add Miri to CI

[RalfJung]

This adds a CI job running the test suites in Miri -- at least if Miri is available for the current nightly.

Includes #780.

[RalfJung]

Oh wow, this worked on the first try. :)

[dhardy]

Looks good other than the hacks. Lets wait until your other PRs are merged then rebase.

Shame so many tests had to be disabled, but I guess that's the way it is.

[RalfJung]

Shame so many tests had to be disabled, but I guess that's the way it is.

Yeah... they don't seem to be around any unsafe code though if I didn't miss anything?

[dhardy]

Looks good.

use the UB-free version with proper alignment in Miri

This commit doesn't do what it says any more. But I think the plan is to fix fill_bytes as discussed in #779, then drop this one completely.

[RalfJung]

This commit doesn't do what it says any more.

Why doesn't it? It makes it so that on Miri it will use the fallback version (formerly not(any(target_arch = "x86", target_arch = "x86_64"))).

But I think the plan is to fix fill_bytes as discussed in #779, then drop this one completely.

That would be best. Unfortunately, doing that is beyond my knowledge of rand.

[dhardy]

So I we rebase this, fingers crossed it'll work perfectly...

[RalfJung]

Looking good.

[dhardy]

We're now seeing the test fail frequently in many PRs:

   Compiling rustc-std-workspace-alloc v1.0.0
error[E0463]: can't find crate for `std`

Is this a case of Miri not being enabled in the nightly build, and if so can we hide the error?

[RalfJung]

You are running into rust-lang/miri#713. I will submit a PR.