https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117294
--- Comment #6 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
With the above patch, the original testcase now gives the following diagnostic
(using experimental-nesting=yes for clarity):
$ g++-16 -std=c++20 -S -fdiagnostics-set-output=text:experimental-nesting=yes
test.cpp
test.cpp: In function ‘auto tryit()’:
test.cpp:19:24: error: no matching function for call to ‘make<Foo<A> >()’
19 | return make<Foo<A>>();
| ~~~~~~~~~~~~^~
• there is 1 candidate
• candidate 1: ‘template<class T> requires default_initializable<T> auto
make()’
test.cpp:4:6:
4 | auto make() {
| ^~~~
• template argument deduction/substitution failed:
• constraints not satisfied
In file included from test.cpp:1:
• /home/wreien/.local/include/c++/16.0.0/concepts: In substitution of
‘template<class T> requires default_initializable<T> auto make() [with T =
Foo<A>]’:
• required from here
test.cpp:19:24:
19 | return make<Foo<A>>();
| ~~~~~~~~~~~~^~
• required for the satisfaction of ‘constructible_from<_Tp>’ [with
_Tp = Foo<A>]
/home/wreien/.local/include/c++/16.0.0/concepts:161:13:
161 | concept constructible_from
| ^~~~~~~~~~~~~~~~~~
• required for the satisfaction of ‘default_initializable<T>’ [with T
= Foo<A>]
/home/wreien/.local/include/c++/16.0.0/concepts:166:13:
166 | concept default_initializable = constructible_from<_Tp>
| ^~~~~~~~~~~~~~~~~~~~~
• the expression ‘is_constructible_v<_Tp, _Args ...> [with _Tp =
Foo<A>; _Args = {}]’ evaluated to ‘false’
/home/wreien/.local/include/c++/16.0.0/concepts:162:30:
162 | = destructible<_Tp> && is_constructible_v<_Tp,
_Args...>;
|
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• ‘Foo<A>’ is not default constructible, because
• test.cpp: In instantiation of ‘constexpr Foo<A>::Foo()’:
• required by substitution of ‘template<class T> requires
default_initializable<T> auto make() [with T = Foo<A>]’
/home/wreien/.local/include/c++/16.0.0/concepts:162:30:
• required from here
test.cpp:19:24:
19 | return make<Foo<A>>();
| ~~~~~~~~~~~~^~
• error: could not convert ‘1’ from ‘int’ to ‘A’
test.cpp:15:11:
15 | T a = 1;
| ^
| |
| int
This is still not perfect, there's a chunk of extra noise, and the ordering of
the diagnostics IMO could have improvement, but at least the relevant
information is there now.
