[C++] PR 84423 ("[6/7/8/9 Regression] [concepts] ICE with invalid using declaration")

Message ID 61471b27-ea85-8fc2-a7e3-178547e518d6@oracle.com
State New
Headers show
Series
  • [C++] PR 84423 ("[6/7/8/9 Regression] [concepts] ICE with invalid using declaration")
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Commit Message

Paolo Carlini Sept. 28, 2018, 4:42 p.m.
Hi,

the primary issue here is a rather straightforward error-recovery, 
where, after a sensible (but see below) error message we ICE in 
get_underlying_template - called by convert_template_argument - because 
we don't handle correctly error_mark_node as TREE_TYPE, as set in 
grokdeclarator. While working on it I noticed that the error message 
emitted by grokdeclarator seems suboptimal, because, per 10.1.3/2, we 
correctly handle the alias declaration like a typedef but, I believe, we 
don't want to just say *typedef* in the error message: luckily the 
infrastructure to be more accurate is fully available, because we need 
it to set TYPE_DECL_ALIAS_P anyway.

Tested x86_64-linux.

Thanks, Paolo.

//////////////////////
/cp
2018-09-28  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/84423
	* pt.c (convert_template_argument): Immediately return error_mark_node
	if the second argument is erroneous.
	* decl.c (grokdeclarator): Improve error message for 'auto' in
	alias declaration.

/testsuite
2018-09-28  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/84423
	* g++.dg/concepts/pr84423.C: New.

Comments

Jason Merrill Sept. 28, 2018, 5:18 p.m. | #1
On Fri, Sep 28, 2018 at 12:42 PM, Paolo Carlini
<paolo.carlini@oracle.com> wrote:
> Hi,

>

> the primary issue here is a rather straightforward error-recovery, where,

> after a sensible (but see below) error message we ICE in

> get_underlying_template - called by convert_template_argument - because we

> don't handle correctly error_mark_node as TREE_TYPE, as set in

> grokdeclarator. While working on it I noticed that the error message emitted

> by grokdeclarator seems suboptimal, because, per 10.1.3/2, we correctly

> handle the alias declaration like a typedef but, I believe, we don't want to

> just say *typedef* in the error message: luckily the infrastructure to be

> more accurate is fully available, because we need it to set

> TYPE_DECL_ALIAS_P anyway.


OK, though as long as you're messing with this error you might want to
improve its location as well.

Jason
Paolo Carlini Sept. 28, 2018, 7:15 p.m. | #2
Hi,

On 9/28/18 7:18 PM, Jason Merrill wrote:
> On Fri, Sep 28, 2018 at 12:42 PM, Paolo Carlini

> <paolo.carlini@oracle.com> wrote:

>> Hi,

>>

>> the primary issue here is a rather straightforward error-recovery, where,

>> after a sensible (but see below) error message we ICE in

>> get_underlying_template - called by convert_template_argument - because we

>> don't handle correctly error_mark_node as TREE_TYPE, as set in

>> grokdeclarator. While working on it I noticed that the error message emitted

>> by grokdeclarator seems suboptimal, because, per 10.1.3/2, we correctly

>> handle the alias declaration like a typedef but, I believe, we don't want to

>> just say *typedef* in the error message: luckily the infrastructure to be

>> more accurate is fully available, because we need it to set

>> TYPE_DECL_ALIAS_P anyway.

> OK, though as long as you're messing with this error you might want to

> improve its location as well.


Thanks. About the location, you are certainly right, but doesn't seem 
trivial. Something we can do *now* is using 
declspecs->locations[ds_typedef] and declspecs->locations[ds_alias], but 
that gives us the location of the keyword 'typedef' and 'using', 
respectively, whereas I think that we would like to have the location of 
'auto' itself. I could look into that as a follow-up piece work (by the 
way, I'm always reluctant to embark in non trivial work having to do 
with locations because I suppose David is already on it?!?)

Paolo.

///////////////////
Index: constraint.cc
===================================================================
--- constraint.cc	(revision 264687)
+++ constraint.cc	(working copy)
@@ -1164,6 +1164,9 @@ build_constraints (tree tmpl_reqs, tree decl_reqs)
   if (!tmpl_reqs && !decl_reqs)
     return NULL_TREE;
 
+  //if (tmpl_reqs == error_mark_node || decl_reqs == error_mark_node)
+  //return NULL_TREE;
+
   tree_constraint_info* ci = build_constraint_info ();
   ci->template_reqs = tmpl_reqs;
   ci->declarator_reqs = decl_reqs;
Index: decl.c
===================================================================
--- decl.c	(revision 264687)
+++ decl.c	(working copy)
@@ -11879,6 +11879,7 @@ grokdeclarator (const cp_declarator *declarator,
   /* If this is declaring a typedef name, return a TYPE_DECL.  */
   if (typedef_p && decl_context != TYPENAME)
     {
+      bool alias_p = decl_spec_seq_has_spec_p (declspecs, ds_alias);
       tree decl;
 
       /* This declaration:
@@ -11901,7 +11902,12 @@ grokdeclarator (const cp_declarator *declarator,
 
       if (type_uses_auto (type))
 	{
-	  error ("typedef declared %<auto%>");
+	  if (alias_p)
+	    error_at (declspecs->locations[ds_alias],
+		      "%<auto%> not allowed in alias declaration");
+	  else
+	    error_at (declspecs->locations[ds_typedef],
+		      "typedef declared %<auto%>");
 	  type = error_mark_node;
 	}
 
@@ -11961,7 +11967,7 @@ grokdeclarator (const cp_declarator *declarator,
 		      inlinep, friendp, raises != NULL_TREE,
 		      declspecs->locations);
 
-      if (decl_spec_seq_has_spec_p (declspecs, ds_alias))
+      if (alias_p)
 	/* Acknowledge that this was written:
 	     `using analias = atype;'.  */
 	TYPE_DECL_ALIAS_P (decl) = 1;
Index: pt.c
===================================================================
--- pt.c	(revision 264687)
+++ pt.c	(working copy)
@@ -7776,7 +7776,7 @@ convert_template_argument (tree parm,
   tree val;
   int is_type, requires_type, is_tmpl_type, requires_tmpl_type;
 
-  if (parm == error_mark_node)
+  if (parm == error_mark_node || error_operand_p (arg))
     return error_mark_node;
 
   /* Trivially convert placeholders. */
Paolo Carlini Sept. 29, 2018, 7:27 p.m. | #3
Hi again,

On 9/28/18 9:15 PM, Paolo Carlini wrote:
> Thanks. About the location, you are certainly right, but doesn't seem 

> trivial. Something we can do *now* is using 

> declspecs->locations[ds_typedef] and declspecs->locations[ds_alias], 

> but that gives us the location of the keyword 'typedef' and 'using', 

> respectively, whereas I think that we would like to have the location 

> of 'auto' itself. I could look into that as a follow-up piece work


In fact, completing the work turned out to be easy: ensure that 
cp_parser_alias_declaration saves the location of the defining-type-id 
too and then consistently use locations[ds_type_spec] in the error 
messages. Tested x86_64-linux. Still Ok? ;)

Thanks, Paolo.

///////////////////
/cp
2018-09-29  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/84423
	* pt.c (convert_template_argument): Immediately return error_mark_node
	if the second argument is erroneous.
	* parser.c (cp_parser_alias_declaration): Save the location
	of the type-id too. 
	* decl.c (grokdeclarator): Improve error message for 'auto' in
	alias declaration.

/testsuite
2018-09-29  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/84423
	* g++.dg/concepts/pr84423.C: New.
Index: cp/decl.c
===================================================================
--- cp/decl.c	(revision 264687)
+++ cp/decl.c	(working copy)
@@ -11879,6 +11879,7 @@ grokdeclarator (const cp_declarator *declarator,
   /* If this is declaring a typedef name, return a TYPE_DECL.  */
   if (typedef_p && decl_context != TYPENAME)
     {
+      bool alias_p = decl_spec_seq_has_spec_p (declspecs, ds_alias);
       tree decl;
 
       /* This declaration:
@@ -11901,7 +11902,12 @@ grokdeclarator (const cp_declarator *declarator,
 
       if (type_uses_auto (type))
 	{
-	  error ("typedef declared %<auto%>");
+	  if (alias_p)
+	    error_at (declspecs->locations[ds_type_spec],
+		      "%<auto%> not allowed in alias declaration");
+	  else
+	    error_at (declspecs->locations[ds_type_spec],
+		      "typedef declared %<auto%>");
 	  type = error_mark_node;
 	}
 
@@ -11961,7 +11967,7 @@ grokdeclarator (const cp_declarator *declarator,
 		      inlinep, friendp, raises != NULL_TREE,
 		      declspecs->locations);
 
-      if (decl_spec_seq_has_spec_p (declspecs, ds_alias))
+      if (alias_p)
 	/* Acknowledge that this was written:
 	     `using analias = atype;'.  */
 	TYPE_DECL_ALIAS_P (decl) = 1;
Index: cp/parser.c
===================================================================
--- cp/parser.c	(revision 264687)
+++ cp/parser.c	(working copy)
@@ -19073,6 +19073,7 @@ cp_parser_alias_declaration (cp_parser* parser)
 	G_("types may not be defined in alias template declarations");
     }
 
+  cp_token *type_token = cp_lexer_peek_token (parser->lexer);
   type = cp_parser_type_id (parser);
 
   /* Restore the error message if need be.  */
@@ -19107,6 +19108,9 @@ cp_parser_alias_declaration (cp_parser* parser)
   set_and_check_decl_spec_loc (&decl_specs,
 			       ds_alias,
 			       using_token);
+  set_and_check_decl_spec_loc (&decl_specs,
+			       ds_type_spec,
+			       type_token);
 
   if (parser->num_template_parameter_lists
       && !cp_parser_check_template_parameters (parser,
Index: cp/pt.c
===================================================================
--- cp/pt.c	(revision 264687)
+++ cp/pt.c	(working copy)
@@ -7776,7 +7776,7 @@ convert_template_argument (tree parm,
   tree val;
   int is_type, requires_type, is_tmpl_type, requires_tmpl_type;
 
-  if (parm == error_mark_node)
+  if (parm == error_mark_node || error_operand_p (arg))
     return error_mark_node;
 
   /* Trivially convert placeholders. */
Index: testsuite/g++.dg/concepts/pr84423.C
===================================================================
--- testsuite/g++.dg/concepts/pr84423.C	(nonexistent)
+++ testsuite/g++.dg/concepts/pr84423.C	(working copy)
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fconcepts" }
+
+template<typename> using A = auto;  // { dg-error "30:.auto. not allowed in alias declaration" }
+
+template<template<typename> class> struct B {};
+
+B<A> b;
+
+typedef auto C;  // { dg-error "9:typedef declared .auto." }
Paolo Carlini Oct. 9, 2018, 10:06 a.m. | #4
Hi,

gently pinging the below...

On 29/09/18 21:27, Paolo Carlini wrote:
> Hi again,

>

> On 9/28/18 9:15 PM, Paolo Carlini wrote:

>> Thanks. About the location, you are certainly right, but doesn't seem 

>> trivial. Something we can do *now* is using 

>> declspecs->locations[ds_typedef] and declspecs->locations[ds_alias], 

>> but that gives us the location of the keyword 'typedef' and 'using', 

>> respectively, whereas I think that we would like to have the location 

>> of 'auto' itself. I could look into that as a follow-up piece work

>

> In fact, completing the work turned out to be easy: ensure that 

> cp_parser_alias_declaration saves the location of the defining-type-id 

> too and then consistently use locations[ds_type_spec] in the error 

> messages. Tested x86_64-linux. Still Ok? ;)


     https://gcc.gnu.org/ml/gcc-patches/2018-09/msg01773.html

Thanks! Paolo.
Jason Merrill Oct. 9, 2018, 3:17 p.m. | #5
On Sat, Sep 29, 2018 at 3:27 PM Paolo Carlini <paolo.carlini@oracle.com> wrote:
> Hi again,

>

> On 9/28/18 9:15 PM, Paolo Carlini wrote:

> > Thanks. About the location, you are certainly right, but doesn't seem

> > trivial. Something we can do *now* is using

> > declspecs->locations[ds_typedef] and declspecs->locations[ds_alias],

> > but that gives us the location of the keyword 'typedef' and 'using',

> > respectively, whereas I think that we would like to have the location

> > of 'auto' itself. I could look into that as a follow-up piece work

>

> In fact, completing the work turned out to be easy: ensure that

> cp_parser_alias_declaration saves the location of the defining-type-id

> too and then consistently use locations[ds_type_spec] in the error

> messages. Tested x86_64-linux. Still Ok? ;)


Hmm, I think you need to look past any cv-qualifiers at the beginning
of the type-id.

Jason
Paolo Carlini Oct. 9, 2018, 5:48 p.m. | #6
Hi,

On 09/10/18 17:17, Jason Merrill wrote:
> On Sat, Sep 29, 2018 at 3:27 PM Paolo Carlini <paolo.carlini@oracle.com> wrote:

>> Hi again,

>>

>> On 9/28/18 9:15 PM, Paolo Carlini wrote:

>>> Thanks. About the location, you are certainly right, but doesn't seem

>>> trivial. Something we can do *now* is using

>>> declspecs->locations[ds_typedef] and declspecs->locations[ds_alias],

>>> but that gives us the location of the keyword 'typedef' and 'using',

>>> respectively, whereas I think that we would like to have the location

>>> of 'auto' itself. I could look into that as a follow-up piece work

>> In fact, completing the work turned out to be easy: ensure that

>> cp_parser_alias_declaration saves the location of the defining-type-id

>> too and then consistently use locations[ds_type_spec] in the error

>> messages. Tested x86_64-linux. Still Ok? ;)

> Hmm, I think you need to look past any cv-qualifiers at the beginning

> of the type-id.


Ah, good point. The information is readily available in 
cp_parser_type_id thus we can simply return it to 
cp_parser_alias_declaration. I guess an alternate approach would be 
adding a pointer to the whole cp_decl_specifier_seq parameter to 
cp_parser_type_id (and cp_parser_type_id_1, etc), but that seems over 
killing to me.

Thanks! Paolo.

/////////////////////
Index: cp/decl.c
===================================================================
--- cp/decl.c	(revision 264985)
+++ cp/decl.c	(working copy)
@@ -11879,6 +11879,7 @@ grokdeclarator (const cp_declarator *declarator,
   /* If this is declaring a typedef name, return a TYPE_DECL.  */
   if (typedef_p && decl_context != TYPENAME)
     {
+      bool alias_p = decl_spec_seq_has_spec_p (declspecs, ds_alias);
       tree decl;
 
       /* This declaration:
@@ -11901,7 +11902,12 @@ grokdeclarator (const cp_declarator *declarator,
 
       if (type_uses_auto (type))
 	{
-	  error ("typedef declared %<auto%>");
+	  if (alias_p)
+	    error_at (declspecs->locations[ds_type_spec],
+		      "%<auto%> not allowed in alias declaration");
+	  else
+	    error_at (declspecs->locations[ds_type_spec],
+		      "typedef declared %<auto%>");
 	  type = error_mark_node;
 	}
 
@@ -11961,7 +11967,7 @@ grokdeclarator (const cp_declarator *declarator,
 		      inlinep, friendp, raises != NULL_TREE,
 		      declspecs->locations);
 
-      if (decl_spec_seq_has_spec_p (declspecs, ds_alias))
+      if (alias_p)
 	/* Acknowledge that this was written:
 	     `using analias = atype;'.  */
 	TYPE_DECL_ALIAS_P (decl) = 1;
Index: cp/parser.c
===================================================================
--- cp/parser.c	(revision 264985)
+++ cp/parser.c	(working copy)
@@ -2216,12 +2216,12 @@ static tree cp_parser_late_return_type_opt
 static tree cp_parser_declarator_id
   (cp_parser *, bool);
 static tree cp_parser_type_id
-  (cp_parser *);
+  (cp_parser *, location_t * = NULL);
 static tree cp_parser_template_type_arg
   (cp_parser *);
 static tree cp_parser_trailing_type_id (cp_parser *);
 static tree cp_parser_type_id_1
-  (cp_parser *, bool, bool);
+  (cp_parser *, bool, bool, location_t *);
 static void cp_parser_type_specifier_seq
   (cp_parser *, bool, bool, cp_decl_specifier_seq *);
 static tree cp_parser_parameter_declaration_clause
@@ -19034,7 +19034,7 @@ static tree
 cp_parser_alias_declaration (cp_parser* parser)
 {
   tree id, type, decl, pushed_scope = NULL_TREE, attributes;
-  location_t id_location;
+  location_t id_location, type_location;
   cp_declarator *declarator;
   cp_decl_specifier_seq decl_specs;
   bool member_p;
@@ -19086,7 +19086,7 @@ cp_parser_alias_declaration (cp_parser* parser)
 	G_("types may not be defined in alias template declarations");
     }
 
-  type = cp_parser_type_id (parser);
+  type = cp_parser_type_id (parser, &type_location);
 
   /* Restore the error message if need be.  */
   if (parser->num_template_parameter_lists)
@@ -19120,6 +19120,7 @@ cp_parser_alias_declaration (cp_parser* parser)
   set_and_check_decl_spec_loc (&decl_specs,
 			       ds_alias,
 			       using_token);
+  decl_specs.locations[ds_type_spec] = type_location;
 
   if (parser->num_template_parameter_lists
       && !cp_parser_check_template_parameters (parser,
@@ -21110,7 +21111,7 @@ cp_parser_declarator_id (cp_parser* parser, bool o
 
 static tree
 cp_parser_type_id_1 (cp_parser* parser, bool is_template_arg,
-		     bool is_trailing_return)
+		     bool is_trailing_return, location_t * type_location)
 {
   cp_decl_specifier_seq type_specifier_seq;
   cp_declarator *abstract_declarator;
@@ -21119,6 +21120,9 @@ cp_parser_type_id_1 (cp_parser* parser, bool is_te
   cp_parser_type_specifier_seq (parser, /*is_declaration=*/false,
 				is_trailing_return,
 				&type_specifier_seq);
+  if (type_location)
+    *type_location = type_specifier_seq.locations[ds_type_spec];
+
   if (is_template_arg && type_specifier_seq.type
       && TREE_CODE (type_specifier_seq.type) == TEMPLATE_TYPE_PARM
       && CLASS_PLACEHOLDER_TEMPLATE (type_specifier_seq.type))
@@ -21184,9 +21188,9 @@ cp_parser_type_id_1 (cp_parser* parser, bool is_te
 }
 
 static tree
-cp_parser_type_id (cp_parser *parser)
+cp_parser_type_id (cp_parser *parser, location_t * type_location)
 {
-  return cp_parser_type_id_1 (parser, false, false);
+  return cp_parser_type_id_1 (parser, false, false, type_location);
 }
 
 static tree
@@ -21196,7 +21200,7 @@ cp_parser_template_type_arg (cp_parser *parser)
   const char *saved_message = parser->type_definition_forbidden_message;
   parser->type_definition_forbidden_message
     = G_("types may not be defined in template arguments");
-  r = cp_parser_type_id_1 (parser, true, false);
+  r = cp_parser_type_id_1 (parser, true, false, NULL);
   parser->type_definition_forbidden_message = saved_message;
   if (cxx_dialect >= cxx14 && !flag_concepts && type_uses_auto (r))
     {
@@ -21209,7 +21213,7 @@ cp_parser_template_type_arg (cp_parser *parser)
 static tree
 cp_parser_trailing_type_id (cp_parser *parser)
 {
-  return cp_parser_type_id_1 (parser, false, true);
+  return cp_parser_type_id_1 (parser, false, true, NULL);
 }
 
 /* Parse a type-specifier-seq.
Index: cp/pt.c
===================================================================
--- cp/pt.c	(revision 264985)
+++ cp/pt.c	(working copy)
@@ -7776,7 +7776,7 @@ convert_template_argument (tree parm,
   tree val;
   int is_type, requires_type, is_tmpl_type, requires_tmpl_type;
 
-  if (parm == error_mark_node)
+  if (parm == error_mark_node || error_operand_p (arg))
     return error_mark_node;
 
   /* Trivially convert placeholders. */
Index: testsuite/g++.dg/concepts/pr84423-1.C
===================================================================
--- testsuite/g++.dg/concepts/pr84423-1.C	(nonexistent)
+++ testsuite/g++.dg/concepts/pr84423-1.C	(working copy)
@@ -0,0 +1,8 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fconcepts" }
+
+template<typename> using A = auto;  // { dg-error "30:.auto. not allowed in alias declaration" }
+
+template<template<typename> class> struct B {};
+
+B<A> b;
Index: testsuite/g++.dg/concepts/pr84423-2.C
===================================================================
--- testsuite/g++.dg/concepts/pr84423-2.C	(nonexistent)
+++ testsuite/g++.dg/concepts/pr84423-2.C	(working copy)
@@ -0,0 +1,18 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fconcepts" }
+
+using A = auto;  // { dg-error "11:.auto. not allowed in alias declaration" }
+
+using A1 = const auto;  // { dg-error "18:.auto. not allowed in alias declaration" }
+
+using A2 = volatile auto;  // { dg-error "21:.auto. not allowed in alias declaration" }
+
+using A3 = const volatile auto;  // { dg-error "27:.auto. not allowed in alias declaration" }
+
+typedef auto B;  // { dg-error "9:typedef declared .auto." }
+
+typedef const auto B1;  // { dg-error "15:typedef declared .auto." }
+
+typedef volatile auto B2;  // { dg-error "18:typedef declared .auto." }
+
+typedef const volatile auto B3;  // { dg-error "24:typedef declared .auto." }
Index: testsuite/g++.dg/cpp0x/auto39.C
===================================================================
--- testsuite/g++.dg/cpp0x/auto39.C	(revision 264985)
+++ testsuite/g++.dg/cpp0x/auto39.C	(working copy)
@@ -1,6 +1,6 @@
 // PR c++/58560
 // { dg-do compile { target c++11 } }
 
-typedef auto T;     // { dg-error "typedef declared 'auto'" }
+typedef auto T;     // { dg-error "9:typedef declared 'auto'" }
 
 void foo() { T(); }
Index: testsuite/g++.dg/cpp0x/auto9.C
===================================================================
--- testsuite/g++.dg/cpp0x/auto9.C	(revision 264985)
+++ testsuite/g++.dg/cpp0x/auto9.C	(working copy)
@@ -120,4 +120,4 @@ void qq (auto);		       // { dg-error "auto" "" {
 void qr (auto*);	       // { dg-error "auto" "" { target { ! concepts } } }
 
 // PR c++/46145
-typedef auto autot;		// { dg-error "auto" }
+typedef auto autot;		// { dg-error "9:typedef declared .auto." }
Index: testsuite/g++.dg/cpp1y/pr60384.C
===================================================================
--- testsuite/g++.dg/cpp1y/pr60384.C	(revision 264985)
+++ testsuite/g++.dg/cpp1y/pr60384.C	(working copy)
@@ -5,5 +5,5 @@ template<typename> int foo();
 
 struct A
 {
-  typedef auto foo<>();  // { dg-error "typedef declared 'auto'" }
+  typedef auto foo<>();  // { dg-error "11:typedef declared 'auto'" }
 };
Jason Merrill Oct. 9, 2018, 7:08 p.m. | #7
OK.
On Tue, Oct 9, 2018 at 1:49 PM Paolo Carlini <paolo.carlini@oracle.com> wrote:
>

> Hi,

>

> On 09/10/18 17:17, Jason Merrill wrote:

> > On Sat, Sep 29, 2018 at 3:27 PM Paolo Carlini <paolo.carlini@oracle.com> wrote:

> >> Hi again,

> >>

> >> On 9/28/18 9:15 PM, Paolo Carlini wrote:

> >>> Thanks. About the location, you are certainly right, but doesn't seem

> >>> trivial. Something we can do *now* is using

> >>> declspecs->locations[ds_typedef] and declspecs->locations[ds_alias],

> >>> but that gives us the location of the keyword 'typedef' and 'using',

> >>> respectively, whereas I think that we would like to have the location

> >>> of 'auto' itself. I could look into that as a follow-up piece work

> >> In fact, completing the work turned out to be easy: ensure that

> >> cp_parser_alias_declaration saves the location of the defining-type-id

> >> too and then consistently use locations[ds_type_spec] in the error

> >> messages. Tested x86_64-linux. Still Ok? ;)

> > Hmm, I think you need to look past any cv-qualifiers at the beginning

> > of the type-id.

>

> Ah, good point. The information is readily available in

> cp_parser_type_id thus we can simply return it to

> cp_parser_alias_declaration. I guess an alternate approach would be

> adding a pointer to the whole cp_decl_specifier_seq parameter to

> cp_parser_type_id (and cp_parser_type_id_1, etc), but that seems over

> killing to me.

>

> Thanks! Paolo.

>

> /////////////////////

>

Patch

Index: cp/decl.c
===================================================================
--- cp/decl.c	(revision 264687)
+++ cp/decl.c	(working copy)
@@ -11879,6 +11879,7 @@  grokdeclarator (const cp_declarator *declarator,
   /* If this is declaring a typedef name, return a TYPE_DECL.  */
   if (typedef_p && decl_context != TYPENAME)
     {
+      bool alias_p = decl_spec_seq_has_spec_p (declspecs, ds_alias);
       tree decl;
 
       /* This declaration:
@@ -11901,7 +11902,10 @@  grokdeclarator (const cp_declarator *declarator,
 
       if (type_uses_auto (type))
 	{
-	  error ("typedef declared %<auto%>");
+	  if (alias_p)
+	    error ("%<auto%> not allowed in alias declaration");
+	  else
+	    error ("typedef declared %<auto%>");
 	  type = error_mark_node;
 	}
 
@@ -11961,7 +11965,7 @@  grokdeclarator (const cp_declarator *declarator,
 		      inlinep, friendp, raises != NULL_TREE,
 		      declspecs->locations);
 
-      if (decl_spec_seq_has_spec_p (declspecs, ds_alias))
+      if (alias_p)
 	/* Acknowledge that this was written:
 	     `using analias = atype;'.  */
 	TYPE_DECL_ALIAS_P (decl) = 1;
Index: cp/pt.c
===================================================================
--- cp/pt.c	(revision 264687)
+++ cp/pt.c	(working copy)
@@ -7776,7 +7776,7 @@  convert_template_argument (tree parm,
   tree val;
   int is_type, requires_type, is_tmpl_type, requires_tmpl_type;
 
-  if (parm == error_mark_node)
+  if (parm == error_mark_node || error_operand_p (arg))
     return error_mark_node;
 
   /* Trivially convert placeholders. */
Index: testsuite/g++.dg/concepts/pr84423.C
===================================================================
--- testsuite/g++.dg/concepts/pr84423.C	(nonexistent)
+++ testsuite/g++.dg/concepts/pr84423.C	(working copy)
@@ -0,0 +1,8 @@ 
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fconcepts" }
+
+template<typename> using A = auto;  // { dg-error "alias declaration" }
+
+template<template<typename> class> struct B {};
+
+B<A> b;