Hi!
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->...
Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux (with
GXX_TESTSUITE_STDS=98,11,14,17,20,2b ), ok for trunk?
2021-04-14 Jakub Jelinek <ja...@redhat.com>
PR c++/99850
* parser.c (cp_parser_constraint_requires_parens) <case CPP_DEREF>:
If lambda_p, return pce_ok for C++23 or later instead of
pce_maybe_postfix.
* g++.dg/cpp23/lambda-specifiers2.C: New test.
--- gcc/cp/parser.c.jj 2021-04-14 10:48:41.318103715 +0200
+++ gcc/cp/parser.c 2021-04-14 14:52:03.220235527 +0200
@@ -28526,7 +28526,19 @@ cp_parser_constraint_requires_parens (cp
case CPP_PLUS_PLUS:
case CPP_MINUS_MINUS:
case CPP_DOT:
+ /* Unenclosed postfix operator. */
+ return pce_maybe_postfix;
+
case CPP_DEREF:
+ /* A primary constraint that precedes the lambda-declarator of a
+ lambda expression is followed by trailing return type.
+
+ []<typename T> requires C -> void {}
+
+ Don't try to re-parse this as a postfix expression in
+ C++23 and later. In C++20 ( needs to come in between. */
+ if (lambda_p && cxx_dialect >= cxx23)
+ return pce_ok;
/* Unenclosed postfix operator. */
return pce_maybe_postfix;
}
--- gcc/testsuite/g++.dg/cpp23/lambda-specifiers2.C.jj 2021-04-14
15:01:41.728714721 +0200
+++ gcc/testsuite/g++.dg/cpp23/lambda-specifiers2.C 2021-04-14
15:01:32.959813534 +0200
@@ -0,0 +1,7 @@
+// PR c++/99850
+// P1102R2 - Down with ()!
+// { dg-do compile { target c++23 } }
+
+auto l = []<auto> requires true -> void {};
+template <typename...> concept C = true;
+auto m = []<typename... Ts> requires (C<Ts> && ...) -> void {};
Jakub
