Ignore arbitrary Python requests in version files (#12909)

Closes https://github.com/astral-sh/uv/issues/12605

crates/uv-python/src/version_files.rs

@@ -6,6 +6,7 @@ use itertools::Itertools;
 use tracing::debug;
 use uv_dirs::user_uv_config_dir;
 use uv_fs::Simplified;
+use uv_warnings::warn_user_once;
 
 use crate::PythonRequest;
 
@@ -171,6 +172,17 @@ impl PythonVersionFile {
                     })
                     .map(ToString::to_string)
                     .map(|version| PythonRequest::parse(&version))
+                    .filter(|request| {
+                        if let PythonRequest::ExecutableName(name) = request {
+                            warn_user_once!(
+                                "Ignoring unsupported Python request `{name}` in version file: {}",
+                                path.display()
+                            );
+                            false
+                        } else {
+                            true
+                        }
+                    })
                     .collect();
                 Ok(Some(Self { path, versions }))
             }

crates/uv/src/commands/python/pin.rs

@@ -76,6 +76,10 @@ pub(crate) async fn pin(
     };
     let request = PythonRequest::parse(&request);
 
+    if let PythonRequest::ExecutableName(name) = request {
+        bail!("Requests for arbitrary names (e.g., `{name}`) are not supported in version files");
+    }
+
     let python = match PythonInstallation::find(
         &request,
         EnvironmentPreference::OnlySystem,

crates/uv/tests/it/python_find.rs

@@ -217,6 +217,82 @@ fn python_find_pin() {
     "###);
 }
 
+#[test]
+fn python_find_pin_arbitrary_name() {
+    let context: TestContext = TestContext::new_with_versions(&["3.11", "3.12"]);
+
+    // Try to pin to an arbitrary name
+    uv_snapshot!(context.filters(), context.python_pin().arg("foo"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Requests for arbitrary names (e.g., `foo`) are not supported in version files
+    ");
+
+    // Pin to an arbitrary name, bypassing uv
+    context
+        .temp_dir
+        .child(".python-version")
+        .write_str("foo")
+        .unwrap();
+
+    // The arbitrary name should be ignored
+    uv_snapshot!(context.filters(), context.python_find(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    warning: Ignoring unsupported Python request `foo` in version file: [TEMP_DIR]/.python-version
+    ");
+
+    // The pin should be updatable
+    uv_snapshot!(context.filters(), context.python_pin().arg("3.11"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Pinned `.python-version` to `3.11`
+
+    ----- stderr -----
+    warning: Ignoring unsupported Python request `foo` in version file: [TEMP_DIR]/.python-version
+    ");
+
+    // Warnings shouldn't appear afterwards...
+    uv_snapshot!(context.filters(), context.python_pin().arg("3.12"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    Updated `.python-version` from `3.11` -> `3.12`
+
+    ----- stderr -----
+    ");
+
+    // Pin in a sub-directory
+    context.temp_dir.child("foo").create_dir_all().unwrap();
+    context
+        .temp_dir
+        .child("foo")
+        .child(".python-version")
+        .write_str("foo")
+        .unwrap();
+
+    // The arbitrary name should be ignored, but we won't walk up to the parent `.python-version`
+    // file (which contains 3.12); this behavior is a little questionable but we probably want to
+    // ignore all empty version files if we want to change this?
+    uv_snapshot!(context.filters(), context.python_find().current_dir(context.temp_dir.child("foo").path()), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.11]
+
+    ----- stderr -----
+    warning: Ignoring unsupported Python request `foo` in version file: [TEMP_DIR]/foo/.python-version
+    ");
+}
+
 #[test]
 fn python_find_project() {
     let context: TestContext = TestContext::new_with_versions(&["3.10", "3.11", "3.12"]);