c++: Fix up C++23 [] <...> requires primary -> type {} parsing [PR99850]
The requires clause parsing has code to suggest users wrapping non-primary expressions in (), so if it e.g. parses a primary expression and sees it is followed by ++, --, ., ( or -> among other things it will try to reparse it as assignment expression or what and if that works suggests wrapping it inside of parens. When it is requires-clause that is after <typename T> etc. it already has an exception from that as ( can occur in valid C++20 expression there - starting the parameters of the lambda. In C++23 another case can occur, as the parameters with the ()s can be omitted, requires C can be followed immediately by -> which starts a trailing return type. Even in that case, we don't want to parse that as C->... 2021-04-16 Jakub Jelinek <jakub@redhat.com> PR c++/99850 * parser.c (cp_parser_constraint_requires_parens) <case CPP_DEREF>: If lambda_p, return pce_ok instead of pce_maybe_postfix. * g++.dg/cpp23/lambda-specifiers2.C: New test.
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@ -28530,7 +28530,20 @@ cp_parser_constraint_requires_parens (cp_parser *parser, bool lambda_p)
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case CPP_PLUS_PLUS:
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case CPP_PLUS_PLUS:
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case CPP_MINUS_MINUS:
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case CPP_MINUS_MINUS:
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case CPP_DOT:
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case CPP_DOT:
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/* Unenclosed postfix operator. */
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return pce_maybe_postfix;
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case CPP_DEREF:
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case CPP_DEREF:
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/* A primary constraint that precedes the lambda-declarator of a
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lambda expression is followed by trailing return type.
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[]<typename T> requires C -> void {}
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Don't try to re-parse this as a postfix expression in
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C++23 and later. In C++20 ( needs to come in between but we
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allow it to be omitted with pedwarn. */
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if (lambda_p)
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return pce_ok;
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/* Unenclosed postfix operator. */
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/* Unenclosed postfix operator. */
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return pce_maybe_postfix;
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return pce_maybe_postfix;
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}
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}
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@ -0,0 +1,7 @@
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// PR c++/99850
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// P1102R2 - Down with ()!
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// { dg-do compile { target c++23 } }
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auto l = []<auto> requires true -> void {};
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template <typename...> concept C = true;
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auto m = []<typename... Ts> requires (C<Ts> && ...) -> void {};
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