Add support for tidy linting via external tools for non-rust files

This change adds the flag `--check-extras` to `tidy`. It accepts a comma
separated list of any of the options:

- py (test everything applicable for python files)
- py:lint (lint python files using `ruff`)
- py:fmt (check formatting for python files using `black`)
- shell or shell:lint (lint shell files using `shellcheck`)

Specific files to check can also be specified via positional args.
Examples:

- `./x test tidy --check-extras=shell,py`
- `./x test tidy --check-extras=py:fmt -- src/bootstrap/bootstrap.py`
- `./x test tidy --check-extras=shell -- src/ci/*.sh`
- Python formatting can be applied with bless:
  `./x test tidy --ckeck-extras=py:fmt --bless`

`ruff` and `black` need to be installed via pip; this tool manages these
within a virtual environment at `build/venv`. `shellcheck` needs to be
installed on the system already.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index 4bfb16928f1..14c5167cba4 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -4,6 +4,7 @@
 //! our CI.
 
 use std::env;
+use std::ffi::OsStr;
 use std::ffi::OsString;
 use std::fs;
 use std::iter;
@@ -1094,6 +1095,14 @@ impl Step for Tidy {
         if builder.config.cmd.bless() {
             cmd.arg("--bless");
         }
+        if let Some(s) = builder.config.cmd.extra_checks() {
+            cmd.arg(format!("--extra-checks={s}"));
+        }
+        let mut args = std::env::args_os();
+        if let Some(_) = args.find(|arg| arg == OsStr::new("--")) {
+            cmd.arg("--");
+            cmd.args(args);
+        }
 
         if builder.config.channel == "dev" || builder.config.channel == "nightly" {
             builder.info("fmt check");