https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105351
--- Comment #2 from Gawain Bolton <gawain.bolton at free dot fr> --- Yes I believe this is a bug and strangely enough clang also seems to have this issue. >From the draft C++20 standard concerning "simple requirements" (cf. https://isocpp.org/files/papers/N4860.pdf page 109): A simple-requirement asserts the validity of an expression. [Note: The enclosing requires-expression will evaluate to false if substitution of template arguments into the expression fails. The expression is an unevaluated operand (7.2). — end note] [Example: template<typename T> concept C = requires (T a, T b) { a + b; // C<T> is true if a + b is a valid expression }; — end example] Clearly T::attr2 is not a valid expression for struct T { int attr2; }
