The old documentation suggested the use of yield_now for repeated
polling instead of discouraging it; it also made the false claim that
channels are implementing using yield_now. (They are not, except for
a corner case).
The only change here is a fix for `sys.platform` on Linux. Python 3.3
changed the API to return "linux" instead of "linux2"/"linux3", so this
commit uses `.startswith("python")` to make the code work on Python 3
without breaking Python 2.
Replace per-target ABI denylist with an allowlist
It makes very little sense to maintain denylists of ABIs when, as far as
non-generic ABIs are concerned, targets usually only support a small
subset of the available ABIs.
This has historically been a cause of bugs such as us allowing use of
the platform-specific ABIs on x86 targets – these in turn would cause
LLVM errors or assertions to fire.
In this PR we got rid of the per-target ABI denylists, and instead compute
which ABIs are supported with a simple match based on, mostly, the
`Target::arch` field. Among other things, this makes it impossible to
forget to consider this problem (in either direction) and forces one to
consider what the ABI support looks like when adding an ABI (rarely)
rather than target (often), which should hopefully also reduce the
cognitive load on both contributors as well as reviewers.
Fixes#57182
Sponsored by: standard.ai
---
## Summary for teams
One significant user-facing change after this PR is that there's now a future compat warning when building…
* `stdcall`, `fastcall`, `thiscall` using code with targets other than 32-bit x86 (i386...i686) or *-windows-*;
* `vectorcall` using code when building for targets other than x86 (either 32 or 64 bit) or *-windows-*.
Previously these ABIs have been accepted much more broadly, even for architectures and targets where this made no sense (e.g. on wasm32) and would fall back to the C ABI. In practice this doesn't seem to be used too widely and the [breakages in crater](https://github.com/rust-lang/rust/pull/86231#issuecomment-866300943) that we see are mostly about Windows-specific code that was missing relevant `cfg`s and just happened to successfully `check` on Linux for one reason or another.
The intention is that this warning becomes a hard error after some time.
It makes very little sense to maintain denylists of ABIs when, as far as
non-generic ABIs are concerned, targets usually only support a small
subset of the available ABIs.
This has historically been a cause of bugs such as us allowing use of
the platform-specific ABIs on x86 targets – these in turn would cause
LLVM errors or assertions to fire.
Fixes#57182
Sponsored by: standard.ai
rustdoc: Replace `FakeDefId` with new `ItemId` type
Follow up from #84707
`@Manishearth` [suggested](https://github.com/rust-lang/rust/pull/84707#issuecomment-831994669) that there should be a new `ItemId` type that can distinguish between auto traits, normal ids, and blanket impls instead of using `FakeDefId`s.
This type is introduced by this PR.
There are still some `FIXME`s left, because I was unsure what the best solution for them would be.
Especially the naming in general now is a bit weird right now and needs to be cleaned up. Now there are no "fake" ids so the `is_fake` method on `Item` does not really make sense and maybe the methods on `ItemId` should be renamed too?
Also, we need to represent the new item ids in the JSON backend somehow.
