https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104798
--- Comment #2 from Jonathan Stein <jstein27 at binghamton dot edu> --- Further, after some back and forth with a colleague, I don't know if this is an extension or not. I'm not too clear on the language, but from the C++20 published draft n4849: > An attribute-specifier-seq in a lambda-declarator appertains to the **type > of** the corresponding function call operator or **operator template**. Emphasis mine. A decl-specifier-seq is also allowed, which can have it's own attribute-specifier-seq which apertains to the type of item that the decl-specifiers were for. But the decl specifiers for a lambda expression are only allowed to contain mutable, constexpr, or consteval. The latter two would be for the operator, but I believe mutable would be for anonymous class. Is the type of a function call operator the same as the operator? I assume so, because as far as I'm aware templates ( don't have a type. Which would then mean, if there's "decl-specifier-seq [[...]] noexcept-spec [[...]]" (noexcept-spec is optional), the first attribute-specifier-seq _may_ pertain to the anonymous class (because what does it mean *exactly* to be mutable here other than for the class), the second to the call operator. If there's only an attribute-specifier-seq, it's to the call operator. Which means both the lack of warning and the change in behavior are wrong. On the other hand, if not, then it applies to the type of the function yet not the function itself. Which means there's no way to provide function-related attributes to lambdas pre C++2b except by extension, and the change in behavior is correct but the lack of warning is not.
