Co-authored-by: bjorn3 <[email protected]>

This will allow the `run-coverage` mode to easily set environment variable
`LLVM_PROFILE_FILE`, and to prevent the executable from being deleted after a
successful run.

Currently a test without a `failure-status` directive is treated as having an
expected failure-status of 1, but `run-coverage` tests will want to treat those
tests as expecting success instead.

…rustdoc`

…coverage`

To make it easier to verify that the output snapshots have been migrated
faithfully, this change adds some temporary helper code that lets us avoid
having to completely re-bless the existing snapshots.

A later change in this PR will then re-bless the tests and remove the temporary
helper code.

Signed-off-by: ozkanonur <[email protected]>

Support for native WASM exceptions

### Motivation
Currently, rustc does not support native WASM exceptions. It does support JavaScript based exceptions for the wasm32-emscripten-target, but this requires back&forth with javascript for many calls, which is very slow.

Native wasm support for exceptions is quite common: Clang+LLVM implemented them years ago, and all major browsers support them by now. They enable zero-cost exceptions, at least with regard to runtime-performance-cost. They may increase startup-time and code size, though.

### Important: This PR does not change default behaviour
Exceptions usually add a lot of code in form of unwinding blocks, increasing the binary size. Most users probably do not want that, especially which regard to web development.

Therefore, wasm exceptions play a similar role as WASM-threads: rustc should support them, like clang does, but users who want to use it have to use some command-line magic like rustflags to opt in.

### What does this PR do?
As stated above, the default behaviour is not changed. It is already possible to opt-in into wasm exceptions using the command line. Unfortunately, the LLVM IR is invalid and the LLVM backend crashes.
```
rustc <sourcefile>
  --target wasm32-unknown-unknown
  -C panic=unwind
  -C llvm-args=-wasm-enable-eh
  -C target-feature=+exception-handling
```
As it turns out, LLVM is quite picky when it comes to IR for exception handling. If the IR does not look exactly like it should, some LLVM-assertions fail and the code generation crashes.

This PR adds the necessary modifications to the code generator to make it work. It also adds `exception-handling` as a wasm target feature.

### What this PR does not / what is missing
This PR is not a full fledges solution. It is the first step. A few parts are still missing; however, it is already useable (see next section).

Currently missing:
* The std library has to be adapted. Currently, only [no_std] crates work
* Usually, nested exceptions abort the program (i.e. a panic during the cleanup of another panic). This is currently not done yet.
  - Currently, code inside cleanup handlers does not unwind
  - To fix this requires a little more work: The code generator currently maintains a single terminate block per function for this. Unfortunately, WASM requires funclet based exception handling. Therefore, we need to create a terminate block per funclet. This is probably not a big problem, but I want to keep this PR simple.

### How to use the compiler given this PR?
This PR does not add any command line flags or features. It uses those which are already there. To compile with exceptions enabled, you need
* to set the panic strategy to unwind, i.e. `-C panic=unwind`
* to enable the exception-handling target feature, i.e. `-C target-feature=+exception-handling`
* to tell LLVM about the exception handling, i.e. `-C llvm-args=-wasm-enable-eh`

Since the standard library has not been adapted, you can only use it in [no_std] crates as of now. The intrinsic `core::intrinsics::r#try` works. To throw exceptions, you need the ````@llvm.wasm.throw```` intrinsic.

I created a sample application which works for me: https://github.com/mirkootter/rust-wasm-demos
This example can be run at https://webassembly.sh

…-errors

suggest `slice::swap` for `mem::swap(&mut x[0], &mut x[1])` borrowck error

Recently saw someone ask why this code (example slightly modified):
```rs
fn main() {
  let mut foo = [1, 2];
  std::mem::swap(&mut foo[0], &mut foo[1]);
}
```
triggers this error and how to fix it:
```
error[E0499]: cannot borrow `foo[_]` as mutable more than once at a time
 --> src/main.rs:4:33
  |
4 |     std::mem::swap(&mut foo[0], &mut foo[1]);
  |     -------------- -----------  ^^^^^^^^^^^ second mutable borrow occurs here
  |     |              |
  |     |              first mutable borrow occurs here
  |     first borrow later used by call
  |
  = help: consider using `.split_at_mut(position)` or similar method to obtain two mutable non-overlapping sub-slices
```
The current help message is nice and goes in the right direction, but I think we can do better for this specific instance and suggest `slice::swap`, which makes this compile

resolve: Remove artificial import ambiguity errors

Fixes rust-lang#56414.

FCP report: rust-lang#112086 (comment)

refactor `tool_doc!`

resolves rust-lang#112211 (comment)

Convert `run-make/coverage-reports` tests to use a custom compiletest mode

I was frustrated by the fact that most of the coverage tests are glued together with makefiles and shell scripts, so I tried my hand at converting most of them over to a newly-implemented `run-coverage` mode/suite in compiletest.

This ~~*mostly*~~ resolves rust-lang#85009, ~~though I've left a small number of the existing tests as-is because they would require more work to fix/support~~.

---

I had time to go back and add support for the more troublesome tests that I had initially skipped over, so this PR now manages to completely get rid of `run-make/coverage-reports`.

---

The patches are arranged as follows:

- Declare the new mode/suite in bootstrap
- Small changes to compiletest that will be used by the new mode
- Implement the new mode in compiletest
- Migrate most of the tests over
- Add more code to bootstrap and compiletest to support the remaining tests
- Migrate the remaining tests (with some temporary hacks to avoid re-blessing them)
- Remove the temporary hacks and re-bless the migrated tests
- Remove the unused remnants of `run-make/coverage-reports`

…r=davidtwco

Migrate some rustc_builtin_macros to SessionDiagnostic

Part of rust-lang#100717.

```@rustbot``` label +A-translation

…time-args-in-apit, r=eholk

Account for late-bound vars from parent arg-position impl trait

We should be reporting an error like we do for late-bound args coming from a parent APIT.

Fixes rust-lang#113016