Improve handling of invalid virtual environments during interpreter discovery (#8086)

## Summary

Fix #8075.

Invalid discovered environments in the working directory should be
filtered out.

## Test Plan

- Test python_find

---------

Co-authored-by: Zanie Blue <[email protected]>

Author: potoo0

crates/uv-python/src/discovery.rs

@@ -25,6 +25,7 @@ use crate::managed::ManagedPythonInstallations;
 use crate::microsoft_store::find_microsoft_store_pythons;
 #[cfg(windows)]
 use crate::py_launcher::{registry_pythons, WindowsPython};
+use crate::virtualenv::Error as VirtualEnvError;
 use crate::virtualenv::{
     conda_environment_from_env, virtualenv_from_env, virtualenv_from_working_dir,
     virtualenv_python_executable, CondaEnvironmentKind,
@@ -729,10 +730,27 @@ impl Error {
                     false
                 }
                 InterpreterError::NotFound(path) => {
-                    trace!("Skipping missing interpreter at {}", path.display());
-                    false
+                    // If the interpreter is from an active, valid virtual environment, we should
+                    // fail because it's broken
+                    if let Some(Ok(true)) = matches!(source, PythonSource::ActiveEnvironment)
+                        .then(|| {
+                            path.parent()
+                                .and_then(Path::parent)
+                                .map(|path| path.join("pyvenv.cfg").try_exists())
+                        })
+                        .flatten()
+                    {
+                        true
+                    } else {
+                        trace!("Skipping missing interpreter at {}", path.display());
+                        false
+                    }
                 }
             },
+            Error::VirtualEnv(VirtualEnvError::MissingPyVenvCfg(path)) => {
+                trace!("Skipping broken virtualenv at {}", path.display());
+                false
+            }
             _ => true,
         }
     }

crates/uv/tests/it/python_find.rs

@@ -6,7 +6,7 @@ use indoc::indoc;
 use uv_python::platform::{Arch, Os};
 use uv_static::EnvVars;
 
-use crate::common::{uv_snapshot, TestContext};
+use crate::common::{uv_snapshot, venv_bin_path, TestContext};
 
 #[test]
 fn python_find() {
@@ -560,3 +560,57 @@ fn python_find_unsupported_version() {
     error: Invalid version request: Python <3.13 does not support free-threading but 3.12t was requested.
     "###);
 }
+
+#[test]
+fn python_find_venv_invalid() {
+    let context: TestContext = TestContext::new("3.12")
+        // Enable additional filters for Windows compatibility
+        .with_filtered_exe_suffix()
+        .with_filtered_python_names()
+        .with_filtered_virtualenv_bin();
+
+    // We find the virtual environment
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [VENV]/[BIN]/python
+
+    ----- stderr -----
+    "###);
+
+    // If the binaries are missing from a virtual environment, we fail
+    fs_err::remove_dir_all(venv_bin_path(&context.venv)).unwrap();
+
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Failed to inspect Python interpreter from active virtual environment at `.venv/[BIN]/python`
+      Caused by: Python interpreter not found at `[VENV]/[BIN]/python`
+    "###);
+
+    // Unless the virtual environment is not active
+    uv_snapshot!(context.filters(), context.python_find().env_remove("VIRTUAL_ENV"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+
+    // If there's not a `pyvenv.cfg` file, it's also non-fatal, we ignore the environment
+    fs_err::remove_file(context.venv.join("pyvenv.cfg")).unwrap();
+
+    uv_snapshot!(context.filters(), context.python_find(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [PYTHON-3.12]
+
+    ----- stderr -----
+    "###);
+}