lspmux-rust-cc

lspmux-cc

Share one rust-analyzer instance across editors, Claude Code, Codex, and other MCP-capable agents in the same Rust workspace. Built on lspmux by p2502.

How It Works

lspmux multiplexes multiple LSP client connections to one rust-analyzer process. lspmux-cc adds an MCP server that exposes rust-analyzer capabilities as agent-callable tools, plus a Claude Code plugin for transparent LSP routing.

The transport is configurable. TCP loopback is the easiest sandbox-friendly path for agent hosts; Unix sockets remain supported when the host can connect to the socket.

graph LR
    NV[Editor LSP clients<br/>rustaceanvim / Neovim / Vim / VS Code] -->|lspmux client| EP
    CC[Claude Code LSP] -->|plugin lspServers<br/>lspmux client| EP
    MCP[MCP hosts<br/>Claude Code / Codex / generic MCP] -->|lspmux-cc-mcp<br/>spawns lspmux client| EP
    CLI[lspmux client CLI] --> EP
    EP{{Transport<br/>tcp://127.0.0.1:27631<br/>or Unix socket}}
    EP --> S[lspmux server<br/>spawned on demand]
    S --> RA[rust-analyzer]

Install

Prerequisites

• macOS or Linux
• Rust toolchain (cargo) for the manual path
• jq
• rust-analyzer available on PATH, via RUST_ANALYZER_PATH, or from the flake package

Install Matrix

Path	Command	What it gives you
Cargo/manual	cargo install --path mcp-server	Installs lspmux-cc-mcp from this checkout.
Cargo/manual	./setup core	Installs or finds lspmux, validates rust-analyzer, writes the lspmux config, and leaves the daemon to be spawned on demand.
Cargo/manual	./setup doctor	Verifies local binaries, config, legacy service state, and Claude Code sandbox hints.
Nix flake	nix build	Builds the default lspmux-cc-mcp package.
Nix flake	nix build .#plugin	Builds the assembled Claude Code plugin with bundled wrappers and pinned binaries.
Nix flake	nix build .#rust-analyzer-nightly	Builds the pinned rust-analyzer package exported by the flake.
Nix flake	nix develop	Enters a shell with lspmux, rust-analyzer, cargo, just, jq, and shell tooling.
Nix flake	nix flake check	Runs the flake checks, including Rust checks, formatting, tests, and plugin structure checks.

./setup core does not install or start a launchd/systemd service. Users upgrading from a pre-M5 install should run ./setup migrate to remove the legacy unit. See docs/migration-m5.md.

Transport

For sandboxed hosts, prefer TCP loopback:

listen = "tcp://127.0.0.1:27631"
connect = "tcp://127.0.0.1:27631"

Then export:

export LSPMUX_CONNECT=tcp://127.0.0.1:27631

Unix sockets are still supported and are the default generated by ./setup core. They are a good fit for unsandboxed editor clients or hosts that can allowlist the exact socket path.

MCP Tools

All tools are read-only: they return data and never modify your files. The edits from rust_code_actions and rust_rename are returned for you or the agent to apply.

Tool	Description	Parameters
rust_diagnostics	Compiler errors and warnings for a file	file_path
rust_hover	Type signature and docs at a position	file_path, line, character
rust_goto_definition	Jump to where a symbol is defined	file_path, line, character
rust_goto_implementation	Implementations of a trait or trait method	file_path, line, character
rust_find_references	All references to a symbol	file_path, line, character
rust_workspace_symbol	Search symbols by name across the workspace	query
rust_document_symbols	A file's hierarchical symbol tree	file_path
rust_code_actions	Quick fixes / refactors for a range, with their edits (unapplied)	file_path, start_line, start_character, end_line, end_character
rust_rename	The workspace edit to rename a symbol (unapplied)	file_path, line, character, new_name
rust_call_hierarchy_incoming	Callers of the symbol at a position	file_path, line, character
rust_call_hierarchy_outgoing	Functions called by the symbol at a position	file_path, line, character
rust_expand_macro	Expand the macro invocation at a position	file_path, line, character
rust_server_status	Server health, readiness, and workspace info	(none)
rust_workspace_registry	All rust-analyzer instances the daemon is hosting	(none)

Coordinates: line and character inputs are zero-based (first line = 0). Output locations are one-based. Subtract 1 from output values before passing them as input to another tool.

All file paths must be absolute.

Host and Editor Integrations

Start with docs/hosts/README.md for the comparison table.