re PR c++/79790 ([C++17] ICE class template argument deduction failed)

/cp
2017-08-04  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/79790
	* pt.c (do_class_deduction): Handle the case of no viable implicit
	deduction guides; simplify the code generating implicit deduction
	guides.

/testsuite
2017-08-04  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/79790
	* g++.dg/cpp1z/class-deduction42.C: New.

From-SVN: r250882

gcc/cp/ChangeLog

+2017-08-04  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/79790
+	* pt.c (do_class_deduction): Handle the case of no viable implicit
+	deduction guides; simplify the code generating implicit deduction
+	guides.
+
 2017-08-03  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/71440

gcc/cp/pt.c

@@ -25452,11 +25452,7 @@ do_class_deduction (tree ptype, tree tmpl, tree init, int flags,
       if (gtype)
 	{
 	  tree guide = build_deduction_guide (gtype, outer_args, complain);
-	  if ((flags & LOOKUP_ONLYCONVERTING)
-	      && DECL_NONCONVERTING_P (STRIP_TEMPLATE (guide)))
-	    elided = true;
-	  else
-	    cands = lookup_add (guide, cands);
+	  cands = lookup_add (guide, cands);
 	}
     }
 
@@ -25467,6 +25463,12 @@ do_class_deduction (tree ptype, tree tmpl, tree init, int flags,
 	     "user-declared constructors", type);
       return error_mark_node;
     }
+  else if (!cands && call == error_mark_node)
+    {
+      error ("cannot deduce template arguments of %qT, as it has no viable "
+	     "deduction guides", type);
+      return error_mark_node;
+    }
 
   if (call == error_mark_node)
     {

gcc/testsuite/ChangeLog

+2017-08-04  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/79790
+	* g++.dg/cpp1z/class-deduction42.C: New.
+
 2017-08-04  Yury Gribov  <tetra2005@gmail.com>
 
 	PR tree-optimization/57371