[PATCH] Fix PR c++/30044

[Patrick Palka <patrick at parcs dot ath dot cx>]

The crux of the issue causing PR 30044 is that, in the middle of
processing a template parameter list, current_template_parms is not
up-to-date.  This causes problems particularly when we attempt to
instantiate a type that's defined within the very parameter list we are
processing.  Of course, more details to follow...

When processing the default template argument C<1> in (this is not the
reproducer in the PR but it better exhibits the same problem)

  template <class A, class B, template <B> class C, class D = C<1> >
  struct Z { };

we try to "instantiate" B with itself before the parameter list that B
resides has been finished.  At that point B is not even in
current_template_parms because we only update current_template_parms
when the entire parameter list is finished.  So when tsubst gets called
on B with an incomplete template argument list (because
current_template_parms hasn't been updated), tsubst ICEs with an
out-of-bounds error when trying to look up the template argument to
substitute for B, which has level=1 and index=1.

[ Note that we don't ICE for the similar test case

    template <class B, template <B> class C, class D = C<1> >
    struct Z { };

  because of a hack in template_parms_to_args() to add a dummy argument
  corresponding to level=1 and index=0 in the template argument list of a
  template template.  Here tsubst() has to look up the argument
  corresponding to B, which now has level=1 and index=0.  The lookup
  succeeds (returning NULL_TREE) and tsubst proceeds. ]

To fix this PR, this patch attempts to more frequently update
current_template_parms.  Instead of updating current_template_parms only
after the whole parameter list has been processed, this patch makes
current_template_parms get updated as soon as each template parameter is
processed.

Aside from directly fixing the PR, this approach allows us to remove two
now-obsolete hacks (there may be more) which attempted to work around
this delay in updating.  One hack is in the aforementioned
template_parms_to_args() and another is in splite_lat_return_type().

As a plus, we now detect shadowing of template variables across nested
template parameter lists, e.g.

   template <typename T, template <typename T> class> struct A { };

and now we no longer bogusly error out on late-specified return types
inside nested template parameter lists:

    template <template <auto f()->int> class> struct A { };

[ We can't use vec_grow() (which uses ggc_realloc()) to update
  current_template_parms because of sharing issues that I haven't
  investigated deeply.  ]

[ In check_default_tmpl_args we now have to account for nested template
  parameter lists the same way we account for template class depth, so
  that we don't inspect default template args not belonging to the nested
  parameter list we just finished.  last_level_to_check now defaults to 1
  instead of 0 since template "level"s are 1-based anyway.  ]

Does this approach make sense?

OK to install after bootstrap + regtesting succeeds?

gcc/cp/ChangeLog:

	* parser.c (cp_parser_template_parameter_list): Update
	current_template_parms right after processing a paramater.
	* pt.c (template_parms_to_args): Remove obsolete hack for
	giving template template arguments the proper level.
	(check_default_tmpl_args): Account for tested template
	parameter_lists.
	(splite_late_return_type): Remove obsolete hack for giving
	template template arguments the proper level.

gcc/testsuite/ChangeLog

	* g++.dg/cpp0x/auto45.C: New test.
	* g++.dg/template/pr30044.C: New test.
	* g++.dg/template/crash83.C: Accept any error string.
	* g++.dg/cpp0x/variadic18.C: Adjust to not shadow template
	parameters.
	* g++.dg/cpp0x/variadic18.C: Likewise
	* g++.dg/template/canon-type-13.C: Likewise.
	* g++.old-deja/g++.pt/ttp42.C: Likewise.
---
 gcc/cp/parser.c                               | 25 ++++++++++++++++++++
 gcc/cp/pt.c                                   | 33 ++++++++-------------------
 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/pr30044.C       | 14 ++++++++++++
 gcc/testsuite/g++.old-deja/g++.pt/ttp42.C     |  2 +-
 9 files changed, 58 insertions(+), 29 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/auto45.C
 create mode 100644 gcc/testsuite/g++.dg/template/pr30044.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 5fdb2a7..d0a3c09 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -13259,6 +13259,11 @@ cp_parser_template_parameter_list (cp_parser* parser)
 
   begin_template_parm_list ();
 
+  current_template_parms
+    = tree_cons (size_int (processing_template_decl),
+		 make_tree_vec (0),
+		 current_template_parms);
+
   /* The loop below parses the template parms.  We first need to know
      the total number of template parms to be able to compute proper
      canonical types of each dependent type. So after the loop, when
@@ -13271,6 +13276,7 @@ cp_parser_template_parameter_list (cp_parser* parser)
       bool is_non_type;
       bool is_parameter_pack;
       location_t parm_loc;
+      tree parameter_vec;
 
       /* Parse the template-parameter.  */
       parm_loc = cp_lexer_peek_token (parser->lexer)->location;
@@ -13295,8 +13301,27 @@ cp_parser_template_parameter_list (cp_parser* parser)
 	break;
       /* Otherwise, consume the `,' token.  */
       cp_lexer_consume_token (parser->lexer);
+
+      /* Add the parameter we just processed to current_template_parms.  */
+
+      parameter_vec = make_tree_vec
+	(TREE_VEC_LENGTH (TREE_VALUE (current_template_parms)) + 1);
+
+      for (int i = 0; i < TREE_VEC_LENGTH (parameter_vec) - 1; i++)
+	TREE_VEC_ELT (parameter_vec, i)
+	  = TREE_VEC_ELT (TREE_VALUE (current_template_parms), i);
+
+      TREE_VEC_ELT (parameter_vec, TREE_VEC_LENGTH (parameter_vec) - 1)
+	= tree_last (parameter_list);
+
+      current_template_parms
+	= tree_cons (TREE_PURPOSE (current_template_parms),
+		     parameter_vec,
+		     TREE_CHAIN (current_template_parms));
     }
 
+  current_template_parms = TREE_CHAIN (current_template_parms);
+
   return end_template_parm_list (parameter_list);
 }
 
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 7f04fe6..d1eb833 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -3990,21 +3990,6 @@ 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;
 }
 
@@ -4647,6 +4632,9 @@ check_default_tmpl_args (tree decl, tree parms, bool is_primary,
   else
     msg = G_("default argument for template parameter for class enclosing %qD");
 
+  /* By default check everything.  */
+  last_level_to_check = 1;
+
   if (current_class_type && TYPE_BEING_DEFINED (current_class_type))
     /* If we're inside a class definition, there's no need to
        examine the parameters to the class itself.  On the one
@@ -4656,10 +4644,12 @@ check_default_tmpl_args (tree decl, tree parms, bool is_primary,
 	 struct S { template <class U> void f(U); };
        Here the default argument for `S' has no bearing on the
        declaration of `f'.  */
-    last_level_to_check = template_class_depth (current_class_type) + 1;
-  else
-    /* Check everything.  */
-    last_level_to_check = 0;
+    last_level_to_check += template_class_depth (current_class_type);
+
+  if (processing_template_parmlist)
+    /* Likewise for parameters outside of the nested parameter list we have
+       just finished defining.  */
+    last_level_to_check += processing_template_parmlist;
 
   for (parm_level = parms;
        parm_level && TMPL_PARMS_DEPTH (parm_level) >= last_level_to_check;
@@ -22348,11 +22338,6 @@ 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..5f539a2
--- /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 A { };
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/pr30044.C b/gcc/testsuite/g++.dg/template/pr30044.C
new file mode 100644
index 0000000..c1d0d29
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr30044.C
@@ -0,0 +1,14 @@
+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++.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
 {};
 
-- 
2.4.3.413.ga5fe668