Fix PR 28885: Fix AST Printer output for inheriting constructor using declarations

[arphaman]

Summary

This patch ensures that the AST printer outputs the correct C++ type for an inheriting constructor using declaration.

For example, for a using declaration in a code sample like this:

struct A {
	A();
};

struct B : A {
  using A::A;
};

The AST printer will now print "using A::A" instead of "using A::B".

This bug is a regression since r274049.

[rsmith]

Minor comment, otherwise LGTM.

lib/AST/DeclPrinter.cpp

1350–1351

Don't list PR numbers here. Your code and its comments should be sufficient to explain what you're doing and why without this.

[arphaman]

In D25131#558004, @rsmith wrote:

Minor comment, otherwise LGTM.

This makes sense, thanks for pointing it out!
I'll update the comment when I commit.

lib/AST/DeclPrinter.cpp

 }
 
 void DeclPrinter::VisitUsingDecl(UsingDecl *D) {
   if (!D->isAccessDeclaration())
     Out << "using ";
   if (D->hasTypename())
     Out << "typename ";
   D->getQualifier()->print(Out, Policy);
+
+  // PR 28885: Use the correct record name when the using declaration is used
+  // for inheriting constructors.
+  for (const auto *Shadow : D->shadows()) {
+    if (const auto *ConstructorShadow =
+            dyn_cast<ConstructorUsingShadowDecl>(Shadow)) {
+      assert(Shadow->getDeclContext() == ConstructorShadow->getDeclContext());
+      Out << *ConstructorShadow->getNominatedBaseClass();
+      return;
+    }
+  }
   Out << *D;
 }
 
 void
 DeclPrinter::VisitUnresolvedUsingTypenameDecl(UnresolvedUsingTypenameDecl *D) {
   Out << "using typename ";
   D->getQualifier()->print(Out, Policy);
   Out << D->getDeclName();

test/SemaCXX/cxx11-ast-print.cpp

 const char *p9 = 0x42e3F_fritz;
 // CHECK: const char *p10 = 3.300e+15_fritz;
 const char *p10 = 3.300e+15_fritz;
 
 template <class C, C...> const char *operator"" _suffix();
 // CHECK: const char *PR23120 = operator""_suffix<char32_t, 66615>();
 const char *PR23120 = U"𐐷"_suffix;
 
+// PR28885
+struct A {
+  A();
+};
+struct B : A {
+  using A::A; // CHECK:      using A::A;
+};            // CHECK-NEXT: };
+
 // CHECK: ;
 ;
 // CHECK-NOT: ;