: FxHashMap<u32, AbsoluteBytePos>,
+    expn_data: UnhashMap<ExpnHash, AbsoluteBytePos>,
     // Additional information used when decoding hygiene data.
     hygiene_context: HygieneDecodeContext,
     // Maps `DefPathHash`es to their `RawDefId`s from the *previous*
@@ -92,6 +91,8 @@ pub struct OnDiskCache<'sess> {
     // we try to map a `DefPathHash` to its `DefId` in the current compilation
     // session.
     foreign_def_path_hashes: UnhashMap<DefPathHash, RawDefId>,
+    // Likewise for ExpnId.
+    foreign_expn_data: UnhashMap<ExpnHash, u32>,
 
     // The *next* compilation sessison's `foreign_def_path_hashes` - at
     // the end of our current compilation session, this will get written
@@ -119,8 +120,9 @@ struct Footer {
     // See `OnDiskCache.syntax_contexts`
     syntax_contexts: FxHashMap<u32, AbsoluteBytePos>,
     // See `OnDiskCache.expn_data`
-    expn_data: FxHashMap<u32, AbsoluteBytePos>,
+    expn_data: UnhashMap<ExpnHash, AbsoluteBytePos>,
     foreign_def_path_hashes: UnhashMap<DefPathHash, RawDefId>,
+    foreign_expn_data: UnhashMap<ExpnHash, u32>,
 }
 
 pub type EncodedQueryResultIndex = Vec<(SerializedDepNodeIndex, AbsoluteBytePos)>;
@@ -218,6 +220,7 @@ impl<'sess> OnDiskCache<'sess> {
             alloc_decoding_state: AllocDecodingState::new(footer.interpret_alloc_index),
             syntax_contexts: footer.syntax_contexts,
             expn_data: footer.expn_data,
+            foreign_expn_data: footer.foreign_expn_data,
             hygiene_context: Default::default(),
             foreign_def_path_hashes: footer.foreign_def_path_hashes,
             latest_foreign_def_path_hashes: Default::default(),
@@ -237,7 +240,8 @@ impl<'sess> OnDiskCache<'sess> {
             prev_diagnostics_index: Default::default(),
             alloc_decoding_state: AllocDecodingState::new(Vec::new()),
             syntax_contexts: FxHashMap::default(),
-            expn_data: FxHashMap::default(),
+            expn_data: UnhashMap::default(),
+            foreign_expn_data: UnhashMap::default(),
             hygiene_context: Default::default(),
             foreign_def_path_hashes: Default::default(),
             latest_foreign_def_path_hashes: Default::default(),
@@ -351,7 +355,8 @@ impl<'sess> OnDiskCache<'sess> {
             };
 
             let mut syntax_contexts = FxHashMap::default();
-            let mut expn_ids = FxHashMap::default();
+            let mut expn_data = UnhashMap::default();
+            let mut foreign_expn_data = UnhashMap::default();
 
             // Encode all hygiene data (`SyntaxContextData` and `ExpnData`) from the current
             // session.
@@ -364,10 +369,14 @@ impl<'sess> OnDiskCache<'sess> {
                     syntax_contexts.insert(index, pos);
                     Ok(())
                 },
-                |encoder, index, expn_data, hash| -> FileEncodeResult {
-                    let pos = AbsoluteBytePos::new(encoder.position());
-                    encoder.encode_tagged(TAG_EXPN_DATA, &(expn_data, hash))?;
-                    expn_ids.insert(index, pos);
+                |encoder, expn_id, data, hash| -> FileEncodeResult {
+                    if expn_id.krate == LOCAL_CRATE {
+                        let pos = AbsoluteBytePos::new(encoder.position());
+                        encoder.encode_tagged(TAG_EXPN_DATA, data)?;
+                        expn_data.insert(hash, pos);
+                    } else {
+                        foreign_expn_data.insert(hash, expn_id.local_id.as_u32());
+                    }
                     Ok(())
                 },
             )?;
@@ -385,7 +394,8 @@ impl<'sess> OnDiskCache<'sess> {
                     diagnostics_index,
                     interpret_alloc_index,
                     syntax_contexts,
-                    expn_data: expn_ids,
+                    expn_data,
+                    foreign_expn_data,
                     foreign_def_path_hashes,
                 },
             )?;
@@ -547,6 +557,7 @@ impl<'sess> OnDiskCache<'sess> {
             alloc_decoding_session: self.alloc_decoding_state.new_decoding_session(),
             syntax_contexts: &self.syntax_contexts,
             expn_data: &self.expn_data,
+            foreign_expn_data: &self.foreign_expn_data,
             hygiene_context: &self.hygiene_context,
         };
         f(&mut decoder)
@@ -641,7 +652,8 @@ pub struct CacheDecoder<'a, 'tcx> {
     file_index_to_stable_id: &'a FxHashMap<SourceFileIndex, EncodedSourceFileId>,
     alloc_decoding_session: AllocDecodingSession<'a>,
     syntax_contexts: &'a FxHashMap<u32, AbsoluteBytePos>,
-    expn_data: &'a FxHashMap<u32, AbsoluteBytePos>,
+    expn_data: &'a UnhashMap<ExpnHash, AbsoluteBytePos>,
+    foreign_expn_data: &'a UnhashMap<ExpnHash, u32>,
     hygiene_context: &'a HygieneDecodeContext,
 }
 
@@ -792,23 +804,43 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for SyntaxContext {
 
 impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for ExpnId {
     fn decode(decoder: &mut CacheDecoder<'a, 'tcx>) -> Result<Self, String> {
-        let expn_data = decoder.expn_data;
-        rustc_span::hygiene::decode_expn_id(
-            decoder,
-            ExpnDataDecodeMode::incr_comp(decoder.hygiene_context),
-            |this, index| {
-                // This closure is invoked if we haven't already decoded the data for the `ExpnId` we are deserializing.
-                // We look up the position of the associated `ExpnData` and decode it.
-                let pos = expn_data
-                    .get(&index)
-                    .unwrap_or_else(|| panic!("Bad index {:?} (map {:?})", index, expn_data));
+        let hash = ExpnHash::decode(decoder)?;
+        if hash.is_root() {
+            return Ok(ExpnId::root());
+        }
 
-                this.with_position(pos.to_usize(), |decoder| {
-                    let data: (ExpnData, ExpnHash) = decode_tagged(decoder, TAG_EXPN_DATA)?;
-                    Ok(data)
-                })
-            },
-        )
+        if let Some(expn_id) = ExpnId::from_hash(hash) {
+            return Ok(expn_id);
+        }
+
+        let krate = decoder.cnum_map[&hash.stable_crate_id()];
+
+        let expn_id = if krate == LOCAL_CRATE {
+            // We look up the position of the associated `ExpnData` and decode it.
+            let pos = decoder
+                .expn_data
+                .get(&hash)
+                .unwrap_or_else(|| panic!("Bad hash {:?} (map {:?})", hash, decoder.expn_data));
+
+            let data: ExpnData = decoder
+                .with_position(pos.to_usize(), |decoder| decode_tagged(decoder, TAG_EXPN_DATA))?;
+            rustc_span::hygiene::register_local_expn_id(data, hash)
+        } else {
+            let index_guess = decoder.foreign_expn_data[&hash];
+            decoder.tcx.untracked_resolutions.cstore.expn_hash_to_expn_id(krate, index_guess, hash)
+        };
+
+        #[cfg(debug_assertions)]
+        {
+            use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+            let mut hcx = decoder.tcx.create_stable_hashing_context();
+            let mut hasher = StableHasher::new();
+            hcx.while_hashing_spans(true, |hcx| expn_id.expn_data().hash_stable(hcx, &mut hasher));
+            let local_hash: u64 = hasher.finish();
+            debug_assert_eq!(hash.local_hash(), local_hash);
+        }
+
+        Ok(expn_id)
     }
 }
 
@@ -983,12 +1015,8 @@ where
     E: 'a + OpaqueEncoder,
 {
     fn encode(&self, s: &mut CacheEncoder<'a, 'tcx, E>) -> Result<(), E::Error> {
-        rustc_span::hygiene::raw_encode_expn_id(
-            *self,
-            s.hygiene_context,
-            ExpnDataEncodeMode::IncrComp,
-            s,
-        )
+        s.hygiene_context.schedule_expn_data_for_encoding(*self);
+        self.expn_hash().encode(s)
     }
 }
 
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index 35e7688fbe4..178d727418d 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -31,7 +31,7 @@ use rustc_middle::bug;
 use rustc_middle::hir::exports::Export;
 use rustc_middle::middle::cstore::CrateStore;
 use rustc_middle::ty;
-use rustc_span::hygiene::{ExpnId, MacroKind};
+use rustc_span::hygiene::{ExpnId, LocalExpnId, MacroKind};
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
@@ -42,7 +42,7 @@ use tracing::debug;
 
 type Res = def::Res<NodeId>;
 
-impl<'a> ToNameBinding<'a> for (Module<'a>, ty::Visibility, Span, ExpnId) {
+impl<'a> ToNameBinding<'a> for (Module<'a>, ty::Visibility, Span, LocalExpnId) {
     fn to_name_binding(self, arenas: &'a ResolverArenas<'a>) -> &'a NameBinding<'a> {
         arenas.alloc_name_binding(NameBinding {
             kind: NameBindingKind::Module(self.0),
@@ -54,7 +54,7 @@ impl<'a> ToNameBinding<'a> for (Module<'a>, ty::Visibility, Span, ExpnId) {
     }
 }
 
-impl<'a> ToNameBinding<'a> for (Res, ty::Visibility, Span, ExpnId) {
+impl<'a> ToNameBinding<'a> for (Res, ty::Visibility, Span, LocalExpnId) {
     fn to_name_binding(self, arenas: &'a ResolverArenas<'a>) -> &'a NameBinding<'a> {
         arenas.alloc_name_binding(NameBinding {
             kind: NameBindingKind::Res(self.0, false),
@@ -68,7 +68,7 @@ impl<'a> ToNameBinding<'a> for (Res, ty::Visibility, Span, ExpnId) {
 
 struct IsMacroExport;
 
-impl<'a> ToNameBinding<'a> for (Res, ty::Visibility, Span, ExpnId, IsMacroExport) {
+impl<'a> ToNameBinding<'a> for (Res, ty::Visibility, Span, LocalExpnId, IsMacroExport) {
     fn to_name_binding(self, arenas: &'a ResolverArenas<'a>) -> &'a NameBinding<'a> {
         arenas.alloc_name_binding(NameBinding {
             kind: NameBindingKind::Res(self.0, true),
@@ -157,7 +157,12 @@ impl<'a> Resolver<'a> {
     crate fn macro_def_scope(&mut self, expn_id: ExpnId) -> Module<'a> {
         let def_id = match expn_id.expn_data().macro_def_id {
             Some(def_id) => def_id,
-            None => return self.ast_transform_scopes.get(&expn_id).unwrap_or(&self.graph_root),
+            None => {
+                return expn_id
+                    .as_local()
+                    .and_then(|expn_id| self.ast_transform_scopes.get(&expn_id))
+                    .unwrap_or(&self.graph_root);
+            }
         };
         self.macro_def_scope_from_def_id(def_id)
     }
@@ -739,7 +744,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 if ptr::eq(parent, self.r.graph_root) {
                     if let Some(entry) = self.r.extern_prelude.get(&ident.normalize_to_macros_2_0())
                     {
-                        if expansion != ExpnId::root()
+                        if expansion != LocalExpnId::ROOT
                             && orig_name.is_some()
                             && entry.extern_crate_item.is_none()
                         {
@@ -769,7 +774,13 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                     no_implicit_prelude: parent.no_implicit_prelude || {
                         self.r.session.contains_name(&item.attrs, sym::no_implicit_prelude)
                     },
-                    ..ModuleData::new(Some(parent), module_kind, def_id, expansion, item.span)
+                    ..ModuleData::new(
+                        Some(parent),
+                        module_kind,
+                        def_id,
+                        expansion.to_expn_id(),
+                        item.span,
+                    )
                 });
                 self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
                 self.r.module_map.insert(local_def_id, module);
@@ -808,7 +819,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                     parent,
                     module_kind,
                     parent.nearest_parent_mod,
-                    expansion,
+                    expansion.to_expn_id(),
                     item.span,
                 );
                 self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
@@ -883,7 +894,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                     parent,
                     module_kind,
                     parent.nearest_parent_mod,
-                    expansion,
+                    expansion.to_expn_id(),
                     item.span,
                 );
                 self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
@@ -926,7 +937,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 parent,
                 ModuleKind::Block(block.id),
                 parent.nearest_parent_mod,
-                expansion,
+                expansion.to_expn_id(),
                 block.span,
             );
             self.r.block_map.insert(block.id, module);
@@ -946,7 +957,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                     parent,
                     ModuleKind::Def(kind, def_id, ident.name),
                     def_id,
-                    expansion,
+                    expansion.to_expn_id(),
                     span,
                 );
                 self.r.define(parent, ident, TypeNS, (module, vis, span, expansion));
@@ -1112,7 +1123,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             })
         };
 
-        let allow_shadowing = self.parent_scope.expansion == ExpnId::root();
+        let allow_shadowing = self.parent_scope.expansion == LocalExpnId::ROOT;
         if let Some(span) = import_all {
             let import = macro_use_import(self, span);
             self.r.potentially_unused_imports.push(import);
@@ -1175,7 +1186,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
         false
     }
 
-    fn visit_invoc(&mut self, id: NodeId) -> ExpnId {
+    fn visit_invoc(&mut self, id: NodeId) -> LocalExpnId {
         let invoc_id = id.placeholder_to_expn_id();
         let old_parent_scope = self.r.invocation_parent_scopes.insert(invoc_id, self.parent_scope);
         assert!(old_parent_scope.is_none(), "invocation data is reset for an invocation");
diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
index 17f0c39e397..6f4f1bdaea1 100644
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/compiler/rustc_resolve/src/def_collector.rs
@@ -6,7 +6,7 @@ use rustc_ast_lowering::ResolverAstLowering;
 use rustc_expand::expand::AstFragment;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::definitions::*;
-use rustc_span::hygiene::ExpnId;
+use rustc_span::hygiene::LocalExpnId;
 use rustc_span::symbol::{kw, sym};
 use rustc_span::Span;
 use tracing::debug;
@@ -14,7 +14,7 @@ use tracing::debug;
 crate fn collect_definitions(
     resolver: &mut Resolver<'_>,
     fragment: &AstFragment,
-    expansion: ExpnId,
+    expansion: LocalExpnId,
 ) {
     let (parent_def, impl_trait_context) = resolver.invocation_parents[&expansion];
     fragment.visit_with(&mut DefCollector { resolver, parent_def, expansion, impl_trait_context });
@@ -25,14 +25,14 @@ struct DefCollector<'a, 'b> {
     resolver: &'a mut Resolver<'b>,
     parent_def: LocalDefId,
     impl_trait_context: ImplTraitContext,
-    expansion: ExpnId,
+    expansion: LocalExpnId,
 }
 
 impl<'a, 'b> DefCollector<'a, 'b> {
     fn create_def(&mut self, node_id: NodeId, data: DefPathData, span: Span) -> LocalDefId {
         let parent_def = self.parent_def;
         debug!("create_def(node_id={:?}, data={:?}, parent_def={:?})", node_id, data, parent_def);
-        self.resolver.create_def(parent_def, node_id, data, self.expansion, span)
+        self.resolver.create_def(parent_def, node_id, data, self.expansion.to_expn_id(), span)
     }
 
     fn with_parent<F: FnOnce(&mut Self)>(&mut self, parent_def: LocalDefId, f: F) {
@@ -285,7 +285,7 @@ impl<'a, 'b> visit::Visitor<'a> for DefCollector<'a, 'b> {
                         item_def,
                         node_id,
                         DefPathData::ImplTrait,
-                        self.expansion,
+                        self.expansion.to_expn_id(),
                         ty.span,
                     ),
                     ImplTraitContext::Existential => {
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 26858915f45..acfa389fed5 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -22,7 +22,7 @@ use rustc_middle::span_bug;
 use rustc_middle::ty;
 use rustc_session::lint::builtin::{PUB_USE_OF_PRIVATE_EXTERN_CRATE, UNUSED_IMPORTS};
 use rustc_session::lint::BuiltinLintDiagnostics;
-use rustc_span::hygiene::ExpnId;
+use rustc_span::hygiene::LocalExpnId;
 use rustc_span::lev_distance::find_best_match_for_name;
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::{MultiSpan, Span};
@@ -237,8 +237,9 @@ impl<'a> Resolver<'a> {
                 if ns == TypeNS {
                     if ident.name == kw::Crate || ident.name == kw::DollarCrate {
                         let module = self.resolve_crate_root(ident);
-                        let binding = (module, ty::Visibility::Public, module.span, ExpnId::root())
-                            .to_name_binding(self.arenas);
+                        let binding =
+                            (module, ty::Visibility::Public, module.span, LocalExpnId::ROOT)
+                                .to_name_binding(self.arenas);
                         return Ok(binding);
                     } else if ident.name == kw::Super || ident.name == kw::SelfLower {
                         // FIXME: Implement these with renaming requirements so that e.g.
@@ -265,7 +266,7 @@ impl<'a> Resolver<'a> {
             self.resolution(module, key).try_borrow_mut().map_err(|_| (Determined, Weak::No))?; // This happens when there is a cycle of imports.
 
         if let Some(binding) = resolution.binding {
-            if !restricted_shadowing && binding.expansion != ExpnId::root() {
+            if !restricted_shadowing && binding.expansion != LocalExpnId::ROOT {
                 if let NameBindingKind::Res(_, true) = binding.kind {
                     self.macro_expanded_macro_export_errors.insert((path_span, binding.span));
                 }
@@ -307,7 +308,7 @@ impl<'a> Resolver<'a> {
                         if let Some(shadowed_glob) = resolution.shadowed_glob {
                             // Forbid expanded shadowing to avoid time travel.
                             if restricted_shadowing
-                                && binding.expansion != ExpnId::root()
+                                && binding.expansion != LocalExpnId::ROOT
                                 && binding.res() != shadowed_glob.res()
                             {
                                 self.ambiguity_errors.push(AmbiguityError {
@@ -521,7 +522,7 @@ impl<'a> Resolver<'a> {
                             if old_glob { (old_binding, binding) } else { (binding, old_binding) };
                         if glob_binding.res() != nonglob_binding.res()
                             && key.ns == MacroNS
-                            && nonglob_binding.expansion != ExpnId::root()
+                            && nonglob_binding.expansion != LocalExpnId::ROOT
                         {
                             resolution.binding = Some(this.ambiguity(
                                 AmbiguityKind::GlobVsExpanded,
@@ -1271,7 +1272,7 @@ impl<'a, 'b> ImportResolver<'a, 'b> {
         target: Ident,
     ) {
         // Skip if the import was produced by a macro.
-        if import.parent_scope.expansion != ExpnId::root() {
+        if import.parent_scope.expansion != LocalExpnId::ROOT {
             return;
         }
 
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index fb2eb749e11..7114fd33188 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -53,7 +53,7 @@ use rustc_session::lint;
 use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
 use rustc_session::Session;
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::{ExpnId, ExpnKind, MacroKind, SyntaxContext, Transparency};
+use rustc_span::hygiene::{ExpnId, ExpnKind, LocalExpnId, MacroKind, SyntaxContext, Transparency};
 use rustc_span::source_map::{CachingSourceMapView, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -103,7 +103,7 @@ impl Determinacy {
 /// but not for late resolution yet.
 #[derive(Clone, Copy)]
 enum Scope<'a> {
-    DeriveHelpers(ExpnId),
+    DeriveHelpers(LocalExpnId),
     DeriveHelpersCompat,
     MacroRules(MacroRulesScopeRef<'a>),
     CrateRoot,
@@ -143,7 +143,7 @@ enum ScopeSet<'a> {
 #[derive(Clone, Copy, Debug)]
 pub struct ParentScope<'a> {
     module: Module<'a>,
-    expansion: ExpnId,
+    expansion: LocalExpnId,
     macro_rules: MacroRulesScopeRef<'a>,
     derives: &'a [ast::Path],
 }
@@ -154,7 +154,7 @@ impl<'a> ParentScope<'a> {
     pub fn module(module: Module<'a>, resolver: &Resolver<'a>) -> ParentScope<'a> {
         ParentScope {
             module,
-            expansion: ExpnId::root(),
+            expansion: LocalExpnId::ROOT,
             macro_rules: resolver.arenas.alloc_macro_rules_scope(MacroRulesScope::Empty),
             derives: &[],
         }
@@ -515,7 +515,7 @@ pub struct ModuleData<'a> {
     populate_on_access: Cell<bool>,
 
     /// Macro invocations that can expand into items in this module.
-    unexpanded_invocations: RefCell<FxHashSet<ExpnId>>,
+    unexpanded_invocations: RefCell<FxHashSet<LocalExpnId>>,
 
     /// Whether `#[no_implicit_prelude]` is active.
     no_implicit_prelude: bool,
@@ -645,7 +645,7 @@ impl<'a> fmt::Debug for ModuleData<'a> {
 pub struct NameBinding<'a> {
     kind: NameBindingKind<'a>,
     ambiguity: Option<(&'a NameBinding<'a>, AmbiguityKind)>,
-    expansion: ExpnId,
+    expansion: LocalExpnId,
     span: Span,
     vis: ty::Visibility,
 }
@@ -829,7 +829,11 @@ impl<'a> NameBinding<'a> {
     // in some later round and screw up our previously found resolution.
     // See more detailed explanation in
     // https://github.com/rust-lang/rust/pull/53778#issuecomment-419224049
-    fn may_appear_after(&self, invoc_parent_expansion: ExpnId, binding: &NameBinding<'_>) -> bool {
+    fn may_appear_after(
+        &self,
+        invoc_parent_expansion: LocalExpnId,
+        binding: &NameBinding<'_>,
+    ) -> bool {
         // self > max(invoc, binding) => !(self <= invoc || self <= binding)
         // Expansions are partially ordered, so "may appear after" is an inversion of
         // "certainly appears before or simultaneously" and includes unordered cases.
@@ -966,7 +970,7 @@ pub struct Resolver<'a> {
     dummy_ext_derive: Lrc<SyntaxExtension>,
     non_macro_attrs: [Lrc<SyntaxExtension>; 2],
     local_macro_def_scopes: FxHashMap<LocalDefId, Module<'a>>,
-    ast_transform_scopes: FxHashMap<ExpnId, Module<'a>>,
+    ast_transform_scopes: FxHashMap<LocalExpnId, Module<'a>>,
     unused_macros: FxHashMap<LocalDefId, (NodeId, Span)>,
     proc_macro_stubs: FxHashSet<LocalDefId>,
     /// Traces collected during macro resolution and validated when it's complete.
@@ -978,18 +982,18 @@ pub struct Resolver<'a> {
     /// `derive(Copy)` marks items they are applied to so they are treated specially later.
     /// Derive macros cannot modify the item themselves and have to store the markers in the global
     /// context, so they attach the markers to derive container IDs using this resolver table.
-    containers_deriving_copy: FxHashSet<ExpnId>,
+    containers_deriving_copy: FxHashSet<LocalExpnId>,
     /// Parent scopes in which the macros were invoked.
     /// FIXME: `derives` are missing in these parent scopes and need to be taken from elsewhere.
-    invocation_parent_scopes: FxHashMap<ExpnId, ParentScope<'a>>,
+    invocation_parent_scopes: FxHashMap<LocalExpnId, ParentScope<'a>>,
     /// `macro_rules` scopes *produced* by expanding the macro invocations,
     /// include all the `macro_rules` items and other invocations generated by them.
-    output_macro_rules_scopes: FxHashMap<ExpnId, MacroRulesScopeRef<'a>>,
+    output_macro_rules_scopes: FxHashMap<LocalExpnId, MacroRulesScopeRef<'a>>,
     /// Helper attributes that are in scope for the given expansion.
-    helper_attrs: FxHashMap<ExpnId, Vec<Ident>>,
+    helper_attrs: FxHashMap<LocalExpnId, Vec<Ident>>,
     /// Ready or in-progress results of resolving paths inside the `#[derive(...)]` attribute
     /// with the given `ExpnId`.
-    derive_data: FxHashMap<ExpnId, DeriveData>,
+    derive_data: FxHashMap<LocalExpnId, DeriveData>,
 
     /// Avoid duplicated errors for "name already defined".
     name_already_seen: FxHashMap<Symbol, Span>,
@@ -1018,7 +1022,7 @@ pub struct Resolver<'a> {
     /// When collecting definitions from an AST fragment produced by a macro invocation `ExpnId`
     /// we know what parent node that fragment should be attached to thanks to this table,
     /// and how the `impl Trait` fragments were introduced.
-    invocation_parents: FxHashMap<ExpnId, (LocalDefId, ImplTraitContext)>,
+    invocation_parents: FxHashMap<LocalExpnId, (LocalDefId, ImplTraitContext)>,
 
     next_disambiguator: FxHashMap<(LocalDefId, DefPathData), u32>,
     /// Some way to know that we are in a *trait* impl in `visit_assoc_item`.
@@ -1268,7 +1272,7 @@ impl<'a> Resolver<'a> {
         node_id_to_def_id.insert(CRATE_NODE_ID, root);
 
         let mut invocation_parents = FxHashMap::default();
-        invocation_parents.insert(ExpnId::root(), (root, ImplTraitContext::Existential));
+        invocation_parents.insert(LocalExpnId::ROOT, (root, ImplTraitContext::Existential));
 
         let mut extern_prelude: FxHashMap<Ident, ExternPreludeEntry<'_>> = session
             .opts
@@ -1342,7 +1346,7 @@ impl<'a> Resolver<'a> {
             dummy_binding: arenas.alloc_name_binding(NameBinding {
                 kind: NameBindingKind::Res(Res::Err, false),
                 ambiguity: None,
-                expansion: ExpnId::root(),
+                expansion: LocalExpnId::ROOT,
                 span: DUMMY_SP,
                 vis: ty::Visibility::Public,
             }),
@@ -1392,7 +1396,7 @@ impl<'a> Resolver<'a> {
         };
 
         let root_parent_scope = ParentScope::module(graph_root, &resolver);
-        resolver.invocation_parent_scopes.insert(ExpnId::root(), root_parent_scope);
+        resolver.invocation_parent_scopes.insert(LocalExpnId::ROOT, root_parent_scope);
 
         resolver
     }
@@ -1810,7 +1814,8 @@ impl<'a> Resolver<'a> {
             }
 
             scope = match scope {
-                Scope::DeriveHelpers(expn_id) if expn_id != ExpnId::root() => {
+                Scope::DeriveHelpers(LocalExpnId::ROOT) => Scope::DeriveHelpersCompat,
+                Scope::DeriveHelpers(expn_id) => {
                     // Derive helpers are not visible to code generated by bang or derive macros.
                     let expn_data = expn_id.expn_data();
                     match expn_data.kind {
@@ -1818,10 +1823,9 @@ impl<'a> Resolver<'a> {
                         | ExpnKind::Macro(MacroKind::Bang | MacroKind::Derive, _) => {
                             Scope::DeriveHelpersCompat
                         }
-                        _ => Scope::DeriveHelpers(expn_data.parent),
+                        _ => Scope::DeriveHelpers(expn_data.parent.expect_local()),
                     }
                 }
-                Scope::DeriveHelpers(..) => Scope::DeriveHelpersCompat,
                 Scope::DeriveHelpersCompat => Scope::MacroRules(parent_scope.macro_rules),
                 Scope::MacroRules(macro_rules_scope) => match macro_rules_scope.get() {
                     MacroRulesScope::Binding(binding) => {
@@ -3248,7 +3252,7 @@ impl<'a> Resolver<'a> {
                 };
                 let crate_root = self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
                 Some(
-                    (crate_root, ty::Visibility::Public, DUMMY_SP, ExpnId::root())
+                    (crate_root, ty::Visibility::Public, DUMMY_SP, LocalExpnId::ROOT)
                         .to_name_binding(self.arenas),
                 )
             }
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 8686704388f..86f271fdece 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -30,7 +30,7 @@ use rustc_session::lint::BuiltinLintDiagnostics;
 use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::{self, ExpnData, ExpnId, ExpnKind};
+use rustc_span::hygiene::{self, ExpnData, ExpnKind, LocalExpnId};
 use rustc_span::hygiene::{AstPass, MacroKind};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -62,7 +62,7 @@ pub enum MacroRulesScope<'a> {
     Binding(&'a MacroRulesBinding<'a>),
     /// The scope introduced by a macro invocation that can potentially
     /// create a `macro_rules!` macro definition.
-    Invocation(ExpnId),
+    Invocation(LocalExpnId),
 }
 
 /// `macro_rules!` scopes are always kept by reference and inside a cell.
@@ -190,7 +190,11 @@ impl<'a> ResolverExpand for Resolver<'a> {
         });
     }
 
-    fn visit_ast_fragment_with_placeholders(&mut self, expansion: ExpnId, fragment: &AstFragment) {
+    fn visit_ast_fragment_with_placeholders(
+        &mut self,
+        expansion: LocalExpnId,
+        fragment: &AstFragment,
+    ) {
         // Integrate the new AST fragment into all the definition and module structures.
         // We are inside the `expansion` now, but other parent scope components are still the same.
         let parent_scope = ParentScope { expansion, ..self.invocation_parent_scopes[&expansion] };
@@ -216,9 +220,9 @@ impl<'a> ResolverExpand for Resolver<'a> {
         pass: AstPass,
         features: &[Symbol],
         parent_module_id: Option<NodeId>,
-    ) -> ExpnId {
+    ) -> LocalExpnId {
         let parent_module = parent_module_id.map(|module_id| self.local_def_id(module_id));
-        let expn_id = ExpnId::fresh(
+        let expn_id = LocalExpnId::fresh(
             ExpnData::allow_unstable(
                 ExpnKind::AstPass(pass),
                 call_site,
@@ -244,7 +248,7 @@ impl<'a> ResolverExpand for Resolver<'a> {
     fn resolve_macro_invocation(
         &mut self,
         invoc: &Invocation,
-        eager_expansion_root: ExpnId,
+        eager_expansion_root: LocalExpnId,
         force: bool,
     ) -> Result<Lrc<SyntaxExtension>, Indeterminate> {
         let invoc_id = invoc.expansion_data.id;
@@ -328,7 +332,7 @@ impl<'a> ResolverExpand for Resolver<'a> {
                             | ExpnKind::Macro(MacroKind::Bang | MacroKind::Derive, _) => {
                                 break;
                             }
-                            _ => expn_id = expn_data.parent,
+                            _ => expn_id = expn_data.parent.expect_local(),
                         }
                     }
                 }
@@ -344,7 +348,7 @@ impl<'a> ResolverExpand for Resolver<'a> {
         }
     }
 
-    fn lint_node_id(&self, expn_id: ExpnId) -> NodeId {
+    fn lint_node_id(&self, expn_id: LocalExpnId) -> NodeId {
         // FIXME - make this more precise. This currently returns the NodeId of the
         // nearest closing item - we should try to return the closest parent of the ExpnId
         self.invocation_parents
@@ -352,13 +356,13 @@ impl<'a> ResolverExpand for Resolver<'a> {
             .map_or(ast::CRATE_NODE_ID, |id| self.def_id_to_node_id[id.0])
     }
 
-    fn has_derive_copy(&self, expn_id: ExpnId) -> bool {
+    fn has_derive_copy(&self, expn_id: LocalExpnId) -> bool {
         self.containers_deriving_copy.contains(&expn_id)
     }
 
     fn resolve_derives(
         &mut self,
-        expn_id: ExpnId,
+        expn_id: LocalExpnId,
         force: bool,
         derive_paths: &dyn Fn() -> DeriveResolutions,
     ) -> Result<(), Indeterminate> {
@@ -423,7 +427,7 @@ impl<'a> ResolverExpand for Resolver<'a> {
         Ok(())
     }
 
-    fn take_derive_resolutions(&mut self, expn_id: ExpnId) -> Option<DeriveResolutions> {
+    fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions> {
         self.derive_data.remove(&expn_id).map(|data| data.resolutions)
     }
 
@@ -431,7 +435,11 @@ impl<'a> ResolverExpand for Resolver<'a> {
     // Returns true if the path can certainly be resolved in one of three namespaces,
     // returns false if the path certainly cannot be resolved in any of the three namespaces.
     // Returns `Indeterminate` if we cannot give a certain answer yet.
-    fn cfg_accessible(&mut self, expn_id: ExpnId, path: &ast::Path) -> Result<bool, Indeterminate> {
+    fn cfg_accessible(
+        &mut self,
+        expn_id: LocalExpnId,
+        path: &ast::Path,
+    ) -> Result<bool, Indeterminate> {
         let span = path.span;
         let path = &Segment::from_path(path);
         let parent_scope = self.invocation_parent_scopes[&expn_id];
@@ -714,7 +722,8 @@ impl<'a> Resolver<'a> {
                 let ident = Ident::new(orig_ident.name, orig_ident.span.with_ctxt(ctxt));
                 let ok = |res, span, arenas| {
                     Ok((
-                        (res, ty::Visibility::Public, span, ExpnId::root()).to_name_binding(arenas),
+                        (res, ty::Visibility::Public, span, LocalExpnId::ROOT)
+                            .to_name_binding(arenas),
                         Flags::empty(),
                     ))
                 };
diff --git a/compiler/rustc_span/src/def_id.rs b/compiler/rustc_span/src/def_id.rs
index c5d605ab578..64baf94cc00 100644
--- a/compiler/rustc_span/src/def_id.rs
+++ b/compiler/rustc_span/src/def_id.rs
@@ -136,7 +136,7 @@ impl Borrow<Fingerprint> for DefPathHash {
 /// further trouble.
 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
 #[derive(HashStable_Generic, Encodable, Decodable)]
-pub struct StableCrateId(u64);
+pub struct StableCrateId(pub(crate) u64);
 
 impl StableCrateId {
     pub fn to_u64(self) -> u64 {
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index d292f652896..cb3a08439d1 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -29,12 +29,13 @@ use crate::symbol::{kw, sym, Symbol};
 use crate::with_session_globals;
 use crate::{HashStableContext, Span, DUMMY_SP};
 
-use crate::def_id::{CrateNum, DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
+use crate::def_id::{CrateNum, DefId, StableCrateId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_data_structures::unhash::UnhashMap;
+use rustc_index::vec::IndexVec;
 use rustc_macros::HashStable_Generic;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::fmt;
@@ -58,14 +59,67 @@ pub struct SyntaxContextData {
     dollar_crate_name: Symbol,
 }
 
+rustc_index::newtype_index! {
+    /// A unique ID associated with a macro invocation and expansion.
+    pub struct ExpnIndex {
+        ENCODABLE = custom
+    }
+}
+
 /// A unique ID associated with a macro invocation and expansion.
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
-pub struct ExpnId(u32);
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+pub struct ExpnId {
+    pub krate: CrateNum,
+    pub local_id: ExpnIndex,
+}
+
+impl fmt::Debug for ExpnId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // Generate crate_::{{expn_}}.
+        write!(f, "{:?}::{{{{expn{}}}}}", self.krate, self.local_id.private)
+    }
+}
+
+rustc_index::newtype_index! {
+    /// A unique ID associated with a macro invocation and expansion.
+    pub struct LocalExpnId {
+        ENCODABLE = custom
+        DEBUG_FORMAT = "expn{}"
+    }
+}
 
 /// A unique hash value associated to an expansion.
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, Encodable, Decodable, HashStable_Generic)]
 pub struct ExpnHash(Fingerprint);
 
+impl ExpnHash {
+    /// Returns the [StableCrateId] identifying the crate this [ExpnHash]
+    /// originates from.
+    #[inline]
+    pub fn stable_crate_id(self) -> StableCrateId {
+        StableCrateId(self.0.as_value().0)
+    }
+
+    /// Returns the crate-local part of the [ExpnHash].
+    ///
+    /// Used for tests.
+    #[inline]
+    pub fn local_hash(self) -> u64 {
+        self.0.as_value().1
+    }
+
+    #[inline]
+    pub fn is_root(self) -> bool {
+        self.0 == Fingerprint::ZERO
+    }
+
+    /// Builds a new [ExpnHash] with the given [StableCrateId] and
+    /// `local_hash`, where `local_hash` must be unique within its crate.
+    fn new(stable_crate_id: StableCrateId, local_hash: u64) -> ExpnHash {
+        ExpnHash(Fingerprint::new(stable_crate_id.0, local_hash))
+    }
+}
+
 /// A property of a macro expansion that determines how identifiers
 /// produced by that expansion are resolved.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Hash, Debug, Encodable, Decodable)]
@@ -86,31 +140,102 @@ pub enum Transparency {
     Opaque,
 }
 
-impl ExpnId {
-    pub fn fresh_empty() -> Self {
-        HygieneData::with(|data| data.fresh_expn(None))
-    }
-
-    pub fn fresh(expn_data: ExpnData, ctx: impl HashStableContext) -> Self {
-        let expn_id = HygieneData::with(|data| data.fresh_expn(Some(expn_data)));
-        update_disambiguator(expn_id, ctx);
-        expn_id
-    }
-
+impl LocalExpnId {
     /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
-    #[inline]
-    pub fn root() -> Self {
-        ExpnId(0)
+    pub const ROOT: LocalExpnId = LocalExpnId::from_u32(0);
+
+    pub fn from_raw(idx: ExpnIndex) -> LocalExpnId {
+        LocalExpnId::from_u32(idx.as_u32())
+    }
+
+    pub fn as_raw(self) -> ExpnIndex {
+        ExpnIndex::from_u32(self.as_u32())
+    }
+
+    pub fn fresh_empty() -> LocalExpnId {
+        HygieneData::with(|data| {
+            let expn_id = data.local_expn_data.push(None);
+            let _eid = data.local_expn_hashes.push(ExpnHash(Fingerprint::ZERO));
+            debug_assert_eq!(expn_id, _eid);
+            expn_id
+        })
+    }
+
+    pub fn fresh(mut expn_data: ExpnData, ctx: impl HashStableContext) -> LocalExpnId {
+        debug_assert_eq!(expn_data.parent.krate, LOCAL_CRATE);
+        let expn_hash = update_disambiguator(&mut expn_data, ctx);
+        HygieneData::with(|data| {
+            let expn_id = data.local_expn_data.push(Some(expn_data));
+            let _eid = data.local_expn_hashes.push(expn_hash);
+            debug_assert_eq!(expn_id, _eid);
+            let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, expn_id.to_expn_id());
+            debug_assert!(_old_id.is_none());
+            expn_id
+        })
     }
 
     #[inline]
-    pub fn as_u32(self) -> u32 {
-        self.0
+    pub fn expn_hash(self) -> ExpnHash {
+        HygieneData::with(|data| data.local_expn_hash(self))
     }
 
     #[inline]
-    pub fn from_u32(raw: u32) -> ExpnId {
-        ExpnId(raw)
+    pub fn expn_data(self) -> ExpnData {
+        HygieneData::with(|data| data.local_expn_data(self).clone())
+    }
+
+    #[inline]
+    pub fn to_expn_id(self) -> ExpnId {
+        ExpnId { krate: LOCAL_CRATE, local_id: self.as_raw() }
+    }
+
+    #[inline]
+    pub fn set_expn_data(self, mut expn_data: ExpnData, ctx: impl HashStableContext) {
+        debug_assert_eq!(expn_data.parent.krate, LOCAL_CRATE);
+        let expn_hash = update_disambiguator(&mut expn_data, ctx);
+        HygieneData::with(|data| {
+            let old_expn_data = &mut data.local_expn_data[self];
+            assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");
+            *old_expn_data = Some(expn_data);
+            debug_assert_eq!(data.local_expn_hashes[self].0, Fingerprint::ZERO);
+            data.local_expn_hashes[self] = expn_hash;
+            let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, self.to_expn_id());
+            debug_assert!(_old_id.is_none());
+        });
+    }
+
+    #[inline]
+    pub fn is_descendant_of(self, ancestor: LocalExpnId) -> bool {
+        self.to_expn_id().is_descendant_of(ancestor.to_expn_id())
+    }
+
+    /// `expn_id.outer_expn_is_descendant_of(ctxt)` is equivalent to but faster than
+    /// `expn_id.is_descendant_of(ctxt.outer_expn())`.
+    #[inline]
+    pub fn outer_expn_is_descendant_of(self, ctxt: SyntaxContext) -> bool {
+        self.to_expn_id().outer_expn_is_descendant_of(ctxt)
+    }
+
+    /// Returns span for the macro which originally caused this expansion to happen.
+    ///
+    /// Stops backtracing at include! boundary.
+    #[inline]
+    pub fn expansion_cause(self) -> Option<Span> {
+        self.to_expn_id().expansion_cause()
+    }
+
+    #[inline]
+    #[track_caller]
+    pub fn parent(self) -> LocalExpnId {
+        self.expn_data().parent.as_local().unwrap()
+    }
+}
+
+impl ExpnId {
+    /// The ID of the theoretical expansion that generates freshly parsed, unexpanded AST.
+    /// Invariant: we do not create any ExpnId with local_id == 0 and krate != 0.
+    pub const fn root() -> ExpnId {
+        ExpnId { krate: LOCAL_CRATE, local_id: ExpnIndex::from_u32(0) }
     }
 
     #[inline]
@@ -124,20 +249,19 @@ impl ExpnId {
     }
 
     #[inline]
-    pub fn expn_data(self) -> ExpnData {
-        HygieneData::with(|data| data.expn_data(self).clone())
+    pub fn as_local(self) -> Option<LocalExpnId> {
+        if self.krate == LOCAL_CRATE { Some(LocalExpnId::from_raw(self.local_id)) } else { None }
     }
 
     #[inline]
-    pub fn set_expn_data(self, mut expn_data: ExpnData, ctx: impl HashStableContext) {
-        HygieneData::with(|data| {
-            let old_expn_data = &mut data.expn_data[self.0 as usize];
-            assert!(old_expn_data.is_none(), "expansion data is reset for an expansion ID");
-            assert_eq!(expn_data.orig_id, None);
-            expn_data.orig_id = Some(self.as_u32());
-            *old_expn_data = Some(expn_data);
-        });
-        update_disambiguator(self, ctx)
+    #[track_caller]
+    pub fn expect_local(self) -> LocalExpnId {
+        self.as_local().unwrap()
+    }
+
+    #[inline]
+    pub fn expn_data(self) -> ExpnData {
+        HygieneData::with(|data| data.expn_data(self).clone())
     }
 
     pub fn is_descendant_of(self, ancestor: ExpnId) -> bool {
@@ -175,34 +299,39 @@ pub struct HygieneData {
     /// Each expansion should have an associated expansion data, but sometimes there's a delay
     /// between creation of an expansion ID and obtaining its data (e.g. macros are collected
     /// first and then resolved later), so we use an `Option` here.
-    expn_data: Vec<Option<ExpnData>>,
-    expn_hashes: Vec<ExpnHash>,
+    local_expn_data: IndexVec<LocalExpnId, Option<ExpnData>>,
+    local_expn_hashes: IndexVec<LocalExpnId, ExpnHash>,
+    /// Data and hash information from external crates.  We may eventually want to remove these
+    /// maps, and fetch the information directly from the other crate's metadata like DefIds do.
+    foreign_expn_data: FxHashMap<ExpnId, ExpnData>,
+    foreign_expn_hashes: FxHashMap<ExpnId, ExpnHash>,
     expn_hash_to_expn_id: UnhashMap<ExpnHash, ExpnId>,
     syntax_context_data: Vec<SyntaxContextData>,
     syntax_context_map: FxHashMap<(SyntaxContext, ExpnId, Transparency), SyntaxContext>,
-    /// Maps the `Fingerprint` of an `ExpnData` to the next disambiguator value.
+    /// Maps the `local_hash` of an `ExpnData` to the next disambiguator value.
     /// This is used by `update_disambiguator` to keep track of which `ExpnData`s
     /// would have collisions without a disambiguator.
     /// The keys of this map are always computed with `ExpnData.disambiguator`
     /// set to 0.
-    expn_data_disambiguators: FxHashMap<Fingerprint, u32>,
+    expn_data_disambiguators: FxHashMap<u64, u32>,
 }
 
 impl HygieneData {
     crate fn new(edition: Edition) -> Self {
-        let mut root_data = ExpnData::default(
+        let root_data = ExpnData::default(
             ExpnKind::Root,
             DUMMY_SP,
             edition,
-            Some(DefId::local(CRATE_DEF_INDEX)),
+            Some(CRATE_DEF_ID.to_def_id()),
             None,
         );
-        root_data.orig_id = Some(0);
 
         HygieneData {
-            expn_data: vec![Some(root_data)],
-            expn_hashes: vec![ExpnHash(Fingerprint::ZERO)],
-            expn_hash_to_expn_id: std::iter::once((ExpnHash(Fingerprint::ZERO), ExpnId(0)))
+            local_expn_data: IndexVec::from_elem_n(Some(root_data), 1),
+            local_expn_hashes: IndexVec::from_elem_n(ExpnHash(Fingerprint::ZERO), 1),
+            foreign_expn_data: FxHashMap::default(),
+            foreign_expn_hashes: FxHashMap::default(),
+            expn_hash_to_expn_id: std::iter::once((ExpnHash(Fingerprint::ZERO), ExpnId::root()))
                 .collect(),
             syntax_context_data: vec![SyntaxContextData {
                 outer_expn: ExpnId::root(),
@@ -221,24 +350,29 @@ impl HygieneData {
         with_session_globals(|session_globals| f(&mut *session_globals.hygiene_data.borrow_mut()))
     }
 
-    fn fresh_expn(&mut self, mut expn_data: Option<ExpnData>) -> ExpnId {
-        let raw_id = self.expn_data.len() as u32;
-        if let Some(data) = expn_data.as_mut() {
-            assert_eq!(data.orig_id, None);
-            data.orig_id = Some(raw_id);
-        }
-        self.expn_data.push(expn_data);
-        self.expn_hashes.push(ExpnHash(Fingerprint::ZERO));
-        ExpnId(raw_id)
+    #[inline]
+    fn local_expn_hash(&self, expn_id: LocalExpnId) -> ExpnHash {
+        self.local_expn_hashes[expn_id]
     }
 
     #[inline]
     fn expn_hash(&self, expn_id: ExpnId) -> ExpnHash {
-        self.expn_hashes[expn_id.0 as usize]
+        match expn_id.as_local() {
+            Some(expn_id) => self.local_expn_hashes[expn_id],
+            None => self.foreign_expn_hashes[&expn_id],
+        }
+    }
+
+    fn local_expn_data(&self, expn_id: LocalExpnId) -> &ExpnData {
+        self.local_expn_data[expn_id].as_ref().expect("no expansion data for an expansion ID")
     }
 
     fn expn_data(&self, expn_id: ExpnId) -> &ExpnData {
-        self.expn_data[expn_id.0 as usize].as_ref().expect("no expansion data for an expansion ID")
+        if let Some(expn_id) = expn_id.as_local() {
+            self.local_expn_data[expn_id].as_ref().expect("no expansion data for an expansion ID")
+        } else {
+            &self.foreign_expn_data[&expn_id]
+        }
     }
 
     fn is_descendant_of(&self, mut expn_id: ExpnId, ancestor: ExpnId) -> bool {
@@ -453,17 +587,21 @@ pub fn debug_hygiene_data(verbose: bool) -> String {
         } else {
             let mut s = String::from("");
             s.push_str("Expansions:");
-            data.expn_data.iter().enumerate().for_each(|(id, expn_info)| {
-                let expn_info = expn_info.as_ref().expect("no expansion data for an expansion ID");
+            let mut debug_expn_data = |(id, expn_data): (&ExpnId, &ExpnData)| {
                 s.push_str(&format!(
-                    "\n{}: parent: {:?}, call_site_ctxt: {:?}, def_site_ctxt: {:?}, kind: {:?}",
+                    "\n{:?}: parent: {:?}, call_site_ctxt: {:?}, def_site_ctxt: {:?}, kind: {:?}",
                     id,
-                    expn_info.parent,
-                    expn_info.call_site.ctxt(),
-                    expn_info.def_site.ctxt(),
-                    expn_info.kind,
-                ));
+                    expn_data.parent,
+                    expn_data.call_site.ctxt(),
+                    expn_data.def_site.ctxt(),
+                    expn_data.kind,
+                ))
+            };
+            data.local_expn_data.iter_enumerated().for_each(|(id, expn_data)| {
+                let expn_data = expn_data.as_ref().expect("no expansion data for an expansion ID");
+                debug_expn_data((&id.to_expn_id(), expn_data))
             });
+            data.foreign_expn_data.iter().for_each(debug_expn_data);
             s.push_str("\n\nSyntaxContexts:");
             data.syntax_context_data.iter().enumerate().for_each(|(id, ctxt)| {
                 s.push_str(&format!(
@@ -696,7 +834,7 @@ impl Span {
         transparency: Transparency,
         ctx: impl HashStableContext,
     ) -> Span {
-        let expn_id = ExpnId::fresh(expn_data, ctx);
+        let expn_id = LocalExpnId::fresh(expn_data, ctx).to_expn_id();
         HygieneData::with(|data| {
             self.with_ctxt(data.apply_mark(SyntaxContext::root(), expn_id, transparency))
         })
@@ -738,20 +876,6 @@ pub struct ExpnData {
     /// call_site span would have its own ExpnData, with the call_site
     /// pointing to the `foo!` invocation.
     pub call_site: Span,
-    /// The crate that originally created this `ExpnData`. During
-    /// metadata serialization, we only encode `ExpnData`s that were
-    /// created locally - when our serialized metadata is decoded,
-    /// foreign `ExpnId`s will have their `ExpnData` looked up
-    /// from the crate specified by `Crate
-    krate: CrateNum,
-    /// The raw that this `ExpnData` had in its original crate.
-    /// An `ExpnData` can be created before being assigned an `ExpnId`,
-    /// so this might be `None` until `set_expn_data` is called
-    // This is used only for serialization/deserialization purposes:
-    // two `ExpnData`s that differ only in their `orig_id` should
-    // be considered equivalent.
-    #[stable_hasher(ignore)]
-    orig_id: Option<u32>,
     /// Used to force two `ExpnData`s to have different `Fingerprint`s.
     /// Due to macro expansion, it's possible to end up with two `ExpnId`s
     /// that have identical `ExpnData`s. This violates the contract of `HashStable`
@@ -790,7 +914,6 @@ pub struct ExpnData {
     pub parent_module: Option<DefId>,
 }
 
-// These would require special handling of `orig_id`.
 impl !PartialEq for ExpnData {}
 impl !Hash for ExpnData {}
 
@@ -818,8 +941,6 @@ impl ExpnData {
             edition,
             macro_def_id,
             parent_module,
-            krate: LOCAL_CRATE,
-            orig_id: None,
             disambiguator: 0,
         }
     }
@@ -843,8 +964,6 @@ impl ExpnData {
             edition,
             macro_def_id,
             parent_module,
-            krate: LOCAL_CRATE,
-            orig_id: None,
             disambiguator: 0,
         }
     }
@@ -869,7 +988,7 @@ impl ExpnData {
     }
 
     #[inline]
-    fn hash_expn(&self, ctx: &mut impl HashStableContext) -> Fingerprint {
+    fn hash_expn(&self, ctx: &mut impl HashStableContext) -> u64 {
         let mut hasher = StableHasher::new();
         self.hash_stable(ctx, &mut hasher);
         hasher.finish()
@@ -1020,11 +1139,18 @@ pub struct HygieneEncodeContext {
 }
 
 impl HygieneEncodeContext {
+    /// Record the fact that we need to serialize the corresponding `ExpnData`.
+    pub fn schedule_expn_data_for_encoding(&self, expn: ExpnId) {
+        if !self.serialized_expns.lock().contains(&expn) {
+            self.latest_expns.lock().insert(expn);
+        }
+    }
+
     pub fn encode<T, R>(
         &self,
         encoder: &mut T,
         mut encode_ctxt: impl FnMut(&mut T, u32, &SyntaxContextData) -> Result<(), R>,
-        mut encode_expn: impl FnMut(&mut T, u32, ExpnData, ExpnHash) -> Result<(), R>,
+        mut encode_expn: impl FnMut(&mut T, ExpnId, &ExpnData, ExpnHash) -> Result<(), R>,
     ) -> Result<(), R> {
         // When we serialize a `SyntaxContextData`, we may end up serializing
         // a `SyntaxContext` that we haven't seen before
@@ -1051,9 +1177,9 @@ impl HygieneEncodeContext {
 
             let latest_expns = { std::mem::take(&mut *self.latest_expns.lock()) };
 
-            for_all_expns_in(latest_expns.into_iter(), |index, expn, data, hash| {
+            for_all_expns_in(latest_expns.into_iter(), |expn, data, hash| {
                 if self.serialized_expns.lock().insert(expn) {
-                    encode_expn(encoder, index, data, hash)?;
+                    encode_expn(encoder, expn, data, hash)?;
                 }
                 Ok(())
             })?;
@@ -1072,78 +1198,70 @@ pub struct HygieneDecodeContext {
     // so that multiple occurrences of the same serialized id are decoded to the same
     // `SyntaxContext`
     remapped_ctxts: Lock<Vec<Option<SyntaxContext>>>,
-    // The same as `remapepd_ctxts`, but for `ExpnId`s
-    remapped_expns: Lock<Vec<Option<ExpnId>>>,
 }
 
-pub fn decode_expn_id<'a, D: Decoder, G>(
-    d: &mut D,
-    mode: ExpnDataDecodeMode<'a, G>,
-    decode_data: impl FnOnce(&mut D, u32) -> Result<(ExpnData, ExpnHash), D::Error>,
-) -> Result<ExpnId, D::Error>
-where
-    G: FnOnce(CrateNum) -> &'a HygieneDecodeContext,
-{
-    let index = u32::decode(d)?;
-    let context = match mode {
-        ExpnDataDecodeMode::IncrComp(context) => context,
-        ExpnDataDecodeMode::Metadata(get_context) => {
-            let krate = CrateNum::decode(d)?;
-            get_context(krate)
-        }
-    };
+/// Register an expansion which has been decoded from the on-disk-cache for the local crate.
+pub fn register_local_expn_id(data: ExpnData, hash: ExpnHash) -> ExpnId {
+    HygieneData::with(|hygiene_data| {
+        let expn_id = hygiene_data.local_expn_data.next_index();
+        hygiene_data.local_expn_data.push(Some(data));
+        let _eid = hygiene_data.local_expn_hashes.push(hash);
+        debug_assert_eq!(expn_id, _eid);
 
-    // Do this after decoding, so that we decode a `CrateNum`
-    // if necessary
-    if index == ExpnId::root().as_u32() {
+        let expn_id = expn_id.to_expn_id();
+
+        let _old_id = hygiene_data.expn_hash_to_expn_id.insert(hash, expn_id);
+        debug_assert!(_old_id.is_none());
+        expn_id
+    })
+}
+
+/// Register an expansion which has been decoded from the metadata of a foreign crate.
+pub fn register_expn_id(
+    krate: CrateNum,
+    local_id: ExpnIndex,
+    data: ExpnData,
+    hash: ExpnHash,
+) -> ExpnId {
+    let expn_id = ExpnId { krate, local_id };
+    HygieneData::with(|hygiene_data| {
+        let _old_data = hygiene_data.foreign_expn_data.insert(expn_id, data);
+        debug_assert!(_old_data.is_none());
+        let _old_hash = hygiene_data.foreign_expn_hashes.insert(expn_id, hash);
+        debug_assert!(_old_hash.is_none());
+        let _old_id = hygiene_data.expn_hash_to_expn_id.insert(hash, expn_id);
+        debug_assert!(_old_id.is_none());
+    });
+    expn_id
+}
+
+/// Decode an expansion from the metadata of a foreign crate.
+pub fn decode_expn_id(
+    krate: CrateNum,
+    index: u32,
+    decode_data: impl FnOnce(ExpnId) -> (ExpnData, ExpnHash),
+) -> ExpnId {
+    if index == 0 {
         debug!("decode_expn_id: deserialized root");
-        return Ok(ExpnId::root());
+        return ExpnId::root();
     }
 
-    let outer_expns = &context.remapped_expns;
+    let index = ExpnIndex::from_u32(index);
 
-    // Ensure that the lock() temporary is dropped early
-    {
-        if let Some(expn_id) = outer_expns.lock().get(index as usize).copied().flatten() {
-            return Ok(expn_id);
-        }
+    // This function is used to decode metadata, so it cannot decode information about LOCAL_CRATE.
+    debug_assert_ne!(krate, LOCAL_CRATE);
+    let expn_id = ExpnId { krate, local_id: index };
+
+    // Fast path if the expansion has already been decoded.
+    if HygieneData::with(|hygiene_data| hygiene_data.foreign_expn_data.contains_key(&expn_id)) {
+        return expn_id;
     }
 
     // Don't decode the data inside `HygieneData::with`, since we need to recursively decode
     // other ExpnIds
-    let (mut expn_data, hash) = decode_data(d, index)?;
+    let (expn_data, hash) = decode_data(expn_id);
 
-    let expn_id = HygieneData::with(|hygiene_data| {
-        if let Some(&expn_id) = hygiene_data.expn_hash_to_expn_id.get(&hash) {
-            return expn_id;
-        }
-
-        let expn_id = ExpnId(hygiene_data.expn_data.len() as u32);
-
-        // If we just deserialized an `ExpnData` owned by
-        // the local crate, its `orig_id` will be stale,
-        // so we need to update it to its own value.
-        // This only happens when we deserialize the incremental cache,
-        // since a crate will never decode its own metadata.
-        if expn_data.krate == LOCAL_CRATE {
-            expn_data.orig_id = Some(expn_id.0);
-        }
-
-        hygiene_data.expn_data.push(Some(expn_data));
-        hygiene_data.expn_hashes.push(hash);
-        let _old_id = hygiene_data.expn_hash_to_expn_id.insert(hash, expn_id);
-        debug_assert!(_old_id.is_none());
-
-        let mut expns = outer_expns.lock();
-        let new_len = index as usize + 1;
-        if expns.len() < new_len {
-            expns.resize(new_len, None);
-        }
-        expns[index as usize] = Some(expn_id);
-        drop(expns);
-        expn_id
-    });
-    Ok(expn_id)
+    register_expn_id(krate, index, expn_data, hash)
 }
 
 // Decodes `SyntaxContext`, using the provided `HygieneDecodeContext`
@@ -1234,29 +1352,37 @@ fn for_all_ctxts_in<E, F: FnMut(u32, SyntaxContext, &SyntaxContextData) -> Resul
 
 fn for_all_expns_in<E>(
     expns: impl Iterator<Item = ExpnId>,
-    mut f: impl FnMut(u32, ExpnId, ExpnData, ExpnHash) -> Result<(), E>,
+    mut f: impl FnMut(ExpnId, &ExpnData, ExpnHash) -> Result<(), E>,
 ) -> Result<(), E> {
     let all_data: Vec<_> = HygieneData::with(|data| {
         expns
-            .map(|expn| {
-                let idx = expn.0 as usize;
-                (expn, data.expn_data[idx].clone(), data.expn_hashes[idx].clone())
-            })
+            .map(|expn| (expn, data.expn_data(expn).clone(), data.expn_hash(expn).clone()))
             .collect()
     });
     for (expn, data, hash) in all_data.into_iter() {
-        let data = data.unwrap_or_else(|| panic!("Missing data for {:?}", expn));
-        f(expn.0, expn, data, hash)?;
+        f(expn, &data, hash)?;
     }
     Ok(())
 }
 
+impl<E: Encoder> Encodable<E> for LocalExpnId {
+    fn encode(&self, e: &mut E) -> Result<(), E::Error> {
+        self.to_expn_id().encode(e)
+    }
+}
+
 impl<E: Encoder> Encodable<E> for ExpnId {
     default fn encode(&self, _: &mut E) -> Result<(), E::Error> {
         panic!("cannot encode `ExpnId` with `{}`", std::any::type_name::<E>());
     }
 }
 
+impl<D: Decoder> Decodable<D> for LocalExpnId {
+    fn decode(d: &mut D) -> Result<Self, D::Error> {
+        ExpnId::decode(d).map(ExpnId::expect_local)
+    }
+}
+
 impl<D: Decoder> Decodable<D> for ExpnId {
     default fn decode(_: &mut D) -> Result<Self, D::Error> {
         panic!("cannot decode `ExpnId` with `{}`", std::any::type_name::<D>());
@@ -1274,58 +1400,6 @@ pub fn raw_encode_syntax_context<E: Encoder>(
     ctxt.0.encode(e)
 }
 
-pub fn raw_encode_expn_id<E: Encoder>(
-    expn: ExpnId,
-    context: &HygieneEncodeContext,
-    mode: ExpnDataEncodeMode,
-    e: &mut E,
-) -> Result<(), E::Error> {
-    // Record the fact that we need to serialize the corresponding
-    // `ExpnData`
-    let needs_data = || {
-        if !context.serialized_expns.lock().contains(&expn) {
-            context.latest_expns.lock().insert(expn);
-        }
-    };
-
-    match mode {
-        ExpnDataEncodeMode::IncrComp => {
-            // Always serialize the `ExpnData` in incr comp mode
-            needs_data();
-            expn.0.encode(e)
-        }
-        ExpnDataEncodeMode::Metadata => {
-            let data = expn.expn_data();
-            // We only need to serialize the ExpnData
-            // if it comes from this crate.
-            // We currently don't serialize any hygiene information data for
-            // proc-macro crates: see the `SpecializedEncoder<Span>` impl
-            // for crate metadata.
-            if data.krate == LOCAL_CRATE {
-                needs_data();
-            }
-            data.orig_id.expect("Missing orig_id").encode(e)?;
-            data.krate.encode(e)
-        }
-    }
-}
-
-pub enum ExpnDataEncodeMode {
-    IncrComp,
-    Metadata,
-}
-
-pub enum ExpnDataDecodeMode<'a, F: FnOnce(CrateNum) -> &'a HygieneDecodeContext> {
-    IncrComp(&'a HygieneDecodeContext),
-    Metadata(F),
-}
-
-impl<'a> ExpnDataDecodeMode<'a, Box<dyn FnOnce(CrateNum) -> &'a HygieneDecodeContext>> {
-    pub fn incr_comp(ctxt: &'a HygieneDecodeContext) -> Self {
-        ExpnDataDecodeMode::IncrComp(ctxt)
-    }
-}
-
 impl<E: Encoder> Encodable<E> for SyntaxContext {
     default fn encode(&self, _: &mut E) -> Result<(), E::Error> {
         panic!("cannot encode `SyntaxContext` with `{}`", std::any::type_name::<E>());
@@ -1345,10 +1419,9 @@ impl<D: Decoder> Decodable<D> for SyntaxContext {
 /// This method is called only when an `ExpnData` is first associated
 /// with an `ExpnId` (when the `ExpnId` is initially constructed, or via
 /// `set_expn_data`). It is *not* called for foreign `ExpnId`s deserialized
-/// from another crate's metadata - since `ExpnData` includes a `krate` field,
+/// from another crate's metadata - since `ExpnHash` includes the stable crate id,
 /// collisions are only possible between `ExpnId`s within the same crate.
-fn update_disambiguator(expn_id: ExpnId, mut ctx: impl HashStableContext) {
-    let mut expn_data = expn_id.expn_data();
+fn update_disambiguator(expn_data: &mut ExpnData, mut ctx: impl HashStableContext) -> ExpnHash {
     // This disambiguator should not have been set yet.
     assert_eq!(
         expn_data.disambiguator, 0,
@@ -1367,8 +1440,7 @@ fn update_disambiguator(expn_id: ExpnId, mut ctx: impl HashStableContext) {
     });
 
     if disambiguator != 0 {
-        debug!("Set disambiguator for {:?} (hash {:?})", expn_id, expn_hash);
-        debug!("expn_data = {:?}", expn_data);
+        debug!("Set disambiguator for expn_data={:?} expn_hash={:?}", expn_data, expn_hash);
 
         expn_data.disambiguator = disambiguator;
         expn_hash = expn_data.hash_expn(&mut ctx);
@@ -1384,14 +1456,7 @@ fn update_disambiguator(expn_id: ExpnId, mut ctx: impl HashStableContext) {
         });
     }
 
-    let expn_hash = ExpnHash(expn_hash);
-    HygieneData::with(|data| {
-        data.expn_data[expn_id.0 as usize].as_mut().unwrap().disambiguator = disambiguator;
-        debug_assert_eq!(data.expn_hashes[expn_id.0 as usize].0, Fingerprint::ZERO);
-        data.expn_hashes[expn_id.0 as usize] = expn_hash;
-        let _old_id = data.expn_hash_to_expn_id.insert(expn_hash, expn_id);
-        debug_assert!(_old_id.is_none());
-    });
+    ExpnHash::new(ctx.def_path_hash(LOCAL_CRATE.as_def_id()).stable_crate_id(), expn_hash)
 }
 
 impl<CTX: HashStableContext> HashStable<CTX> for SyntaxContext {
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 7a1ee20ee79..1c95cc91208 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -38,7 +38,7 @@ use edition::Edition;
 pub mod hygiene;
 use hygiene::Transparency;
 pub use hygiene::{DesugaringKind, ExpnKind, ForLoopLoc, MacroKind};
-pub use hygiene::{ExpnData, ExpnHash, ExpnId, SyntaxContext};
+pub use hygiene::{ExpnData, ExpnHash, ExpnId, LocalExpnId, SyntaxContext};
 pub mod def_id;
 use def_id::{CrateNum, DefId, DefPathHash, LOCAL_CRATE};
 pub mod lev_distance;
diff --git a/src/test/ui/hygiene/unpretty-debug.stdout b/src/test/ui/hygiene/unpretty-debug.stdout
index 84ca046212d..ffb9f9eed41 100644
--- a/src/test/ui/hygiene/unpretty-debug.stdout
+++ b/src/test/ui/hygiene/unpretty-debug.stdout
@@ -19,10 +19,10 @@ fn y /* 0#0 */() { }
 
 /*
 Expansions:
-0: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: Root
-1: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Bang, "foo")
+crate0::{{expn0}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Root
+crate0::{{expn1}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Bang, "foo")
 
 SyntaxContexts:
-#0: parent: #0, outer_mark: (ExpnId(0), Opaque)
-#1: parent: #0, outer_mark: (ExpnId(1), SemiTransparent)
+#0: parent: #0, outer_mark: (crate0::{{expn0}}, Opaque)
+#1: parent: #0, outer_mark: (crate0::{{expn1}}, SemiTransparent)
 */
diff --git a/src/test/ui/proc-macro/meta-macro-hygiene.stdout b/src/test/ui/proc-macro/meta-macro-hygiene.stdout
index dc63d014451..2524d8273b7 100644
--- a/src/test/ui/proc-macro/meta-macro-hygiene.stdout
+++ b/src/test/ui/proc-macro/meta-macro-hygiene.stdout
@@ -43,23 +43,23 @@ fn main /* 0#0 */() { ; }
 
 /*
 Expansions:
-0: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: Root
-1: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
-2: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Bang, "produce_it")
-3: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
-4: parent: ExpnId(2), call_site_ctxt: #4, def_site_ctxt: #0, kind: Macro(Bang, "meta_macro::print_def_site")
-5: parent: ExpnId(4), call_site_ctxt: #5, def_site_ctxt: #0, kind: Macro(Bang, "$crate::dummy")
+crate0::{{expn0}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Root
+crate0::{{expn1}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
+crate0::{{expn2}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Bang, "produce_it")
+crate0::{{expn3}}: parent: crate0::{{expn2}}, call_site_ctxt: #4, def_site_ctxt: #0, kind: Macro(Bang, "meta_macro::print_def_site")
+crate0::{{expn4}}: parent: crate0::{{expn3}}, call_site_ctxt: #5, def_site_ctxt: #0, kind: Macro(Bang, "$crate::dummy")
+crate2::{{expn1}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
 
 SyntaxContexts:
-#0: parent: #0, outer_mark: (ExpnId(0), Opaque)
-#1: parent: #0, outer_mark: (ExpnId(1), Opaque)
-#2: parent: #0, outer_mark: (ExpnId(1), Transparent)
-#3: parent: #0, outer_mark: (ExpnId(3), Opaque)
-#4: parent: #0, outer_mark: (ExpnId(2), SemiTransparent)
-#5: parent: #0, outer_mark: (ExpnId(4), Opaque)
-#6: parent: #4, outer_mark: (ExpnId(4), Transparent)
-#7: parent: #0, outer_mark: (ExpnId(4), SemiTransparent)
-#8: parent: #0, outer_mark: (ExpnId(5), Opaque)
-#9: parent: #5, outer_mark: (ExpnId(5), Transparent)
-#10: parent: #5, outer_mark: (ExpnId(5), SemiTransparent)
+#0: parent: #0, outer_mark: (crate0::{{expn0}}, Opaque)
+#1: parent: #0, outer_mark: (crate0::{{expn1}}, Opaque)
+#2: parent: #0, outer_mark: (crate0::{{expn1}}, Transparent)
+#3: parent: #0, outer_mark: (crate2::{{expn1}}, Opaque)
+#4: parent: #0, outer_mark: (crate0::{{expn2}}, SemiTransparent)
+#5: parent: #0, outer_mark: (crate0::{{expn3}}, Opaque)
+#6: parent: #4, outer_mark: (crate0::{{expn3}}, Transparent)
+#7: parent: #0, outer_mark: (crate0::{{expn3}}, SemiTransparent)
+#8: parent: #0, outer_mark: (crate0::{{expn4}}, Opaque)
+#9: parent: #5, outer_mark: (crate0::{{expn4}}, Transparent)
+#10: parent: #5, outer_mark: (crate0::{{expn4}}, SemiTransparent)
 */
diff --git a/src/test/ui/proc-macro/nonterminal-token-hygiene.stdout b/src/test/ui/proc-macro/nonterminal-token-hygiene.stdout
index 75e6a49b314..b5ab82737e9 100644
--- a/src/test/ui/proc-macro/nonterminal-token-hygiene.stdout
+++ b/src/test/ui/proc-macro/nonterminal-token-hygiene.stdout
@@ -67,22 +67,22 @@ fn main /* 0#0 */() { }
 
 /*
 Expansions:
-0: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: Root
-1: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
-2: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Bang, "outer")
-3: parent: ExpnId(0), call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
-4: parent: ExpnId(2), call_site_ctxt: #4, def_site_ctxt: #4, kind: Macro(Bang, "inner")
-5: parent: ExpnId(4), call_site_ctxt: #6, def_site_ctxt: #0, kind: Macro(Bang, "print_bang")
+crate0::{{expn0}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Root
+crate0::{{expn1}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
+crate0::{{expn2}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: Macro(Bang, "outer")
+crate0::{{expn3}}: parent: crate0::{{expn2}}, call_site_ctxt: #4, def_site_ctxt: #4, kind: Macro(Bang, "inner")
+crate0::{{expn4}}: parent: crate0::{{expn3}}, call_site_ctxt: #6, def_site_ctxt: #0, kind: Macro(Bang, "print_bang")
+crate2::{{expn1}}: parent: crate0::{{expn0}}, call_site_ctxt: #0, def_site_ctxt: #0, kind: AstPass(StdImports)
 
 SyntaxContexts:
-#0: parent: #0, outer_mark: (ExpnId(0), Opaque)
-#1: parent: #0, outer_mark: (ExpnId(1), Opaque)
-#2: parent: #0, outer_mark: (ExpnId(1), Transparent)
-#3: parent: #0, outer_mark: (ExpnId(3), Opaque)
-#4: parent: #0, outer_mark: (ExpnId(2), SemiTransparent)
-#5: parent: #0, outer_mark: (ExpnId(4), Opaque)
-#6: parent: #4, outer_mark: (ExpnId(4), Opaque)
-#7: parent: #0, outer_mark: (ExpnId(5), Opaque)
-#8: parent: #6, outer_mark: (ExpnId(5), Transparent)
-#9: parent: #5, outer_mark: (ExpnId(5), SemiTransparent)
+#0: parent: #0, outer_mark: (crate0::{{expn0}}, Opaque)
+#1: parent: #0, outer_mark: (crate0::{{expn1}}, Opaque)
+#2: parent: #0, outer_mark: (crate0::{{expn1}}, Transparent)
+#3: parent: #0, outer_mark: (crate2::{{expn1}}, Opaque)
+#4: parent: #0, outer_mark: (crate0::{{expn2}}, SemiTransparent)
+#5: parent: #0, outer_mark: (crate0::{{expn3}}, Opaque)
+#6: parent: #4, outer_mark: (crate0::{{expn3}}, Opaque)
+#7: parent: #0, outer_mark: (crate0::{{expn4}}, Opaque)
+#8: parent: #6, outer_mark: (crate0::{{expn4}}, Transparent)
+#9: parent: #5, outer_mark: (crate0::{{expn4}}, SemiTransparent)
 */
diff --git a/src/tools/rustfmt/src/utils.rs b/src/tools/rustfmt/src/utils.rs
index d3c349fb701..614cda5f911 100644
--- a/src/tools/rustfmt/src/utils.rs
+++ b/src/tools/rustfmt/src/utils.rs
@@ -6,7 +6,7 @@ use rustc_ast::ast::{
 };
 use rustc_ast::ptr;
 use rustc_ast_pretty::pprust;
-use rustc_span::{sym, symbol, BytePos, ExpnId, Span, Symbol, SyntaxContext};
+use rustc_span::{sym, symbol, BytePos, LocalExpnId, Span, Symbol, SyntaxContext};
 use unicode_width::UnicodeWidthStr;
 
 use crate::comment::{filter_normal_code, CharClasses, FullCodeCharKind, LineClasses};
@@ -675,7 +675,7 @@ pub(crate) trait NodeIdExt {
 
 impl NodeIdExt for NodeId {
     fn root() -> NodeId {
-        NodeId::placeholder_from_expn_id(ExpnId::root())
+        NodeId::placeholder_from_expn_id(LocalExpnId::ROOT)
     }
 }