It prevents a full rebuild of stage 1 compiler when issuing "x.py test"
with rust.lto != thin-local in config.toml.

`Diagnostic` has 40 methods that return `&mut Self` and could be
considered setters. Four of them have a `set_` prefix. This doesn't seem
necessary for a type that implements the builder pattern. This commit
removes the `set_` prefixes on those four methods.

It's not used, and doesn't quite fit the general pattern.

Also, `Diagnostic::downgrade_to_delayed_bug` doesn't need to return
`&mut Self` for the same reason.

- Move comments onto corresponding `Diagnostic` methods.
- Make formatting more consistent.

`create_almost_fatal` and `emit_almost_fatal` are always used instead.

These are misleading, because the mixture of `Level` and
`rustc_errors::Level` makes it look like there are two different types
involved.

It has a single call site.

Because it's redundant w.r.t. `Diagnostic::is_lint`, which is present
for every diagnostic level.

`struct_lint_level_impl` was the only place that set the `Error` field
to `true`, and it's also the only place that calls
`Diagnostic::is_lint()` to set the `is_lint` field.

It's not used within the repository in any way (e.g. in tests), and
doesn't seem useful.

…ature

It appears it was intended to be tier 3, but was accidentally added to
tier 2.

No functional changes - all checks have been emitted conditionally on
block being rechable already.

Reevaluate `body.should_skip()` after updating the MIR phase to ensure
that injected MIR is processed correctly.

Update a few custom MIR tests that were ill-formed for the injected
phase.

The check attempts to identify potential undefined behaviour, rather
than whether MIR is well-formed. It belongs in the lint not validator.

…mpiler-errors

Make `negative_bounds` internal & fix some of its issues

r? compiler-errors

…ulacrum

bootstrap: Move -Clto= setting from Rustc::run to rustc_cargo

It prevents a full rebuild of stage 1 compiler when issuing "x.py test" with rust.lto != thin-local in config.toml.

…errors

Handle ForeignItem as TAIT scope.

Fixes rust-lang#119295

…bject-safety-error, r=Nilstrieb

Use `resolutions(()).effective_visiblities` to avoid cycle errors in `report_object_error`

Inside of `report_object_error`, using the `effective_visibilities` query causes cycles since it calls `type_of`, which itself may call `typeck`, which may end up reporting its own object-safety errors.

Fixes rust-lang#119346
Fixes rust-lang#119502

…mpiler-errors

Cleanup error handlers: round 5

More rustc_errors cleanups. A sequel to rust-lang#119171.

r? ```@compiler-errors```

…em,Nilstrieb

Remove `-Zdump-mir-spanview`

The `-Zdump-mir-spanview` flag was added back in rust-lang#76074, as a development/debugging aid for the initial work on what would eventually become `-Cinstrument-coverage`. It causes the compiler to emit an HTML file containing a function's source code, with various spans highlighted based on the contents of MIR.

When the suggestion was made to [triage and remove unnecessary `-Z` flags (Zulip)](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/.60-Z.60.20option.20triage), I noted that this flag could potentially be worth removing, but I wanted to keep it around to see whether I found it useful for my own coverage work.

But when I actually tried to use it, I ran into various issues (e.g. it crashes on `tests/coverage/closure.rs`). If I can't trust it to work properly without a full overhaul, then instead of diving down a rabbit hole of trying to fix arcane span-handling bugs, it seems better to just remove this obscure old code entirely.

---

```@rustbot``` label +A-code-coverage

…s, r=oli-obk

Remove `-Zreport-delayed-bugs`.

It's not used within the repository in any way (e.g. in tests), and doesn't seem useful.

It was added in rust-lang#52568.

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

Migrate memory overlap check from validator to lint

The check attempts to identify potential undefined behaviour, rather
than whether MIR is well-formed. It belongs in the lint not validator.

Follow up to changes from rust-lang#119077.

…methods, r=notriddle

[rustdoc] Fix invalid handling for static method calls in jump to definition feature

I realized when working on a clippy lint that static method calls on `Self` could not give me the method `Res`. For that, we need to use `typeck` and so that's what I did in here.

It fixes the linking to static method calls.

r? ```@notriddle```

…trieb

Move `i586-unknown-netbsd` from tier 2 to tier 3 platform support table

It appears it was intended to be tier 3, but was accidentally added to tier 2. Based on inspecting the PR adding it the table rust-lang#117170 and the fact that it is not built in CI which is one of the tier 2 requirements.

cc ```@he32```

r? ```@Nilstrieb```