https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97610
Bug ID: 97610
Summary: [10/11] template argument deduction fails for function
with defaulted lambda as non-type-template parameter
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: lutztonineubert at gmail dot com
Target Milestone: ---
The following code (with C++20 enabled):
template<auto = []{}>
constexpr auto nested() {
return 1;
}
template<typename T>
constexpr void test() {
static_assert(nested());
}
------------------
Fails with:
<source>: In function 'constexpr void test()':
<source>:8:30: error: no matching function for call to 'nested()'
8 | static_assert(nested());
| ^
<source>:2:16: note: candidate: 'template<auto <anonymous> > constexpr auto
nested()'
2 | constexpr auto nested() {
| ^~~~~~
<source>:2:16: note: template argument deduction/substitution failed:
------------------
* same error happens if nested() has template<typename = decltype([]{})> as
this template parameters
* if the template non-type parameter of nested() is defaulted to 1, it compiles
* if test() is not a template function, it compiles
* if static_assert(nested<[]{}>()); is used, it compiles
