`Deref`/`DerefMut` can be useful, but they can also obfuscate. I don't
think they're worth it for `RegionConstraintCollector`. They're also not
present on the similar types `OpaqueTypeTable` and `TypeVariableTable`.
`LeakCheck` can own `mini_graph` and `rcc` instead of holding references
to them. This requires inlining `assign_scc_value` to avoid a borrowck
error, but that's fine because it has a single call site.
It's a weird method, and used weirdly:
- It's on `RegionConstraintCollector` but operates on
`RegionConstraintStorage`. So at both call sites we create a temporary
`RegionConstraintCollector`, using `with_log`, to call it.
- It `take`s just two of the six fields in `RegionConstraintStorage`.
At one of the two call sites we unnecessarily clone the entire
`RegionConstraintStorage` just to take those two fields.
This commit just inlines and removes it. We no longer need to `take` the
two fields, we can just use them directly.
`OutlivesEnvironment::new` can call `OutlivesEnvironment::with_bounds`
with an empty `extra_bounds`. And once that's done,
`OutlivesEnvironmentBuilder` has a single use and can be inlined and
removed into `OutlivesEnvironment::with_bounds`.
Remove `CombineFields`
This conflicts with #131263, but if this one lands first then perhaps #131263 could then go ahead and remove all the branching on solver in `TypeRelating`. We could perhaps then rename `TypeRelating` to `OldSolverRelating` or something, idk.
r? lcnr
`FixupError` is isomorphic with `TyOrConstInferVar`, so this commit
changes it to just be a wrapper around `TyOrConstInferVar`.
Also, move the `Display` impl for `FixupError` next to `FixupError`.
Three of the modules don't need to be `pub`, and then
`warn(unreachable_pub)` identifies a bunch more things that also
shouldn't be `pub`, plus a couple of things that are unused.
Stabilize the `map`/`value` methods on `ControlFlow`
And fix the stability attribute on the `pub use` in `core::ops`.
libs-api in https://github.com/rust-lang/rust/issues/75744#issuecomment-2231214910 seemed reasonably happy with naming for these, so let's try for an FCP.
Summary:
```rust
impl<B, C> ControlFlow<B, C> {
pub fn break_value(self) -> Option<B>;
pub fn map_break<T>(self, f: impl FnOnce(B) -> T) -> ControlFlow<T, C>;
pub fn continue_value(self) -> Option<C>;
pub fn map_continue<T>(self, f: impl FnOnce(C) -> T) -> ControlFlow<B, T>;
}
```
Resolves#75744
``@rustbot`` label +needs-fcp +t-libs-api -t-libs
---
Aside, in case it keeps someone else from going down the same dead end: I looked at the `{break,continue}_value` methods and tried to make them `const` as part of this, but that's disallowed because of not having `const Drop`, so put it back to not even unstably-const.
