Errors on file close are silently ignored

[adamreeve]

We write Parquet files to network shares using Polars, and have found that closing a file occasionally returns an error that is ignored, so we have no indication that there was a failure. This is a wider issue with Rust rather than specific to Polars, eg. see rust-lang/rust#98338, but it would be very helpful for us if Polars could raise these errors when files are closed. For a stronger guarantee that data has been persisted, File::sync_all should be called, but this would have a performance impact for some users, and for the failure scenarios we're concerned about it would be sufficient to just check the return value of close.

Rust doesn't have a close method on files, but it should be possible to implement this fairly easily using the libc and winapi crates, see the close_file crate for example. I suspect that rather than adding a dependency on this old crate Polars might want to reimplement similar functionality.

I'd be happy to implement this change if it would be accepted.

[ritchie46]

We understand this problem. It needs some research. The extension trait in close_file for instance doesn't prevent double closing of files. De drop call will close it again.

[adamreeve]

It looks like using into_raw_fd means the File won't be closed twice, as this uses std::mem::ManuallyDrop: https://github.com/rust-lang/rust/blob/25a16572a36321deae83546b63f5595d75361179/library/std/src/os/fd/owned.rs#L142

(and similarly for Windows: https://github.com/rust-lang/rust/blob/25a16572a36321deae83546b63f5595d75361179/library/std/src/os/windows/io/handle.rs#L318)