Re: [C++ RFC / Patch] PR 51213 ("access control under SFINAE")

[Jason Merrill <jason at redhat dot com>]

These patches fix the typedef11.C and friend13/15.C failures.  Each 
fixes a latent bug in the compiler.

1) We shouldn't do access control checking for typedefs used in the body 
of a function when the declaration is instantiated; we should wait until 
the body is instantiated.

2) We shouldn't try to do any access checking when deducing template 
arguments, that can wait until we call instantiate_template later in 
add_template_candidate_real, when we actually have a FUNCTION_DECL to 
compare to any friend declarations.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit 37c9b524e42df0b5843af5ceab1f958b9e17dfe4
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Jul 12 17:17:12 2012 +0200

    	* pt.c (instantiate_decl): Check typedefs access here.
    	(instantiate_template_1): Not here.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index fec88eb..95c6464 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -8334,7 +8334,7 @@ apply_late_template_attributes (tree *decl_p, tree attributes, int attr_flags,
 
 /* Perform (or defer) access check for typedefs that were referenced
    from within the template TMPL code.
-   This is a subroutine of instantiate_template and instantiate_class_template.
+   This is a subroutine of instantiate_decl and instantiate_class_template.
    TMPL is the template to consider and TARGS is the list of arguments of
    that template.  */
 
@@ -14380,12 +14380,6 @@ instantiate_template_1 (tree tmpl, tree orig_args, tsubst_flags_t complain)
   /* Now we know the specialization, compute access previously
      deferred.  */
   push_access_scope (fndecl);
-
-  /* Some typedefs referenced from within the template code need to be access
-     checked at template instantiation time, i.e now. These types were
-     added to the template at parsing time. Let's get those and perfom
-     the acces checks then.  */
-  perform_typedefs_access_check (DECL_TEMPLATE_RESULT (tmpl), targ_ptr);
   perform_deferred_access_checks ();
   pop_access_scope (fndecl);
   pop_deferring_access_checks ();
@@ -18395,6 +18389,13 @@ instantiate_decl (tree d, int defer_ok,
       /* Set up context.  */
       start_preparsed_function (d, NULL_TREE, SF_PRE_PARSED);
 
+      /* Some typedefs referenced from within the template code need to be
+	 access checked at template instantiation time, i.e now. These
+	 types were added to the template at parsing time. Let's get those
+	 and perform the access checks then.  */
+      perform_typedefs_access_check (DECL_TEMPLATE_RESULT (gen_tmpl),
+				     gen_args);
+
       /* Create substitution entries for the parameters.  */
       subst_decl = DECL_TEMPLATE_RESULT (template_for_substitution (d));
       tmpl_parm = DECL_ARGUMENTS (subst_decl);
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 0cacf74..a32e48a 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -1625,7 +1625,7 @@ finish_non_static_data_member (tree decl, tree object, tree qualifying_scope)
 /* If we are currently parsing a template and we encountered a typedef
    TYPEDEF_DECL that is being accessed though CONTEXT, this function
    adds the typedef to a list tied to the current template.
-   At tempate instantiatin time, that list is walked and access check
+   At template instantiation time, that list is walked and access check
    performed for each typedef.
    LOCATION is the location of the usage point of TYPEDEF_DECL.  */
 
diff --git a/gcc/testsuite/g++.dg/template/typedef11.C b/gcc/testsuite/g++.dg/template/typedef11.C
index c7c7c98..a08d7b3 100644
--- a/gcc/testsuite/g++.dg/template/typedef11.C
+++ b/gcc/testsuite/g++.dg/template/typedef11.C
@@ -18,8 +18,8 @@ template <int>
 int
 bar ()
 {
-  Beta<0>::Y i = 0;
-  return Alpha::X ();
+  Beta<0>::Y i = 0;		// { dg-error "within this context" }
+  return Alpha::X ();		// { dg-error "within this context" }
 }
 
-int i = bar<0> (); // { dg-error "within this context" }
+int i = bar<0> ();

commit 56a4aeb321d97093da7ac7b0cc4a4783adc83494
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Jul 12 12:20:36 2012 +0200

    	* pt.c (deduction_tsubst_fntype): Just suppress access checking.
    	(instantiate_template_1): Set DECL_TI_TEMPLATE before access checking.
    	(push_deduction_access_scope, pop_deduction_access_scope): Remove.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 72b0c4f..fec88eb 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -116,8 +116,6 @@ enum template_base_result {
 
 static void push_access_scope (tree);
 static void pop_access_scope (tree);
-static void push_deduction_access_scope (tree);
-static void pop_deduction_access_scope (tree);
 static bool resolve_overloaded_unification (tree, tree, tree, tree,
 					    unification_kind_t, int,
 					    bool);
@@ -14263,9 +14261,10 @@ deduction_tsubst_fntype (tree fn, tree targs, tsubst_flags_t complain)
 
   input_location = DECL_SOURCE_LOCATION (fn);
   ++deduction_depth;
-  push_deduction_access_scope (fn);
+  /* We will do access checks in instantiate_template.  */
+  push_deferring_access_checks (dk_deferred);
   r = tsubst (fntype, targs, complain, NULL_TREE);
-  pop_deduction_access_scope (fn);
+  pop_deferring_access_checks ();
   --deduction_depth;
 
   if (excessive_deduction_depth)
@@ -14374,6 +14373,10 @@ instantiate_template_1 (tree tmpl, tree orig_args, tsubst_flags_t complain)
   if (fndecl == error_mark_node)
     return error_mark_node;
 
+  /* The DECL_TI_TEMPLATE should always be the immediate parent
+     template, not the most general template.  */
+  DECL_TI_TEMPLATE (fndecl) = tmpl;
+
   /* Now we know the specialization, compute access previously
      deferred.  */
   push_access_scope (fndecl);
@@ -14387,10 +14390,6 @@ instantiate_template_1 (tree tmpl, tree orig_args, tsubst_flags_t complain)
   pop_access_scope (fndecl);
   pop_deferring_access_checks ();
 
-  /* The DECL_TI_TEMPLATE should always be the immediate parent
-     template, not the most general template.  */
-  DECL_TI_TEMPLATE (fndecl) = tmpl;
-
   /* If we've just instantiated the main entry point for a function,
      instantiate all the alternate entry points as well.  We do this
      by cloning the instantiation of the main entry point, not by
@@ -14413,36 +14412,6 @@ instantiate_template (tree tmpl, tree orig_args, tsubst_flags_t complain)
   return ret;
 }
 
-/* We're going to do deduction substitution on the type of TMPL, a function
-   template.  In C++11 mode, push into that access scope.  In C++03 mode,
-   disable access checking.  */
-
-static void
-push_deduction_access_scope (tree tmpl)
-{
-  if (cxx_dialect >= cxx0x)
-    {
-      int ptd = processing_template_decl;
-      push_access_scope (DECL_TEMPLATE_RESULT (tmpl));
-      /* Preserve processing_template_decl across push_to_top_level.  */
-      if (ptd && !processing_template_decl)
-	++processing_template_decl;
-    }
-  else
-    push_deferring_access_checks (dk_no_check);
-}
-
-/* And pop back out.  */
-
-static void
-pop_deduction_access_scope (tree tmpl)
-{
-  if (cxx_dialect >= cxx0x)
-    pop_access_scope (DECL_TEMPLATE_RESULT (tmpl));
-  else
-    pop_deferring_access_checks ();
-}
-
 /* PARM is a template parameter pack for FN.  Returns true iff
    PARM is used in a deducible way in the argument list of FN.  */
 
diff --git a/gcc/testsuite/g++.dg/template/sfinae6_neg.C b/gcc/testsuite/g++.dg/template/sfinae6_neg.C
index 9b7bdfd1..c238222 100644
--- a/gcc/testsuite/g++.dg/template/sfinae6_neg.C
+++ b/gcc/testsuite/g++.dg/template/sfinae6_neg.C
@@ -14,7 +14,7 @@ template<typename T> struct enable_if<false, T> { };
 template<typename F, typename T1, typename T2>
   typename enable_if<sizeof(create_a<F>()(create_a<T1>(), create_a<T2>()), 1),
 		     yes_type>::type
-  check_is_callable2(type<F>, type<T1>, type<T2>); // { dg-error "within this context" "" { target c++11 } }
+  check_is_callable2(type<F>, type<T1>, type<T2>);
 
 no_type check_is_callable2(...);