Class template argument deduction refinements

	* call.c (joust): Move deduction guide tiebreaker down.
	* decl.c (start_decl_1, cp_finish_decl, grokdeclarator): Allow class
	deduction with no initializer.
	* pt.c (build_deduction_guide): Handle implicit default/copy ctor.
	(do_class_deduction): Use that rather than special case.
	(do_auto_deduction): Handle null initializer.

From-SVN: r245796

gcc/cp/ChangeLog

+2017-02-28  Jason Merrill  <jason@redhat.com>
+
+	Class template argument deduction refinements
+	* call.c (joust): Move deduction guide tiebreaker down.
+	* decl.c (start_decl_1, cp_finish_decl, grokdeclarator): Allow class
+	deduction with no initializer.
+	* pt.c (build_deduction_guide): Handle implicit default/copy ctor.
+	(do_class_deduction): Use that rather than special case.
+	(do_auto_deduction): Handle null initializer.
+
 2017-02-28  Jakub Jelinek  <jakub@redhat.com>
 
 	* decl.c (find_decomp_class_base): Use cond ? G_("...") : G_("...")

gcc/cp/call.c

@@ -9670,18 +9670,6 @@ joust (struct z_candidate *cand1, struct z_candidate *cand2, bool warn,
 	return winner;
     }
 
-  /* F1 is generated from a deduction-guide (13.3.1.8) and F2 is not */
-  if (deduction_guide_p (cand1->fn))
-    {
-      gcc_assert (deduction_guide_p (cand2->fn));
-      /* We distinguish between candidates from an explicit deduction guide and
-	 candidates built from a constructor based on DECL_ARTIFICIAL.  */
-      int art1 = DECL_ARTIFICIAL (cand1->fn);
-      int art2 = DECL_ARTIFICIAL (cand2->fn);
-      if (art1 != art2)
-	return art2 - art1;
-    }
-
   /* or, if not that,
      F1 is a non-template function and F2 is a template function
      specialization.  */
@@ -9719,6 +9707,18 @@ joust (struct z_candidate *cand1, struct z_candidate *cand2, bool warn,
 	return winner;
     }
 
+  /* F1 is generated from a deduction-guide (13.3.1.8) and F2 is not */
+  if (deduction_guide_p (cand1->fn))
+    {
+      gcc_assert (deduction_guide_p (cand2->fn));
+      /* We distinguish between candidates from an explicit deduction guide and
+	 candidates built from a constructor based on DECL_ARTIFICIAL.  */
+      int art1 = DECL_ARTIFICIAL (cand1->fn);
+      int art2 = DECL_ARTIFICIAL (cand2->fn);
+      if (art1 != art2)
+	return art2 - art1;
+    }
+
   /* or, if not that, F2 is from a using-declaration, F1 is not, and the
      conversion sequences are equivalent.
      (proposed in http://lists.isocpp.org/core/2016/10/1142.php) */

gcc/cp/decl.c

@@ -5238,13 +5238,15 @@ start_decl_1 (tree decl, bool initialized)
   else if (aggregate_definition_p && !complete_p)
     {
       if (type_uses_auto (type))
-	gcc_unreachable ();
+	gcc_assert (CLASS_PLACEHOLDER_TEMPLATE (type));
       else
-	error ("aggregate %q#D has incomplete type and cannot be defined",
-	       decl);
-      /* Change the type so that assemble_variable will give
-	 DECL an rtl we can live with: (mem (const_int 0)).  */
-      type = TREE_TYPE (decl) = error_mark_node;
+	{
+	  error ("aggregate %q#D has incomplete type and cannot be defined",
+		 decl);
+	  /* Change the type so that assemble_variable will give
+	     DECL an rtl we can live with: (mem (const_int 0)).  */
+	  type = TREE_TYPE (decl) = error_mark_node;
+	}
     }
 
   /* Create a new scope to hold this declaration if necessary.
@@ -6816,14 +6818,17 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
 	      return;
 	    }
 
-	  gcc_unreachable ();
+	  gcc_assert (CLASS_PLACEHOLDER_TEMPLATE (auto_node));
 	}
       d_init = init;
-      if (TREE_CODE (d_init) == TREE_LIST
-	  && !CLASS_PLACEHOLDER_TEMPLATE (auto_node))
-	d_init = build_x_compound_expr_from_list (d_init, ELK_INIT,
-						  tf_warning_or_error);
-      d_init = resolve_nondeduced_context (d_init, tf_warning_or_error);
+      if (d_init)
+	{
+	  if (TREE_CODE (d_init) == TREE_LIST
+	      && !CLASS_PLACEHOLDER_TEMPLATE (auto_node))
+	    d_init = build_x_compound_expr_from_list (d_init, ELK_INIT,
+						      tf_warning_or_error);
+	  d_init = resolve_nondeduced_context (d_init, tf_warning_or_error);
+	}
       enum auto_deduction_context adc = adc_variable_type;
       if (VAR_P (decl) && DECL_DECOMPOSITION_P (decl))
 	adc = adc_decomp_type;
@@ -12323,19 +12328,12 @@ grokdeclarator (const cp_declarator *declarator,
 
     if (VAR_P (decl) && !initialized)
       if (tree auto_node = type_uses_auto (type))
-	{
-	  location_t loc = declspecs->locations[ds_type_spec];
-	  if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node))
-	    {
-	      error_at (loc, "invalid use of template-name %qE without an "
-			"argument list", tmpl);
-	      inform (loc, "class template argument deduction "
-		      "requires an initializer");
-	    }
-	  else
+	if (!CLASS_PLACEHOLDER_TEMPLATE (auto_node))
+	  {
+	    location_t loc = declspecs->locations[ds_type_spec];
 	    error_at (loc, "declaration of %q#D has no initializer", decl);
-	  TREE_TYPE (decl) = error_mark_node;
-	}
+	    TREE_TYPE (decl) = error_mark_node;
+	  }
 
     if (storage_class == sc_extern && initialized && !funcdef_flag)
       {

gcc/testsuite/g++.dg/cpp1z/class-deduction17.C

+// { dg-options -std=c++1z }
+
+#include <initializer_list>
+template <class T>
+struct A
+{
+  A (std::initializer_list<T>);
+};
+
+A a{1,2};
+

gcc/testsuite/g++.dg/cpp1z/class-deduction25.C

@@ -15,10 +15,10 @@ template<class T> struct A {
 template<class T, int N = remove_ref_t<T>::value> A(T&&, int*) -> A<T>; //#3
 
 A a{1,0}; // uses #1 to deduce A<int> and initializes with #1
-A b{a,0}; // uses #3 (not #2) to deduce A<A<int>&> and initializes with #1
+A b{a,0}; // uses #2 to deduce A<int> and initializes with #2
 
 template <class,class> struct same;
 template <class T> struct same<T,T> {};
 
 same<decltype(a),A<int>> s1;
-same<decltype(b),A<A<int>&>> s2;
+same<decltype(b),A<int>> s2;

gcc/testsuite/g++.dg/cpp1z/class-deduction30.C

@@ -3,4 +3,4 @@
 template <class T = void> struct A { };
 
 A a{};
-
+A a2;

gcc/testsuite/g++.dg/cpp1z/class-deduction31.C

+// { dg-options -std=c++1z }
+
+template <class T> struct A {
+  A(T); // #1
+  A(const A&); // #2
+};
+
+template <class T> A(T) -> A<T>;  // #3
+
+A a (42); // uses #3 to deduce A<int> and initializes with #1
+A b = a;  // uses #2 (not #3) to deduce A<int> and initializes with #2; #2 is more specialized
+
+template <class T> A(A<T>) -> A<A<T>>;  // #4
+
+A b2 = a;  // uses #4 to deduce A<A<int>> and initializes with #1; #4 is as specialized as #2
+
+template <class,class> struct same;
+template <class T> struct same<T,T> {};
+
+same<decltype(a),A<int>> s1;
+same<decltype(b),A<int>> s2;
+same<decltype(b2),A<A<int>>> s3;

gcc/testsuite/g++.dg/cpp1z/class-deduction32.C

+// { dg-options -std=c++1z }
+
+#include <initializer_list>
+
+std::initializer_list l { 1, 2, 3 };

gcc/testsuite/g++.dg/parse/error15.C

@@ -10,12 +10,13 @@ namespace N
   int K;
 }
 
-N::A f2;              // { dg-error "1:invalid use of template-name 'N::A' without an argument list" }
+N::A f2;              // { dg-error "1:invalid use of template-name 'N::A' without an argument list" "" { target c++14_down } }
+				// { dg-error "deduction|no match" "" { target c++1z } .-1 }
 N::INVALID f3;        // { dg-error "4:'INVALID' in namespace 'N' does not name a type" }
 N::C::INVALID f4;     // { dg-error "7:'INVALID' in 'struct N::C' does not name a type" }
 N::K f6;              // { dg-error "4:'K' in namespace 'N' does not name a type" }
 typename N::A f7;
-// { dg-error "13:invalid use of template-name 'N::A' without an argument list" "13" { target *-*-* } 17 }
+// { dg-error "13:invalid use of template-name 'N::A' without an argument list" "13" { target *-*-* } .-1 }
 
 struct B
 {
@@ -24,7 +25,7 @@ struct B
   N::C::INVALID f4;   // { dg-error "9:'INVALID' in 'struct N::C' does not name a type" }
   N::K f6;            // { dg-error "6:'K' in namespace 'N' does not name a type" }
   typename N::A f7;
-// { dg-error "15:invalid use of template-name 'N::A' without an argument list" "15" { target *-*-* } 26 }
+// { dg-error "15:invalid use of template-name 'N::A' without an argument list" "15" { target *-*-* } .-1 }
 };
 
 template <int>
@@ -36,5 +37,3 @@ struct C
   N::K f6;            // { dg-error "6:'K' in namespace 'N' does not name a type" }
   typename N::A f7;   // { dg-error "15:invalid use of template-name 'N::A' without an argument list" }
 };
-
-// { dg-bogus "bogus excess errors in declaration" "bogus excess errors in declaration" { target *-*-* } 17 }

gcc/testsuite/g++.dg/template/error52.C

@@ -9,11 +9,11 @@ namespace H {
     struct B {};
     }
 
-A a;             // { dg-error "template" }
-H::B b;          // { dg-error "template" }
+A a;             // { dg-error "template|no match" }
+H::B b;          // { dg-error "template|no match" }
 
 int main() {
-    A a;         // { dg-error "template" }
-    H::B b;      // { dg-error "template" }
+    A a;         // { dg-error "template|no match" }
+    H::B b;      // { dg-error "template|no match" }
     return 0;
     }