fix(ruff): restore a leading -- before routing

src/cmds/python/ruff_cmd.rs

@@ -1,5 +1,6 @@
 //! Filters Ruff linter and formatter output.
 
+use crate::core::args_utils;
 use crate::core::config;
 use crate::core::runner;
 use crate::core::shell::display_args;
@@ -49,6 +50,7 @@ struct RuffDiagnostic {
 }
 
 pub fn run(args: &[String], verbose: u8) -> Result<i32> {
+    let args = &args_utils::restore_double_dash(args);
     let is_check = is_check_invocation(args);
 
     let is_format = args.iter().any(|a| a == "format");

tests/ruff_double_dash_test.rs

@@ -0,0 +1,79 @@
+//! `--` handling for `rtk ruff`. clap's `trailing_var_arg` strips a `--` that leads `args`, so
+//! without `restore_double_dash` `rtk ruff -- check` reached `run()` as `["check"]`, was routed
+//! as the `check` subcommand with no path, and linted the whole working directory. ruff itself
+//! answers `ruff -- check` with its usage error, and `ruff check -- check` lints only the file
+//! named `check`. Stubs `ruff` on PATH with a script that records its argv.
+
+#![cfg(unix)]
+
+use std::fs;
+use std::os::unix::fs::PermissionsExt;
+
+mod common;
+
+fn shell_quote(path: &std::path::Path) -> String {
+    format!("'{}'", path.display().to_string().replace('\'', "'\\''"))
+}
+
+/// Runs `rtk ruff <args>` against a `ruff` stub and returns the argv the stub received.
+fn ruff_argv(args: &[&str]) -> Vec<String> {
+    let dir = common::tempdir();
+    let argv_file = dir.path().join("argv.txt");
+    let stub_path = dir.path().join("ruff");
+
+    // `[]` is a clean `check --output-format=json` run, so the filtered path exits 0 too.
+    fs::write(
+        &stub_path,
+        format!(
+            "#!/bin/sh\nprintf '%s\\n' \"$@\" > {}\necho '[]'\n",
+            shell_quote(&argv_file)
+        ),
+    )
+    .expect("write stub");
+    fs::set_permissions(&stub_path, fs::Permissions::from_mode(0o755)).expect("chmod stub");
+
+    let path_with_stub = format!(
+        "{}:{}",
+        dir.path().display(),
+        std::env::var("PATH").unwrap_or_default()
+    );
+
+    let out = common::rtk_command()
+        .arg("ruff")
+        .args(args)
+        .env("PATH", path_with_stub)
+        .env("LC_ALL", "C")
+        .current_dir(dir.path())
+        .output()
+        .expect("spawn rtk");
+
+    fs::read_to_string(&argv_file)
+        .unwrap_or_else(|e| {
+            panic!(
+                "read captured argv: {e}; rtk stdout={} stderr={}",
+                String::from_utf8_lossy(&out.stdout),
+                String::from_utf8_lossy(&out.stderr)
+            )
+        })
+        .lines()
+        .map(str::to_string)
+        .collect()
+}
+
+#[test]
+fn ruff_leading_double_dash_reaches_ruff() {
+    let argv = ruff_argv(&["--", "check"]);
+    assert_eq!(argv, vec!["--", "check"]);
+}
+
+#[test]
+fn ruff_check_double_dash_is_forwarded_once() {
+    let argv = ruff_argv(&["check", "--", "check"]);
+    assert_eq!(argv, vec!["check", "--output-format=json", "--", "check"]);
+}
+
+#[test]
+fn ruff_double_dash_after_a_flag_is_forwarded_once() {
+    let argv = ruff_argv(&["--isolated", "--", "check"]);
+    assert_eq!(argv, vec!["--isolated", "--", "check"]);
+}