Hash only the spans that we care ended up reading in Span::try_metavars

Author: compiler-errors

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -13,7 +13,7 @@ use rustc_parse::parser::ParseNtResult;
 use rustc_session::parse::{ParseSess, SymbolGallery};
 use rustc_span::hygiene::{LocalExpnId, Transparency};
 use rustc_span::{
-    Ident, MacroRulesNormalizedIdent, Span, Symbol, SyntaxContext, sym, with_metavar_spans_mut,
+    Ident, MacroRulesNormalizedIdent, Span, Symbol, SyntaxContext, sym, with_metavar_spans,
 };
 use smallvec::{SmallVec, smallvec};
 
@@ -283,13 +283,17 @@ pub(super) fn transcribe<'a>(
                         }
                         MatchedSingle(ParseNtResult::Ident(ident, is_raw)) => {
                             marker.visit_span(&mut sp);
-                            with_metavar_spans_mut(|mspans| mspans.insert(ident.span, sp));
+                            with_metavar_spans(|mspans| {
+                                mspans.write().insert(ident.span, (sp, false))
+                            });
                             let kind = token::NtIdent(*ident, *is_raw);
                             TokenTree::token_alone(kind, sp)
                         }
                         MatchedSingle(ParseNtResult::Lifetime(ident, is_raw)) => {
                             marker.visit_span(&mut sp);
-                            with_metavar_spans_mut(|mspans| mspans.insert(ident.span, sp));
+                            with_metavar_spans(|mspans| {
+                                mspans.write().insert(ident.span, (sp, false))
+                            });
                             let kind = token::NtLifetime(*ident, *is_raw);
                             TokenTree::token_alone(kind, sp)
                         }
@@ -299,7 +303,9 @@ pub(super) fn transcribe<'a>(
                             // `Interpolated` is currently used for such groups in rustc parser.
                             marker.visit_span(&mut sp);
                             let use_span = nt.use_span();
-                            with_metavar_spans_mut(|mspans| mspans.insert(use_span, sp));
+                            with_metavar_spans(|mspans| {
+                                mspans.write().insert(use_span, (sp, false))
+                            });
                             TokenTree::token_alone(token::Interpolated(Lrc::clone(nt)), sp)
                         }
                         MatchedSeq(..) => {
@@ -415,16 +421,17 @@ fn maybe_use_metavar_location(
         return orig_tt.clone();
     }
 
-    let insert = |mspans: &mut UnordMap<_, _>, s, ms| match mspans.try_insert(s, ms) {
+    let insert = |mspans: &mut UnordMap<_, _>, s, ms| match mspans.try_insert(s, (ms, false)) {
         Ok(_) => true,
-        Err(err) => *err.entry.get() == ms, // Tried to insert the same span, still success
+        Err(err) => err.entry.get().0 == ms, // Tried to insert the same span, still success
     };
     marker.visit_span(&mut metavar_span);
     let no_collision = match orig_tt {
         TokenTree::Token(token, ..) => {
-            with_metavar_spans_mut(|mspans| insert(mspans, token.span, metavar_span))
+            with_metavar_spans(|mspans| insert(&mut mspans.write(), token.span, metavar_span))
         }
-        TokenTree::Delimited(dspan, ..) => with_metavar_spans_mut(|mspans| {
+        TokenTree::Delimited(dspan, ..) => with_metavar_spans(|mspans| {
+            let mspans = &mut mspans.write();
             insert(mspans, dspan.open, metavar_span)
                 && insert(mspans, dspan.close, metavar_span)
                 && insert(mspans, dspan.entire(), metavar_span)
@@ -439,13 +446,14 @@ fn maybe_use_metavar_location(
     match orig_tt {
         TokenTree::Token(Token { kind, span }, spacing) => {
             let span = metavar_span.with_ctxt(span.ctxt());
-            with_metavar_spans_mut(|mspans| insert(mspans, span, metavar_span));
+            with_metavar_spans(|mspans| insert(&mut mspans.write(), span, metavar_span));
             TokenTree::Token(Token { kind: kind.clone(), span }, *spacing)
         }
         TokenTree::Delimited(dspan, dspacing, delimiter, tts) => {
             let open = metavar_span.with_ctxt(dspan.open.ctxt());
             let close = metavar_span.with_ctxt(dspan.close.ctxt());
-            with_metavar_spans_mut(|mspans| {
+            with_metavar_spans(|mspans| {
+                let mspans = &mut mspans.write();
                 insert(mspans, open, metavar_span) && insert(mspans, close, metavar_span)
             });
             let dspan = DelimSpan::from_pair(open, close);

compiler/rustc_middle/src/hir/map/mod.rs

@@ -4,6 +4,7 @@ use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::{DynSend, DynSync, par_for_each_in, try_par_for_each_in};
+use rustc_data_structures::unord::UnordMap;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId, LocalModDefId};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
@@ -1122,7 +1123,14 @@ pub(super) fn crate_hash(tcx: TyCtxt<'_>, _: LocalCrate) -> Svh {
         // and combining it with other hashes here.
         resolutions.visibilities_for_hashing.hash_stable(&mut hcx, &mut stable_hasher);
         with_metavar_spans(|mspans| {
-            mspans.hash_stable(&mut hcx, &mut stable_hasher);
+            // Only hash the spans we ended up using.
+            let filtered_spans: UnordMap<_, _> = mspans
+                .read()
+                .items()
+                .filter(|(_, (_, b))| *b)
+                .map(|(s1, (s2, _))| (*s1, *s2))
+                .collect();
+            filtered_spans.hash_stable(&mut hcx, &mut stable_hasher);
         });
         stable_hasher.finish()
     });

compiler/rustc_span/src/lib.rs

@@ -103,7 +103,7 @@ pub struct SessionGlobals {
     span_interner: Lock<span_encoding::SpanInterner>,
     /// Maps a macro argument token into use of the corresponding metavariable in the macro body.
     /// Collisions are possible and processed in `maybe_use_metavar_location` on best effort basis.
-    metavar_spans: FreezeLock<UnordMap<Span, Span>>,
+    metavar_spans: FreezeLock<UnordMap<Span, (Span, bool)>>,
     hygiene_data: Lock<hygiene::HygieneData>,
 
     /// The session's source map, if there is one. This field should only be
@@ -178,13 +178,8 @@ pub fn create_default_session_globals_then<R>(f: impl FnOnce() -> R) -> R {
 scoped_tls::scoped_thread_local!(static SESSION_GLOBALS: SessionGlobals);
 
 #[inline]
-pub fn with_metavar_spans_mut<R>(f: impl FnOnce(&mut UnordMap<Span, Span>) -> R) -> R {
-    with_session_globals(|session_globals| f(&mut session_globals.metavar_spans.write()))
-}
-
-#[inline]
-pub fn with_metavar_spans<R>(f: impl FnOnce(&UnordMap<Span, Span>) -> R) -> R {
-    with_session_globals(|session_globals| f(&session_globals.metavar_spans.read()))
+pub fn with_metavar_spans<R>(f: impl FnOnce(&FreezeLock<UnordMap<Span, (Span, bool)>>) -> R) -> R {
+    with_session_globals(|session_globals| f(&session_globals.metavar_spans))
 }
 
 #[inline]
@@ -884,7 +879,18 @@ impl Span {
 
     /// Check if you can select metavar spans for the given spans to get matching contexts.
     fn try_metavars(a: SpanData, b: SpanData, a_orig: Span, b_orig: Span) -> (SpanData, SpanData) {
-        let get = |mspans: &UnordMap<_, _>, s| mspans.get(&s).copied();
+        let get = |mspans: &FreezeLock<UnordMap<_, _>>, s| {
+            if let Some(mut mspans) = mspans.try_write() {
+                if let Some((span, read)) = mspans.get_mut(&s) {
+                    *read = true;
+                    Some(*span)
+                } else {
+                    None
+                }
+            } else {
+                if let Some((span, true)) = mspans.read().get(&s) { Some(*span) } else { None }
+            }
+        };
         match with_metavar_spans(|mspans| (get(mspans, a_orig), get(mspans, b_orig))) {
             (None, None) => {}
             (Some(meta_a), None) => {