... if they use arbitrary enum discriminant. Code like

```rust
enum Enum {
    Foo = 1,
    Bar(),
    Baz{}
}
```

seems to be unintentionally allowed so we couldn't disallow them now,
but we could disallow them if arbitrary enum discriminant is used before
1.56 hits stable.

When we point at a binding to suggest giving it a type, erase all the
type for ADTs that have been resolved, leaving only the ones that could
not be inferred. For small shallow types this is not a problem, but for
big nested types with lots of params, this can otherwise cause a lot of
unnecessary visual output.

When the value of a const param isn't inferred, replace it with the
param name from the definition.

Version 5 adds Branch Regions which are a prerequisite for branch coverage.
Version 6 can use the zeroth filename as prefix for other relative files.

This commit augments Swatinem's initial commit in uncommitted PR rust-lang#90047,
which was a great starting point, but did not fully support LLVM
Coverage Mapping Format version 6.

Version 6 requires adding the compilation directory when file paths are
relative, and since Rustc coverage maps use relative paths, we should
add the expected compilation directory entry.

Note, however, that with the compilation directory, coverage reports
from `llvm-cov show` can now report file names (when the report includes
more than one file) with the full absolute path to the file.

This would be a problem for test results, but the workaround (for the
rust coverage tests) is to include an additional `llvm-cov show`
parameter: `--compilation-dir=.`

Disallow non-c-like but "fieldless" ADTs from being casted to integer if they use arbitrary enum discriminant

Code like

```rust
#[repr(u8)]
enum Enum {
    Foo /* = 0 */,
    Bar(),
    Baz{}
}

let x = Enum::Bar() as u8;
```

seems to be unintentionally allowed so we couldn't disallow them now ~~, but we could disallow them if arbitrary enum discriminant is used before 1.56 hits stable~~ (stabilization was reverted).

Related: rust-lang#88621

`@rustbot` label +T-lang

…=nagisa

Only shown relevant type params in E0283 label

When we point at a binding to suggest giving it a type, erase all the
type for ADTs that have been resolved, leaving only the ones that could
not be inferred. For small shallow types this is not a problem, but for
big nested types with lots of params, this can otherwise cause a lot of
unnecessary visual output.

Use `get_diagnostic_name` more

…kh726

Remove all migrate.nll.stderr files

There are a few ui tests that setup the revisions like:
```rust
// revisions: migrate nll`
// [nll]compile-flags: -Zborrowck=mir
```

However most of them fail to disable the nll compare mode like this:
```rust
// ignore-compare-mode-nll
```

This ends up generating confusing files ending in `.migrate.nll.stderr` because the nll compare mode is run on top of the migrate revision.

This PR fixes this by adding `ignore-compare-mode-nll` to these tests.

I would have just made these tests use compare modes instead but I assume the reason these tests are messing around with revisions instead of just letting the nll compare mode do its thing is to enforce error annotations for both migrate and nll.
Relying on just compare modes would only have the error annotations for migrate.

… r=tmandry

Add support for LLVM coverage mapping format versions 5 and 6

This PR cherry-pick's Swatinem's initial commit in unsubmitted PR rust-lang#90047.

My additional commit augments Swatinem's great starting point, but adds full support for LLVM
Coverage Mapping Format version 6, conditionally, if compiling with LLVM 13.

Version 6 requires adding the compilation directory when file paths are
relative, and since Rustc coverage maps use relative paths, we should
add the expected compilation directory entry.

Note, however, that with the compilation directory, coverage reports
from `llvm-cov show` can now report file names (when the report includes
more than one file) with the full absolute path to the file.

This would be a problem for test results, but the workaround (for the
rust coverage tests) is to include an additional `llvm-cov show`
parameter: `--compilation-dir=.`

…l, r=cjgillot

Improve error message for `E0659` if the source is not available

Fixes rust-lang#91028. The fix is similar to those in rust-lang#89233 and rust-lang#87088. With this change, instead of the dangling
```
note: `Option` could also refer to the enum defined here
```
I get
```
note: `Option` could also refer to an enum from prelude
```
If the standard library source code _is_ available, the output does not change.