C++ PATCH for c++/85135, ICE with omitted template arguments

[Jason Merrill]

A deduced class type can't appear in a function return type; we
already check for that in a leading return type, but we weren't
checking in a trailing return type.  This fixes that, and return
error_mark_node.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit d39ccab0e8762fc4d1dd03e079e2c4cf925337d7
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue Apr 3 17:03:29 2018 -0400

            PR c++/85135 - ICE with omitted template arguments.
    
            * decl.c (grokdeclarator): Catch deduced class type in trailing
            return type.

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index c8309979a4d..dca903d9b68 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -11093,20 +11093,29 @@ grokdeclarator (const cp_declarator *declarator,
 			       name, type);
 			return error_mark_node;
 		      }
-		    if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node))
+		    tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node);
+		    if (!tmpl)
+		      if (tree late_auto = type_uses_auto (late_return_type))
+			tmpl = CLASS_PLACEHOLDER_TEMPLATE (late_auto);
+		    if (tmpl)
 		      {
-			if (!late_return_type)
+			if (!dguide_name_p (unqualified_id))
 			  {
-			    if (dguide_name_p (unqualified_id))
-			      error_at (declarator->id_loc, "deduction guide "
-					"for %qT must have trailing return "
-					"type", TREE_TYPE (tmpl));
-			    else
-			      error_at (declarator->id_loc, "deduced class "
-					"type %qT in function return type",
-					type);
+			    error_at (declarator->id_loc, "deduced class "
+				      "type %qD in function return type",
+				      DECL_NAME (tmpl));
 			    inform (DECL_SOURCE_LOCATION (tmpl),
 				    "%qD declared here", tmpl);
+			    return error_mark_node;
+			  }
+			else if (!late_return_type)
+			  {
+			    error_at (declarator->id_loc, "deduction guide "
+				      "for %qT must have trailing return "
+				      "type", TREE_TYPE (tmpl));
+			    inform (DECL_SOURCE_LOCATION (tmpl),
+				    "%qD declared here", tmpl);
+			    return error_mark_node;
 			  }
 			else if (CLASS_TYPE_P (late_return_type)
 				 && CLASSTYPE_TEMPLATE_INFO (late_return_type)
diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction53.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction53.C
new file mode 100644
index 00000000000..6025dc47cf5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction53.C
@@ -0,0 +1,10 @@
+// PR c++/85135
+// { dg-do compile { target c++11 } }
+
+template<int> struct A {};
+
+auto foo() -> A;		// { dg-error "A" }
+
+template<typename> struct B {};
+
+auto foo() -> A;		// { dg-error "A" }