[ASTUnit] Fix crash when trying to load a module file via ASTUnit::LoadFromASTFile.

rdar://19997358

llvm-svn: 231060

1 files changed, 7 insertions, 5 deletions

diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index bfb1efe3522..d153ca245c3 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -714,6 +714,13 @@ std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
       *AST->PP, Context, AST->ASTFileLangOpts, AST->TargetOpts, AST->Target,
       Counter));
 
+  // Attach the AST reader to the AST context as an external AST
+  // source, so that declarations will be deserialized from the
+  // AST file as needed.
+  // We need the external source to be set up before we read the AST, because
+  // eagerly-deserialized declarations may use it.
+  Context.setExternalSource(AST->Reader);
+
   switch (AST->Reader->ReadAST(Filename, serialization::MK_MainFile,
                           SourceLocation(), ASTReader::ARR_None)) {
   case ASTReader::Success:
@@ -733,11 +740,6 @@ std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
 
   PP.setCounterValue(Counter);
 
-  // Attach the AST reader to the AST context as an external AST
-  // source, so that declarations will be deserialized from the
-  // AST file as needed.
-  Context.setExternalSource(AST->Reader);
-
   // Create an AST consumer, even though it isn't used.
   AST->Consumer.reset(new ASTConsumer);