Fix `let` keyword removal suggestion in structs
(1.) Fixes a bug where, given this code:
```rust
struct Foo {
let x: i32,
}
```
We were parsing the field name as `let` instead of `x`, which causes issues later on in the type-checking phase.
(2.) Also, suggestions for `let: i32` as a field regressed, displaying this extra `help:` which is removed by this PR
```
help: remove the let, the `let` keyword is not allowed in struct field definitions
|
2 - let: i32,
2 + : i32,
```
(3.) Makes the suggestion text a bit more succinct, since we don't need to re-explain that `let` is not allowed in this position (since it's in a note that follows). This causes the suggestion to render inline as well.
cc `@gimbles,` this addresses a few nits I mentioned in your PR.
Remove `expr_parentheses_needed` from `ParseSess`
Not sure why this method needed to exist on `ParseSess`, but we can achieve the same behavior by just inlining it everywhere.
Group together more size assertions.
Also add a few more assertions for some relevant token-related types.
And fix an erroneous comment in `rustc_errors`.
r? `@lqd`
Improve errors for incomplete functions in struct definitions
Given the following code:
```rust
fn main() {}
struct Foo {
fn
}
```
[playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=29139f870511f6918324be5ddc26c345)
The current output is:
```
Compiling playground v0.0.1 (/playground)
error: functions are not allowed in struct definitions
--> src/main.rs:4:5
|
4 | fn
| ^^
|
= help: unlike in C++, Java, and C#, functions are declared in `impl` blocks
= help: see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information
error: could not compile `playground` due to previous error
```
In this case, rustc should suggest escaping `fn` to use it as an identifier.
Migrate more of rustc_parse to SessionDiagnostic
Still far from complete, but I thought I'd add a checkpoint here because rebasing was starting to get annoying.
Rollup of 5 pull requests
Successful merges:
- #102143 (Recover from struct nested in struct)
- #102178 (bootstrap: the backtrace feature is stable, no need to allow it any more)
- #102197 (Stabilize const `BTree{Map,Set}::new`)
- #102267 (Don't set RUSTC in the bootstrap build script)
- #102270 (Remove benches from `rustc_middle`)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
FIX - ambiguous Diagnostic link in docs
UPDATE - rename diagnostic_items to IntoDiagnostic and AddToDiagnostic
[Gardening] FIX - formatting via `x fmt`
FIX - rebase conflicts. NOTE: Confirm wheather or not we want to handle TargetDataLayoutErrorsWrapper this way
DELETE - unneeded allow attributes in Handler method
FIX - broken test
FIX - Rebase conflict
UPDATE - rename residual _SessionDiagnostic and fix LintDiag link
