…args.rs`

…p of files

This is a straightforward wrapper that uses the existing helpers for C
string handling and errno handling.

Having this available is convenient for UNIX utility programs written in
Rust, and avoids having to call unsafe functions like `libc::chown`
directly and handle errors manually, in a program that may otherwise be
entirely safe code.

In addition, these functions provide a more Rustic interface by
accepting appropriate traits and using `None` rather than `-1`.

If #![feature] is used outside the nightly channel for only lib
features, the check will be delayed to the stability pass after
parsing. This is done so that appropriate help messages can be shown if
the #![feature] has been used needlessly

…op, r=estebank

Emit clearer diagnostics for parens around `for` loop heads

Fixes rust-lang#63113
r? `@estebank`

Point to closure when emitting 'cannot move out' for captured variable

Attempts to fix rust-lang#87456. The error message now points to the capturing closure, but I was not able to explain _why_ the closure implements `Fn` or `FnMut` (`TypeckResults::closure_kind_origins` did not contain anything for the closure in question).

cc `@Aaron1011`

…ounds, r=estebank

Recover invalid assoc type bounds using `==`

Fix rust-lang#87493
r? `@estebank`

…k-Simulacrum

Improve build command for compiler docs

It was rather complicated to document rustc crates. With this, you can directly run:

```console
x.py doc compiler
x.py doc compiler/rustc_hir_pretty
```

The second commit adds the handling of the `--open` flag.

r? `@Mark-Simulacrum`

…asper

Do not issue E0071 if a type error has already been reported

Fixes rust-lang#88844. A suggested fix is already included in the error message for E0412, so with my changes, E0071 is simply not emitted anymore if the type in question is a "type error". This makes sense, I think, because we cannot confidently state that something is "not a struct" if we couldn't resolve it properly; and it's unnecessary to pollute the output with this additional error message, as it is a direct consequence of the former error.

I have also addressed the issue mentioned in rust-lang#88844 (comment) by changing the fixed example in the documentation to more closely match the erroneous code example.

Fix handling of `hir::GenericArg::Infer` in `wrong_number_of_generic_args.rs`

Fixes rust-lang#87563. More precisely, I have fixed the "index out of bounds" error, which is what rust-lang#87563 is about. The example given there still ICEs due to running into this `todo!()`, but I'd say that this is a separate issue:
https://github.com/rust-lang/rust/blob/c3c0f80d6081092faff801542dd82f0e2420152b/compiler/rustc_typeck/src/astconv/mod.rs#L460-L463

Add chown functions to std::os::unix::fs to change the owner and group of files

This is a straightforward wrapper that uses the existing helpers for C
string handling and errno handling.

Having this available is convenient for UNIX utility programs written in
Rust, and avoids having to call unsafe functions like `libc::chown`
directly and handle errors manually, in a program that may otherwise be
entirely safe code.

In addition, these functions provide a more Rustic interface by
accepting appropriate traits and using `None` rather than `-1`.

Allow `panic!("{}", computed_str)` in const fn.

Special-case `panic!("{}", arg)` and translate it to `panic_display(&arg)`. `panic_display` will behave like `panic_any` in cosnt eval and behave like `panic!(format_args!("{}", arg))` in runtime.

This should bring Rust 2015 and 2021 to feature parity in terms of `const_panic`; and hopefully would unblock the stabilisation of rust-lang#51999.

`@rustbot` modify labels: +T-compiler +T-libs +A-const-eval +A-const-fn

r? `@oli-obk`

Add rustdoc version into the help popup

After a discussion with a rustdoc user about a specific behaviour, we realized we were not talking about the same version. To add on top of it, it was actually not that simple to find out the version since it was hosted documentation.

So to simplify things, I added the version into the help popup:

![Screenshot from 2021-09-16 10-45-52](https://user-images.githubusercontent.com/3050060/133581128-b93b460a-e1cb-4a31-9f2f-97c7a916cfcc.png)

Does the version format looks or would you prefer that I add more information? We can also add the commit hash, commit date, host and release.

cc `@rust-lang/rustdoc`
r? `@jyn514`

Suggest removing `#![feature]` for library features that have been stabilized

Issue: rust-lang#88802
Delayed the check if #![feature] has been used to enable lib features in a non-nightly build to occur after TyCtxt has been constructed.