7 files changed, 34 insertions, 18 deletions
diff --git a/clang/include/clang/Frontend/CompilerInstance.h b/clang/include/clang/Frontend/CompilerInstance.h
index 0f49b346107..e0996d40f31 100644
--- a/clang/include/clang/Frontend/CompilerInstance.h
+++ b/clang/include/clang/Frontend/CompilerInstance.h
@@ -588,7 +588,7 @@ public:
   /// Create an external AST source to read a PCH file.
   ///
   /// \return - The new object on success, or null on failure.
-  static ExternalASTSource *createPCHExternalASTSource(
+  static IntrusiveRefCntPtr<ASTReader> createPCHExternalASTSource(
       StringRef Path, const std::string &Sysroot, bool DisablePCHValidation,
       bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext &Context,
       void *DeserializationListener, bool OwnDeserializationListener,
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 041a1e95225..9cb26f86c79 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -388,32 +388,30 @@ void CompilerInstance::createASTContext() {
 void CompilerInstance::createPCHExternalASTSource(
     StringRef Path, bool DisablePCHValidation, bool AllowPCHWithCompilerErrors,
     void *DeserializationListener, bool OwnDeserializationListener) {
-  IntrusiveRefCntPtr<ExternalASTSource> Source;
   bool Preamble = getPreprocessorOpts().PrecompiledPreambleBytes.first != 0;
-  Source = createPCHExternalASTSource(
+  ModuleManager = createPCHExternalASTSource(
       Path, getHeaderSearchOpts().Sysroot, DisablePCHValidation,
       AllowPCHWithCompilerErrors, getPreprocessor(), getASTContext(),
       DeserializationListener, OwnDeserializationListener, Preamble,
       getFrontendOpts().UseGlobalModuleIndex);
-  ModuleManager = static_cast<ASTReader*>(Source.get());
-  getASTContext().setExternalSource(Source);
 }
 
-ExternalASTSource *CompilerInstance::createPCHExternalASTSource(
+IntrusiveRefCntPtr<ASTReader> CompilerInstance::createPCHExternalASTSource(
     StringRef Path, const std::string &Sysroot, bool DisablePCHValidation,
     bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext &Context,
     void *DeserializationListener, bool OwnDeserializationListener,
     bool Preamble, bool UseGlobalModuleIndex) {
   HeaderSearchOptions &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();
 
-  std::unique_ptr<ASTReader> Reader;
-  Reader.reset(new ASTReader(PP, Context,
-                             Sysroot.empty() ? "" : Sysroot.c_str(),
-                             DisablePCHValidation,
-                             AllowPCHWithCompilerErrors,
-                             /*AllowConfigurationMismatch*/false,
-                             HSOpts.ModulesValidateSystemHeaders,
-                             UseGlobalModuleIndex));
+  IntrusiveRefCntPtr<ASTReader> Reader(
+      new ASTReader(PP, Context, Sysroot.empty() ? "" : Sysroot.c_str(),
+                    DisablePCHValidation, AllowPCHWithCompilerErrors,
+                    /*AllowConfigurationMismatch*/ false,
+                    HSOpts.ModulesValidateSystemHeaders, UseGlobalModuleIndex));
+
+  // We need the external source to be set up before we read the AST, because
+  // eagerly-deserialized declarations may use it.
+  Context.setExternalSource(Reader.get());
 
   Reader->setDeserializationListener(
       static_cast<ASTDeserializationListener *>(DeserializationListener),
@@ -427,7 +425,7 @@ ExternalASTSource *CompilerInstance::createPCHExternalASTSource(
     // Set the predefines buffer as suggested by the PCH reader. Typically, the
     // predefines buffer will be empty.
     PP.setPredefines(Reader->getSuggestedPredefines());
-    return Reader.release();
+    return Reader;
 
   case ASTReader::Failure:
     // Unrecoverable failure: don't even try to process the input file.
@@ -442,6 +440,7 @@ ExternalASTSource *CompilerInstance::createPCHExternalASTSource(
     break;
   }
 
+  Context.setExternalSource(nullptr);
   return nullptr;
 }
 
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 87b5296c946..56506073af2 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2591,6 +2591,11 @@ DeclContext *ASTDeclReader::getPrimaryContextForMerging(ASTReader &Reader,
     return ED->getASTContext().getLangOpts().CPlusPlus? ED->getDefinition()
                                                       : nullptr;
 
+  // We can see the TU here only if we have no Sema object. In that case,
+  // there's no TU scope to look in, so using the DC alone is sufficient.
+  if (auto *TU = dyn_cast<TranslationUnitDecl>(DC))
+    return TU;
+
   return nullptr;
 }
 
diff --git a/clang/test/Modules/Inputs/preprocess/file.h b/clang/test/Modules/Inputs/preprocess/file.h
new file mode 100644
index 00000000000..808ade5768b
--- /dev/null
+++ b/clang/test/Modules/Inputs/preprocess/file.h
@@ -0,0 +1,3 @@
+struct __FILE;
+#include "fwd.h"
+typedef struct __FILE FILE;
diff --git a/clang/test/Modules/Inputs/preprocess/fwd.h b/clang/test/Modules/Inputs/preprocess/fwd.h
new file mode 100644
index 00000000000..4a19c6d0c05
--- /dev/null
+++ b/clang/test/Modules/Inputs/preprocess/fwd.h
@@ -0,0 +1 @@
+struct __FILE;
diff --git a/clang/test/Modules/Inputs/preprocess/module.modulemap b/clang/test/Modules/Inputs/preprocess/module.modulemap
new file mode 100644
index 00000000000..a5c5b61dddc
--- /dev/null
+++ b/clang/test/Modules/Inputs/preprocess/module.modulemap
@@ -0,0 +1,2 @@
+module fwd { header "fwd.h" export * }
+module file { header "file.h" export * }
diff --git a/clang/test/Modules/preprocess.m b/clang/test/Modules/preprocess.m
index 5c32997f62f..9b563fef821 100644
--- a/clang/test/Modules/preprocess.m
+++ b/clang/test/Modules/preprocess.m
@@ -1,9 +1,14 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -include %S/Inputs/preprocess-prefix.h -E %s | FileCheck -strict-whitespace %s
-// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -x objective-c-header -emit-pch %S/Inputs/preprocess-prefix.h -o %t.pch
-// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -include-pch %t.pch -E %s | FileCheck -strict-whitespace %s
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I %S/Inputs/preprocess -include %S/Inputs/preprocess-prefix.h -E %s | FileCheck -strict-whitespace %s
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I %S/Inputs/preprocess -x objective-c-header -emit-pch %S/Inputs/preprocess-prefix.h -o %t.pch
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I %S/Inputs/preprocess -include-pch %t.pch -E %s | FileCheck -strict-whitespace %s
+//
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I %S/Inputs/preprocess -x objective-c++ -include %S/Inputs/preprocess-prefix.h -E %s | FileCheck -strict-whitespace %s
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I %S/Inputs/preprocess -x objective-c++-header -emit-pch %S/Inputs/preprocess-prefix.h -o %t.pch
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I %S/Inputs/preprocess -x objective-c++ -include-pch %t.pch -E %s | FileCheck -strict-whitespace %s
 #import "diamond_right.h"
 #import "diamond_right.h" // to check that imports get their own line
+#include "file.h"
 void test() {
   top_left_before();
   left_and_right();
@@ -15,6 +20,7 @@ void test() {
 
 // CHECK: @import diamond_right; /* clang -E: implicit import for "{{.*}}diamond_right.h" */{{$}}
 // CHECK: @import diamond_right; /* clang -E: implicit import for "{{.*}}diamond_right.h" */{{$}}
+// CHECK: @import file; /* clang -E: implicit import for "{{.*}}file.h" */{{$}}
 // CHECK-NEXT: void test() {{{$}}
 // CHECK-NEXT:    top_left_before();{{$}}
 // CHECK-NEXT:    left_and_right();{{$}}