1 files changed, 20 insertions, 0 deletions
diff --git a/clang/lib/AST/ExternalASTSource.cpp b/clang/lib/AST/ExternalASTSource.cpp
index 05a17db6bf0..ae8297cecd1 100644
--- a/clang/lib/AST/ExternalASTSource.cpp
+++ b/clang/lib/AST/ExternalASTSource.cpp
@@ -14,7 +14,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/AST/ExternalASTSource.h"
+#include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclarationName.h"
+#include "llvm/Support/ErrorHandling.h"
 
 using namespace clang;
 
@@ -60,3 +62,21 @@ ExternalASTSource::FindExternalLexicalDecls(const DeclContext *DC,
 }
 
 void ExternalASTSource::getMemoryBufferSizes(MemoryBufferSizes &sizes) const { }
+
+uint32_t ExternalASTSource::incrementGeneration(ASTContext &C) {
+  uint32_t OldGeneration = CurrentGeneration;
+
+  // Make sure the generation of the topmost external source for the context is
+  // incremented. That might not be us.
+  auto *P = C.getExternalSource();
+  if (P && P != this)
+    CurrentGeneration = P->incrementGeneration(C);
+  else {
+    // FIXME: Only bump the generation counter if the current generation number
+    // has been observed?
+    if (!++CurrentGeneration)
+      llvm::report_fatal_error("generation counter overflowed", false);
+  }
+
+  return OldGeneration;
+}