https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115844
Bug ID: 115844
Summary: [14 Regression] Invalid diagnostics for
correctly-rejected non-consteval call in consteval
function called in a regular lambda
Product: gcc
Version: 14.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ali.mpfard at gmail dot com
Target Milestone: ---
(Presumably post-<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107687>)
Diagnostics are completely wrong about consteval-ness of surrounding context
when an immediate function evaluation fails due to calling a non-consteval
function.
Furthermore, the actual cause is nowhere to be seen in the diagnostics.
Reproducer (CE link: https://gcc.godbolt.org/z/hdjecKsEn)
template<typename>
void point_at_me();
template<typename T>
consteval void point_at_that() {
point_at_me<T>();
}
int main() {
auto x = 42;
auto l = [&x] {
x += 1;
point_at_that<int>();
};
l();
}
Diagnostics on trunk:
repro.cpp: In function 'int main()':
repro.cpp:16:6: error: call to consteval function 'l.main()::<lambda()>()'
is not a constant expression
16 | l();
| ~^~
repro.cpp:16:6: in 'constexpr' expansion of 'l.main()::<lambda()>()'
repro.cpp:12:11: error: the value of 'l' is not usable in a constant
expression
12 | x += 1;
| ~~^~~~
repro.cpp:11:10: note: 'l' was not declared 'constexpr'
11 | auto l = [&x] {
| ^
repro.cpp:13:27: note: 'main()::<lambda()>' was promoted to an immediate
function because its body contains an immediate-escalating expression
'point_at_that<int>()'
13 | point_at_that<int>();
| ~~~~~~~~~~~~~~~~~~^~
Diagnostics on 13.3 (expected):
repro.cpp: In lambda function:
repro.cpp:13:27: error: 'consteval void point_at_that() [with T = int]'
called in a constant expression
13 | point_at_that<int>();
| ~~~~~~~~~~~~~~~~~~^~
repro.cpp:5:16: note: 'consteval void point_at_that() [with T = int]' is
not usable as a 'constexpr' function because:
5 | consteval void point_at_that() {
| ^~~~~~~~~~~~~
repro.cpp:6:19: error: call to non-'constexpr' function 'void
point_at_me() [with <template-parameter-1-1> = int]'
6 | point_at_me<T>();
| ~~~~~~~~~~~~~~^~
repro.cpp:2:6: note: 'void point_at_me() [with <template-parameter-1-1> =
int]' declared here
2 | void point_at_me();
| ^~~~~~~~~~~
