[generic_assert] "Constify" the Debug trait

[c410-f3r]

cc #44838

With the merging of #135423, it now appears possible to start "constifying" arbitrary traits. Therefore, I am starting the "constification" of all the traits involved in the execution of the formatting system to unblock generic_assert.

const _: () = { panic!("{}", "foo"); };

r? @rust-lang/project-const-traits

[compiler-errors]

This is a duplicate of #134628.

[compiler-errors]

And no, #135423 does not complete the picture unfortunately. We still need to enforce const stability of calls in MIR.

[c410-f3r]

This is a duplicate of #134628.

Looks like #134628 is trying to constify Default as well as Debug?! There is a related code in https://github.com/rust-lang/rust/pull/134628/files#diff-9968f2500861825aa70c0aefa037007a3759556f8ff4e742c6d826117dc5740b but the file is a test.

And no, #135423 does not complete the picture unfortunately. We still need to enforce const stability of calls in MIR.

Oh, OK. Thanks for the heads up. I will be back when things are ready.

[compiler-errors]

No, I'm so sorry @c410-f3r, I misread this as "constify the Default trait", not the Debug trait.

I will reopen this because I was blind and can't read the difference between Default and Debug. However, this is still blocked like that other one.

[c410-f3r]

Don't worry! After all, keeping up with the relentless pace of delivering so many important features in short periods of time is no easy task and it takes its toll. BTW, looking forward to see the stabilization of RTN 🎉

[Sky9x]

just wondering how this is useful... all you can do in a const fmt fn is return without printing anything, and I don't think the Formatter writing methods will become const any time soon (#44838 (comment))

[c410-f3r]

It seems so