PCH: fix a crash caused by a circular deserialization dependency

We started by trying to deserialize decltype(func-param) in a trailing return
type, which causes the function parameter decl to be deserialized, which pulls
in the function decl, which pulls the function type, which pulls the same
decltype() in the return type, and then we crashed.

llvm-svn: 197644

1 files changed, 7 insertions, 4 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 70fb062b2c5..c2e286814bc 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -356,11 +356,14 @@ void ASTDeclReader::Visit(Decl *D) {
 }
 
 void ASTDeclReader::VisitDecl(Decl *D) {
-  if (D->isTemplateParameter()) {
+  if (D->isTemplateParameter() || D->isTemplateParameterPack() ||
+      isa<ParmVarDecl>(D)) {
     // We don't want to deserialize the DeclContext of a template
-    // parameter immediately, because the template parameter might be
-    // used in the formulation of its DeclContext. Use the translation
-    // unit DeclContext as a placeholder.
+    // parameter or of a parameter of a function template immediately.   These
+    // entities might be used in the formulation of its DeclContext (for
+    // example, a function parameter can be used in decltype() in trailing
+    // return type of the function).  Use the translation unit DeclContext as a
+    // placeholder.
     GlobalDeclID SemaDCIDForTemplateParmDecl = ReadDeclID(Record, Idx);
     GlobalDeclID LexicalDCIDForTemplateParmDecl = ReadDeclID(Record, Idx);
     Reader.addPendingDeclContextInfo(D,