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* [Bug c++/110497] New: Wrong error on non-static data member referenced in concept definition
@ 2023-06-30 9:23 fchelnokov at gmail dot com
2023-06-30 9:41 ` [Bug c++/110497] " redi at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: fchelnokov at gmail dot com @ 2023-06-30 9:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110497
Bug ID: 110497
Summary: Wrong error on non-static data member referenced in
concept definition
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: fchelnokov at gmail dot com
Target Milestone: ---
This program
struct B {
const bool b = true;
};
template <typename T>
concept C = T::b;
static_assert( !C<B> );
is accepted in Clang. And I think correctly accepted because of substitution
failure per https://eel.is/c++draft/temp.constr.constr#temp.constr.op-5
> [...] Furthermore, if substitution to determine whether an atomic constraint is satisfied ([temp.constr.atomic]) encounters a substitution failure, the constraint is not satisfied, regardless of the presence of a negation operator.
But GCC emits a weird error (at least the error text must be adjusted):
error: '*(B*)(void)0' is not a constant expression
Online demo: https://gcc.godbolt.org/z/xKf13cb6v
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/110497] Wrong error on non-static data member referenced in concept definition
2023-06-30 9:23 [Bug c++/110497] New: Wrong error on non-static data member referenced in concept definition fchelnokov at gmail dot com
@ 2023-06-30 9:41 ` redi at gcc dot gnu.org
2023-06-30 13:44 ` ppalka at gcc dot gnu.org
2023-07-02 8:08 ` daniel-dev at hotmail dot de
2 siblings, 0 replies; 4+ messages in thread
From: redi at gcc dot gnu.org @ 2023-06-30 9:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110497
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |rejects-valid
Last reconfirmed| |2023-06-30
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/110497] Wrong error on non-static data member referenced in concept definition
2023-06-30 9:23 [Bug c++/110497] New: Wrong error on non-static data member referenced in concept definition fchelnokov at gmail dot com
2023-06-30 9:41 ` [Bug c++/110497] " redi at gcc dot gnu.org
@ 2023-06-30 13:44 ` ppalka at gcc dot gnu.org
2023-07-02 8:08 ` daniel-dev at hotmail dot de
2 siblings, 0 replies; 4+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-06-30 13:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110497
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Blocks| |67491
CC| |ppalka at gcc dot gnu.org
--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
It seems we're issuing a hard error during satisfaction here because
substitution failure didn't occur, and the substituted constraint is
non-constant which renders the program ill-formed as per
[temp.constr.atomic]/3:
> If substitution results in an invalid type or expression, the constraint is not satisfied. Otherwise, the lvalue-to-rvalue conversion is performed if necessary, and E shall be a constant expression of type bool.
One might argue substitution failure should occur for T::b with T=B, but this
seems to be permitted by [expr.prim.id.general]/3 since constraint-expressions
are unevaluated contexts.
Note that if we use B::b directly in the concept definition then Clang also
rejects the program due to non-constant satisfaction rule:
struct B { const bool b = true; };
template <typename T>
concept C = B::b;
static_assert( !C<B> );
error: substitution into constraint expression resulted in a non-constant
expression
So GCC might be correct to reject the original program.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67491
[Bug 67491] [meta-bug] concepts issues
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/110497] Wrong error on non-static data member referenced in concept definition
2023-06-30 9:23 [Bug c++/110497] New: Wrong error on non-static data member referenced in concept definition fchelnokov at gmail dot com
2023-06-30 9:41 ` [Bug c++/110497] " redi at gcc dot gnu.org
2023-06-30 13:44 ` ppalka at gcc dot gnu.org
@ 2023-07-02 8:08 ` daniel-dev at hotmail dot de
2 siblings, 0 replies; 4+ messages in thread
From: daniel-dev at hotmail dot de @ 2023-07-02 8:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110497
--- Comment #2 from Daniel <daniel-dev at hotmail dot de> ---
Just some observations:
There was a similar discussion in
https://stackoverflow.com/questions/75443227/static-assert-on-an-ill-formed-no-diagnostic-required-expression
Note that if we use anything else which leads to the ill-formed expression for
T::b itself, e.g. B&, B*, int - gcc compiles without errors:
struct B {
const bool b = true;
};
template <typename T>
concept C = T::b;
static_assert( !C<B*> );
static_assert( !C<B&> );
static_assert( !C<int> );
https://gcc.godbolt.org/z/9c6YW1vWe
I would expect (at least as a user) the same behaviour for static_assert(!C<B>)
too, in that case.
So gcc seems to consider T::b (with T=b) in this context as a well-formed
expression, but not a constant expression.
Looks strange.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2023-06-30 9:23 [Bug c++/110497] New: Wrong error on non-static data member referenced in concept definition fchelnokov at gmail dot com
2023-06-30 9:41 ` [Bug c++/110497] " redi at gcc dot gnu.org
2023-06-30 13:44 ` ppalka at gcc dot gnu.org
2023-07-02 8:08 ` daniel-dev at hotmail dot de
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