See rust-lang/unsafe-code-guidelines#500.

Co-authored-by: Ralf Jung <post@ralfj.de>

Use more accurate spans for multipart suggestion.

Do not leave a `+ ` line with only whitespace. In reality, the user will want to remove the entire line.

Use multispan suggestion.

…fix`

…c error tainting and error translations

…s, r=oli-obk

Disable dead variant removal for `#[repr(C)]` enums.

This prevents removing dead branches from a `#[repr(C)]` enum (they now get discriminants allocated as if they were inhabited).

Implementation notes: ABI of something like

```rust
#[repr(C)]
enum Foo {
    Foo(!),
}
```

is still `Uninhabited`, but its layout is now computed as if all the branches were inhabited.
This seemed to me like a proper way to do it, especially given that ABI sanity check explicitly asserts that type-level uninhabitedness implies ABI uninhabitedness.

This probably needs some sort of FCP (given that it changes `#[repr(C)]` layout, which is a stable guarantee), but I’m not sure how to call for one or which team is the most relevant.

See rust-lang/unsafe-code-guidelines#500.

…, r=davidtwco

Migrate some rustc_builtin_macros to SessionDiagnostic

<!--
If this PR is related to an unstable feature or an otherwise tracked effort,
please link to the relevant tracking issue here. If you don't know of a related
tracking issue or there are none, feel free to ignore this.

This PR will get automatically assigned to a reviewer. In case you would like
a specific user to review your work, you can assign it to them by using

    r​? <reviewer name>
-->

Part of rust-lang#100717.
pick up abandoned pr: rust-lang#101935
`@rustbot` label +A-translation

…avidtwco

Remove some duplicated tests

probably some parallel PR development that happened here, copying over the same examples from issues.

…arent, r=davidtwco

Reject SmartPointer constructions not serving the purpose

Tracking issue: rust-lang#123430

With this PR we will reject a row of malformed `SmartPointer` implementor candidates.

cc `@Darksonn` `@davidtwco` for context.

Tweak some structured suggestions to be more verbose and accurate

Addressing some issues I found while working on rust-lang#127282.
```
error: this URL is not a hyperlink
  --> $DIR/auxiliary/include-str-bare-urls.md:1:11
   |
LL | HEADS UP! https://example.com MUST SHOW UP IN THE STDERR FILE!
   |           ^^^^^^^^^^^^^^^^^^^
   |
   = note: bare URLs are not automatically turned into clickable links
note: the lint level is defined here
  --> $DIR/include-str-bare-urls.rs:14:9
   |
LL | #![deny(rustdoc::bare_urls)]
   |         ^^^^^^^^^^^^^^^^^^
help: use an automatic link instead
   |
LL | HEADS UP! <https://example.com> MUST SHOW UP IN THE STDERR FILE!
   |           +                   +
```
```
error[E0384]: cannot assign twice to immutable variable `v`
  --> $DIR/assign-imm-local-twice.rs:7:5
   |
LL |     v = 1;
   |     ----- first assignment to `v`
LL |     println!("v={}", v);
LL |     v = 2;
   |     ^^^^^ cannot assign twice to immutable variable
   |
help: consider making this binding mutable
   |
LL |     let mut v: isize;
   |         +++
```
```
error[E0393]: the type parameter `Rhs` must be explicitly specified
  --> $DIR/issue-22560.rs:9:23
   |
LL | trait Sub<Rhs=Self> {
   | ------------------- type parameter `Rhs` must be specified for this
...
LL | type Test = dyn Add + Sub;
   |                       ^^^
   |
   = note: because of the default `Self` reference, type parameters must be specified on object types
help: set the type parameter to the desired type
   |
LL | type Test = dyn Add + Sub<Rhs>;
   |                          +++++
```
```
error[E0596]: cannot borrow `v` as mutable, as it is not declared as mutable
  --> $DIR/issue-33819.rs:4:34
   |
LL |         Some(ref v) => { let a = &mut v; },
   |                                  ^^^^^^ cannot borrow as mutable
   |
help: try removing `&mut` here
   |
LL -         Some(ref v) => { let a = &mut v; },
LL +         Some(ref v) => { let a = v; },
   |
```
```
help: remove the invocation before committing it to a version control system
   |
LL -     dbg!();
   |
```
```
error[E0308]: mismatched types
  --> $DIR/issue-39974.rs:1:21
   |
LL | const LENGTH: f64 = 2;
   |                     ^ expected `f64`, found integer
   |
help: use a float literal
   |
LL | const LENGTH: f64 = 2.0;
   |                      ++
```
```
error[E0529]: expected an array or slice, found `Vec<i32>`
  --> $DIR/match-ergonomics.rs:8:9
   |
LL |         [&v] => {},
   |         ^^^^ pattern cannot match with input type `Vec<i32>`
   |
help: consider slicing here
   |
LL |     match x[..] {
   |            ++++
```
```
error[E0609]: no field `0` on type `[u32; 1]`
  --> $DIR/parenthesized-deref-suggestion.rs:10:21
   |
LL |     (x as [u32; 1]).0;
   |                     ^ unknown field
   |
help: instead of using tuple indexing, use array indexing
   |
LL |     (x as [u32; 1])[0];
   |                    ~ +
```

…ap_path_prefix, r=Kobzol

Allow to have different types for arguments of `Rustc::remap_path_prefix`

r? `@Kobzol`

…var, r=aDotInTheVoid

jsondocck: add `$FILE` built-in variable

This built-in variable will allow accessing the full path to the currently tested file and allow to test things like source code spans generated by rustdoc-json, and that is exactly the reason why I've come up with the idea to add this

[futher discussion on zulip](https://rust-lang.zulipchat.com/#narrow/stream/266220-t-rustdoc/topic/rustdoc-json.20test.20help/near/449039819)

…r=albertlarsan68

Trivial update on tidy bless note

Make the notes more verbose.

Remove a use of `StructuredDiag`, which is incompatible with automatic error tainting and error translations

fixes rust-lang#127219

I want to remove all of `StructuredDiag`, but it's a bit more involved as it is also used from the `ItemCtxt`, which doesn't support tainting yet.