I suppose I'm saying "it would be nice to have these two distinct feature-test macros, but it may be too late now since __cpp_coroutines has an established history."

On Wed, Jan 15, 2020 at 4:13 PM Casey Carter <cartec69@gmail.com> wrote:

As a rule, it's useful to have distinct macros to indicate compiler and library support of a feature that has both core language and library surface. Standard libraries can then provide the library support / define the library macro only when the necessary compiler support is present. If the feature is unusable without library support, e.g., coroutines, users check only the library macro.