tempdir: Add a persist method

I have a use case where I want the equivalent of `into_path()`.

Signed-off-by: Colin Walters <walters@verbum.org>

cap-tempfile/src/lib.rs

@@ -101,6 +101,15 @@ impl TempDir {
         Err(Self::already_exists())
     }
 
+    /// Make this directory persistent.
+    ///
+    /// This corresponds to [`tempfile::TempDir::into_path`].
+    ///
+    /// [`tempfile::TempDir::into_path`]: https://docs.rs/tempfile/latest/tempfile/struct.TempDir.html#method.into_path
+    pub fn persist(mut self) -> io::Result<Dir> {
+        Ok(self.dir.take().unwrap())
+    }
+
     /// Closes and removes the temporary directory, returning a `Result`.
     ///
     /// This corresponds to [`tempfile::TempDir::close`].
@@ -222,6 +231,15 @@ fn close_tempdir() {
     t.close().unwrap();
 }
 
+#[test]
+fn persist_tempdir() {
+    use crate::ambient_authority;
+
+    let t = tempdir(ambient_authority()).unwrap();
+    let d = t.persist().unwrap();
+    assert!(d.exists("."));
+}
+
 #[test]
 fn drop_tempdir_in() {
     use crate::ambient_authority;