[C++ PATCH] Reject invalid reference type non-static data members in unions (PR c++/78890)

[Jakub Jelinek]

On Wed, Jan 04, 2017 at 04:24:55PM -0500, Jason Merrill wrote:
> On Mon, Jan 2, 2017 at 2:32 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> >           if (TREE_CODE (type) == REFERENCE_TYPE)
> >             {
> > -             error ("in C++98 %q+D may not have reference type %qT "
> > -                    "because it is a member of a union", x, type);
> > -             continue;
> > +             if (cxx_dialect < cxx11)
> > +               {
> > +                 error ("in C++98 %q+D may not have reference type %qT "
> > +                        "because it is a member of a union", x, type);
> > +                 continue;
> > +               }
> 
> I don't think we need the old error anymore; in C++98 mode we will
> have already complained about a static data member reference, so we
> can drop the above and just keep the below.
> 
> > +             else if (TREE_CODE (x) == FIELD_DECL)
> > +               {
> > +                 error ("non-static data member %q+D in a union may not "
> > +                        "have reference type %qT", x, type);
> > +                 continue;
> > +               }

Like this?  Ok for trunk if bootstrap/regtest passes (just started them;
make check-c++-all didn't show regressions)?

2017-01-04  Jakub Jelinek  <jakub@redhat.com>

	PR c++/78890
	* class.c (check_field_decls): Diagnose REFERENCE_TYPE fields in
	unions even for C++11 and later.

	* g++.dg/init/ref14.C: Expect error even in C++11 and later.
	* g++.dg/init/union1.C: Likewise.
	* g++.dg/cpp0x/union6.C: Expect errors.
	* g++.dg/cpp0x/union8.C: New test.
	* g++.dg/cpp0x/pr78890-1.C: New test.
	* g++.dg/cpp0x/pr78890-2.C: New test.

--- gcc/cp/class.c.jj	2017-01-03 08:12:27.154511815 +0100
+++ gcc/cp/class.c	2017-01-04 22:41:32.669279309 +0100
@@ -3759,25 +3759,27 @@ check_field_decls (tree t, tree *access_
       /* When this goes into scope, it will be a non-local reference.  */
       DECL_NONLOCAL (x) = 1;
 
-      if (TREE_CODE (t) == UNION_TYPE
-	  && cxx_dialect < cxx11)
+      if (TREE_CODE (t) == UNION_TYPE)
 	{
 	  /* [class.union] (C++98)
 
 	     If a union contains a static data member, or a member of
 	     reference type, the program is ill-formed.
 
-	     In C++11 this limitation doesn't exist anymore.  */
-	  if (VAR_P (x))
+	     In C++11 [class.union] says:
+	     If a union contains a non-static data member of reference type
+	     the program is ill-formed.  */
+	  if (VAR_P (x) && cxx_dialect < cxx11)
 	    {
 	      error ("in C++98 %q+D may not be static because it is "
 		     "a member of a union", x);
 	      continue;
 	    }
-	  if (TREE_CODE (type) == REFERENCE_TYPE)
+	  if (TREE_CODE (type) == REFERENCE_TYPE
+	      && TREE_CODE (x) == FIELD_DECL)
 	    {
-	      error ("in C++98 %q+D may not have reference type %qT "
-		     "because it is a member of a union", x, type);
+	      error ("non-static data member %q+D in a union may not "
+		     "have reference type %qT", x, type);
 	      continue;
 	    }
 	}
--- gcc/testsuite/g++.dg/init/ref14.C.jj	2017-01-03 08:12:26.878515378 +0100
+++ gcc/testsuite/g++.dg/init/ref14.C	2017-01-04 22:40:35.789996635 +0100
@@ -4,7 +4,7 @@
 
 union A
 {
-  int &i; // { dg-error "may not have reference type" "" { target { ! c++11 } } }
+  int &i; // { dg-error "may not have reference type" }
 };
 
 void foo()
--- gcc/testsuite/g++.dg/init/union1.C.jj	2017-01-03 08:12:26.862515585 +0100
+++ gcc/testsuite/g++.dg/init/union1.C	2017-01-04 22:40:35.789996635 +0100
@@ -1,5 +1,5 @@
 // PR c++/14401
 
 union U {
-  int& i; // { dg-error "reference type" "" { target { ! c++11 } } }
+  int& i; // { dg-error "reference type" }
 };
--- gcc/testsuite/g++.dg/cpp0x/pr78890-2.C.jj	2017-01-04 22:40:35.821996232 +0100
+++ gcc/testsuite/g++.dg/cpp0x/pr78890-2.C	2017-01-04 22:40:35.821996232 +0100
@@ -0,0 +1,44 @@
+// PR c++/78890
+// { dg-do compile { target c++11 } }
+
+template <typename T>
+int
+foo ()
+{
+  union {
+    int a;
+    int &b = a;			// { dg-error "may not have reference type" }
+  };
+  a = 1;
+  auto c = b + 1;
+  return c;
+}
+
+template <typename T>
+T
+bar ()
+{
+  union {
+    T a;
+    T &b = a;			// { dg-error "may not have reference type" }
+  };
+  a = 1;
+  auto c = b + 1;
+  return c;
+}
+
+template <typename T, typename U>
+T baz()
+{
+  union {
+    T a;
+    U b = a;			// { dg-error "may not have reference type" }
+  };
+  a = 1;
+  auto c = b + 1;
+  return c;
+}
+
+int a = foo<int> ();
+int b = bar<int> ();
+int c = baz<int, int &> ();
--- gcc/testsuite/g++.dg/cpp0x/union8.C.jj	2017-01-04 22:40:35.820996244 +0100
+++ gcc/testsuite/g++.dg/cpp0x/union8.C	2017-01-04 22:40:35.820996244 +0100
@@ -0,0 +1,26 @@
+// PR c++/78890
+// { dg-do compile { target c++11 } }
+
+union Test1 {
+  static int kConstant;
+};
+
+union Test2 {
+  static const int kConstant;
+};
+
+const int Test2::kConstant = 10;
+
+int k;
+
+union Test3 {
+  static int& kRef;
+};
+
+int& Test3::kRef = k;
+
+union Test4 {
+  static const int& kRef;
+};
+
+const int& Test4::kRef = 10;
--- gcc/testsuite/g++.dg/cpp0x/union6.C.jj	2017-01-03 08:12:26.926514759 +0100
+++ gcc/testsuite/g++.dg/cpp0x/union6.C	2017-01-04 22:40:35.820996244 +0100
@@ -12,9 +12,9 @@ union Test2 {
 const int Test2::kConstant = 10;
 
 union Test3 {
-  int& kConstant;
+  int& kConstant;	// { dg-error "may not have reference type" }
 };
 
 union Test4 {
-  const int& kConstant = 10;
+  const int& kConstant = 10;	// { dg-error "may not have reference type" }
 };
--- gcc/testsuite/g++.dg/cpp0x/pr78890-1.C.jj	2017-01-04 22:40:35.820996244 +0100
+++ gcc/testsuite/g++.dg/cpp0x/pr78890-1.C	2017-01-04 22:40:35.820996244 +0100
@@ -0,0 +1,13 @@
+// PR c++/78890
+// { dg-do compile { target c++11 } }
+
+int
+main()
+{
+  union {
+    int a;
+    int &b = a;		// { dg-error "may not have reference type" }
+  };
+  a = 1;
+  auto c = b + 1;
+}


	Jakub