Signed-off-by: Alex Chi <iskyzh@gmail.com>

Signed-off-by: Alex Chi <iskyzh@gmail.com>

this test was added for rust 0.4 and doesn't test anything specific.
The repro originally relied on extern functions which are now just
ordinary methods. It's also a run pass test even though `main` has
been commented out.

This is necessary for the subsequent commits.

So that people have to keep them sorted in future.

Re-phrase in a way that handles input values being either 0 or
negative.

…rename usages of bound_impl_subject to impl_subject

…re, r=compiler-errors

suggest lifetime for closure parameter type when mismatch

This is a draft PR, will add test cases later and be ready for review.

This PR fixes rust-lang#105675 by adding a diagnostics suggestion. Also a partial fix to rust-lang#105528.

The following code will have a compile error now:

```
fn const_if_unit(input: bool) -> impl for<'a> FnOnce(&'a ()) -> usize {
    let x = |_| 1;
    x
}
```

Before this PR:

```
error[E0308]: mismatched types
 --> src/lib.rs:3:5
  |
3 |     x
  |     ^ one type is more general than the other
  |
  = note: expected trait `for<'a> FnOnce<(&'a (),)>`
             found trait `FnOnce<(&(),)>`
note: this closure does not fulfill the lifetime requirements
 --> src/lib.rs:2:13
  |
2 |     let x = |_| 1;
  |             ^^^

error: implementation of `FnOnce` is not general enough
 --> src/lib.rs:3:5
  |
3 |     x
  |     ^ implementation of `FnOnce` is not general enough
  |
  = note: closure with signature `fn(&'2 ()) -> usize` must implement `FnOnce<(&'1 (),)>`, for any lifetime `'1`...
  = note: ...but it actually implements `FnOnce<(&'2 (),)>`, for some specific lifetime `'2`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `rust-test` due to 2 previous errors
```

After this PR:

```
error[E0308]: mismatched types
 --> src/lib.rs:3:5
  |
3 |     x
  |     ^ one type is more general than the other
  |
  = note: expected trait `for<'a> FnOnce<(&'a (),)>`
             found trait `FnOnce<(&(),)>`
note: this closure does not fulfill the lifetime requirements
 --> src/lib.rs:2:13
  |
2 |     let x = |_| 1;
  |             ^^^
help: consider changing the type of the closure parameters
  |
2 |     let x = |_: &_| 1;
  |             ~~~~~~~

error: implementation of `FnOnce` is not general enough
 --> src/lib.rs:3:5
  |
3 |     x
  |     ^ implementation of `FnOnce` is not general enough
  |
  = note: closure with signature `fn(&'2 ()) -> usize` must implement `FnOnce<(&'1 (),)>`, for any lifetime `'1`...
  = note: ...but it actually implements `FnOnce<(&'2 (),)>`, for some specific lifetime `'2`

For more information about this error, try `rustc --explain E0308`.
error: could not compile `rust-test` due to 2 previous errors
```

After applying the suggestion, it compiles. The suggestion might not always be correct as the generation procedure of that suggestion is quite simple...

…14,albertlarsan68

Create "suggested tests" tool in `rustbuild`

Not the claimed person in rust-lang#97339 but:
I've done a very rough implementation of this feature in-tree. I'm very new to `rustc` development (outside of docs) so some help would be greatly appreciated. The UI of this new subcommand obviously will change and I need some mentoring with the `--run` flag.

r? ``@jyn514``

Remove obsolete test case

This test case was supposed to cover issue rust-lang#31109 at some point.
It never did anything, as the issue was still open at the time of its creation.
When the issue was resolved, the `issue31109` test case was created,
making the existence of this test pointless.

don't uniquify regions when canonicalizing

uniquifying causes a bunch of issues, most notably it causes `AliasEq(<?x as Trait<'a>>::Assoc, <?x as Trait<'a>>::Assoc)` to result in ambiguity because both `normalizes-to` paths result in ambiguity and substs equate should trivially succeed but doesn't because we uniquified `'a` to two different regions.

I originally added uniquification to make it easier to deal with requirement 6 from the dev-guide: https://rustc-dev-guide.rust-lang.org/solve/trait-solving.html#requirements

> ### 6. Trait solving must be (free) lifetime agnostic
>
> Trait solving during codegen should have the same result as during typeck. As we erase
> all free regions during codegen we must not rely on them during typeck. A noteworthy example
> is special behavior for `'static`.

cc rust-lang/rustc-dev-guide#1671

Relying on regions being identical may cause ICE during MIR typeck, but even without this PR we can end up relying on that as type inference vars can resolve to types which contain an identical region. Let's land this and deal with any ICE that crop up as we go. Will look at this issue again before stabilization.

r? `@compiler-errors`

Add `tidy-alphabetical` to features in `core`

So that people have to keep them sorted in future, rather than just sticking them on the end where they conflict more often.

…h726

Remove all but one of the spans in `BoundRegionKind::BrAnon`

There are only three places where `BoundRegionKind::BrAnon` uses `Some(span)` instead of `None`. Two of them are easy to remove, which this PR does.

r? `@jackh726`

…ses, r=thomcc

Cover edge cases for {f32, f64}.hypot() docs

Fixes rust-lang#88944

The Euclidean distance is a more general way to express what these functions do, and covers the edge cases of zero and negative inputs.

Does not cover the case of non-normal input values (as the [POSIX docs](https://pubs.opengroup.org/onlinepubs/9699919799.2008edition/) do), but the docs for the rest of the functions in these modules do not address this, I assumed it was not desired.

…ct, r=compiler-errors

Switch to `EarlyBinder` for `impl_subject` query

Part of the work to finish rust-lang#105779.

Several queries `X` have a `bound_X` variant that wraps the output in `EarlyBinder`. This adds `EarlyBinder` to the return type of the `impl_subject` query and removes `bound_impl_subject`.

r? `@lcnr`