Multiplex server for rust-analyzer, allows multiple LSP clients (editor windows) to share a single rust-analyzer instance per cargo workspace.

The project has two binaries, ra-multiplex which is a thin wrapper that acts like rust-analyzer but only connects to a TCP socket at 127.0.0.1:27631 and pipes stdin and stdout through it.

The second binary ra-multiplex-server will listen on :27631 and spawn the rust-analyzer server, depending on the working directory the ra-multiplex client was spawned from it can reuse an already spawned rust-analyzer instance. It detects workspace root as the furthermost ancestor directory containing a Cargo.toml file. If the automatic workspace detection fails or if you're not using rust-analyzer as a server you can create a marker file .ra-multiplex-workspace-root in the directory you want to use as a workspace root, the first ancestor directory containing this file will be used.

Because neither LSP nor rust-analyzer itself support multiple clients per server ra-multiplex-server caches the handshake messages and modifies IDs of requests & responses to track which response belongs to which client. Because not all messages can be tracked this way it drops some, notably it drops any requests from the server, this appears to not be a problem with coc-rust-analyzer in neovim but YMMV.

If you have any problems you're welcome to open issues on this repository.

Build the project with

$ cargo build --release

Run the ra-multiplex-server, make sure that rust-analyzer is in your PATH:

$ which rust-analyzer
/home/user/.cargo/bin/rust-analyzer
$ target/release/ra-multiplex-server

ra-multiplex-server can run as a systemd user service, see the example ra-mux.service.

Configure your editor to use ra-multiplex as rust-analyzer, for example for CoC in neovim edit ~/.config/nvim/coc-settings.json, add:

{
    "rust-analyzer.serverPath": "/path/to/ra-multiplex"
}

Configuration is stored in a TOML file in your system's default configuration directory, for example ~/.config/ra-multiplex/config.toml. If you're not sure where that is on your system starting either ra-multiplex or ra-multiplex-server without a config file present will print a warning with the expected path.

Note that the configuration file is likely not necessary and ra-multiplex should be usable with all defaults.

Example configuration file:

# this is an example configuration file for ra-multiplex
#
# all configuration options here are set to their default value they'll have if
# they're not present in the file or if the config file is missing completely.

# time in seconds after which a rust-analyzer server instance with no clients
# connected will get killed to save system memory.
#
# you can set this option to `false` for infinite timeout
instance_timeout = 300 # after 5 minutes

# time in seconds how long to wait between the gc task checks for disconnected
# clients and possibly starts a timeout task. the value must be at least 1.
gc_interval = 10 # every 10 seconds

# ip address and port on which ra-multiplex-server listens
#
# the default "127.0.0.1" only allows connections from localhost which is
# preferred since the protocol doesn't worry about security.
# ra-multiplex-server expects the filesystem structure and contents to be the
# same on its machine as on ra-multiplex's machine. if you want to run the
# server on a different computer it's theoretically possible but at least for
# now you're on your own.
#
# ports below 1024 will typically require root privileges and should be
# avoided, the default was picked at random, this only needs to change if
# another application happens to collide with ra-multiplex.
listen = ["127.0.0.1", 27631] # localhost & some random unprivileged port

# ip address and port to which ra-multiplex will connect to
#
# this should usually just match the value of `listen`
connect = ["127.0.0.1", 27631] # same as `listen`

# default log filters
#
# RUST_LOG env variable overrides this option, both use the same syntax which
# is documented in the `env_logger` documentation here:
# <https://docs.rs/env_logger/0.9.0/env_logger/index.html#enabling-logging>
log_filters = "info"

# attempt automatic workspace root detection
#
# when enabled every connected client will attempt to discover the root of the
# workspace it was spawned in. otherwise the client CWD is always used
workspace_detection = true

By default ra-multplex uses a rust-analyzer binary found in its $PATH as the server. This can be overriden using the --ra-mux-server cli option or RA_MUX_SERVER environment variable. You can usually configure one of these in your editor configuration. If both are specified the cli option overrides the environment variable.

For example with coc-clangd in CoC for neovim add to ~/.config/nvim/coc-settings.json:

{
    "clangd.path": "/home/user/.cargo/bin/ra-multiplex",
    "clangd.arguments": ["--ra-mux-server", "/usr/bin/clangd"]
}

Or to set a custom path for rust-analyzer with coc-rust-analyzer add to ~/.config/nvim/coc-settings.json:

{
    "rust-analyzer.server.path": "/home/user/.cargo/bin/ra-multiplex",
    "rust-analyzer.server.extraEnv": { "RA_MUX_SERVER": "/custom/path/rust-analyzer" }
}

If your editor configuration or plugin doesn't allow to add either you can instead create a wrapper shell script and set it as the server path directly. For example if coc-clangd didn't allow to pass additional arguments you'd need a script like /usr/local/bin/clangd-proxy:

#!/bin/sh
RA_MUX_SERVER=/usr/bin/clangd exec /home/user/.cargo/bin/ra-multiplex $@

And configure the editor to use the wrapper script in ~/.config/nvim/coc-settings.json:

{
    "clangd.path": "/usr/local/bin/clangd-proxy"
}