On Fri, Mar 20, 2020 at 9:51 PM Richard Smith via SG10 <sg10@lists.isocpp.org> wrote:
On Fri, Mar 20, 2020 at 6:41 PM Leo Carreon via SG10 <sg10@lists.isocpp.org> wrote:
Are there any feature test macros for the following?
  1. init-statement for if and while statements (P0614R1)
  2. init-statement for range-for (P0305R1)
I’m asking because I couldn’t find any reference to them in the C++20 draft or in SD-6.

No, there are no feature test macros for those features. Generally we don't provide feature test macros in the case where you could use the "feature not available" version of the code unconditionally with no loss of functionality, which would generally be the case for these features.

FWIW one of my users was disappointed with this response, because he wants to static_assert all the features he depends on, and leaving some features out "makes C++ look less uniform".  I told him I'd pass his feedback along.