Add a test

crates/uv-virtualenv/src/bare.rs

@@ -48,11 +48,28 @@ pub fn create_bare_venv(
     system_site_packages: bool,
     extra_cfg: Vec<(String, String)>,
 ) -> Result<Virtualenv, Error> {
+    // Determine the base Python executable; that is, the Python executable that should be
+    // considered the "base" for the virtual environment. This is typically the Python executable
+    // from the [`Interpreter`]; however, if the interpreter is a virtual environment itself, then
+    // the base Python executable is the Python executable of the interpreter's base interpreter.
     let base_python = if cfg!(unix) {
+        // On Unix, follow symlinks to resolve the base interpreter, since the Python executable in
+        // a virtual environment is a symlink to the base interpreter.
         fs_err::canonicalize(interpreter.sys_executable())?
     } else if cfg!(windows) {
-        if let Some(base_executable) = interpreter.base_executable() {
-            base_executable.to_path_buf()
+        // On Windows, follow `virtualenv`. If we're in a virtual environment, use
+        // `sys._base_executable` if it exists; if not, use `sys.base_prefix`. If we're _not_ in a
+        // virtual environment, use the interpreter's executable, since it's already a "system
+        // Python". We canonicalize the path to ensure that it's consistent, though we don't expect
+        // any symlinks on Windows.
+        if interpreter.is_virtualenv() {
+            if let Some(base_executable) = interpreter.base_executable() {
+                base_executable.to_path_buf()
+            } else {
+                // Assume `python.exe`, though the exact executable name is never used (below) on
+                // Windows, only its parent directory.
+                interpreter.base_prefix().join("python.exe")
+            }
         } else {
             fs_err::canonicalize(interpreter.sys_executable())?
         }
@@ -202,7 +219,7 @@ pub fn create_bare_venv(
         .ok_or_else(|| {
             io::Error::new(
                 io::ErrorKind::NotFound,
-                "The python interpreter needs to have a parent directory",
+                "The Python interpreter needs to have a parent directory",
             )
         })?
         .simplified_display()

crates/uv/tests/venv.rs

@@ -3,6 +3,7 @@
 use std::process::Command;
 
 use anyhow::Result;
+use assert_cmd::prelude::*;
 use assert_fs::prelude::*;
 
 use uv_fs::Simplified;
@@ -663,3 +664,70 @@ fn verify_pyvenv_cfg() {
     let search_string = format!("uv = {version}");
     pyvenv_cfg.assert(predicates::str::contains(search_string));
 }
+
+/// Ensure that a nested virtual environment uses the same `home` directory as the parent.
+#[test]
+fn verify_nested_pyvenv_cfg() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let bin = create_bin_with_executables(&temp_dir, &["3.12"]).expect("Failed to create bin dir");
+    let venv = temp_dir.child(".venv");
+
+    // Create a virtual environment at `.venv`.
+    Command::new(get_bin())
+        .arg("venv")
+        .arg(venv.as_os_str())
+        .arg("--python")
+        .arg("3.12")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .arg("--exclude-newer")
+        .arg(EXCLUDE_NEWER)
+        .env("UV_TEST_PYTHON_PATH", bin.clone())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    let pyvenv_cfg = venv.child("pyvenv.cfg");
+
+    // Check pyvenv.cfg exists
+    pyvenv_cfg.assert(predicates::path::is_file());
+
+    // Extract the "home" line from the pyvenv.cfg file.
+    let contents = fs_err::read_to_string(pyvenv_cfg.path())?;
+    let venv_home = contents
+        .lines()
+        .find(|line| line.starts_with("home"))
+        .expect("home line not found");
+
+    // Now, create a virtual environment from within the virtual environment.
+    let subvenv = temp_dir.child(".subvenv");
+    Command::new(get_bin())
+        .arg("venv")
+        .arg(subvenv.as_os_str())
+        .arg("--python")
+        .arg("3.12")
+        .arg("--cache-dir")
+        .arg(cache_dir.path())
+        .arg("--exclude-newer")
+        .arg(EXCLUDE_NEWER)
+        .env("VIRTUAL_ENV", venv.as_os_str())
+        .env("UV_TEST_PYTHON_PATH", bin.clone())
+        .current_dir(&temp_dir)
+        .assert()
+        .success();
+
+    let sub_pyvenv_cfg = subvenv.child("pyvenv.cfg");
+
+    // Extract the "home" line from the pyvenv.cfg file.
+    let contents = fs_err::read_to_string(sub_pyvenv_cfg.path())?;
+    let sub_venv_home = contents
+        .lines()
+        .find(|line| line.starts_with("home"))
+        .expect("home line not found");
+
+    // Check that both directories point to the same home.
+    assert_eq!(sub_venv_home, venv_home);
+
+    Ok(())
+}