I did a manual merge of all the extended error PRs as we were getting merge conflicts yesterday. I think this is preferable to merging separately as I ended up having to manually merge @nham and @GuillaumeGomez's commits.
Rollup of #24458, #24482 and #24488.
#24482 and #24488 were already re-approved, and would need to be cancelled if this is merged instead.
I'm on a quest to slowly refactor a lot of the inference code. A first step for that is moving the "pure data structures" out so as to simplify what's left. This PR moves `snapshot_vec`, `graph`, and `unify` into their own crate (`librustc_data_structures`). They can then be unit-tested, benchmarked, etc more easily. As a benefit, I improved the performance of unification slightly on the benchmark I added vs the original code.
r? @nrc
This makes it illegal to have unconstrained lifetimes that appear in an associated type definition. Arguably, we should prohibit all unconstrained lifetimes -- but it would break various macros. It'd be good to evaluate how large a break change it would be. But this seems like the minimal change we need to do to establish soundness, so we should land it regardless. Another variant would be to prohibit all lifetimes that appear in any impl item, not just associated types. I don't think that's necessary for soundness -- associated types are different because they can be projected -- but it would feel a bit more consistent and "obviously" safe. I'll experiment with that in the meantime.
r? @aturon
Fixes#22077.
Extend rustc::middle::dataflow to allow filtering kills from flow-exits.
Fix borrowck analysis so that it will not treat a break that pops through an assignment
```rust
x = { ... break; ... }
```
as a kill of the "moved-out" bit for `x`.
Fix#24267.
[breaking-change], but really, its only breaking code that was already buggy.
Revise rustc::middle::dataflow: one must select kill-kind when calling
add_kill. The current kill-kinds are (1.) kills associated with
ends-of-scopes and (2.) kills associated with the actual action of the
expression/pattern.
Then, use this to fix borrowck analysis so that it will not treat a
break that pops through an assignment `x = { ... break; ... }` as a
kill of the "moved-out" bit for `x`.
Fix#24267.
(incorporated review feedback.)
Don't use skolemized parameters but rather fresh variables in coherence. Skolemized parameters wind up preventing unification. Surprised we had no test for this! Fixes#24241.
r? @pnkfelix
