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* [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures
@ 2022-10-27 15:20 development at jordi dot vilar.cat
2022-10-27 15:31 ` [Bug c++/107437] " development at jordi dot vilar.cat
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: development at jordi dot vilar.cat @ 2022-10-27 15:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
Bug ID: 107437
Summary: nested generic lambdas fail requiring unneded captures
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: development at jordi dot vilar.cat
Target Milestone: ---
This simple valid code fails to compile with all recent versions of gcc, but
compiles nicely with clang (and even msvc!)
(live demo on complier explorer: https://godbolt.org/z/eM1b9e6s9)
// compile with just -std=c++20
#include <array>
#include <functional>
#include <type_traits>
void test()
{
std::invoke([]<typename T>(auto N, std::type_identity<T>)
{
using vector_type = std::array<T, N>;
static_assert(N == std::tuple_size_v<vector_type>);
std::invoke([]<std::size_t... i>(std::index_sequence<i...>)
{
static_assert(std::conjunction_v<std::is_same<std::tuple_element_t<i,
vector_type>, T>...>);
}, std::make_index_sequence<N>{});
}, std::integral_constant<std::size_t, 3>{}, std::type_identity<int>{});
}
It issues the diagnostics output:
<source>: In instantiation of 'test()::<lambda(auto:3, std::type_identity<T>)>
[with T = int; auto:3 = std::integral_constant<long unsigned int, 3>]':
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/type_traits:2565:26:
required by substitution of 'template<class _Fn, class ... _Args> static
std::__result_of_success<decltype (declval<_Fn>()((declval<_Args>)()...)),
std::__invoke_other> std::__result_of_other_impl::_S_test(int) [with _Fn =
test()::<lambda(auto:3, std::type_identity<T>)>; _Args =
{std::integral_constant<long unsigned int, 3>, std::type_identity<int>}]'
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/type_traits:2576:55:
required from 'struct std::__result_of_impl<false, false,
test()::<lambda(auto:3, std::type_identity<T>)>, std::integral_constant<long
unsigned int, 3>, std::type_identity<int> >'
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/type_traits:2581:12:
required from 'struct std::__invoke_result<test()::<lambda(auto:3,
std::type_identity<T>)>, std::integral_constant<long unsigned int, 3>,
std::type_identity<int> >'
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/type_traits:3022:12:
required from 'struct std::invoke_result<test()::<lambda(auto:3,
std::type_identity<T>)>, std::integral_constant<long unsigned int, 3>,
std::type_identity<int> >'
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/type_traits:3034:11:
required by substitution of 'template<class _Fn, class ... _Args> using
invoke_result_t = typename std::invoke_result::type [with _Fn =
test()::<lambda(auto:3, std::type_identity<T>)>; _Args =
{std::integral_constant<long unsigned int, 3>, std::type_identity<int>}]'
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/functional:107:5:
required by substitution of 'template<class _Callable, class ... _Args>
constexpr std::invoke_result_t<_Fn, _Args ...> std::invoke(_Callable&&, _Args&&
...) [with _Callable = test()::<lambda(auto:3, std::type_identity<T>)>; _Args =
{std::integral_constant<long unsigned int, 3>, std::type_identity<int>}]'
<source>:7:16: required from here
<source>:13:32: error: 'N' is not captured
13 |
static_assert(std::conjunction_v<std::is_same<std::tuple_element_t<i,
vector_type>, T>...>);
|
~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>:11:21: note: the lambda has no capture-default
11 | std::invoke([]<std::size_t... i>(std::index_sequence<i...>)
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
12 | {
| ~
13 |
static_assert(std::conjunction_v<std::is_same<std::tuple_element_t<i,
vector_type>, T>...>);
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
14 | }, std::make_index_sequence<N>{});
| ~
<source>:7:37: note: 'std::integral_constant<long unsigned int, 3> N' declared
here
7 | std::invoke([]<typename T>(auto N, std::type_identity<T>)
| ~~~~~^
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107437] nested generic lambdas fail requiring unneded captures
2022-10-27 15:20 [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures development at jordi dot vilar.cat
@ 2022-10-27 15:31 ` development at jordi dot vilar.cat
2022-11-01 23:05 ` pinskia at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: development at jordi dot vilar.cat @ 2022-10-27 15:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
Jordi Vilar <development at jordi dot vilar.cat> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |development at jordi dot vilar.cat
--- Comment #1 from Jordi Vilar <development at jordi dot vilar.cat> ---
BTW, capturing (the unneded!) N in the nested lambda, raises a beautiful error:
error: integral expression '(std::integral_constant<long unsigned int,
3>::value_type)N' is not constant.
Should I fill a new issue for this?
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107437] nested generic lambdas fail requiring unneded captures
2022-10-27 15:20 [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures development at jordi dot vilar.cat
2022-10-27 15:31 ` [Bug c++/107437] " development at jordi dot vilar.cat
@ 2022-11-01 23:05 ` pinskia at gcc dot gnu.org
2022-12-17 16:25 ` cvs-commit at gcc dot gnu.org
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-11-01 23:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect this is the same as PR 105518.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107437] nested generic lambdas fail requiring unneded captures
2022-10-27 15:20 [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures development at jordi dot vilar.cat
2022-10-27 15:31 ` [Bug c++/107437] " development at jordi dot vilar.cat
2022-11-01 23:05 ` pinskia at gcc dot gnu.org
@ 2022-12-17 16:25 ` cvs-commit at gcc dot gnu.org
2022-12-17 16:34 ` ppalka at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-12-17 16:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:982629bea416df976686467f235e09cb1a5531cc
commit r13-4761-g982629bea416df976686467f235e09cb1a5531cc
Author: Patrick Palka <ppalka@redhat.com>
Date: Sat Dec 17 11:24:44 2022 -0500
c++: constantness of non-dependent NTTP argument [PR107437]
Here we're rejecting the use of the lambda capture of 't' (of empty
type) as a template argument ultimately because convert_nontype_argument
checks constantness using is_constant_expression, which returns false
for lambda captures since want_rval=false. But in this case I believe
an lvalue-to-rvalue conversion of the argument is implied, so we should
be using is_rvalue_constant_expression instead (which would return true
here).
However, it doesn't seem necessary to consider constantness at all
when deciding whether to instantiate a non-dependent argument in
convert_nontype_argument. So this patch gets rid of the problematic
constantness test altogether, which incidentally also fixes the similar
dg-ice'd testcase from PR87765. This is in line with a similar
change we made to finish_decltype_type in r12-7564-gec0f53a3a542e7.
PR c++/107437
PR c++/87765
gcc/cp/ChangeLog:
* pt.cc (convert_nontype_argument): Relax is_nondep_const_expr
test to !inst_dep_expr_p.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/lambda-generic-107437.C: New test.
* g++.dg/cpp1z/constexpr-lambda26.C: Remove dg-ice.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107437] nested generic lambdas fail requiring unneded captures
2022-10-27 15:20 [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures development at jordi dot vilar.cat
` (2 preceding siblings ...)
2022-12-17 16:25 ` cvs-commit at gcc dot gnu.org
@ 2022-12-17 16:34 ` ppalka at gcc dot gnu.org
2022-12-17 16:39 ` ppalka at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: ppalka at gcc dot gnu.org @ 2022-12-17 16:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
CC| |ppalka at gcc dot gnu.org
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2022-12-17
--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
The capturing version of the testcase is now accepted on trunk, unfortunately
we still reject the original non-capturing version.
Another workaround that's accepted by GCC 9+ is to avoid using N in an
evaluated context in the definition of vector_type:
using vector_type = std::array<T, decltype(N){}>;
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107437] nested generic lambdas fail requiring unneded captures
2022-10-27 15:20 [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures development at jordi dot vilar.cat
` (3 preceding siblings ...)
2022-12-17 16:34 ` ppalka at gcc dot gnu.org
@ 2022-12-17 16:39 ` ppalka at gcc dot gnu.org
2023-06-28 19:44 ` cvs-commit at gcc dot gnu.org
2023-07-04 15:03 ` jason at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: ppalka at gcc dot gnu.org @ 2022-12-17 16:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Reduced version of the original testcase:
struct integral_constant {
constexpr operator int() const { return 42; }
};
template<int N>
struct A {
static constexpr int value = N;
};
template<class T>
struct B {
static constexpr int value = T::value;
};
template<class T>
void f(T t) {
using alias = A<t>;
[](auto) {
B<alias> a; // { dg-bogus "'t' is not captured" }
return a.value;
}(0);
}
template void f(integral_constant);
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107437] nested generic lambdas fail requiring unneded captures
2022-10-27 15:20 [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures development at jordi dot vilar.cat
` (4 preceding siblings ...)
2022-12-17 16:39 ` ppalka at gcc dot gnu.org
@ 2023-06-28 19:44 ` cvs-commit at gcc dot gnu.org
2023-07-04 15:03 ` jason at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-06-28 19:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:4cf64d9cc2faf4001f037a50a350abd0f95f3e29
commit r14-2170-g4cf64d9cc2faf4001f037a50a350abd0f95f3e29
Author: Patrick Palka <ppalka@redhat.com>
Date: Wed Jun 28 15:43:33 2023 -0400
c++: ahead of time variable template-id coercion [PR89442]
This patch makes us coerce the arguments of a variable template-id ahead
of time, as we do for class template-ids, which causes us to immediately
diagnose template parm/arg kind mismatches and arity mismatches.
Unfortunately this causes a regression in cpp1z/constexpr-if20.C: coercing
the variable template-id m<ar, as> ahead of time means we strip it of
typedefs, yielding m<typename C<i>::q, typename C<j>::q>, but in this
stripped form we're directly using 'i' and so we expect to have captured
it. This is a variable template version of PR107437.
PR c++/89442
PR c++/107437
gcc/cp/ChangeLog:
* cp-tree.h (lookup_template_variable): Add complain parameter.
* parser.cc (cp_parser_template_id): Pass tf_warning_or_error
to lookup_template_variable.
* pt.cc (lookup_template_variable): Add complain parameter.
Coerce template arguments here ...
(finish_template_variable): ... instead of here.
(lookup_and_finish_template_variable): Check for error_mark_node
result from lookup_template_variable.
(tsubst_copy) <case TEMPLATE_ID_EXPR>: Pass complain to
lookup_template_variable.
(instantiate_template): Use build2 instead of
lookup_template_variable to build a TEMPLATE_ID_EXPR
for most_specialized_partial_spec.
gcc/testsuite/ChangeLog:
* g++.dg/cpp/pr64127.C: Expect "expected unqualified-id at end
of input" error.
* g++.dg/cpp0x/alias-decl-ttp1.C: Fix template parameter/argument
kind mismatch for variable template has_P_match_V.
* g++.dg/cpp1y/pr72759.C: Expect "template argument 1 is invalid"
error.
* g++.dg/cpp1z/constexpr-if20.C: XFAIL test due to bogus "'i' is
not captured" error.
* g++.dg/cpp1z/noexcept-type21.C: Fix arity of variable template d.
* g++.dg/diagnostic/not-a-function-template-1.C: Add default
template argument to variable template A so that A<> is valid.
* g++.dg/parse/error56.C: Don't expect "ISO C++ forbids
declaration with no type" error.
* g++.dg/parse/template30.C: Don't expect "parse error in
template argument list" error.
* g++.dg/cpp1y/var-templ82.C: New test.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/107437] nested generic lambdas fail requiring unneded captures
2022-10-27 15:20 [Bug c++/107437] New: nested generic lambdas fail requiring unneded captures development at jordi dot vilar.cat
` (5 preceding siblings ...)
2023-06-28 19:44 ` cvs-commit at gcc dot gnu.org
@ 2023-07-04 15:03 ` jason at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: jason at gcc dot gnu.org @ 2023-07-04 15:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107437
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jason at gcc dot gnu.org
--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Created attachment 55466
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55466&action=edit
failed experiment
I wondered if keeping function-local typedefs would be a simple fix, but a
number of modules tests regress with this patch. I guess that's because of
problems with entries in the specialization hash tables referring to
function-local typedefs that we can't then reconnect when loading the module.
Really such entries (if we do add them) shouldn't persist after we're done
compiling the function.
^ permalink raw reply [flat|nested] 8+ messages in thread
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