https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104537
Bug ID: 104537 Summary: ICE when generic-lambda as function parameter fails to be converted to pointer to function Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: nickhuang99 at hotmail dot com Target Milestone: --- Consider this invalid conversion for this generic-lambda to pointer to function which is defined by "decltype(+[](T&& t )->T{return t+1;}". This ICE happens when original accepted parameter type changed from "T" to "T&&". See compiler explorer (https://www.godbolt.org/z/fde1bc3zE) I suspect this is some related issue with another unconfirmed case PR104358. template<typename T> auto foo(T&& t, decltype(+[](T&& t )->T{return t+1;}) lam){ return lam(t); } void test(){ foo<int>(5, [](int t){return t+1;}); } <source>:8:21: error: invalid user-defined conversion from 'test()::<lambda(int)>' to 'int (*)(int&&)' [-fpermissive] 8 | foo<int>(5, [](int t){return t+1;}); | ^~~~~~~~~~~~~~~~~~~~~~ ... internal compiler error: error reporting routines re-entered. 0x2174365 warning_at(unsigned int, int, char const*, ...) ...