c++: constrained variable template issues [PR98486]

This fixes some issues with constrained variable templates:

  - Constraints aren't checked when explicitly specializing a variable
    template.
  - Constraints aren't attached to a static data member template at
    parse time.
  - Constraints don't get propagated when (partially) instantiating a
    static data member template, so we need to make sure to look up
    constraints using the most general template during satisfaction.

	PR c++/98486

gcc/cp/ChangeLog:

	* constraint.cc (get_normalized_constraints_from_decl): Always
	look up constraints using the most general template.
	* decl.c (grokdeclarator): Set constraints on a static data
	member template.
	* pt.c (determine_specialization): Check constraints on a
	variable template.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-var-templ1.C: New test.
	* g++.dg/cpp2a/concepts-var-templ1a.C: New test.
	* g++.dg/cpp2a/concepts-var-templ1b.C: New test.

gcc/cp/constraint.cc

@@ -918,20 +918,22 @@ get_normalized_constraints_from_decl (tree d, bool diag = false)
       tmpl = most_general_template (tmpl);
   }
 
+  d = tmpl ? tmpl : decl;
+
   /* If we're not diagnosing errors, use cached constraints, if any.  */
   if (!diag)
-    if (tree *p = hash_map_safe_get (normalized_map, tmpl))
+    if (tree *p = hash_map_safe_get (normalized_map, d))
       return *p;
 
   tree norm = NULL_TREE;
-  if (tree ci = get_constraints (decl))
+  if (tree ci = get_constraints (d))
     {
       push_access_scope_guard pas (decl);
       norm = get_normalized_constraints_from_info (ci, tmpl, diag);
     }
 
   if (!diag)
-    hash_map_safe_put<hm_ggc> (normalized_map, tmpl, norm);
+    hash_map_safe_put<hm_ggc> (normalized_map, d, norm);
 
   return norm;
 }

gcc/cp/decl.c

@@ -13980,6 +13980,17 @@ grokdeclarator (const cp_declarator *declarator,
 		    if (declspecs->gnu_thread_keyword_p)
 		      SET_DECL_GNU_TLS_P (decl);
 		  }
+
+		/* Set the constraints on the declaration.  */
+		bool memtmpl = (processing_template_decl
+				> template_class_depth (current_class_type));
+		if (memtmpl)
+		  {
+		    tree tmpl_reqs
+		      = TEMPLATE_PARMS_CONSTRAINTS (current_template_parms);
+		    tree ci = build_constraints (tmpl_reqs, NULL_TREE);
+		    set_constraints (decl, ci);
+		  }
 	      }
 	    else
 	      {

gcc/cp/pt.c

@@ -2218,7 +2218,8 @@ determine_specialization (tree template_id,
       targs = coerce_template_parms (parms, explicit_targs, fns,
 				     tf_warning_or_error,
 				     /*req_all*/true, /*use_defarg*/true);
-      if (targs != error_mark_node)
+      if (targs != error_mark_node
+	  && constraints_satisfied_p (fns, targs))
         templates = tree_cons (targs, fns, templates);
     }
   else for (lkp_iterator iter (fns); iter; ++iter)

gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1.C

@@ -0,0 +1,9 @@
+// PR c++/98486
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+template<C<int>> int v;
+
+template<> int v<int>;
+template<> int v<char>; // { dg-error "match" }

gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1a.C

@@ -0,0 +1,14 @@
+// PR c++/98486
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+struct A {
+  template<C<int>> static int v;
+};
+
+template<> int A::v<int>;
+template<> int A::v<char>; // { dg-error "match" }
+
+int x = A::v<int>;
+int y = A::v<char>; // { dg-error "invalid" }

gcc/testsuite/g++.dg/cpp2a/concepts-var-templ1b.C

@@ -0,0 +1,15 @@
+// PR c++/98486
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept C = __is_same(T, U);
+
+template<class T>
+struct A {
+  template<C<T>> static int v;
+};
+
+template<> template<> int A<int>::v<int>;
+template<> template<> int A<int>::v<char>; // { dg-error "match" }
+
+int x = A<int>::v<int>;
+int y = A<int>::v<char>; // { dg-error "invalid" }