Auto merge of #13290 - poliorcetics:multiple-targets, r=Veykril

Support multiple targets for checkOnSave (in conjunction with cargo 1.64.0+)

This PR adds support for the ability to pass multiple `--target` flags when using
`cargo` 1.64.0+.

## Questions

I needed to change the type of two configurations options, but I did not plurialize the names to
avoid too much churn, should I ?

## Zulip thread

https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frust-analyzer/topic/Issue.2013282.20.28supporting.20multiple.20targets.20with.201.2E64.2B.29

## Example

To see it working, on a macOS machine:

```sh
$ cd /tmp
$ cargo new cargo-multiple-targets-support-ra-test
$ cd !$
$ mkdir .cargo
$ echo '
[build]
target = [
    "aarch64-apple-darwin",
    "x86_64-apple-darwin",
]
' > .cargo/config.toml
$ echo '
fn main() {
    #[cfg(all(target_arch = "aarch64", target_os = "macos"))]
    {
        let a = std::fs::read_to_string("/tmp/test-read");
    }

    #[cfg(all(target_arch = "x86_64", target_os = "macos"))]
    {
        let a = std::fs::read_to_string("/tmp/test-read");
    }

    #[cfg(all(target_arch = "x86_64", target_os = "windows"))]
    {
        let a = std::fs::read_to_string("/tmp/test-read");
    }
}
' > src/main.rs
# launch your favorite editor with the version of RA from this PR
#
# You should see warnings under the first two `let a = ...` but not the third
```

## Screen

![Two panes of a terminal emulator, on the left pane is the main.rs file described above, with warnings for the first two let a = declaration, on the right pane is a display of the .cargo/config.toml, an ls of the current files in the directory and a call to cargo build to show the same warnings as in the editor on the left pane](https://user-images.githubusercontent.com/7951708/192122707-7a00606a-e581-4534-b9d5-b81c92694e8e.png)

Helps with #13282

1 files changed, 7 insertions, 3 deletions

diff --git a/docs/user/generated_config.adoc b/docs/user/generated_config.adoc
index da8e6298078..57f950034cb 100644
--- a/docs/user/generated_config.adoc
+++ b/docs/user/generated_config.adoc
@@ -190,11 +190,15 @@ cargo check --workspace --message-format=json --all-targets
 ```
 .
 --
-[[rust-analyzer.checkOnSave.target]]rust-analyzer.checkOnSave.target (default: `null`)::
+[[rust-analyzer.checkOnSave.target]]rust-analyzer.checkOnSave.target (default: `[]`)::
 +
 --
-Check for a specific target. Defaults to
-`#rust-analyzer.cargo.target#`.
+Check for specific targets. Defaults to `#rust-analyzer.cargo.target#` if empty.
+
+Can be a single target, e.g. `"x86_64-unknown-linux-gnu"` or a list of targets, e.g.
+`["aarch64-apple-darwin", "x86_64-apple-darwin"]`.
+
+Aliased as `"checkOnSave.targets"`.
 --
 [[rust-analyzer.completion.autoimport.enable]]rust-analyzer.completion.autoimport.enable (default: `true`)::
 +