# Rust

Rust support is available natively in Zed.

- Tree Sitter: [tree-sitter/tree-sitter-rust](https://github.com/tree-sitter/tree-sitter-rust)
- Language Server: [rust-lang/rust-analyzer](https://github.com/rust-lang/rust-analyzer)

<!--
TBD: Polish Rust Docs. Zed is a good rust editor, good Rust docs make it look like we care about Rust (we do!)
TBD: Users may not know what inlayHints, don't start there.
TBD: Provide explicit examples not just `....`
-->

## Inlay Hints

The following configuration can be used to change the inlay hint settings for `rust-analyzer` in Rust:

```json
{
  "lsp": {
    "rust-analyzer": {
      "initialization_options": {
        "inlayHints": {
          "maxLength": null,
          "lifetimeElisionHints": {
            "enable": "skip_trivial",
            "useParameterNames": true
          },
          "closureReturnTypeHints": {
            "enable": "always"
          }
        }
      }
    }
  }
}
```

See [Inlay Hints](https://rust-analyzer.github.io/manual.html#inlay-hints) in the Rust Analyzer Manual for more information.

## Target directory

The `rust-analyzer` target directory can be set in `initialization_options`:

```json
{
  "lsp": {
    "rust-analyzer": {
      "initialization_options": {
        "rust": {
          "analyzerTargetDir": true
        }
      }
    }
  }
}
```

A `true` setting will set the target directory to `target/rust-analyzer`. You can set a custom directory with a string like `"target/analyzer"` instead of `true`.

## Binary

You can configure which `rust-analyzer` binary Zed should use.

By default, Zed will try to find a `rust-analyzer` in your `$PATH` and try to use that. If that binary successfully executes `rust-analyzer --help`, it's used. Otherwise, Zed will fall back to installing its own `rust-analyzer` version and using that.

If you want to disable Zed looking for a `rust-analyzer` binary, you can set `ignore_system_version` to `true` in your `settings.json`:

```json
{
  "lsp": {
    "rust-analyzer": {
      "binary": {
        "ignore_system_version": true
      }
    }
  }
}
```

If you want to use a binary in a custom location, you can specify a `path` and optional `args`:

```json
{
  "lsp": {
    "rust-analyzer": {
      "binary": {
        "path": "/Users/example/bin/rust-analyzer",
        "args": []
      }
    }
  }
}
```

This `"path"` has to be an absolute path.

## More server configuration

<!--
TBD: Is it possible to specify RUSTFLAGS? https://github.com/zed-industries/zed/issues/14334
-->

Rust-analyzer [manual](https://rust-analyzer.github.io/manual.html) 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/manual.html#diagnostics).

Consider more `rust-analyzer.cargo.` and `rust-analyzer.check.` and `rust-analyzer.diagnostics.` settings from the manual for more fine-grained configuration.
Here's a snippet for Zed settings.json (the language server will restart automatically after the `lsp.rust-analyzer` section is edited and saved):

```json
{
  "lsp": {
    "rust-analyzer": {
      "initialization_options": {
        // get more cargo-less diagnostics from rust-analyzer,
        // which might include false-positives (those can be turned off by their names)
        "diagnostics": {
          "experimental": {
            "enable": true
          }
        },
        // To disable the checking entirely
        // (ignores all cargo and check settings below)
        "checkOnSave": false,
        // To check the `lib` target only.
        "cargo": {
          "allTargets": false
        },
        // Use `-p` instead of `--workspace` for cargo check
        "check": {
          "workspace": false
        }
      }
    }
  }
}
```

### Multi-project workspaces

If you want rust-analyzer to analyze multiple Rust projects in the same folder that are not listed in `[members]` in the Cargo workspace,
you can list them in `linkedProjects` in the local project settings:

```json
{
  "lsp": {
    "rust-analyzer": {
      "initialization_options": {
        "linkedProjects": ["./path/to/a/Cargo.toml", "./path/to/b/Cargo.toml"]
      }
    }
  }
}
```

### Snippets

There's a way get custom completion items from rust-analyzer, that will transform the code according to the snippet body:

```json
{
  "lsp": {
    "rust-analyzer": {
      "initialization_options": {
        "completion": {
          "snippets": {
            "custom": {
              "Arc::new": {
                "postfix": "arc",
                "body": ["Arc::new(${receiver})"],
                "requires": "std::sync::Arc",
                "scope": "expr"
              },
              "Some": {
                "postfix": "some",
                "body": ["Some(${receiver})"],
                "scope": "expr"
              },
              "Ok": {
                "postfix": "ok",
                "body": ["Ok(${receiver})"],
                "scope": "expr"
              },
              "Rc::new": {
                "postfix": "rc",
                "body": ["Rc::new(${receiver})"],
                "requires": "std::rc::Rc",
                "scope": "expr"
              },
              "Box::pin": {
                "postfix": "boxpin",
                "body": ["Box::pin(${receiver})"],
                "requires": "std::boxed::Box",
                "scope": "expr"
              },
              "vec!": {
                "postfix": "vec",
                "body": ["vec![${receiver}]"],
                "description": "vec![]",
                "scope": "expr"
              }
            }
          }
        }
      }
    }
  }
}
```
