[Modules] Fix an issue where the reconstructed redeclaration chain was incomplete, missing the definition from a module.

-Make sure that a deserialized external decl gets added to the TU scope.
-When associating an identifier with a set of decls, use the most recent local ones,
  if they exist, otherwise associating decls from modules (that came after a local one)
  will lead to an incomplete reconstructed re-declaration chain.

rdar://13712705

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@180634 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 1 deletions

diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index c5a055072d..ba53bdaffb 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -3106,7 +3106,28 @@ public:
     for (SmallVector<Decl *, 16>::reverse_iterator D = Decls.rbegin(),
                                                 DEnd = Decls.rend();
          D != DEnd; ++D)
-      clang::io::Emit32(Out, Writer.getDeclID(*D));
+      clang::io::Emit32(Out, Writer.getDeclID(getMostRecentLocalDecl(*D)));
+  }
+
+  /// \brief Returns the most recent local decl or the given decl if there are
+  /// no local ones. The given decl is assumed to be the most recent one.
+  Decl *getMostRecentLocalDecl(Decl *Orig) {
+    // The only way a "from AST file" decl would be more recent from a local one
+    // is if it came from a module.
+    if (!PP.getLangOpts().Modules)
+      return Orig;
+
+    // Look for a local in the decl chain.
+    for (Decl *D = Orig; D; D = D->getPreviousDecl()) {
+      if (!D->isFromASTFile())
+        return D;
+      // If we come up a decl from a (chained-)PCH stop since we won't find a
+      // local one.
+      if (D->getOwningModuleID() == 0)
+        break;
+    }
+
+    return Orig;
   }
 };
 } // end anonymous namespace