c++: requires-expression and tentative parse [PR94480]

The problem here was that cp_parser_requires_expression committing to a
tentative parse confused cp_parser_decltype_expr, which needs to still be
tentative.  The only reason to commit here is to get syntax errors within
the requires-expression, which we can still do when the commit is firewalled
from the enclosing context.

gcc/cp/ChangeLog
2020-04-07  Jason Merrill  <jason@redhat.com>

	PR c++/94480
	* parser.c (cp_parser_requires_expression): Use tentative_firewall.
This commit is contained in:
Jason Merrill 2020-04-07 00:45:26 -04:00
parent f1a6150ecb
commit 845d451e1f
3 changed files with 13 additions and 0 deletions

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@ -1,5 +1,8 @@
2020-04-07 Jason Merrill <jason@redhat.com>
PR c++/94480
* parser.c (cp_parser_requires_expression): Use tentative_firewall.
PR c++/94481
* parser.c (cp_parser_placeholder_type_specifier): Use
matching_parens.

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@ -27740,6 +27740,9 @@ cp_parser_requires_expression (cp_parser *parser)
gcc_assert (cp_lexer_next_token_is_keyword (parser->lexer, RID_REQUIRES));
location_t loc = cp_lexer_consume_token (parser->lexer)->location;
/* Avoid committing to outer tentative parse. */
tentative_firewall firewall (parser);
/* This is definitely a requires-expression. */
cp_parser_commit_to_tentative_parse (parser);

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@ -0,0 +1,7 @@
// PR c++/94480
// { dg-do compile { target c++2a } }
template<typename T, typename U>
constexpr bool is_same_v = __is_same (T, U);
static_assert(is_same_v<bool, decltype(requires { requires false; })>);