[Sema] Fix PR22637 - IndirectFieldDecl's discard qualifiers during template instantiation.

[EricWF]

Summary

Currently Clang fails to propagate qualifiers from the CXXThisExpr to the rebuilt FieldDecl for IndirectFieldDecls. For example:

template <class T> struct Foo {
  struct { int x; };
  int y;
  void foo() const { 
      static_assert(__is_same(int const&, decltype((y))));
      static_assert(__is_same(int const&, decltype((x)))); // assertion fails
  }
};
template struct Foo<int>;

The fix is to delegate rebuilding of the MemberExpr to BuildFieldReferenceExpr which correctly propagates the qualifiers.

[rjmccall]

Okay, LGTM.

lib/Sema/TreeTransform.h

if (!Member->getDeclName()) {
 
       BaseResult =
         getSema().PerformObjectMemberConversion(BaseResult.get(),
                                                 QualifierLoc.getNestedNameSpecifier(),
                                                 FoundDecl, Member);
       if (BaseResult.isInvalid())
         return ExprError();
       Base = BaseResult.get();
-      ExprValueKind VK = isArrow ? VK_LValue : Base->getValueKind();
-      MemberExpr *ME = new (getSema().Context)
-          MemberExpr(Base, isArrow, OpLoc, Member, MemberNameInfo,
-                     cast<FieldDecl>(Member)->getType(), VK, OK_Ordinary);
-      return ME;
+
+      CXXScopeSpec EmptySS;
+      return getSema().BuildFieldReferenceExpr(
+          Base, isArrow, OpLoc, EmptySS, cast<FieldDecl>(Member),
+          DeclAccessPair::make(FoundDecl, FoundDecl->getAccess()), MemberNameInfo);
     }
 
     CXXScopeSpec SS;
     SS.Adopt(QualifierLoc);
 
     Base = BaseResult.get();
     QualType BaseType = Base->getType();
 

test/SemaCXX/PR22637.cpp

+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// expected-no-diagnostics
+
+void check(int&) = delete;
+void check(int const&) { }
+
+template <typename>
+struct A {
+    union {
+        int b;
+    };
+    struct {
+      int c;
+    };
+    union {
+      struct {
+        union {
+          struct {
+            struct {
+              int d;
+            };
+          };
+        };
+      };
+    };
+    int e;
+    void foo() const {
+      check(b);
+      check(c);
+      check(d);
+      check(d);
+      check(e);
+    }
+};
+
+int main(){
+    A<int> a;
+    a.foo();
+}

test/SemaCXX/cxx0x-nontrivial-union.cpp

template<typename T> struct optional {
     }
 
     ~optional() {
       if (has)
         value.~T();
     }
 
     explicit operator bool() const { return has; }
-    T &operator*() const { return value; }
+    T &operator*() { return value; }
   };
 
   optional<non_trivial> o1;
   optional<non_trivial> o2{non_trivial()};
   optional<non_trivial> o3{*o2};
   void f() {
     if (o2)
       o1 = o2;