https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109870
Bug ID: 109870
Summary: Miscomputation of return type of unevaluated lambda in
type alias in template context
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ed at catmur dot uk
Target Milestone: ---
template<class> struct X {};
template<class T>
struct M {
using R = decltype([] { return 1; }());
template<class U> struct S { X<R> p; };
};
M<int>::S<void> s;
9.1 through 14.0.0 trunk reject with:
<source>: In instantiation of 'struct M<int>::S<void>':
<source>:7:17: required from here
<source>:4:36: error: return-statement with a value, in function returning
'void' [-fpermissive]
4 | using R = decltype([] { return 1; }());
| ^
It appears the `U` type parameter in `M<T>::S<U>` is overwriting the lambda
deduced return type.
Possibly related to #92707, #103569
