commit a2223328af8276d1796501e8706ca3c6b559eff6
Author: Jason Merrill <jason@redhat.com>
Date: Mon Jun 4 09:41:04 2018 +0200
PR c++/85765 - SFINAE and non-type default template arg.
* pt.c (type_unification_real): Do full semantic processing if
substituting a partial args list replaces all template parms.
@@ -20387,8 +20387,6 @@ type_unification_real (tree tparms,
location_t save_loc = input_location;
if (DECL_P (parm))
input_location = DECL_SOURCE_LOCATION (parm);
- if (saw_undeduced == 1)
- ++processing_template_decl;
if (saw_undeduced == 1
&& TREE_CODE (parm) == PARM_DECL
@@ -20396,11 +20394,14 @@ type_unification_real (tree tparms,
{
/* The type of this non-type parameter depends on undeduced
parameters. Don't try to use its default argument yet,
+ since we might deduce an argument for it on the next pass,
but do check whether the arguments we already have cause
substitution failure, so that that happens before we try
later default arguments (78489). */
+ ++processing_template_decl;
tree type = tsubst (TREE_TYPE (parm), full_targs, complain,
NULL_TREE);
+ --processing_template_decl;
if (type == error_mark_node)
arg = error_mark_node;
else
@@ -20408,10 +20409,27 @@ type_unification_real (tree tparms,
}
else
{
- arg = tsubst_template_arg (arg, full_targs, complain, NULL_TREE);
+ tree substed = NULL_TREE;
+ if (saw_undeduced == 1 && processing_template_decl == 0)
+ {
+ /* First instatiate in template context, in case we still
+ depend on undeduced template parameters. */
+ ++processing_template_decl;
+ substed = tsubst_template_arg (arg, full_targs, complain,
+ NULL_TREE);
+ --processing_template_decl;
+ if (substed != error_mark_node
+ && !uses_template_parms (substed))
+ /* We replaced all the tparms, substitute again out of
+ template context. */
+ substed = NULL_TREE;
+ }
+ if (!substed)
+ substed = tsubst_template_arg (arg, full_targs, complain,
+ NULL_TREE);
- if (!uses_template_parms (arg))
- arg = convert_template_argument (parm, arg, full_targs,
+ if (!uses_template_parms (substed))
+ arg = convert_template_argument (parm, substed, full_targs,
complain, i, NULL_TREE);
else if (saw_undeduced == 1)
arg = NULL_TREE;
@@ -20419,8 +20437,6 @@ type_unification_real (tree tparms,
arg = error_mark_node;
}
- if (saw_undeduced == 1)
- --processing_template_decl;
input_location = save_loc;
*checks = get_deferred_access_checks ();
pop_deferring_access_checks ();
new file mode 100644
@@ -0,0 +1,18 @@
+// PR c++/85765
+// { dg-do compile { target c++11 } }
+
+struct il { il(); il(const il&); };
+
+int* begin(il);
+
+template<class T> T&& declval();
+
+template<class T, class U = decltype(begin(declval<T&>())), decltype(*U(),0) = 0>
+U g(T& t, long) { return begin(t); } // #1
+
+template<class T>
+int g(T& t, ...); // #2
+
+volatile il a;
+
+auto n = g(a, 0); // calls #1 and ends with a hard error, should call #2
My patch for 84785 started setting processing_template_decl while substituting into a default template argument that might use template parameters we don't yet have arguments for. That broke this testcase because when processing_template_decl is set, we don't actually try to perform the conversion: /* In a template, there is no need to perform all of the work that is normally done. We are only interested in the type of the call expression, i.e., the return type of the function. Any semantic errors will be deferred until the template is instantiated. */ But in this case we aren't actually in a template, so we want to get the error for SFINAE. With this patch, if the initial substitution replaces all template parameters, we then do a full substitution. Tested x86_64-pc-linux-gnu, applying to trunk.