c++: Fix deprecated attribute handling on templates (PR c++/93228)

As the following testcase shows, when deprecated attribute is on a template,
we'd never print the message if any, because the attribute is not
present on the TEMPLATE_DECL with which warn_deprecated_use is called,
but on its DECL_TEMPLATE_RESULT or its type.

2020-01-17  Jakub Jelinek  <jakub@redhat.com>

	PR c++/93228
	* parser.c (cp_parser_template_name): Look up deprecated attribute
	in DECL_TEMPLATE_RESULT or its type's attributes.

	* g++.dg/cpp1y/attr-deprecated-3.C: New test.

gcc/cp/ChangeLog

+2020-01-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/93228
+	* parser.c (cp_parser_template_name): Look up deprecated attribute
+	in DECL_TEMPLATE_RESULT or its type's attributes.
+
 2020-01-16  Jason Merrill  <jason@redhat.com>
 
 	PR c++/93286 - ICE with __is_constructible and variadic template.

gcc/cp/parser.c

@@ -16884,7 +16884,17 @@ cp_parser_template_name (cp_parser* parser,
     {
       if (TREE_DEPRECATED (decl)
 	  && deprecated_state != DEPRECATED_SUPPRESS)
-	warn_deprecated_use (decl, NULL_TREE);
+	{
+	  tree d = DECL_TEMPLATE_RESULT (decl);
+	  tree attr;
+	  if (TREE_CODE (d) == TYPE_DECL)
+	    attr = lookup_attribute ("deprecated",
+				     TYPE_ATTRIBUTES (TREE_TYPE (d)));
+	  else
+	    attr = lookup_attribute ("deprecated",
+				     DECL_ATTRIBUTES (d));
+	  warn_deprecated_use (decl, attr);
+	}
     }
   else
     {

gcc/testsuite/ChangeLog

+2020-01-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/93228
+	* g++.dg/cpp1y/attr-deprecated-3.C: New test.
+
 2020-01-17  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* g++.target/aarch64/sve/acle/general-c++/gimplify_1.C: New test.

gcc/testsuite/g++.dg/cpp1y/attr-deprecated-3.C

+// PR c++/93228
+// { dg-do compile { target c++14 } }
+
+template <typename T>
+struct [[deprecated("foo")]] bar {};	// { dg-message "declared here" }
+struct [[deprecated("baz")]] qux {}; 	// { dg-message "declared here" }
+
+void
+quux ()
+{
+  bar<int> b;	// { dg-warning "is deprecated: foo" }
+  qux c;	// { dg-warning "is deprecated: baz" }
+}