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

[Jan Svoboda via cfe-commits]

================
@@ -2220,33 +2221,40 @@ class ASTReader
     return Sema::AlignPackInfo::getFromRawEncoding(Raw);
   }
 
+  using RawLocEncoding = SourceLocationEncoding::RawLocEncoding;
+
   /// Read a source location from raw form and return it in its
   /// originating module file's source location space.
-  SourceLocation ReadUntranslatedSourceLocation(SourceLocation::UIntTy Raw,
-                                                LocSeq *Seq = nullptr) const {
+  std::pair<SourceLocation, unsigned>
+  ReadUntranslatedSourceLocation(RawLocEncoding Raw,
+                                 LocSeq *Seq = nullptr) const {
     return SourceLocationEncoding::decode(Raw, Seq);
   }
 
   /// Read a source location from raw form.
-  SourceLocation ReadSourceLocation(ModuleFile &ModuleFile,
-                                    SourceLocation::UIntTy Raw,
-                                    LocSeq *Seq = nullptr) const {
-    SourceLocation Loc = ReadUntranslatedSourceLocation(Raw, Seq);
-    return TranslateSourceLocation(ModuleFile, Loc);
+  SourceLocation ReadSourceLocation(ModuleFile &MF, RawLocEncoding Raw,
+                                       LocSeq *Seq = nullptr) const {
+    if (!MF.ModuleOffsetMap.empty())
+      ReadModuleOffsetMap(MF);
+
+    auto [Loc, ModuleFileIndex] = ReadUntranslatedSourceLocation(Raw, Seq);
+    ModuleFile *OwningModuleFile =
+        ModuleFileIndex ? MF.DependentModules[ModuleFileIndex - 1] : &MF;
----------------
jansvoboda11 wrote:

Since the type of `ModuleFileIndex` is not obvious due to `auto`, I suggest comparing it to `0` explicitly.

```suggestion
        ModuleFileIndex == 0 ? &MF : MF.DependentModules[ModuleFileIndex - 1];
```

Or maybe the element at index `0` in `DependentModules` could be `MF` itself to simplify this further?

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