[clang][modules] Report failures from lightweight deserialization, save potentially unnecessary heavyweight deserialization

Author: jansvoboda11

clang/include/clang/Basic/SourceManager.h

@@ -534,6 +534,9 @@ class ExternalSLocEntrySource {
   virtual bool ReadSLocEntry(int ID) = 0;
 
   /// Get the index ID for the loaded SourceLocation offset.
+  ///
+  /// \returns Invalid index ID (0) if an error occurred that prevented the
+  /// SLocEntry  from being loaded.
   virtual int getSLocEntryID(SourceLocation::UIntTy SLocOffset) = 0;
 
   /// Retrieve the module import location and name for the given ID, if

clang/include/clang/Serialization/ASTReader.h

@@ -2155,8 +2155,8 @@ class ASTReader
   bool ReadSLocEntry(int ID) override;
   /// Get the index ID for the loaded SourceLocation offset.
   int getSLocEntryID(SourceLocation::UIntTy SLocOffset) override;
-  /// Read the offset of the SLocEntry at the given index in the given module
-  /// file.
+  /// Try to read the offset of the SLocEntry at the given index in the given
+  /// module file.
   std::optional<SourceLocation::UIntTy> readSLocOffset(ModuleFile *F,
                                                        unsigned Index);
 

clang/lib/Basic/SourceManager.cpp

@@ -864,10 +864,7 @@ FileID SourceManager::getFileIDLocal(SourceLocation::UIntTy SLocOffset) const {
 /// This function knows that the SourceLocation is in a loaded buffer, not a
 /// local one.
 FileID SourceManager::getFileIDLoaded(SourceLocation::UIntTy SLocOffset) const {
-  int ID = ExternalSLocEntries->getSLocEntryID(SLocOffset);
-  bool Invalid = false;
-  (void)getLoadedSLocEntryByID(ID, &Invalid);
-  return Invalid ? FileID() : FileID::get(ID);
+  return FileID::get(ExternalSLocEntries->getSLocEntryID(SLocOffset));
 }
 
 SourceLocation SourceManager::

clang/lib/Serialization/ASTReader.cpp

@@ -1491,20 +1491,28 @@ int ASTReader::getSLocEntryID(SourceLocation::UIntTy SLocOffset) {
          "Corrupted global sloc offset map");
   ModuleFile *F = SLocMapI->second;
 
+  bool Invalid = false;
+
   auto It = llvm::upper_bound(
       llvm::index_range(0, F->LocalNumSLocEntries), SLocOffset,
       [&](SourceLocation::UIntTy Offset, std::size_t Index) {
         if (F->SLocEntryOffsetLoaded[Index] == -1U) {
           auto MaybeEntryOffset = readSLocOffset(F, Index);
-          assert(MaybeEntryOffset && "Corrupted AST file");
+          if (!MaybeEntryOffset) {
+            Invalid = true;
+            return true;
+          }
           F->SLocEntryOffsetLoaded[Index] = *MaybeEntryOffset;
         }
         return Offset < F->SLocEntryOffsetLoaded[Index];
       });
+
+  if (Invalid)
+    return 0;
+
   // The iterator points to the first entry with start offset greater than the
   // offset of interest. The previous entry must contain the offset of interest.
-  It = std::prev(It);
-  return F->SLocEntryBaseID + *It;
+  return F->SLocEntryBaseID + *std::prev(It);
 }
 
 bool ASTReader::ReadSLocEntry(int ID) {