remove tmp file on error

src/main.rs

@@ -95,7 +95,7 @@ async fn transcode(src: &Path, dest: &Path) -> Result<()> {
         &gmake("flacparse")?,
         &gmake("flacdec")?,
         &resample,
-        // `audioconvert` converts the bitdepth
+        // `audioconvert` converts audio format, bitdepth, ...
         &gmake("audioconvert")?,
         encoder.upcast_ref(),
         &gmake("oggmux")?,
@@ -114,6 +114,7 @@ async fn transcode(src: &Path, dest: &Path) -> Result<()> {
             .with_context(|| format!("could not get parent dir for {}", dest.display()))?,
     )?;
 
+    rm_file_on_err(&tmp_dest, async {
         pipeline
             .set_state(gstreamer::State::Playing)
             .context("Unable to set the pipeline to the `Playing` state")?;
@@ -142,7 +143,25 @@ async fn transcode(src: &Path, dest: &Path) -> Result<()> {
             .set_state(gstreamer::State::Null)
             .context("Unable to set the pipeline to the `Null` state")?;
 
-    std::fs::rename(tmp_dest, dest)?;
+        std::fs::rename(&tmp_dest, dest)?;
 
         Ok(())
+    })
+    .await
+}
+
+async fn rm_file_on_err<F, T>(path: &Path, f: F) -> F::Output
+where
+    F: Future<Output = Result<T>>,
+{
+    match f.await {
+        Err(err) => match std::fs::remove_file(path) {
+            Ok(..) => Err(err),
+            Err(rm_err) if rm_err.kind() == std::io::ErrorKind::NotFound => Err(err),
+            Err(rm_err) => Err(rm_err)
+                .context(format!("removing {}", path.display()))
+                .context(err),
+        },
+        res @ Ok(..) => res,
+    }
 }