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* [Bug c++/95127] New: Self-calling lambda with auto return type gives misleading error message
@ 2020-05-14 10:41 xzlsmc at gmail dot com
2020-05-14 10:48 ` [Bug c++/95127] " xzlsmc at gmail dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: xzlsmc at gmail dot com @ 2020-05-14 10:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95127
Bug ID: 95127
Summary: Self-calling lambda with auto return type gives
misleading error message
Product: gcc
Version: 9.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xzlsmc at gmail dot com
Target Milestone: ---
$ cat bug.cc
int main() {
auto f = [](const auto &g, auto x) { return g(g, x); };
f(f, 0);
}
$ gcc -std=c++14 bug.cc
bug.cc: In instantiation of ‘main()::<lambda(const auto:1&, auto:2)> [with
auto:1 = main()::<lambda(const auto:1&, auto:2)>; auto:2 = int]’:
bug.cc:3:9: required from here
bug.cc:2:48: error: use of ‘main()::<lambda(const auto:1&, auto:2)> [with
auto:1 = main()::<lambda(const auto:1&, auto:2)>; auto:2 = int]’ before
deduction of ‘auto’
2 | auto f = [](const auto &g, auto x) { return g(g, x); };
| ~^~~~~~
This error message is technically correct, but the `auto' it refers to is very
misleading here: it's the implicit `auto' return type of the lambda expression,
rather than either `auto' argument type. The message can become clearer if
changed to "use of ... before deduction of _return type_".
GCC version: 9.3.1
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/95127] Self-calling lambda with auto return type gives misleading error message
2020-05-14 10:41 [Bug c++/95127] New: Self-calling lambda with auto return type gives misleading error message xzlsmc at gmail dot com
@ 2020-05-14 10:48 ` xzlsmc at gmail dot com
2021-08-07 1:43 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: xzlsmc at gmail dot com @ 2020-05-14 10:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95127
xzlsmc <xzlsmc at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Attachment #48532|0 |1
is obsolete| |
--- Comment #1 from xzlsmc <xzlsmc at gmail dot com> ---
Created attachment 48534
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48534&action=edit
`gcc -v' and bug.ii stuff
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/95127] Self-calling lambda with auto return type gives misleading error message
2020-05-14 10:41 [Bug c++/95127] New: Self-calling lambda with auto return type gives misleading error message xzlsmc at gmail dot com
2020-05-14 10:48 ` [Bug c++/95127] " xzlsmc at gmail dot com
@ 2021-08-07 1:43 ` pinskia at gcc dot gnu.org
2021-09-02 1:22 ` egallager at gcc dot gnu.org
2021-09-02 1:26 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-07 1:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95127
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
All 4 compilers (GCC, ICC, clang and MSVC) I have access to reject this code.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/95127] Self-calling lambda with auto return type gives misleading error message
2020-05-14 10:41 [Bug c++/95127] New: Self-calling lambda with auto return type gives misleading error message xzlsmc at gmail dot com
2020-05-14 10:48 ` [Bug c++/95127] " xzlsmc at gmail dot com
2021-08-07 1:43 ` pinskia at gcc dot gnu.org
@ 2021-09-02 1:22 ` egallager at gcc dot gnu.org
2021-09-02 1:26 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: egallager at gcc dot gnu.org @ 2021-09-02 1:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95127
--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> All 4 compilers (GCC, ICC, clang and MSVC) I have access to reject this code.
Could you post their error messages for comparison?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/95127] Self-calling lambda with auto return type gives misleading error message
2020-05-14 10:41 [Bug c++/95127] New: Self-calling lambda with auto return type gives misleading error message xzlsmc at gmail dot com
` (2 preceding siblings ...)
2021-09-02 1:22 ` egallager at gcc dot gnu.org
@ 2021-09-02 1:26 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-02 1:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95127
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Literally all of the same error message even:
clang:
<source>:2:47: error: function 'operator()<(lambda at <source>:2:12), int>'
with deduced return type cannot be used before it is defined
auto f = [](const auto &g, auto x) { return g(g, x); };
^
<source>:3:4: note: in instantiation of function template specialization
'main()::(anonymous class)::operator()<(lambda at <source>:2:12), int>'
requested here
f(f, 0);
^
<source>:2:12: note: 'operator()<(lambda at <source>:2:12), int>' declared here
auto f = [](const auto &g, auto x) { return g(g, x); };
^
ICC:
<source>(2): error: cannot deduce the return type of function "lambda [](const
auto &, auto)->auto [with <auto-1>=lambda [](const auto &, auto)->auto,
<auto-2>=int]" (declared at line 2); it has not been defined
auto f = [](const auto &g, auto x) { return g(g, x); };
^
detected during instantiation of function "lambda [](const auto &,
auto)->auto [with <auto-1>=lambda [](const auto &, auto)->auto, <auto-2>=int]"
at line 3
compilation aborted for <source> (code 2)
MSVC:
<source>(2): error C3779: 'main::<lambda_1>::operator ()': a function that
returns 'auto' cannot be used before it is defined
<source>(2): note: see declaration of 'main::<lambda_1>::operator ()'
<source>(3): note: see reference to function template instantiation 'auto
main::<lambda_1>::operator ()<main::<lambda_1>,int>(const _T1 &,_T2) const'
being compiled
with
[
_T1=main::<lambda_1>,
_T2=int
]
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-09-02 1:26 UTC | newest]
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2020-05-14 10:41 [Bug c++/95127] New: Self-calling lambda with auto return type gives misleading error message xzlsmc at gmail dot com
2020-05-14 10:48 ` [Bug c++/95127] " xzlsmc at gmail dot com
2021-08-07 1:43 ` pinskia at gcc dot gnu.org
2021-09-02 1:22 ` egallager at gcc dot gnu.org
2021-09-02 1:26 ` pinskia at gcc dot gnu.org
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