This approach didn't seem to work well.

+ Add some information to the README.md

PR 107844 made DropAndReplace unused, let's remove it completely
from the codebase.

…, r=pietroalbini

use problem matchers for tidy CI

Place size limits on query keys and values

This just prevents these from growing accidentally too large. I'm not sure if there's an easy way to also print the actual size too.

Retry `pred_known_to_hold_modulo_regions` with fulfillment if ambiguous

Fixes rust-lang#108721

The problem here is that when we're checking `is_sized_raw` during codegen on some type that has a lot of opaques in it, something emits several nested obligations that are individually ambiguous, but when processed together in a loop then apply modulo regions. Since the `evaluate_predicates_recursively` inner loop doesn't process predicates until they stop changing, we return `EvaluatedToAmbig`, which makes the sized check return false incorrectly. See:

https://github.com/rust-lang/rust/blob/f15f0ea73972786e426732c5b92ba9a904b866c4/compiler/rustc_trait_selection/src/traits/select/mod.rs#L596-L606

... Compared to the analogous loop in the new solver:

https://github.com/rust-lang/rust/blob/f15f0ea73972786e426732c5b92ba9a904b866c4/compiler/rustc_trait_selection/src/solve/mod.rs#L481-L512

To fix this, if we get ambiguous during `pred_known_to_hold_modulo_regions`, just retry the obligation in a fulfillment context.

--

Unfortunately... I don't have a test for this. I've only tested this locally. Pending minimization :/

r? types

…t-release-notes-for-1.41.1-apple32, r=Mark-Simulacrum

1.41.1 supported 32-bit Apple targets

This question was raised by rust-lang#108556.

StableMIR: Proof-of-concept implementation + test

This PR is part of the [project Stable MIR](https://github.com/rust-lang/project-stable-mir). The PR deletes old re-exports from rustc_smir and introduces a proof-of-concept implementation for APIs to retrieve crate information.

The implementation follows the [design described here](https://hackmd.io/XhnYHKKuR6-LChhobvlT-g?view), but instead of using separate crates for the implementation, it uses separate modules inside `rustc_smir`.

The API introduced at this point should be seen just as an example on how we are planning to structure the communication between tools and the compiler.

I have not explored yet what should be the right granularity, the best starting point for users, neither the best way to implement it.

r? ```@oli-obk```

…asko

Remove DropAndReplace terminator

rust-lang#107844 made DropAndReplace unused, let's remove it completely from the codebase.

…, r=BoxyUwU

Suppress copy impl error when post-normalized type references errors

Suppress spurious errors from the `Copy` impl validity check when fields have bad types *post*-normalization, instead of just pre-normalization.

----

The const-generics test regressed recently due to rust-lang#107965, cc ``@BoxyUwU.``
 * I think it's because `[_; 0u32]: Copy` now fails to hold because a nested obligation `ConstArgHasType(0u32, usize)` fails.
 * It's interesting that `[const_error]` shows up in the type only after normalization, though, but I'm pretty sure that it's due to the evaluate call that happens when normalizing unevaluated consts.