Also hash spans inside the same file as relative.

compiler/rustc_middle/src/query/on_disk_cache.rs

@@ -38,6 +38,7 @@ const TAG_FULL_SPAN: u8 = 0;
 // A partial span with no location information, encoded only with a `SyntaxContext`
 const TAG_PARTIAL_SPAN: u8 = 1;
 const TAG_RELATIVE_SPAN: u8 = 2;
+const TAG_RELATIVE_OUTER_SPAN: u8 = 3;
 
 const TAG_SYNTAX_CONTEXT: u8 = 0;
 const TAG_EXPN_DATA: u8 = 1;
@@ -659,6 +660,19 @@ impl<'a, 'tcx> SpanDecoder for CacheDecoder<'a, 'tcx> {
                 parent,
             );
 
+            return span;
+        } else if tag == TAG_RELATIVE_OUTER_SPAN {
+            let dlo = isize::decode(self);
+            let dto = isize::decode(self);
+
+            let enclosing = self.tcx.source_span_untracked(parent.unwrap()).data_untracked();
+            let span = Span::new(
+                BytePos::from_usize((enclosing.lo.to_u32() as isize + dlo) as usize),
+                BytePos::from_usize((enclosing.lo.to_u32() as isize + dto) as usize),
+                ctxt,
+                parent,
+            );
+
             return span;
         } else {
             debug_assert_eq!(tag, TAG_FULL_SPAN);
@@ -897,30 +911,33 @@ impl<'a, 'tcx> SpanEncoder for CacheEncoder<'a, 'tcx> {
             return TAG_PARTIAL_SPAN.encode(self);
         }
 
-        if let Some(parent) = span_data.parent {
-            let enclosing = self.tcx.source_span_untracked(parent).data_untracked();
-            if enclosing.contains(span_data) {
-                TAG_RELATIVE_SPAN.encode(self);
-                (span_data.lo - enclosing.lo).to_u32().encode(self);
-                (span_data.hi - enclosing.lo).to_u32().encode(self);
-                return;
-            }
+        let parent =
+            span_data.parent.map(|parent| self.tcx.source_span_untracked(parent).data_untracked());
+        if let Some(parent) = parent
+            && parent.contains(span_data)
+        {
+            TAG_RELATIVE_SPAN.encode(self);
+            (span_data.lo - parent.lo).to_u32().encode(self);
+            (span_data.hi - parent.lo).to_u32().encode(self);
+            return;
         }
 
-        let pos = self.source_map.byte_pos_to_line_and_col(span_data.lo);
-        let partial_span = match &pos {
-            Some((file_lo, _, _)) => !file_lo.contains(span_data.hi),
-            None => true,
+        let Some((file_lo, line_lo, col_lo)) =
+            self.source_map.byte_pos_to_line_and_col(span_data.lo)
+        else {
+            return TAG_PARTIAL_SPAN.encode(self);
         };
 
-        if partial_span {
-            return TAG_PARTIAL_SPAN.encode(self);
+        if let Some(parent) = parent
+            && file_lo.contains(parent.lo)
+        {
+            TAG_RELATIVE_OUTER_SPAN.encode(self);
+            (span_data.lo.to_u32() as isize - parent.lo.to_u32() as isize).encode(self);
+            (span_data.hi.to_u32() as isize - parent.lo.to_u32() as isize).encode(self);
+            return;
         }
 
-        let (file_lo, line_lo, col_lo) = pos.unwrap();
-
         let len = span_data.hi - span_data.lo;
-
         let source_file_index = self.source_file_index(file_lo);
 
         TAG_FULL_SPAN.encode(self);

compiler/rustc_query_system/src/ich/hcx.rs

@@ -5,9 +5,7 @@ use rustc_hir::definitions::DefPathHash;
 use rustc_session::Session;
 use rustc_session::cstore::Untracked;
 use rustc_span::source_map::SourceMap;
-use rustc_span::{
-    BytePos, CachingSourceMapView, DUMMY_SP, Span, SpanData, StableSourceFileId, Symbol,
-};
+use rustc_span::{BytePos, CachingSourceMapView, DUMMY_SP, SourceFile, Span, SpanData, Symbol};
 
 use crate::ich;
 
@@ -118,7 +116,7 @@ impl<'a> rustc_span::HashStableContext for StableHashingContext<'a> {
     fn span_data_to_lines_and_cols(
         &mut self,
         span: &SpanData,
-    ) -> Option<(StableSourceFileId, usize, BytePos, usize, BytePos)> {
+    ) -> Option<(&SourceFile, usize, BytePos, usize, BytePos)> {
         self.source_map().span_data_to_lines_and_cols(span)
     }
 

compiler/rustc_span/src/caching_source_map_view.rs

@@ -2,7 +2,7 @@ use std::ops::Range;
 use std::sync::Arc;
 
 use crate::source_map::SourceMap;
-use crate::{BytePos, Pos, RelativeBytePos, SourceFile, SpanData, StableSourceFileId};
+use crate::{BytePos, Pos, RelativeBytePos, SourceFile, SpanData};
 
 #[derive(Clone)]
 struct CacheEntry {
@@ -114,7 +114,7 @@ impl<'sm> CachingSourceMapView<'sm> {
     pub fn span_data_to_lines_and_cols(
         &mut self,
         span_data: &SpanData,
-    ) -> Option<(StableSourceFileId, usize, BytePos, usize, BytePos)> {
+    ) -> Option<(&SourceFile, usize, BytePos, usize, BytePos)> {
         self.time_stamp += 1;
 
         // Check if lo and hi are in the cached lines.
@@ -123,27 +123,25 @@ impl<'sm> CachingSourceMapView<'sm> {
 
         if lo_cache_idx != -1 && hi_cache_idx != -1 {
             // Cache hit for span lo and hi. Check if they belong to the same file.
-            let result = {
-                let lo = &self.line_cache[lo_cache_idx as usize];
-                let hi = &self.line_cache[hi_cache_idx as usize];
+            let lo_file_index = self.line_cache[lo_cache_idx as usize].file_index;
+            let hi_file_index = self.line_cache[hi_cache_idx as usize].file_index;
 
-                if lo.file_index != hi.file_index {
-                    return None;
-                }
-
-                (
-                    lo.file.stable_id,
-                    lo.line_number,
-                    span_data.lo - lo.line.start,
-                    hi.line_number,
-                    span_data.hi - hi.line.start,
-                )
-            };
+            if lo_file_index != hi_file_index {
+                return None;
+            }
 
             self.line_cache[lo_cache_idx as usize].touch(self.time_stamp);
             self.line_cache[hi_cache_idx as usize].touch(self.time_stamp);
 
-            return Some(result);
+            let lo = &self.line_cache[lo_cache_idx as usize];
+            let hi = &self.line_cache[hi_cache_idx as usize];
+            return Some((
+                &*lo.file,
+                lo.line_number,
+                span_data.lo - lo.line.start,
+                hi.line_number,
+                span_data.hi - hi.line.start,
+            ));
         }
 
         // No cache hit or cache hit for only one of span lo and hi.
@@ -226,7 +224,7 @@ impl<'sm> CachingSourceMapView<'sm> {
         assert_eq!(lo.file_index, hi.file_index);
 
         Some((
-            lo.file.stable_id,
+            &*lo.file,
             lo.line_number,
             span_data.lo - lo.line.start,
             hi.line_number,

compiler/rustc_span/src/lib.rs

@@ -2623,7 +2623,7 @@ pub trait HashStableContext {
     fn span_data_to_lines_and_cols(
         &mut self,
         span: &SpanData,
-    ) -> Option<(StableSourceFileId, usize, BytePos, usize, BytePos)>;
+    ) -> Option<(&SourceFile, usize, BytePos, usize, BytePos)>;
     fn hashing_controls(&self) -> HashingControls;
 }
 
@@ -2641,6 +2641,7 @@ where
     /// codepoint offsets. For the purpose of the hash that's sufficient.
     /// Also, hashing filenames is expensive so we avoid doing it twice when the
     /// span starts and ends in the same file, which is almost always the case.
+    // Important: changes to this method should be reflected in implementations of `SpanEncoder`.
     fn hash_stable(&self, ctx: &mut CTX, hasher: &mut StableHasher) {
         const TAG_VALID_SPAN: u8 = 0;
         const TAG_INVALID_SPAN: u8 = 1;
@@ -2659,15 +2660,15 @@ where
             return;
         }
 
-        if let Some(parent) = span.parent {
-            let def_span = ctx.def_span(parent).data_untracked();
-            if def_span.contains(span) {
-                // This span is enclosed in a definition: only hash the relative position.
-                Hash::hash(&TAG_RELATIVE_SPAN, hasher);
-                (span.lo - def_span.lo).to_u32().hash_stable(ctx, hasher);
-                (span.hi - def_span.lo).to_u32().hash_stable(ctx, hasher);
-                return;
-            }
+        let parent = span.parent.map(|parent| ctx.def_span(parent).data_untracked());
+        if let Some(parent) = parent
+            && parent.contains(span)
+        {
+            // This span is enclosed in a definition: only hash the relative position.
+            Hash::hash(&TAG_RELATIVE_SPAN, hasher);
+            Hash::hash(&(span.lo - parent.lo), hasher);
+            Hash::hash(&(span.hi - parent.lo), hasher);
+            return;
         }
 
         // If this is not an empty or invalid span, we want to hash the last
@@ -2680,7 +2681,20 @@ where
         };
 
         Hash::hash(&TAG_VALID_SPAN, hasher);
-        Hash::hash(&file, hasher);
+        Hash::hash(&file.stable_id, hasher);
+
+        if let Some(parent) = parent
+            && file.contains(parent.lo)
+        {
+            // This span is relative to another span in the same file,
+            // only hash the relative position.
+            Hash::hash(&TAG_RELATIVE_SPAN, hasher);
+            // Use signed difference as `span` may start before `parent`,
+            // for instance attributes start before their item's span.
+            Hash::hash(&(span.lo.to_u32() as isize - parent.lo.to_u32() as isize), hasher);
+            Hash::hash(&(span.hi.to_u32() as isize - parent.lo.to_u32() as isize), hasher);
+            return;
+        }
 
         // Hash both the length and the end location (line/column) of a span. If we
         // hash only the length, for example, then two otherwise equal spans with