[clang] [Modules] No transitive source location change (PR #86912)

[Jan Svoboda via cfe-commits]

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@@ -5574,10 +5577,34 @@ void ASTWriter::AddFileID(FileID FID, RecordDataImpl &Record) {
   Record.push_back(getAdjustedFileID(FID).getOpaqueValue());
 }
 
+SourceLocationEncoding::RawLocEncoding
+ASTWriter::getRawSourceLocationEncoding(SourceLocation Loc, LocSeq *Seq) {
+  unsigned BaseOffset = 0;
+  unsigned ModuleFileIndex = 0;
+
+  // See SourceLocationEncoding.h for the encoding details.
+  if (Context->getSourceManager().isLoadedSourceLocation(Loc) &&
+      Loc.isValid()) {
+    assert(getChain());
+    auto SLocMapI = getChain()->GlobalSLocOffsetMap.find(
+        SourceManager::MaxLoadedOffset - Loc.getOffset() - 1);
+    assert(SLocMapI != getChain()->GlobalSLocOffsetMap.end() &&
+           "Corrupted global sloc offset map");
+    ModuleFile *F = SLocMapI->second;
+    BaseOffset = F->SLocEntryBaseOffset - 2;
+    // 0 means the location is not loaded. So we need to add 1 to the index to
+    // make it clear.
+    ModuleFileIndex = F->Index + 1;
+    assert(&getChain()->getModuleManager()[F->Index] == F);
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jansvoboda11 wrote:

I don't think `ASTWriter` should be re-checking `ModuleManager` invariants either way.

https://github.com/llvm/llvm-project/pull/86912