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* [Bug c++/101006] New: Request diagnostic for likely concept syntax errors
@ 2021-06-10 1:23 barry.revzin at gmail dot com
2021-06-10 11:42 ` [Bug c++/101006] " redi at gcc dot gnu.org
2021-06-10 11:50 ` redi at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: barry.revzin at gmail dot com @ 2021-06-10 1:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101006
Bug ID: 101006
Summary: Request diagnostic for likely concept syntax errors
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Consider the following:
template <typename T>
concept Thing = true;
template <typename T>
concept MemberThing = requires (T t) {
t.member() -> Thing; // #1
!requires { t.member(); }; // #2
};
These are likely intended to be (obviously not at the same time, this is just
an example):
template <typename T>
concept MemberThing = requires (T t) {
{ t.member() } -> Thing;
requires !requires { t.member(); };
};
But #1 is very likely to be a bug, and #2 is completely pointless as a
requirement since it's tautologically true. It would be nice if gcc could
produce warnings in such cases.
#2 is a similar case to the P2092 fixup of:
template <typename T>
concept MemberThing = requires (T t) {
requires { t.member(); };
};
which is now ill-formed. However, gcc's diagnostic here could be more helpful
too (perhaps including a fixup for an extra requires?)
<source>:6:14: error: expected primary-expression before '{' token
6 | requires { t.member(); };
| ^
#1 might be harder to warn about since that could *theoretically* be intended,
but if unqualified lookup for Thing actually finds a concept, seems like a good
bet for a diagnostic maybe?
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-06-10 1:23 [Bug c++/101006] New: Request diagnostic for likely concept syntax errors barry.revzin at gmail dot com
2021-06-10 11:42 ` [Bug c++/101006] " redi at gcc dot gnu.org
2021-06-10 11:50 ` redi at gcc dot gnu.org
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