Simplify dead code lint
This PR scratches a few itches I had when looking at that code.
The perf improvement comes from keeping the `scanned` set through several marking phases. This pretty much divides by 2 the number of HIR traversals.
Consolidate staging for `rustc_private` tools
This PR continues bootstrap refactoring, this time by consolidating staging for `Mode::ToolRustc` tools. This refactoring was in the critical path of refactoring `test`/`dist`/`clippy`/`doc` steps, and getting rid of the rmeta/rlib sysroot copy, because tools are pervasive and they are being used for a lot of things in bootstrap.
The main idea is to explicitly model the fact that a stage N `Mode::ToolRustc` tool always works with two different compilers:
- Stage N-1 rustc (`build_compiler`) builds stage N rustc (`target_compiler`)
- Rlib artifacts from stage N rustc are copied to the sysroot of stage N-1 rustc
- Stage N-1 rustc builds the (stage N) tool itself, the tool links to the rlib artifacts of the stage N rustc
Before, the code often used `compiler`, which meant sometimes the build compiler, sometimes the target compiler, and sometimes neither (looking at you, `download-rustc`). This is especially annoying when you get to a situation where you have an install step that invokes a dist step that invokes a tool build step, where *some* compiler is being propagated through, without it being clear what does that compiler represent. This refactoring hopefully makes that clearer and more explicit. It also gets rid of a few `builder.ensure(Rustc(...))` calls within bootstrap, which is always nice.
`Rustdoc` needs to be handled a bit specially, because it acts as a compiler itself, I documented that in the changes.
It wasn't practical to do these refactorings in multiple PRs, so I did it all in one PR. The meat of the change is 9ee6d1c1ed112c3dcfb5684b33772b136df0dca3.
I tested manually that `x build rustdoc` and `x build miri` still works even with `download-rustc`, although I cannot promise any extra support for `download-rustc`, IMO we will just have to reimplement it from scratch in a different way.
As usually, I did some drive-by refactorings to bootstrap, trying to document and clarify things, add more step metadata and tests.
Since these changes broke Cargo, which was incorrectly using `Mode::ToolRustc`, I also changed cargo to `ToolTarget` in this PR.
Best reviewed commit-by-commit (note that I renamed `link_compiler` to `target_compiler`, in accordance to the rest of bootstrap, in the last commit).
r? `@jieyouxu`
try-job: x86_64-gnu-aux
try-job: x86_64-msvc-ext1
Delete `tests/ui/threads-sendsync/tcp-stress.rs`
This stress test was originally introduced in 65cca4bd3fa0abe1000662014b3e3ea1420728f5 to detect a UAF in `libuv` (see rust-lang/rust#12823), but we no longer use `libuv`, so remove this test as it no longer serves its original purpose, and is causing flaky timeout failures.
Closesrust-lang/rust#144878 (by removing the test).
r? libs
Rehome 21 `tests/ui/issues/` tests to other subdirectories under `tests/ui/`
rust-lang/rust#143902 divided into smaller, easier to review chunks.
Part of rust-lang/rust#133895
Methodology:
1. Refer to the previously written `tests/ui/SUMMARY.md`
2. Find an appropriate category for the test, using the original issue thread and the test contents.
3. Add the issue URL at the bottom (not at the top, as that would mess up stderr line numbers)
4. Rename the tests to make their purpose clearer
Inspired by the methodology that ``@Kivooeo`` was using.
r? ``@jieyouxu``
This caused rename to remove both, because it couldn't rename the derive-expanded one.
I spent some time trying to create a test for this, before giving up. But I checked manually that this works.
Example
===
```rust
let x = $0;
```
Old completions:
```rust
let x = if $1 {
$0
};
```
This PR current completions:
```rust
let x = if $1 {
$2
} else {
$0
};
```
