…mented]` attribute

This PR stabilizes the `#[diagnostic]` attribute namespace and a minimal
option of the `#[diagnostic::on_unimplemented]` attribute.

The `#[diagnostic]` attribute namespace is meant to provide a home for
attributes that allow users to influence error messages emitted by the
compiler. The compiler is not guaranteed to use any of this hints,
however it should accept any (non-)existing attribute in this namespace
and potentially emit lint-warnings for unused attributes and options.
This is meant to allow discarding certain attributes/options in the
future to allow fundamental changes to the compiler without the need to
keep then non-meaningful options working.

The `#[diagnostic::on_unimplemented]` attribute is allowed to appear
on a trait definition. This allows crate authors to hint the compiler
to emit a specific error message if a certain trait is not implemented.
For the `#[diagnostic::on_unimplemented]` attribute the following
options are implemented:

* `message` which provides the text for the top level error message
* `label` which provides the text for the label shown inline in the
broken code in the error message
* `note` which provides additional notes.

The `note` option can appear several times, which results in several
note messages being emitted. If any of the other options appears several
times the first occurrence of the relevant option specifies the actually
used value. Any other occurrence generates an lint warning. For any
other non-existing option a lint-warning is generated.

All three options accept a text as argument. This text is allowed to
contain format parameters referring to generic argument or `Self` by
name via the `{Self}` or `{NameOfGenericArgument}` syntax. For any
non-existing argument a lint warning is generated.

Tracking issue: rust-lang#111996

With rust 1.75 the absolute build path is embedding into '.rustc' section and which causes reproducibility issues. Detailed issue is here.
rust-lang#120825 (comment)

With this change the 'absolute path' changed back to '/rust/$hash' format.

This makes it much easier to know which test failed without having to wait for compiletest to completely finish running. Before:
```
Testing stage0 compiletest suite=ui mode=ui (x86_64-unknown-linux-gnu)

running 15274 tests
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii    88/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   176/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   264/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   352/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   440/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   528/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiFFiiiiiii
...
```

After:
```
Testing stage0 compiletest suite=ui mode=ui (x86_64-unknown-linux-gnu)

running 15274 tests
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii    88/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   176/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   264/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   352/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   440/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   528/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
[ui] tests/ui/associated-type-bounds/implied-in-supertrait.rs ... F

[ui] tests/ui/associated-type-bounds/return-type-notation/basic.rs#next_with ... F
iiiiiiiiiiiii
...
```

This serves a similar use case to the existing RUSTC_TEST_FAIL_FAST, but is on by default and as a result much more discoverable.
We should consider unifying RUSTC_TEST_FAIL_FAST with the `--no-fail-fast` flag in the future for consistency and discoverability.

Previously, libtest would wait until all tests finished running to print the progress, which made it
annoying to run many tests at once (since you don't know which have failed). Change it to print the
names as soon as they fail.

This also adds a test for the terse output; previously it was untested.

Includes related tests and documentation pages.

Superceded by feature gate tests.

Add a test that `f16` and `f128` are usable with the feature gate
enabled, as well as a test that user types with the same name as
primitives are not improperly gated.

… into queries

bootstrap/libtest: print test name eagerly on failure even with `verbose-tests=false` / `--quiet`

Previously, libtest would wait until all tests finished running to print the progress, which made it
annoying to run many tests at once (since you don't know which have failed). Change it to print the
names as soon as they fail.

This makes it much easier to know which test failed without having to wait for compiletest to completely finish running. Before:
```
Testing stage0 compiletest suite=ui mode=ui (x86_64-unknown-linux-gnu)

running 15274 tests
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii    88/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   176/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   264/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   352/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   440/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   528/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiFFiiiiiii
...
```

After:
```
Testing stage0 compiletest suite=ui mode=ui (x86_64-unknown-linux-gnu)

running 15274 tests
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii    88/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   176/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   264/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   352/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   440/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii   528/15274
iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
[ui] tests/ui/associated-type-bounds/implied-in-supertrait.rs ... F

[ui] tests/ui/associated-type-bounds/return-type-notation/basic.rs#next_with ... F
iiiiiiiiiiiii
...
```

This serves a similar use case to the existing RUSTC_TEST_FAIL_FAST, but is on by default and as a result much more discoverable. We should consider unifying RUSTC_TEST_FAIL_FAST with the `--no-fail-fast` flag in the future for consistency and discoverability.

…pace, r=compiler-errors

Stabilize the `#[diagnostic]` namespace and `#[diagnostic::on_unimplemented]` attribute

This PR stabilizes the `#[diagnostic]` attribute namespace and a minimal option of the `#[diagnostic::on_unimplemented]` attribute.

The `#[diagnostic]` attribute namespace is meant to provide a home for attributes that allow users to influence error messages emitted by the compiler. The compiler is not guaranteed to use any of this hints, however it should accept any (non-)existing attribute in this namespace and potentially emit lint-warnings for unused attributes and options. This is meant to allow discarding certain attributes/options in the future to allow fundamental changes to the compiler without the need to keep then non-meaningful options working.

The `#[diagnostic::on_unimplemented]` attribute is allowed to appear on a trait definition. This allows crate authors to hint the compiler to emit a specific error message if a certain trait is not implemented. For the `#[diagnostic::on_unimplemented]` attribute the following options are implemented:

* `message` which provides the text for the top level error message
* `label` which provides the text for the label shown inline in the broken code in the error message
* `note` which provides additional notes.

The `note` option can appear several times, which results in several note messages being emitted. If any of the other options appears several times the first occurrence of the relevant option specifies the actually used value. Any other occurrence generates an lint warning. For any other non-existing option a lint-warning is generated.

All three options accept a text as argument. This text is allowed to contain format parameters referring to generic argument or `Self` by name via the `{Self}` or `{NameOfGenericArgument}` syntax. For any non-existing argument a lint warning is generated.

This allows to have a trait definition like:

```rust
#[diagnostic::on_unimplemented(
    message = "My Message for `ImportantTrait<{A}>` is not implemented for `{Self}`",
    label = "My Label",
    note = "Note 1",
    note = "Note 2"
)]
trait ImportantTrait<A> {}

```

which then generates for the following code

```rust
fn use_my_trait(_: impl ImportantTrait<i32>) {}

fn main() {
    use_my_trait(String::new());
}
```

this error message:

```
error[E0277]: My Message for `ImportantTrait<i32>` is not implemented for `String`
  --> src/main.rs:14:18
   |
14 |     use_my_trait(String::new());
   |     ------------ ^^^^^^^^^^^^^ My Label
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `ImportantTrait<i32>` is not implemented for `String`
   = note: Note 1
   = note: Note 2
```

[Playground with the unstable feature](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=05133acce8e1d163d481e97631f17536)

Fixes rust-lang#111996

…elix

Detect unused struct impls pub trait

Fixes rust-lang#47851

…te, r=compiler-errors

`f16` and `f128` step 3: compiler support & feature gate

Continuation of rust-lang#121841, another portion of rust-lang#114607

This PR exposes the new types to the world and adds a feature gate. Marking this as a draft because I need some feedback on where I did the feature gate check. It also does not yet catch type via suffixed literals (so the feature gate test will fail, probably some others too because I haven't belssed).

If there is a better place to check all types after resolution, I can do that. If not, I figure maybe I can add a second gate location in AST when it checks numeric suffixes.

Unfortunately I still don't think there is much testing to be done for correctness (codegen tests or parsed value checks) until we have basic library support. I think that will be the next step.

Tracking issue: rust-lang#116909

r? `@compiler-errors`
cc `@Nilstrieb`
`@rustbot` label +F-f16_and_f128

Removing absolute path in proc-macro

With rust 1.75 the absolute build path name is embedding into proc-macro (.rustc section) and which causes reproducibility issues.
Detailed issue description is here - rust-lang#120825 (comment)

With this change the 'absolute path' changed back to '/rust/$hash' format as in earlier revisions.

Add better explanation for `rustc_index::IndexVec`

I feel like I didn't do a great job explaining what this does in rust-lang#119800, so this PR tries to give an example of why and how you would use it.

Addresses rust-lang#93792.

…astorino

Uplift some feeding out of `associated_type_for_impl_trait_in_impl` and into queries

This PR moves the `type_of` and `generics_of` query feeding out of `associated_type_for_impl_trait_in_impl`, since eagerly feeding results in query cycles due to a subtle interaction with `resolve_bound_vars`.

Fixes rust-lang#122019

r? spastorino

…=petrochenkov

Fix linting paths with qself in `unused_qualifications`

Fixes rust-lang#121999

`resolve_qpath` ends up being called again with `qself` set to `None` to check trait items from fully qualified paths. To avoid this the lint is moved to a place that accounts for this already

https://github.com/rust-lang/rust/blob/96561a8fd134e8f2b205769a4fca03b392d9f484/compiler/rustc_resolve/src/late.rs#L4074-L4088

r? `@petrochenkov`

…, r=oli-obk

Move generic `NonZero` `rustc_layout_scalar_valid_range_start` attribute to inner type.

Tracking issue: rust-lang#120257

r? ``@dtolnay``

…ute to inner type.