Rollup of 10 pull requests

Successful merges:

 - #86422 (Emit clearer diagnostics for parens around `for` loop heads)
 - #87460 (Point to closure when emitting 'cannot move out' for captured variable)
 - #87566 (Recover invalid assoc type bounds using `==`)
 - #88666 (Improve build command for compiler docs)
 - #88899 (Do not issue E0071 if a type error has already been reported)
 - #88949 (Fix handling of `hir::GenericArg::Infer` in `wrong_number_of_generic_args.rs`)
 - #88953 (Add chown functions to std::os::unix::fs to change the owner and group of files)
 - #88954 (Allow `panic!("{}", computed_str)` in const fn.)
 - #88964 (Add rustdoc version into the help popup)
 - #89012 (Suggest removing `#![feature]` for library features that have been stabilized)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

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

Issue: https://github.com/rust-lang/rust/issues/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.

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`

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 #51999.

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

r? `@oli-obk`

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`.

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

Fixes #87563. More precisely, I have fixed the "index out of bounds" error, which is what #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

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

Fixes #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 https://github.com/rust-lang/rust/issues/88844#issuecomment-917324856 by changing the fixed example in the documentation to more closely match the erroneous code example.

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`

Recover invalid assoc type bounds using `==`

Fix #87493
r? `@estebank`

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

Attempts to fix #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`

Emit clearer diagnostics for parens around `for` loop heads

Fixes #63113
r? `@estebank`

Remove concept of 'completion' from the projection cache

Fixes #88910

When we initially store a `NormalizedTy` in the projection cache,
we discard all obligations that we can (while ensuring that we
don't cause any issues with incremental compilation).

Marking a projection cache entry as 'completed' discards all
obligations associated with it. This can only cause problems,
since any obligations stored in the cache are there for a reason
(e.g. they evaluate to `EvaluatedToOkModuloRegions`).

This commit removes `complete` and `complete_normalized` entirely.

Rollup of 10 pull requests

Successful merges:

 - #86382 (Make diagnostics clearer for `?` operators)
 - #87529 (Fix ICE in `improper_ctypes_definitions` lint with all-ZST transparent types)
 - #88339 (Add TcpListener::into_incoming and IntoIncoming)
 - #88735 (Don't lint about missing code examples in derived traits)
 - #88751 (Couple of changes to FileSearch and SearchPath)
 - #88883 (Move some tests to more reasonable directories - 7)
 - #88887 (Const Deref)
 - #88911 (Improve error message for type mismatch in generator arguments)
 - #89014 (PassWrapper: handle separate Module*SanitizerPass)
 - #89033 (Set the library path in sysroot-crates-are-unstable)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Set the library path in sysroot-crates-are-unstable

Most of the `run-make-fulldeps` tests use a make-driven rustc command
that includes `HOST_RPATH_DIR` in the library path, but this particular
test runs from python instead. When the toolchain is built without
`rpath` enabled, we need that library path in the environment so it can
find its own libraries.

PassWrapper: handle separate Module*SanitizerPass

Change ab41eef9aca3 in LLVM split MemorySanitizerPass into
MemorySanitizerPass for functions and ModuleMemorySanitizerPass for
modules. There's a related change for ThreadSanitizerPass, and in here
since we're using a ModulePassManager I only add the module flavor of
the pass on LLVM 14.

r? `@nikic` cc `@nagisa`

Improve error message for type mismatch in generator arguments

Fixes #88653. The code example given there is invalid because the `Generator` trait (unlike the `Fn` traits) does not take the generator arguments in tupled-up form (because there can only be one argument, from my understanding). Hence, the type error in the example in #88653 is correct, because the given generator takes a `bool` argument, whereas the function's return type talks about a generator with a `(bool,)` argument.

The error message is both confusing and wrong, though: It is wrong because it displays the wrong "expected signature", and it is confusing because both the "expected" and "found" notes point at the same span. With my changes, I get the following, more helpful output:
```
error[E0631]: type mismatch in generator arguments
 --> test.rs:5:22
  |
5 | fn foo(bar: bool) -> impl Generator<(bool,)> {
  |                      ^^^^^^^^^^^^^^^^^^^^^^^ expected signature of `fn((bool,)) -> _`
6 |     |bar| {
  |     ----- found signature of `fn(bool) -> _`
```

Const Deref

Implements `const Deref`/`const DerefMut` for `&mut T`, `&T`, `Cow<'_, B>` and `ManuallyDrop<T>`

Move some tests to more reasonable directories - 7

cc #73494
r? ``@petrochenkov``

Couple of changes to FileSearch and SearchPath

* Turn a couple of regular comments into doc comments
* Move `get_tools_search_paths` from `FileSearch` to `Session`
* Use Lrc instead of Option to avoid duplication of a `SearchPath`

Don't lint about missing code examples in derived traits

When the `missing_doc_code_examples` lint is performed it also requires that derived Trait implementations have a code example for each member etc., which causes undesirable behavior.

# Examples

With `missing_doc_code_examples` enable we are not able to use the `Clone` derive macro due to the generated code not being documented:
```rust
#[deny(rustdoc::missing_doc_code_examples)]

/// docs
/// ```
/// let s = SomeStruct;
/// ```
#[derive(Clone)]
pub struct SomeStruct;
```
yields:
```
 Documenting testt v0.1.0 (<redacted>)
error: missing code example in this documentation
 --> src/lib.rs:7:10
  |
7 | #[derive(Clone)]
  |          ^^^^^
  |
note: the lint level is defined here
 --> src/lib.rs:1:8
  |
1 | #[deny(rustdoc::missing_doc_code_examples)]
  |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: missing code example in this documentation
 --> src/lib.rs:7:10
  |
7 | #[derive(Clone)]
  |          ^^^^^

error: could not document `testt`

Caused by:
  process didn't exit successfully: `rustdoc ...
```

closes #81775

Add TcpListener::into_incoming and IntoIncoming

The `incoming` method is really useful, however for some use cases the borrow
this introduces is needlessly restricting. Thus, an owned variant is added.

r? ``@joshtriplett``

Fix ICE in `improper_ctypes_definitions` lint with all-ZST transparent types

Fixes #87496. There is also another function in the same file that looks fishy, but I haven't been able to produce an ICE there, and in any case, it's not related to #87496:
https://github.com/rust-lang/rust/blob/fd853c00e255559255885aadff9e93a1760c8728/compiler/rustc_lint/src/types.rs#L720-L734

r? ```@JohnTitor```

Make diagnostics clearer for `?` operators

Re-submission of #75029, fixes #71309
This also revives the `content` methods removed by #83185.
r? `@estebank`

Avoid unnecessary formatting when trace log level is disabled

Introduce a fast path that avoids the `debug_tuple` abstraction when deriving Debug for unit-like enum variants.

The intent here is to allow LLVM to remove the switch entirely in favor of an
indexed load from a table of constant strings, which is likely what the
programmer would write in C. Unfortunately, LLVM currently doesn't perform this
optimization due to a bug, but there is [a
patch](https://reviews.llvm.org/D109565) that fixes this issue. I've verified
that, with that patch applied on top of this commit, Debug for unit-like tuple
variants becomes a load, reducing the O(n) code bloat to O(1).

Note that inlining `DebugTuple::finish()` wasn't enough to allow LLVM to
optimize the code properly; I had to avoid the abstraction entirely. Not using
the abstraction is likely better for compile time anyway.

Part of #88793.

r? `@oli-obk`

Most of the `run-make-fulldeps` tests use a make-driven rustc command
that includes `HOST_RPATH_DIR` in the library path, but this particular
test runs from python instead. When the toolchain is built without
`rpath` enabled, we need that library path in the environment so it can
find its own libraries.

Fixes #81775

Point at argument instead of call for their obligations

When an obligation is introduced by a specific `fn` argument, point at
the argument instead of the `fn` call if the obligation fails to be
fulfilled.

Move the information about pointing at the call argument expression in
an unmet obligation span from the `FulfillmentError` to a new
`ObligationCauseCode`.

When giving an error about an obligation introduced by a function call
that an argument doesn't fulfill, and that argument is a block, add a
span_label pointing at the innermost tail expression.

Current output:

```
error[E0425]: cannot find value `x` in this scope
 --> f10.rs:4:14
  |
4 |         Some(x * 2)
  |              ^ not found in this scope

error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
 --> f10.rs:2:31
  |
2 |       let p = Some(45).and_then({
  |  ______________________--------_^
  | |                      |
  | |                      required by a bound introduced by this call
3 | |         |x| println!("doubling {}", x);
4 | |         Some(x * 2)
  | |         -----------
5 | |     });
  | |_____^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`
  |
  = help: the trait `FnOnce<({integer},)>` is not implemented for `Option<_>`
```

Previous output:

```
error[E0425]: cannot find value `x` in this scope
 --> f10.rs:4:14
  |
4 |         Some(x * 2)
  |              ^ not found in this scope

error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
 --> f10.rs:2:22
  |
2 |     let p = Some(45).and_then({
  |                      ^^^^^^^^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`
  |
  = help: the trait `FnOnce<({integer},)>` is not implemented for `Option<_>`
```

Partially address #27300. Will require rebasing on top of #88546.

Rollup of 10 pull requests

Successful merges:

 - #88292 (Enable --generate-link-to-definition for rustc's docs)
 - #88729 (Recover from `Foo(a: 1, b: 2)`)
 - #88875 (cleanup(rustc_trait_selection): remove vestigial code from rustc_on_unimplemented)
 - #88892 (Move object safety suggestions to the end of the error)
 - #88928 (Document the closure arguments for `reduce`.)
 - #88976 (Clean up and add doc comments for CStr)
 - #88983 (Allow calling `get_body_with_borrowck_facts` without `-Z polonius`)
 - #88985 (Update clobber_abi list to include k[1-7] regs)
 - #88986 (Update the backtrace crate)
 - #89009 (Fix typo in `break` docs)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

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

Fix typo in `break` docs