To check if a method's receiver type is object safe, we create a new receiver type by substituting in a bogus type parameter (let's call it `U`) for `Self`, and checking that the unmodified receiver type implements `DispatchFromDyn<receiver type with Self = U>`. It would be better to use `dyn Trait` directly, and the only reason we don't is because it triggers another check that `Trait` is object safe, resulting in a query cycle. Once the feature `object_safe_for_dispatch` (tracking issue rust-lang#43561) is stabilized, this will no longer be the case, and we'll be able to use `dyn Trait` as the unsized `Self` type. I've updated the comments in object_safety.rs accordingly.

Uploading the toolstate data for each commit will help our release
tooling understand which components are failing, to possibly skip
shipping broken tools to users.

Co-Authored-By: lzutao <taolzu@gmail.com>

The hack was added because upstream msys2 broke the ca-certificates
package, but since then it has been fixed. This reverts CI to use the
upstream package.

Before this commit toolstates.json was stored in /tmp and it wasn't
mounted outside the build container. That caused uploading the file in
the upload-artifacts task to fail, as the file was missing on the host.

Mounting /tmp/toolstates.json alone is not the best approach: if the
file is missing when the container is started the Docker engine will
create a *directory* named /tmp/toolstates.json.

The Docker issue could be solved by pre-creating an empty file named
/tmp/toolstates.json, but doing that could cause problems if bootstrap
fails to generate the file and the toolstate scripts receive an empty
JSON.

The approach I took in this commit is to instead mount a /tmp/toolstate
directory inside Docker, and create the toolstates.json file in it. That
also required a small bootstrap change to ensure the directory is
created if it's missing.

This field is created lazily on first use and after that is read only.
That's exactly what Once is for.

…=alexcrichton

Upload toolstates.json to rust-lang-ci2

This PR does two things:

* Following up with rust-lang#65202, it migrates deploying artifacts to CI in a script. Both uploading release artifacts and CPU stats were merged into the same script, designing it to be easily extended.
* Uploads the toolstate JSON to `rust-lang-ci2` along with the release artifacts, both for Linux and Windows. This is needed because @RalfJung wants to stop shipping MIRI when its tests are failing, and the toolstate repo doesn't have entries for each commit. Having the toolstate data (just for that specific commit) on `rust-lang-ci2` will simplify the code a lot.

r? @alexcrichton
cc @RalfJung

…-E0577, r=Dylan-DPC

Add long error explanation for E0577

Part of rust-lang#61137.

r? @kinnison

Update comments re type parameter hack in object safety

To check if a method's receiver type is object safe, we create a new receiver type by substituting in a bogus type parameter (let's call it `U`) for `Self`, and checking that the unmodified receiver type implements `DispatchFromDyn<receiver type with Self = U>`. It would be better to use `dyn Trait` directly, and the only reason we don't is because it triggers another check that `Trait` is object safe, resulting in a query cycle. Once the feature `object_safe_for_dispatch` (tracking issue rust-lang#43561) is stabilized, this will no longer be the case, and we'll be able to use `dyn Trait` as the unsized `Self` type. I've updated the comments in object_safety.rs accordingly.

cc @Centril @nikomatsakis @bovinebuddha

…ck, r=Mark-Simulacrum

ci: revert msys2 ca-certificates hack

The hack was added because upstream msys2 broke the ca-certificates package, but since then it has been fixed. This reverts CI to use the upstream package.

Part of rust-lang#65767

…twco

Fix an incorrect docstring for Immediate in librustc_mir/interpret.

I suspect `Immediate` was once called `Value`?

…r=Mark-Simulacrum

Switch CrateMetadata's source_map_import_info from RwLock to Once

work around aggressive syntax feature gating

This works around rust-lang#65860; fixing `rustc +nightly lib.rs --test --edition 2018` for libcore and thus unblocking https://github.com/RalfJung/miri-test-libstd.