Avoid warning about bad Python interpreter links for empty project environment directories (#7527)

Someone reported this a while back (will try to find the issue), and I
ran into it working on #7522

crates/uv-python/src/environment.rs

@@ -34,6 +34,12 @@ pub struct EnvironmentNotFound {
     preference: EnvironmentPreference,
 }
 
+#[derive(Clone, Debug, Error)]
+pub struct InvalidEnvironment {
+    path: PathBuf,
+    reason: String,
+}
+
 impl From<PythonNotFound> for EnvironmentNotFound {
     fn from(value: PythonNotFound) -> Self {
         Self {
@@ -98,6 +104,17 @@ impl fmt::Display for EnvironmentNotFound {
     }
 }
 
+impl std::fmt::Display for InvalidEnvironment {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(
+            f,
+            "Invalid environment at `{}`: {}",
+            self.path.user_display(),
+            self.reason
+        )
+    }
+}
+
 impl PythonEnvironment {
     /// Find a [`PythonEnvironment`] matching the given request and preference.
     ///
@@ -133,6 +150,23 @@ impl PythonEnvironment {
             }
             Err(err) => return Err(Error::Discovery(err.into())),
         };
+
+        if venv.is_file() {
+            return Err(InvalidEnvironment {
+                path: venv,
+                reason: "expected directory but found a file".to_string(),
+            }
+            .into());
+        }
+
+        if !venv.join("pyvenv.cfg").is_file() {
+            return Err(InvalidEnvironment {
+                path: venv,
+                reason: "missing a `pyvenv.cfg` marker".to_string(),
+            }
+            .into());
+        }
+
         let executable = virtualenv_python_executable(venv);
         let interpreter = Interpreter::query(executable, cache)?;
 

crates/uv-python/src/lib.rs

@@ -78,6 +78,9 @@ pub enum Error {
 
     #[error(transparent)]
     MissingEnvironment(#[from] environment::EnvironmentNotFound),
+
+    #[error(transparent)]
+    InvalidEnvironment(#[from] environment::InvalidEnvironment),
 }
 
 // The mock interpreters are not valid on Windows so we don't have unit test coverage there

crates/uv/src/commands/project/mod.rs

@@ -120,7 +120,7 @@ pub(crate) enum ProjectError {
     #[error("Environment marker is empty")]
     EmptyEnvironment,
 
-    #[error("Project virtual environment directory `{0}` cannot be used because it has existing, non-virtual environment content")]
+    #[error("Project virtual environment directory `{0}` cannot be used because it is not a virtual environment and is non-empty")]
     InvalidProjectEnvironmentDir(PathBuf),
 
     #[error("Failed to parse `pyproject.toml`")]
@@ -275,14 +275,6 @@ pub(crate) fn validate_requires_python(
     }
 }
 
-/// Find the virtual environment for the current project.
-fn find_environment(
-    workspace: &Workspace,
-    cache: &Cache,
-) -> Result<PythonEnvironment, uv_python::Error> {
-    PythonEnvironment::from_root(workspace.venv(), cache)
-}
-
 #[derive(Debug)]
 #[allow(clippy::large_enum_variant)]
 pub(crate) enum FoundInterpreter {
@@ -374,7 +366,8 @@ impl FoundInterpreter {
         } = WorkspacePython::from_request(python_request, workspace).await?;
 
         // Read from the virtual environment first.
-        match find_environment(workspace, cache) {
+        let venv = workspace.venv();
+        match PythonEnvironment::from_root(&venv, cache) {
             Ok(venv) => {
                 if python_request.as_ref().map_or(true, |request| {
                     if request.satisfied(venv.interpreter(), cache) {
@@ -400,6 +393,13 @@ impl FoundInterpreter {
                 }
             }
             Err(uv_python::Error::MissingEnvironment(_)) => {}
+            Err(uv_python::Error::InvalidEnvironment(_)) => {
+                // If there's an invalid environment with existing content, we error instead of
+                // deleting it later on.
+                if fs_err::read_dir(&venv).is_ok_and(|mut dir| dir.next().is_some()) {
+                    return Err(ProjectError::InvalidProjectEnvironmentDir(venv));
+                }
+            }
             Err(uv_python::Error::Query(uv_python::InterpreterError::NotFound(path))) => {
                 warn_user!(
                     "Ignoring existing virtual environment linked to non-existent Python interpreter: {}",
@@ -491,14 +491,6 @@ pub(crate) async fn get_or_init_environment(
         FoundInterpreter::Interpreter(interpreter) => {
             let venv = workspace.venv();
 
-            // Before deleting the target directory, we confirm that it is either (1) a virtual
-            // environment or (2) an empty directory.
-            if PythonEnvironment::from_root(&venv, cache).is_err()
-                && fs_err::read_dir(&venv).is_ok_and(|mut dir| dir.next().is_some())
-            {
-                return Err(ProjectError::InvalidProjectEnvironmentDir(venv));
-            }
-
             // Remove the existing virtual environment if it doesn't meet the requirements.
             match fs_err::remove_dir_all(&venv) {
                 Ok(()) => {

crates/uv/tests/sync.rs

@@ -1747,9 +1747,7 @@ fn sync_custom_environment_path() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    warning: Ignoring existing virtual environment linked to non-existent Python interpreter: foo/[BIN]/python
+    error: Project virtual environment directory `[TEMP_DIR]/foo` cannot be used because it is not a virtual environment and is non-empty
-    Using Python 3.12.[X] interpreter at: [PYTHON-3.12]
-    error: Project virtual environment directory `[TEMP_DIR]/foo` cannot be used because it has existing, non-virtual environment content
     "###);
 
     // But if it's just an incompatible virtual environment...