Add check for using minor version link when creating a venv on Windows (#14252)

There was a regression introduced in #13954 on Windows where creating a
venv behaved as if there was a minor version link even if none existed.
This PR adds a check to fix this.

Closes #14249.

crates/uv-virtualenv/src/virtualenv.rs

@@ -147,6 +147,7 @@ pub(crate) fn create(
     // Create a `.gitignore` file to ignore all files in the venv.
     fs::write(location.join(".gitignore"), "*")?;
 
+    let mut using_minor_version_link = false;
     let executable_target = if upgradeable && interpreter.is_standalone() {
         if let Some(minor_version_link) = PythonMinorVersionLink::from_executable(
             base_python.as_path(),
@@ -167,6 +168,7 @@ pub(crate) fn create(
                     &minor_version_link.symlink_directory.display(),
                     &base_python.display()
                 );
+                using_minor_version_link = true;
                 minor_version_link.symlink_executable.clone()
             }
         } else {
@@ -228,7 +230,7 @@ pub(crate) fn create(
     // interpreters, this target path includes a minor version junction to enable
     // transparent upgrades.
     if cfg!(windows) {
-        if interpreter.is_standalone() {
+        if using_minor_version_link {
             let target = scripts.join(WindowsExecutable::Python.exe(interpreter));
             create_link_to_executable(target.as_path(), executable_target.clone())
                 .map_err(Error::Python)?;

crates/uv/tests/it/venv.rs

@@ -1052,6 +1052,39 @@ fn non_empty_dir_exists_allow_existing() -> Result<()> {
     Ok(())
 }
 
+/// Run `uv venv` followed by `uv venv --allow-existing`.
+#[test]
+fn create_venv_then_allow_existing() {
+    let context = TestContext::new_with_versions(&["3.12"]);
+
+    // Create a venv
+    uv_snapshot!(context.filters(), context.venv(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
+    Creating virtual environment at: .venv
+    Activate with: source .venv/[BIN]/activate
+    "
+    );
+
+    // Create a venv again with `--allow-existing`
+    uv_snapshot!(context.filters(), context.venv()
+        .arg("--allow-existing"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
+    Creating virtual environment at: .venv
+    Activate with: source .venv/[BIN]/activate
+    "###
+    );
+}
+
 #[test]
 #[cfg(windows)]
 fn windows_shims() -> Result<()> {