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c++: Better diagnostic for decltype(auto) in C++11 [PR96103]

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If you try to use decltype(auto) in C++11, we emit obscure

  error: expected primary-expression before 'auto'

giving the user no hint as to what's wrong.  This patch improves that
diagnostic.  Since we've been giving an error, I'm also using error().

gcc/cp/ChangeLog:

	PR c++/96103
	* parser.c (cp_parser_decltype): Print error about using decltype(auto)
	in C++11.  Check that the token following "auto" is ")".

gcc/testsuite/ChangeLog:

	PR c++/96103
	* g++.dg/cpp0x/decltype77.C: New test.
This commit is contained in:
Marek Polacek 2020-07-07 17:09:42 -04:00
parent 4070208f23
commit a51de1af06
2 changed files with 26 additions and 7 deletions
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23
gcc/cp/parser.c
View File

@ -14894,11 +14894,11 @@ cp_parser_decltype_expr (cp_parser *parser,
return expr;
}
/* Parse a `decltype' type. Returns the type.
/* Parse a `decltype' type. Returns the type.
simple-type-specifier:
decltype-specifier:
decltype ( expression )
C++14 proposal:
C++14:
decltype ( auto ) */
static tree
@ -14938,10 +14938,19 @@ cp_parser_decltype (cp_parser *parser)
tree expr = NULL_TREE;
if (cxx_dialect >= cxx14
&& cp_lexer_next_token_is_keyword (parser->lexer, RID_AUTO))
/* decltype (auto) */
cp_lexer_consume_token (parser->lexer);
if (cp_lexer_next_token_is_keyword (parser->lexer, RID_AUTO)
&& cp_lexer_nth_token_is (parser->lexer, 2, CPP_CLOSE_PAREN))
{
/* decltype (auto) */
cp_lexer_consume_token (parser->lexer);
if (cxx_dialect < cxx14)
{
error_at (start_token->location,
"%<decltype(auto)%> type specifier only available with "
"%<-std=c++14%> or %<-std=gnu++14%>");
expr = error_mark_node;
}
}
else
{
/* decltype (expression) */

10
gcc/testsuite/g++.dg/cpp0x/decltype77.C Normal file
View File

@ -0,0 +1,10 @@
// PR c++/96103
// { dg-do compile { target c++11_only } }
decltype(auto) foo () { return 4; } // { dg-error ".decltype\\(auto\\). type specifier only available" }
void
bar ()
{
decltype(auto) i = 0; // { dg-error ".decltype\\(auto\\). type specifier only available" }
}