Rust Analyzer LSP Tasks, Cargo Diagnostics, and Performance Tuning in Zed

Zed provides tasks using tree-sitter, but rust-analyzer has an LSP extension method for querying file-related tasks via LSP. This is enabled by default and can be configured as ```json "lsp": { "rust-analyzer": { "enable_lsp_tasks": true, } } ``` ## Manual Cargo Diagnostics fetch By default, rust-analyzer has `checkOnSave: true` enabled, which causes every buffer save to trigger a `cargo check --workspace --all-targets` command. For lager projects this might introduce excessive wait times, so a more fine-grained triggering could be enabled by altering the ```json "diagnostics": { "cargo": { // When enabled, Zed disables rust-analyzer's check on save and starts to query // Cargo diagnostics separately. "fetch_cargo_diagnostics": false } } ``` default settings. This will stop rust-analyzer from running `cargo check ...` on save, yet still allow to run `editor: run/clear/cancel flycheck` commands in Rust files to refresh cargo diagnostics; the project diagnostics editor will also refresh cargo diagnostics with `editor: run flycheck` command when the setting is enabled. ## More server configuration  Rust-analyzer [manual](https://rust-analyzer.github.io/book/) describes various features and configuration options for rust-analyzer language server. Rust-analyzer in Zed runs with the default parameters. ### Large projects and performance One of the main caveats that might cause extensive resource usage on large projects, is the combination of the following features: ``` rust-analyzer.checkOnSave (default: true) Run the check command for diagnostics on save. ``` ``` rust-analyzer.check.workspace (default: true) Whether --workspace should be passed to cargo check. If false, -p <package> will be passed instead. ``` ``` rust-analyzer.cargo.allTargets (default: true) Pass --all-targets to cargo invocation ``` Which would mean that every time Zed saves, a `cargo check --workspace --all-targets` command is run, checking the entire project (workspace), lib, doc, test, bin, bench and [other targets](https://doc.rust-lang.org/cargo/reference/cargo-targets.html). While that works fine on small projects, it does not scale well. The alternatives would be to use [tasks](../tasks.md), as Zed already provides a `cargo check --workspace --all-targets` task and the ability to cmd/ctrl-click on the terminal output to navigate to the error, and limit or turn off the check on save feature entirely. Check on save feature is responsible for returning part of the diagnostics based on cargo check output, so turning it off will limit rust-analyzer with its own [diagnostics](https://rust-analyzer.github.io/book/diagnostics.html). Consider more `rust-analyzer.cargo.` and `rust-analyzer.check.` and `rust-analyzer.diagnostics.` settings from the manual for more fine-grained configuration.

This section covers advanced configurations for Rust analyzer in Zed, focusing on LSP tasks, manual Cargo diagnostics fetching, and performance considerations for large projects. It explains how to enable/disable LSP tasks, control Cargo diagnostics to avoid excessive `cargo check` commands on every save, and tune Rust analyzer's behavior for better performance with large Rust projects by adjusting `checkOnSave`, `workspace`, and `allTargets` settings, which could be impacting the project's performance and diagnostics.