Move shell expansion into --config lookup

crates/ruff/src/args.rs

@@ -806,15 +806,18 @@ impl TypedValueParser for ConfigArgumentParser {
         arg: Option<&clap::Arg>,
         value: &std::ffi::OsStr,
     ) -> Result<Self::Value, clap::Error> {
-        let path_to_config_file = PathBuf::from(value);
-        if path_to_config_file.exists() {
-            return Ok(SingleConfigArgument::FilePath(path_to_config_file));
-        }
-
         let value = value
             .to_str()
             .ok_or_else(|| clap::Error::new(clap::error::ErrorKind::InvalidUtf8))?;
 
+        if let Ok(path_to_config_file) =
+            shellexpand::full(value).map(|config| PathBuf::from(config.as_ref()))
+        {
+            if path_to_config_file.is_file() {
+                return Ok(SingleConfigArgument::FilePath(path_to_config_file));
+            }
+        }
+
         let config_parse_error = match toml::Table::from_str(value) {
             Ok(table) => match table.try_into::<Options>() {
                 Ok(option) => {

crates/ruff/src/resolve.rs

@@ -1,4 +1,4 @@
-use std::path::{Path, PathBuf};
+use std::path::Path;
 
 use anyhow::Result;
 use log::debug;
@@ -35,21 +35,16 @@ pub fn resolve(
     // Second priority: the user specified a `pyproject.toml` file. Use that
     // `pyproject.toml` for _all_ configuration, and resolve paths relative to the
     // current working directory. (This matches ESLint's behavior.)
-    if let Some(pyproject) = config_arguments
-        .config_file()
-        .map(|config| config.display().to_string())
-        .map(|config| shellexpand::full(&config).map(|config| PathBuf::from(config.as_ref())))
-        .transpose()?
-    {
-        let settings = resolve_root_settings(&pyproject, Relativity::Cwd, config_arguments)?;
+    if let Some(pyproject) = config_arguments.config_file() {
+        let settings = resolve_root_settings(pyproject, Relativity::Cwd, config_arguments)?;
         debug!(
             "Using user-specified configuration file at: {}",
             pyproject.display()
         );
         return Ok(PyprojectConfig::new(
             PyprojectDiscoveryStrategy::Fixed,
             settings,
-            Some(pyproject),
+            Some(pyproject.to_path_buf()),
         ));
     }
 

crates/ruff/tests/lint.rs

@@ -1126,3 +1126,47 @@ import os
 
     Ok(())
 }
+
+/// Expand environment variables in `--config` paths provided via the CLI.
+#[test]
+fn config_expand() -> Result<()> {
+    let tempdir = TempDir::new()?;
+    let ruff_toml = tempdir.path().join("ruff.toml");
+    fs::write(
+        ruff_toml,
+        r#"
+[lint]
+select = ["F"]
+ignore = ["F841"]
+"#,
+    )?;
+
+    insta::with_settings!({
+        filters => vec![(tempdir_filter(&tempdir).as_str(), "[TMP]/")]
+    }, {
+    assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+        .args(STDIN_BASE_OPTIONS)
+        .arg("--config")
+        .arg("${NAME}.toml")
+        .env("NAME", "ruff")
+        .arg("-")
+        .current_dir(tempdir.path())
+        .pass_stdin(r#"
+import os
+
+def func():
+    x = 1
+"#), @r###"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    -:2:8: F401 [*] `os` imported but unused
+    Found 1 error.
+    [*] 1 fixable with the `--fix` option.
+
+    ----- stderr -----
+    "###);
+    });
+
+    Ok(())
+}