Discover and respect .python-version files in parent directories

crates/uv-python/src/version_files.rs

@@ -4,6 +4,7 @@ use std::path::{Path, PathBuf};
 use fs_err as fs;
 use itertools::Itertools;
 use tracing::debug;
+use uv_fs::Simplified;
 
 use crate::PythonRequest;
 
@@ -23,37 +24,54 @@ pub struct PythonVersionFile {
 }
 
 impl PythonVersionFile {
- /// Find a Python version file in the given directory.
+ /// Find a Python version file in the given directory or any of its parents.
  pub async fn discover(
  working_directory: impl AsRef<Path>,
  // TODO(zanieb): Create a `DiscoverySettings` struct for these options
  no_config: bool,
  prefer_versions: bool,
  ) -> Result<Option<Self>, std::io::Error> {
- let versions_path = working_directory.as_ref().join(PYTHON_VERSIONS_FILENAME);
- let version_path = working_directory.as_ref().join(PYTHON_VERSION_FILENAME);
+ let Some(path) = Self::find_nearest(working_directory, prefer_versions) else {
+ return Ok(None);
+ };
 
  if no_config {
- if version_path.exists() {
- debug!("Ignoring `.python-version` file due to `--no-config`");
- } else if versions_path.exists() {
- debug!("Ignoring `.python-versions` file due to `--no-config`");
- };
+ debug!(
+ "Ignoring Python version file at `{}` due to `--no-config`",
+ path.user_display()
+ );
  return Ok(None);
  }
 
- let paths = if prefer_versions {
- [versions_path, version_path]
- } else {
- [version_path, versions_path]
- };
- for path in paths {
- if let Some(result) = Self::try_from_path(path).await? {
- return Ok(Some(result));
+ // Uses `try_from_path` instead of `from_path` to avoid TOCTOU failures.
+ Self::try_from_path(path).await
+ }
+
+ fn find_nearest(working_directory: impl AsRef<Path>, prefer_versions: bool) -> Option<PathBuf> {
+ let mut current = working_directory.as_ref();
+ loop {
+ let version_path = current.join(PYTHON_VERSION_FILENAME);
+ let versions_path = current.join(PYTHON_VERSIONS_FILENAME);
+
+ let paths = if prefer_versions {
+ [versions_path, version_path]
+ } else {
+ [version_path, versions_path]
  };
+ for path in paths {
+ if path.exists() {
+ return Some(path);
+ }
+ }
+
+ if let Some(parent) = current.parent() {
+ current = parent;
+ } else {
+ break;
+ }
  }
 
- Ok(None)
+ None
  }
 
  /// Try to read a Python version file at the given path.

crates/uv/tests/python_find.rs

@@ -197,6 +197,38 @@ fn python_find_pin() {
 
  ----- stderr -----
  "###);
+
+ let child_dir = context.temp_dir.child("child");
+ child_dir.create_dir_all().unwrap();
+
+ // We should also find pinned versions in the parent directory
+ uv_snapshot!(context.filters(), context.python_find().current_dir(&child_dir), @r###"
+ success: true
+ exit_code: 0
+ ----- stdout -----
+ [PYTHON-3.12]
+
+ ----- stderr -----
+ "###);
+
+ uv_snapshot!(context.filters(), context.python_pin().arg("3.11").current_dir(&child_dir), @r###"
+ success: true
+ exit_code: 0
+ ----- stdout -----
+ Updated `.python-version` from `3.12` -> `3.11`
+
+ ----- stderr -----
+ "###);
+
+ // Unless the child directory also has a pin
+ uv_snapshot!(context.filters(), context.python_find().current_dir(&child_dir), @r###"
+ success: true
+ exit_code: 0
+ ----- stdout -----
+ [PYTHON-3.11]
+
+ ----- stderr -----
+ "###);
 }
 
 #[test]