Previously, attributes on 'if' expressions (e.g. #[attr] if true {})
were disallowed during parsing. This made it impossible for macros to
perform any custom handling of such attributes (e.g. stripping them
away), since a compilation error would be emitted before they ever had a
chance to run.

This PR permits attributes on 'if' expressions ('if-attrs' from here on).
Both built-in attributes (e.g. `#[allow]`, `#[cfg]`) are supported.

We still do *not* accept attributes on 'other parts' of an if-else
chain. That is, the following code snippet still fails to parse:

```rust
if true {} #[attr] else if false {} else #[attr] if false {} #[attr]
else {}
```

Co-Authored-By: bjorn3 <bjorn3@users.noreply.github.com>

Additionally whenever possible match C API provided by the LLVM.

Although `stack_overflow::init` runs very early in the process, even
before `main`, there may already be signal handlers installed for things
like the address sanitizer. In that case, just leave it alone, and don't
bother trying to allocate our own signal stacks either.

…=Centril

Permit attributes on 'if' expressions

Previously, attributes on 'if' expressions (e.g. `#[attr] if true {}`)
were disallowed during parsing. This made it impossible for macros to
perform any custom handling of such attributes (e.g. stripping them
away), since a compilation error would be emitted before they ever had a
chance to run.

This PR permits attributes on 'if' expressions ('if-attrs' from here on).
Both built-in attributes (e.g. `#[allow]`, `#[cfg]`) and proc-macro attributes are supported.

We still do *not* accept attributes on 'other parts' of an if-else
chain. That is, the following code snippet still fails to parse:

```rust
if true {} #[attr] else if false {} else #[attr] if false {} #[attr]
else {}
```

Closes rust-lang#68618

…nison

Extend search

I realized that when looking for "struct:String" in the rustdoc search for example, the "in arguments" and "returned" tabs were always empty. After some investigation, I realized it was because we only provided the name, and not the type, making it impossible to pass the "type filtering" check.

To resolve this, I added the type alongside the name. Note for the future: we could improve this by instead only registering the path id and use the path dictionary directly. The only problem with that solution (which I already tested) is that it becomes complicated for types in other crates. It'd force us to handle both case with an id and a case with `(name, type)`. I found the current PR big enough to not want to provide it directly. However, I think this is definitely worth it to make it work this way in the future.

About the two tests I added: they don't have much interest except checking that we actually have something returned in the search in the cases of a type filtering with and without literal search.

I also had to update a bit the test script to add the new locally global (haha) variable I created (`NO_TYPE_FILTER`). I added this variable to make the code easier to read than just "-1".

r? @kinnison

cc @ollie27

unix: Don't override existing SIGSEGV/BUS handlers

Although `stack_overflow::init` runs very early in the process, even
before `main`, there may already be signal handlers installed for things
like the address sanitizer. In that case, just leave it alone, and don't
bother trying to allocate our own signal stacks either.

Fixes rust-lang#69524.

Ensure that validity only raises validity errors

For now, only as a debug-assertion (similar to const-prop detecting errors that allocate).

Now includes rust-lang#69646.
[Relative diff](RalfJung/rust@layout-visitor...RalfJung:validity-errors).

r? @oli-obk

librustc_codegen_llvm: Use slices in preference to 0-terminated strings

Additionally whenever possible match C API provided by the LLVM.

Add more regression tests

Closes rust-lang#54239
Closes rust-lang#57200
Closes rust-lang#57201
Closes rust-lang#60473
Closes rust-lang#64620
Closes rust-lang#67166

r? @Centril