SubstTemplateTypeParmType can contain an 'auto' type in their replacement type

[serge-sans-paille]

Summary

This fixes bug 36064

[aaron.ballman]

LGTM aside from a style nit, thanks for the fix!

clang/lib/AST/Type.cpp

1804

clang/lib/AST/Type.cpp

public:
     }
 
     // The deduced type itself.
     Type *VisitDeducedType(const DeducedType *AT) {
       return const_cast<DeducedType*>(AT);
     }
 
     // Only these types can contain the desired 'auto' type.
+    Type *VisitSubstTemplateTypeParmType(const SubstTemplateTypeParmType *T) {
+      return Visit(T->getReplacementType());
+    }
 
     Type *VisitElaboratedType(const ElaboratedType *T) {
       return Visit(T->getNamedType());
     }
 
     Type *VisitPointerType(const PointerType *T) {
       return Visit(T->getPointeeType());
     }

clang/test/SemaCXX/crash-auto-36064.cpp

+// RUN: %clang_cc1 -fsyntax-only -std=c++11 %s -verify
+template <typename A, decltype(new A)> // expected-error{{new expression for type 'auto' requires a constructor argument}}
+struct b;
+struct d {
+  static auto c = ;              // expected-error{{expected expression}}
+  decltype(b<decltype(c), int>); // expected-error{{expected '(' for function-style cast or type construction}}
+                                 // expected-note@-1{{while substituting prior template arguments into non-type template parameter [with A = auto]}}
+};