c++: template keyword accepted before destructor names [PR94336]

This came up on the C++ core list recently.  We don't diagnose the case
when 'template' is followed by a destructor name which is not permitted
by [temp.names]/5.

	PR c++/94336 - template keyword accepted before destructor names.
	* parser.c (cp_parser_unqualified_id): Give an error when 'template'
	is followed by a destructor name.

	* g++.dg/template/template-keyword2.C: New test.

gcc/cp/ChangeLog

@@ -1,3 +1,9 @@
+2020-03-26  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94336 - template keyword accepted before destructor names.
+	* parser.c (cp_parser_unqualified_id): Give an error when 'template'
+	is followed by a destructor name.
+
 2020-03-27  Patrick Palka  <ppalka@redhat.com>
 
 	* decl.c (compute_array_index_type_loc): Remove redundant

gcc/cp/parser.c

@@ -6068,6 +6068,15 @@ cp_parser_unqualified_id (cp_parser* parser,
 	      cp_lexer_consume_token (parser->lexer);
 	    return error_mark_node;
 	  }
+	if (template_keyword_p)
+	  {
+	    if (!cp_parser_uncommitted_to_tentative_parse_p (parser))
+	      error_at (tilde_loc, "%<template%> keyword not permitted in "
+			"destructor name");
+	    cp_parser_simulate_error (parser);
+	    return error_mark_node;
+	  }
+
 	gcc_assert (!scope || TYPE_P (scope));
 
 	token = cp_lexer_peek_token (parser->lexer);

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2020-03-26  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94336 - template keyword accepted before destructor names.
+	* g++.dg/template/template-keyword2.C: New test.
+
 2020-03-27 Iain Sandoe <iain@sandoe.co.uk>
 
 	* g++.dg/coroutines/torture/symmetric-transfer-00-basic.C:

gcc/testsuite/g++.dg/template/template-keyword2.C

@@ -0,0 +1,5 @@
+// PR c++/94336 - template keyword accepted before destructor names.
+
+template<typename T> void f(T *p) { p->template ~X(); } // { dg-error ".template. keyword not permitted in destructor name" }
+template<typename T> struct X {};
+void g(X<int> *p) { f(p); }