Make LocalFileSystem an Optional Feature

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Currently LocalFileSystem is always provided, and this in turn bring in a dependency on tokio and walkdir. There are scenarios were users may not need LocalFileSystem support and/or may not wish to link in tokio.

Describe the solution you'd like

Add an fs feature flag that is enabled by default and feature gates LocalFilesystem and its dependencies. It is unclear if this would constitute a breaking change, and so it might need to wait for a breaking release

Describe alternatives you've considered

Additional context

[alamb]

makes sense to me

[jiacai2050]

Hi, after search(query prompt: use tokio) the source code, I found there is no tokio dependency in local.rs

./*ivy-occur counsel-rg "tokio"*:8:./src/client/token.rs:20:use tokio::sync::Mutex;
./*ivy-occur counsel-rg "tokio"*:10:./src/buffered.rs:33:use tokio::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
./*ivy-occur counsel-rg "tokio"*:13:./src/buffered.rs:477:    use tokio::io::{AsyncBufReadExt, AsyncReadExt, AsyncSeekExt, AsyncWriteExt};
./*ivy-occur counsel-rg "tokio"*:24:./src/client/mock_server.rs:31:use tokio::net::TcpListener;
./*ivy-occur counsel-rg "tokio"*:25:./src/client/mock_server.rs:32:use tokio::sync::oneshot;
./*ivy-occur counsel-rg "tokio"*:26:./src/client/mock_server.rs:33:use tokio::task::{JoinHandle, JoinSet};
./*ivy-occur counsel-rg "tokio"*:46:./src/throttle.rs:403:    use tokio::time::Duration;
./*ivy-occur counsel-rg "tokio"*:47:./src/throttle.rs:404:    use tokio::time::Instant;
./*ivy-occur counsel-rg "tokio"*:56:./src/upload.rs:25:use tokio::task::JoinSet;
./*ivy-occur counsel-rg "tokio"*:71:./src/local.rs:219:/// a tokio context, this will use [`tokio::runtime::Handle::spawn_blocking`] to dispatch
./*ivy-occur counsel-rg "tokio"*:101:./src/lib.rs:278://! # use tokio::io::AsyncWriteExt;
./*ivy-occur counsel-rg "tokio"*:102:./src/lib.rs:307://! # use tokio::io::AsyncWriteExt;
./*ivy-occur counsel-rg "tokio"*:103:./src/lib.rs:339://! # use tokio::io::AsyncWriteExt;
./*ivy-occur counsel-rg "tokio"*:104:./src/lib.rs:378://! # use tokio::io::AsyncWriteExt;
./*ivy-occur counsel-rg "tokio"*:105:./src/lib.rs:445://! # use tokio::io::AsyncWriteExt;
./*ivy-occur counsel-rg "tokio"*:109:./src/lib.rs:1082:    /// a tokio context, this will use [`tokio::runtime::Handle::spawn_blocking`] to dispatch
./*ivy-occur counsel-rg "tokio"*:113:./src/lib.rs:1295:    use tokio::io::AsyncWriteExt;
./*ivy-occur counsel-rg "tokio"*:124:./src/limit.rs:32:use tokio::sync::{OwnedSemaphorePermit, Semaphore};
./*ivy-occur counsel-rg "tokio"*:125:./src/limit.rs:283:    use tokio::time::timeout;

[alamb]

Here are a few:

arrow-rs/object_store/src/local.rs

Line 564 in 199ce91

if tokio::runtime::Handle::try_current().is_err() {

arrow-rs/object_store/src/local.rs

Line 846 in 199ce91

match tokio::runtime::Handle::try_current() {

Github search fu suggests there are 32 uses: https://github.com/search?q=repo%3Aapache%2Farrow-rs+tokio+path%3A%2F%5Eobject_store%5C%2F%2F+path%3A%2F%5Eobject_store%5C%2Fsrc%5C%2Flocal%2F&type=code

[jiacai2050]

Thanks for pointing out.

If fs feature in enabled by default, this is not a breaking change for users?

[tustvold]

People could have disabled default features and it would be a breaking change for them