[Sema] Fix the assertion in Sema::ActOnDependentMemberExpr

[ychen]

Summary

617007240cbfb97c introduced the use of ActOnDependentMemberExpr with
variable template specialization. The assertion inside
ActOnDependentMemberExpr should be adjusted accordingly.

Fixes https://bugs.llvm.org/show_bug.cgi?id=47211

[ychen]

• Check that TemplateArgs maybe null.

[ychen]

ping

[aaron.ballman]

LGTM! However, I'd like to hear from @rsmith as he was the original code author here, so please give him a few days to respond before landing.

[ychen]

@aaron.ballman Thanks for taking a look! Yep, I'll wait.

[ychen]

Richard seems very busy. I just committed this based on Aaron's LGTM. Richard could still review this at any time.

clang/lib/Sema/SemaExprMember.cpp

if (PT && (!getLangOpts().ObjC ||
                PT->getPointeeType()->isRecordType())) {
       assert(BaseExpr && "cannot happen with implicit member accesses");
       Diag(OpLoc, diag::err_typecheck_member_reference_struct_union)
         << BaseType << BaseExpr->getSourceRange() << NameInfo.getSourceRange();
       return ExprError();
     }
   }
 
-  assert(BaseType->isDependentType() ||
-         NameInfo.getName().isDependentName() ||
-         isDependentScopeSpecifier(SS));
+  assert(BaseType->isDependentType() || NameInfo.getName().isDependentName() ||
+         isDependentScopeSpecifier(SS) ||
+         (TemplateArgs && llvm::any_of(TemplateArgs->arguments(),
+                                       [](const TemplateArgumentLoc &Arg) {
+                                         return Arg.getArgument().isDependent();
+                                       })));
 
   // Get the type being accessed in BaseType.  If this is an arrow, the BaseExpr
   // must have pointer type, and the accessed type is the pointee.
   return CXXDependentScopeMemberExpr::Create(
       Context, BaseExpr, BaseType, IsArrow, OpLoc,
       SS.getWithLocInContext(Context), TemplateKWLoc, FirstQualifierInScope,
       NameInfo, TemplateArgs);
 }

clang/test/SemaCXX/cxx1y-variable-templates_in_class.cpp

namespace dependent_static_var_template {
   template<typename T>
   int &f() { return T::template n; } // expected-error {{use of variable template 'n' requires template arguments}}
   int &s = f<A>(); // expected-note {{instantiation of}}
 
   namespace B {
     template<int = 0> static int n; // expected-note {{here}}
   }
   int &t = B::template n; // expected-error {{use of variable template 'n' requires template arguments}}
+
+  struct C {
+    template <class T> static T G;
+  };
+  template<class T> T C::G = T(6);
+
+  template <class T> T F() {
+    C c;
+    return c.G<T>;
+  }
+
+  int cf() { return F<int>(); }
 }
 
 #ifndef PRECXX11
 namespace template_vars_in_template {
 template <int> struct TakesInt {};
 
 template <class T2>
 struct S {