https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120015
Bug ID: 120015 Summary: internal compiler error: in unify, at cp/pt.cc:25969 Product: gcc Version: 16.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: ldalessandro at gmail dot com Target Milestone: --- Invalid code uses tag<T> without a second parameter. template <class T, auto = []{}> struct tag {}; template <class T> bool foo(tag<T>); tag<int> x; auto y = foo(x); Works for valid code: template <class T, auto v> bool foo(tag<T, v>); Live: https://godbolt.org/z/YKorqs95P [April 29th, 2025]