1 files changed, 19 insertions, 4 deletions
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 26281cc747c..76f62f5e71a 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -1729,11 +1729,26 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
 #endif
          )) {
       if (Complain) {
-        Error(diag::err_fe_pch_file_modified, Filename, F.FileName);
-        if (Context.getLangOpts().Modules && !Diags.isDiagnosticInFlight()) {
-          Diag(diag::note_module_cache_path)
-            << PP.getHeaderSearchInfo().getModuleCachePath();
+        // Build a list of the PCH imports that got us here (in reverse).
+        SmallVector<ModuleFile *, 4> ImportStack(1, &F);
+        while (ImportStack.back()->ImportedBy.size() > 0)
+          ImportStack.push_back(ImportStack.back()->ImportedBy[0]);
+
+        // The top-level PCH is stale.
+        StringRef TopLevelPCHName(ImportStack.back()->FileName);
+        Error(diag::err_fe_pch_file_modified, Filename, TopLevelPCHName);
+
+        // Print the import stack.
+        if (ImportStack.size() > 1 && !Diags.isDiagnosticInFlight()) {
+          Diag(diag::note_pch_required_by)
+            << Filename << ImportStack[0]->FileName;
+          for (unsigned I = 1; I < ImportStack.size(); ++I)
+            Diag(diag::note_pch_required_by)
+              << ImportStack[I-1]->FileName << ImportStack[I]->FileName;
         }
+
+        if (!Diags.isDiagnosticInFlight())
+          Diag(diag::note_pch_rebuild_required) << TopLevelPCHName;
       }
 
       IsOutOfDate = true;