Also delete empty compressed files

ext/src/save.rs

@@ -204,50 +204,53 @@ impl<T: Read> std::ops::Drop for ChecksumReader<T> {
 
 /// Open the file pointed to by `path` as a `Box<dyn Read>`. If the file does not exist, look for
 /// compressed versions.
-// When compiling to wasm we don't mutate path
-#[allow(unused_mut)]
-fn open_file(mut path: PathBuf) -> Option<Box<dyn Read>> {
-    // We should try in decreasing order of access speed.
-    match File::open(&path) {
-        Ok(f) => {
-            let mut reader = BufReader::new(f);
-            if reader
-                .fill_buf()
-                .unwrap_or_else(|e| panic!("Error when reading from {path:?}: {e}"))
-                .is_empty()
-            {
-                // The file is empty. Delete the file and proceed as if it didn't exist
-                std::fs::remove_file(&path)
-                    .unwrap_or_else(|e| panic!("Error when deleting empty file {path:?}: {e}"));
-                return None;
-            }
-            return Some(Box::new(ChecksumReader::new(reader)));
-        }
-        Err(e) => {
-            if e.kind() != ErrorKind::NotFound {
-                panic!("Error when opening {path:?}: {e}");
-            }
-        }
-    }
-
-    #[cfg(feature = "zstd")]
+fn open_file(path: PathBuf) -> Option<Box<dyn Read>> {
+    fn try_open<F>(path: &Path, wrapper: F) -> Option<Box<dyn Read>>
+    where
+        F: FnOnce(BufReader<File>) -> Box<dyn Read>,
     {
-        path.set_extension("zst");
+        // We should try in decreasing order of access speed.
         match File::open(&path) {
             Ok(f) => {
-                return Some(Box::new(ChecksumReader::new(
-                    zstd::stream::Decoder::new(f).unwrap(),
-                )))
+                let mut reader = BufReader::new(f);
+                if reader
+                    .fill_buf()
+                    .unwrap_or_else(|e| panic!("Error when reading from {path:?}: {e}"))
+                    .is_empty()
+                {
+                    // The file is empty. Delete the file and proceed as if it didn't exist
+                    std::fs::remove_file(&path)
+                        .unwrap_or_else(|e| panic!("Error when deleting empty file {path:?}: {e}"));
+                    None
+                } else {
+                    Some(wrapper(reader))
+                }
             }
             Err(e) => {
                 if e.kind() != ErrorKind::NotFound {
-                    panic!("Error when opening {path:?}");
+                    panic!("Error when opening {path:?}: {e}");
                 }
+                None
             }
         }
     }
 
-    None
+    #[cfg(feature = "zstd")]
+    let try_zstd = || {
+        let mut path = path.clone();
+        path.set_extension("zst");
+        try_open(&path, |f| {
+            Box::new(ChecksumReader::new(
+                zstd::stream::Decoder::new(f).unwrap_or_else(|e| {
+                    panic!("Failed to create zstd stream for file {path:?}: {e}")
+                }),
+            ))
+        })
+    };
+    #[cfg(not(feature = "zstd"))]
+    let try_zstd = || None;
+
+    try_open(&path, |f| Box::new(ChecksumReader::new(f))).or_else(try_zstd)
 }
 
 pub struct SaveFile<A: Algebra> {