Fix PR c++/30044

Here is a more modest approach to fixing this PR.  Instead of updating
current_template_parms with each newly processed template parameter,
this patch just updates it with a "dummy" parameter level once per
parameter list.  So now in tsubst(), to fix the reported ICE we just
have to avoid substituting a template parameter if it corresponds to an
empty "dummy" argument level.

One caveat with this approach is that since template template decls will
now have dummy parameter levels in their DECL_TEMPLATE_PARMS fields, we
have to avoid emitting such dummy levels inside error messages when
printing template template parameters.  Otherwise the parameter B in

  template<template<class A> class B> struct Foo { };

would get printed in error messages as

  template<> template <class A> class B>

Two new test files are added in this version: shadow2.C, which checks
that we emit a shadowing error for identical template parameter names
across nested parameter lists, and error55.C, which checks that we
correctly emit template template decls in error messages.

With this approach the test case provided by Markus no longer takes
forever to compile because the added parameter lists are always empty so
when doing structural type comparison of a TEMPLATE_TEMPLATE_PARM there
is nothing extra to recurse into.

Does this approach seem sensible?

gcc/cp/ChangeLog:

	PR c++/30044
	* pt.c (begin_template_parm_list): Add a dummy parameter level
	to current_template_parms.
	(end_template_parm_list): Remove the dummy parameter level
	before adding the real one.
	(tsubst): Don't attempt to substitute for template parameters
	corresponding to a dummy argument level.
	(template_parms_to_args): Remove obsolete hack for
	giving template template arguments the proper level.
	(splite_late_return_type): Remove obsolete hack for giving
	template template arguments the proper level.
	* error.c (dump_template_decl): Don't print dummy template
	levels.

gcc/testsuite/ChangeLog

	PR c++/30044
	* g++.dg/cpp0x/auto45.C: New test.
	* g++.dg/template/pr30044.C: New test.
	* g++.dg/template/shadow2.C: New test.
	* g++.dg/template/error55.C: New test.
	* g++.dg/template/crash83.C: Accept any error string.
	* g++.dg/cpp0x/variadic18.C: Adjust to avoid shadowing template
	parameters.
	* g++.dg/cpp0x/variadic18.C: Likewise
	* g++.dg/template/canon-type-13.C: Likewise.
	* g++.old-deja/g++.pt/ttp42.C: Likewise.
	* g++.dg/torture/20070621-1.C: Likewise.
---
 gcc/cp/error.c                                |  7 ++++++
 gcc/cp/pt.c                                   | 32 +++++++++------------------
 gcc/testsuite/g++.dg/cpp0x/auto45.C           |  5 +++++
 gcc/testsuite/g++.dg/cpp0x/variadic18.C       |  2 +-
 gcc/testsuite/g++.dg/cpp0x/variadic19.C       |  2 +-
 gcc/testsuite/g++.dg/template/canon-type-13.C |  2 +-
 gcc/testsuite/g++.dg/template/crash83.C       |  2 +-
 gcc/testsuite/g++.dg/template/error55.C       |  8 +++++++
 gcc/testsuite/g++.dg/template/pr30044.C       | 14 ++++++++++++
 gcc/testsuite/g++.dg/template/shadow2.C       |  3 +++
 gcc/testsuite/g++.dg/torture/20070621-1.C     |  2 +-
 gcc/testsuite/g++.old-deja/g++.pt/ttp42.C     |  2 +-
 12 files changed, 54 insertions(+), 27 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/auto45.C
 create mode 100644 gcc/testsuite/g++.dg/template/error55.C
 create mode 100644 gcc/testsuite/g++.dg/template/pr30044.C
 create mode 100644 gcc/testsuite/g++.dg/template/shadow2.C

On Fri, Jun 26, 2015 at 7:40 AM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> Here is a more modest approach to fixing this PR.  Instead of updating
> current_template_parms with each newly processed template parameter,
> this patch just updates it with a "dummy" parameter level once per
> parameter list.  So now in tsubst(), to fix the reported ICE we just
> have to avoid substituting a template parameter if it corresponds to an
> empty "dummy" argument level.
>
> One caveat with this approach is that since template template decls will
> now have dummy parameter levels in their DECL_TEMPLATE_PARMS fields, we
> have to avoid emitting such dummy levels inside error messages when
> printing template template parameters.  Otherwise the parameter B in
>
>   template<template<class A> class B> struct Foo { };
>
> would get printed in error messages as
>
>   template<> template <class A> class B>
>
> Two new test files are added in this version: shadow2.C, which checks
> that we emit a shadowing error for identical template parameter names
> across nested parameter lists, and error55.C, which checks that we
> correctly emit template template decls in error messages.
>
> With this approach the test case provided by Markus no longer takes
> forever to compile because the added parameter lists are always empty so
> when doing structural type comparison of a TEMPLATE_TEMPLATE_PARM there
> is nothing extra to recurse into.
>
> Does this approach seem sensible?
>
> gcc/cp/ChangeLog:
>
>         PR c++/30044
>         * pt.c (begin_template_parm_list): Add a dummy parameter level
>         to current_template_parms.
>         (end_template_parm_list): Remove the dummy parameter level
>         before adding the real one.
>         (tsubst): Don't attempt to substitute for template parameters
>         corresponding to a dummy argument level.
>         (template_parms_to_args): Remove obsolete hack for
>         giving template template arguments the proper level.
>         (splite_late_return_type): Remove obsolete hack for giving
>         template template arguments the proper level.
>         * error.c (dump_template_decl): Don't print dummy template
>         levels.
>
> gcc/testsuite/ChangeLog
>
>         PR c++/30044
>         * g++.dg/cpp0x/auto45.C: New test.
>         * g++.dg/template/pr30044.C: New test.
>         * g++.dg/template/shadow2.C: New test.
>         * g++.dg/template/error55.C: New test.
>         * g++.dg/template/crash83.C: Accept any error string.
>         * g++.dg/cpp0x/variadic18.C: Adjust to avoid shadowing template
>         parameters.
>         * g++.dg/cpp0x/variadic18.C: Likewise
>         * g++.dg/template/canon-type-13.C: Likewise.
>         * g++.old-deja/g++.pt/ttp42.C: Likewise.
>         * g++.dg/torture/20070621-1.C: Likewise.
> ---
>  gcc/cp/error.c                                |  7 ++++++
>  gcc/cp/pt.c                                   | 32 +++++++++------------------
>  gcc/testsuite/g++.dg/cpp0x/auto45.C           |  5 +++++
>  gcc/testsuite/g++.dg/cpp0x/variadic18.C       |  2 +-
>  gcc/testsuite/g++.dg/cpp0x/variadic19.C       |  2 +-
>  gcc/testsuite/g++.dg/template/canon-type-13.C |  2 +-
>  gcc/testsuite/g++.dg/template/crash83.C       |  2 +-
>  gcc/testsuite/g++.dg/template/error55.C       |  8 +++++++
>  gcc/testsuite/g++.dg/template/pr30044.C       | 14 ++++++++++++
>  gcc/testsuite/g++.dg/template/shadow2.C       |  3 +++
>  gcc/testsuite/g++.dg/torture/20070621-1.C     |  2 +-
>  gcc/testsuite/g++.old-deja/g++.pt/ttp42.C     |  2 +-
>  12 files changed, 54 insertions(+), 27 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/cpp0x/auto45.C
>  create mode 100644 gcc/testsuite/g++.dg/template/error55.C
>  create mode 100644 gcc/testsuite/g++.dg/template/pr30044.C
>  create mode 100644 gcc/testsuite/g++.dg/template/shadow2.C
>
> diff --git a/gcc/cp/error.c b/gcc/cp/error.c
> index 96fa94d..b21befe 100644
> --- a/gcc/cp/error.c
> +++ b/gcc/cp/error.c
> @@ -1296,6 +1296,13 @@ dump_template_decl (cxx_pretty_printer *pp, tree t, int flags)
>           tree inner_parms = INNERMOST_TEMPLATE_PARMS (parms);
>           int len = TREE_VEC_LENGTH (inner_parms);
>
> +         if (len == 0)
> +           {
> +             /* Skip over the dummy template levels of a template template parm.  */
> +             gcc_assert (TREE_CODE (TREE_TYPE (t)) == TEMPLATE_TEMPLATE_PARM);
> +             continue;
> +           }
> +
>           pp_cxx_ws_string (pp, "template");
>           pp_cxx_begin_template_argument_list (pp);
>
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index fe5fc14..e7c35d3 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -658,6 +658,12 @@ begin_template_parm_list (void)
>    ++processing_template_decl;
>    ++processing_template_parmlist;
>    note_template_header (0);
> +
> +  /* Add a dummy parameter level while we process the parameter list.  */
> +  current_template_parms
> +    = tree_cons (size_int (processing_template_decl),
> +                make_tree_vec (0),
> +                current_template_parms);
>  }
>
>  /* This routine is called when a specialization is declared.  If it is
> @@ -3854,6 +3860,9 @@ end_template_parm_list (tree parms)
>    tree parm, next;
>    tree saved_parmlist = make_tree_vec (list_length (parms));
>
> +  /* Pop the dummy parameter level and add the real one.  */
> +  current_template_parms = TREE_CHAIN (current_template_parms);
> +
>    current_template_parms
>      = tree_cons (size_int (processing_template_decl),
>                  saved_parmlist, current_template_parms);
> @@ -3989,21 +3998,6 @@ template_parms_to_args (tree parms)
>         args = a;
>      }
>
> -    if (length > 1 && TREE_VEC_ELT (args, 0) == NULL_TREE)
> -      /* This can happen for template parms of a template template
> -        parameter, e.g:
> -
> -        template<template<class T, class U> class TT> struct S;
> -
> -        Consider the level of the parms of TT; T and U both have
> -        level 2; TT has no template parm of level 1. So in this case
> -        the first element of full_template_args is NULL_TREE. If we
> -        leave it like this TMPL_ARGS_DEPTH on args returns 1 instead
> -        of 2. This will make tsubst wrongly consider that T and U
> -        have level 1. Instead, let's create a dummy vector as the
> -        first element of full_template_args so that TMPL_ARGS_DEPTH
> -        returns the correct depth for args.  */
> -      TREE_VEC_ELT (args, 0) = make_tree_vec (1);
>    return args;
>  }
>
> @@ -12029,7 +12023,8 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
>         template_parm_level_and_index (t, &level, &idx);
>
>         levels = TMPL_ARGS_DEPTH (args);
> -       if (level <= levels)
> +       if (level <= levels
> +           && TREE_VEC_LENGTH (TMPL_ARGS_LEVEL (args, level)) > 0)
>           {
>             arg = TMPL_ARG (args, level, idx);
>
> @@ -22394,11 +22389,6 @@ splice_late_return_type (tree type, tree late_return_type)
>      return type;
>    argvec = make_tree_vec (1);
>    TREE_VEC_ELT (argvec, 0) = late_return_type;
> -  if (processing_template_parmlist)
> -    /* For a late-specified return type in a template type-parameter, we
> -       need to add a dummy argument level for its parmlist.  */
> -    argvec = add_to_template_args
> -      (make_tree_vec (processing_template_parmlist), argvec);
>    if (current_template_parms)
>      argvec = add_to_template_args (current_template_args (), argvec);
>    return tsubst (type, argvec, tf_warning_or_error, NULL_TREE);
> diff --git a/gcc/testsuite/g++.dg/cpp0x/auto45.C b/gcc/testsuite/g++.dg/cpp0x/auto45.C
> new file mode 100644
> index 0000000..09e9f44
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/auto45.C
> @@ -0,0 +1,5 @@
> +// Addendum to auto23.C, now with nested template parameter lists
> +// { dg-do compile { target c++11 } }
> +
> +template<template <auto f()->int> class> struct A { };
> +template<template <template <auto f()->int> class> class> struct B { };
> diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic18.C b/gcc/testsuite/g++.dg/cpp0x/variadic18.C
> index fc0e2dd..57fdc86 100644
> --- a/gcc/testsuite/g++.dg/cpp0x/variadic18.C
> +++ b/gcc/testsuite/g++.dg/cpp0x/variadic18.C
> @@ -1,7 +1,7 @@
>  // { dg-do compile { target c++11 } }
>  template<typename...> class tuple { };
>
> -template<typename T, template<typename T> class... Metafunctions>
> +template<typename T, template<typename U> class... Metafunctions>
>  struct apply_all
>  {
>    typedef tuple<typename Metafunctions<T>::type...> type;
> diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic19.C b/gcc/testsuite/g++.dg/cpp0x/variadic19.C
> index 0ae2672..3be9bb0 100644
> --- a/gcc/testsuite/g++.dg/cpp0x/variadic19.C
> +++ b/gcc/testsuite/g++.dg/cpp0x/variadic19.C
> @@ -4,7 +4,7 @@ struct tuple {
>    static const int value = 0;
>  };
>
> -template<typename T, template<class T> class... Metafunctions>
> +template<typename T, template<class U> class... Metafunctions>
>  struct tuple<Metafunctions<T>...> {
>    static const int value = 1;
>  };
> diff --git a/gcc/testsuite/g++.dg/template/canon-type-13.C b/gcc/testsuite/g++.dg/template/canon-type-13.C
> index 4f3702b..5a8d37d 100644
> --- a/gcc/testsuite/g++.dg/template/canon-type-13.C
> +++ b/gcc/testsuite/g++.dg/template/canon-type-13.C
> @@ -11,7 +11,7 @@ struct S1
>  {
>  };
>
> -template<class T, template<class T>  class A, template<class T>  class B = A>
> +template<class T, template<class U>  class A, template<class U>  class B = A>
>  struct C
>  {
>    B<T> m;
> diff --git a/gcc/testsuite/g++.dg/template/crash83.C b/gcc/testsuite/g++.dg/template/crash83.C
> index b83dd21..7dcbed9 100644
> --- a/gcc/testsuite/g++.dg/template/crash83.C
> +++ b/gcc/testsuite/g++.dg/template/crash83.C
> @@ -2,4 +2,4 @@
>
>  template<int> struct A {};
>
> -template<typename = class A<0>: > struct B {}; // { dg-error "explicit specialization|expected" }
> +template<typename = class A<0>: > struct B {}; // { dg-error "" }
> diff --git a/gcc/testsuite/g++.dg/template/error55.C b/gcc/testsuite/g++.dg/template/error55.C
> new file mode 100644
> index 0000000..41f9595
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/error55.C
> @@ -0,0 +1,8 @@
> +// Check that template template parameters get printed properly in error
> +// messages.
> +
> +template <template <class A> class B>
> +struct Y
> +{
> +  B<5> y;  // { dg-error "for 'template<class A> class B'" }
> +};
> diff --git a/gcc/testsuite/g++.dg/template/pr30044.C b/gcc/testsuite/g++.dg/template/pr30044.C
> new file mode 100644
> index 0000000..415e6f0
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/pr30044.C
> @@ -0,0 +1,14 @@
> +// PR c++/30044
> +
> +template <typename T1, typename T2, template <T2> class Comp, class Result = Comp<1> >
> +struct sort { };
> +
> +
> +template <typename Type, template <Type, Type> class Comp, class Result = Comp<1, 2> >
> +struct sort2 { };
> +
> +template <typename Type, template <int, Type> class Comp, class Result = Comp<1, 2> >
> +struct sort3 { };
> +
> +template <template <typename T1, typename T2, template <T2> class Comp, class Result = Comp<1> > class Foo>
> +struct sort4 { };
> diff --git a/gcc/testsuite/g++.dg/template/shadow2.C b/gcc/testsuite/g++.dg/template/shadow2.C
> new file mode 100644
> index 0000000..7f6a6dc
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/shadow2.C
> @@ -0,0 +1,3 @@
> +template <class A, // { dg-error "shadows template parm 'class A'" }
> +          template <class A> class B> // { dg-error "declaration of 'class A'" }
> +class X;
> diff --git a/gcc/testsuite/g++.dg/torture/20070621-1.C b/gcc/testsuite/g++.dg/torture/20070621-1.C
> index 15d1ac7..9bd8cc3 100644
> --- a/gcc/testsuite/g++.dg/torture/20070621-1.C
> +++ b/gcc/testsuite/g++.dg/torture/20070621-1.C
> @@ -89,7 +89,7 @@ namespace __gnu_test {
>          SharedInfo->first=ptr;
>        }
>      };
> -    template <class T, template<class T> class ItType>   struct test_container   {
> +    template <class T, template<class U> class ItType>   struct test_container   {
>        typename ItType<T>::ContainerType bounds;
>        test_container(T* _first, T* _last):bounds(_first, _last)     {
>    }
> diff --git a/gcc/testsuite/g++.old-deja/g++.pt/ttp42.C b/gcc/testsuite/g++.old-deja/g++.pt/ttp42.C
> index 53bdae1..a2ac239 100644
> --- a/gcc/testsuite/g++.old-deja/g++.pt/ttp42.C
> +++ b/gcc/testsuite/g++.old-deja/g++.pt/ttp42.C
> @@ -1,5 +1,5 @@
>  // { dg-do run  }
> -template <class T, template <class T> class C>
> +template <class T, template <class U> class C>
>  struct X
>  {};
>
> --
> 2.5.0.rc0.5.g91e10c5.dirty
>

Ping.

OK, thanks.

Jason