6 files changed, 57 insertions, 6 deletions

diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 95c1620fcbb..331fa385905 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5630,27 +5630,52 @@ void ASTWriter::CompletedTagDefinition(const TagDecl *D) {
   }
 }
 
+static bool isImportedDeclContext(ASTReader *Chain, const Decl *D) {
+  if (D->isFromASTFile())
+    return true;
+
+  // If we've not loaded any modules, this can't be imported.
+  if (!Chain || !Chain->getModuleManager().size())
+    return false;
+
+  // The predefined __va_list_tag struct is imported if we imported any decls.
+  // FIXME: This is a gross hack.
+  return D == D->getASTContext().getVaListTagDecl();
+}
+
 void ASTWriter::AddedVisibleDecl(const DeclContext *DC, const Decl *D) {
   // TU and namespaces are handled elsewhere.
   if (isa<TranslationUnitDecl>(DC) || isa<NamespaceDecl>(DC))
     return;
 
-  if (!(!D->isFromASTFile() && cast<Decl>(DC)->isFromASTFile()))
-    return; // Not a source decl added to a DeclContext from PCH.
+  // We're only interested in cases where a local declaration is added to an
+  // imported context.
+  if (D->isFromASTFile() || !isImportedDeclContext(Chain, cast<Decl>(DC)))
+    return;
 
   assert(DC == DC->getPrimaryContext() && "added to non-primary context");
   assert(!getDefinitiveDeclContext(DC) && "DeclContext not definitive!");
   assert(!WritingAST && "Already writing the AST!");
-  UpdatedDeclContexts.insert(DC);
+  if (UpdatedDeclContexts.insert(DC) && !cast<Decl>(DC)->isFromASTFile()) {
+    // We're adding a visible declaration to a predefined decl context. Ensure
+    // that we write out all of its lookup results so we don't get a nasty
+    // surprise when we try to emit its lookup table.
+    for (auto *Child : DC->decls())
+      UpdatingVisibleDecls.push_back(Child);
+  }
   UpdatingVisibleDecls.push_back(D);
 }
 
 void ASTWriter::AddedCXXImplicitMember(const CXXRecordDecl *RD, const Decl *D) {
   assert(D->isImplicit());
-  if (!(!D->isFromASTFile() && RD->isFromASTFile()))
-    return; // Not a source member added to a class from PCH.
+
+  // We're only interested in cases where a local declaration is added to an
+  // imported context.
+  if (D->isFromASTFile() || !isImportedDeclContext(Chain, RD))
+    return;
+
   if (!isa<CXXMethodDecl>(D))
-    return; // We are interested in lazily declared implicit methods.
+    return;
 
   // A decl coming from PCH was modified.
   assert(RD->isCompleteDefinition());
diff --git a/clang/test/Modules/Inputs/va_list/left.h b/clang/test/Modules/Inputs/va_list/left.h
new file mode 100644
index 00000000000..6842f9f7d0a
--- /dev/null
+++ b/clang/test/Modules/Inputs/va_list/left.h
@@ -0,0 +1,7 @@
+@import top;
+
+template<typename T>
+void f(int k, ...) {
+  va_list va;
+  __builtin_va_start(va, k);
+}
diff --git a/clang/test/Modules/Inputs/va_list/module.modulemap b/clang/test/Modules/Inputs/va_list/module.modulemap
index 870f38bb0ec..bd9c61456fb 100644
--- a/clang/test/Modules/Inputs/va_list/module.modulemap
+++ b/clang/test/Modules/Inputs/va_list/module.modulemap
@@ -1,2 +1,5 @@
 module va_list_a { header "va_list_a.h" }
 module va_list_b { header "va_list_b.h" }
+module top { header "top.h" }
+module left { header "left.h" }
+module right { header "right.h" }
diff --git a/clang/test/Modules/Inputs/va_list/right.h b/clang/test/Modules/Inputs/va_list/right.h
new file mode 100644
index 00000000000..6842f9f7d0a
--- /dev/null
+++ b/clang/test/Modules/Inputs/va_list/right.h
@@ -0,0 +1,7 @@
+@import top;
+
+template<typename T>
+void f(int k, ...) {
+  va_list va;
+  __builtin_va_start(va, k);
+}
diff --git a/clang/test/Modules/Inputs/va_list/top.h b/clang/test/Modules/Inputs/va_list/top.h
new file mode 100644
index 00000000000..5660b876552
--- /dev/null
+++ b/clang/test/Modules/Inputs/va_list/top.h
@@ -0,0 +1 @@
+typedef __builtin_va_list va_list;
diff --git a/clang/test/Modules/va_list.cpp b/clang/test/Modules/va_list.cpp
new file mode 100644
index 00000000000..35694cdec6f
--- /dev/null
+++ b/clang/test/Modules/va_list.cpp
@@ -0,0 +1,8 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -x objective-c++ -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs/va_list %s -verify
+// expected-no-diagnostics
+
+@import left;
+@import right;
+
+void g(int k, ...) { f<int>(k); }