feat: add a new config that limits workspace checks to single crates

crates/flycheck/src/lib.rs

@@ -32,6 +32,7 @@ pub enum FlycheckConfig {
         features: Vec<String>,
         extra_args: Vec<String>,
         extra_env: FxHashMap<String, String>,
+        single_crate: Option<AbsPathBuf>,
     },
     CustomCommand {
         command: String,
@@ -250,7 +251,7 @@ impl FlycheckActor {
     }
 
     fn check_command(&self) -> Command {
-        let mut cmd = match &self.config {
+        match &self.config {
             FlycheckConfig::CargoCommand {
                 command,
                 target_triple,
@@ -260,12 +261,26 @@ impl FlycheckActor {
                 extra_args,
                 features,
                 extra_env,
+                single_crate,
             } => {
                 let mut cmd = Command::new(toolchain::cargo());
                 cmd.arg(command);
                 cmd.current_dir(&self.workspace_root);
-                cmd.args(&["--workspace", "--message-format=json", "--manifest-path"])
-                    .arg(self.workspace_root.join("Cargo.toml").as_os_str());
+                cmd.args(&["--message-format=json"]);
+
+                // If we check single crates, then check just that crate's cargo.toml
+                //
+                // Else, check the entire workspace
+                if let Some(single) = single_crate.as_ref() {
+                    cmd.arg("--manifest-path");
+                    cmd.arg(single.join("Cargo.toml").as_os_str());
+                    cmd.current_dir(single);
+                } else {
+                    cmd.arg("--workspace");
+                    cmd.arg("--manifest-path");
+                    cmd.arg(self.workspace_root.join("Cargo.toml").as_os_str());
+                    cmd.current_dir(&self.workspace_root);
+                }
 
                 if let Some(target) = target_triple {
                     cmd.args(&["--target", target.as_str()]);
@@ -292,11 +307,10 @@ impl FlycheckActor {
                 let mut cmd = Command::new(command);
                 cmd.args(args);
                 cmd.envs(extra_env);
+                cmd.current_dir(&self.workspace_root);
                 cmd
             }
-        };
-        cmd.current_dir(&self.workspace_root);
-        cmd
+        }
     }
 
     fn send(&self, check_task: Message) {

crates/rust-analyzer/src/config.rs

@@ -148,6 +148,18 @@ config_data! {
         /// `#rust-analyzer.cargo.target#`.
         checkOnSave_target: Option<String>               = "null",
 
+        /// Only check the currently opened crate of a workspace.
+        ///
+        /// Lets Rust analyzer perform less work by only checking the currently
+        /// opened crate when a crate of a workspace is opened alone. This
+        /// means you won't receive diagnostics about the entire workspace, but
+        /// can significantly improve performance when single crates are modified
+        /// as part of a much larger workspace.
+        ///
+        ///  Defaults to
+        /// `#rust-analyzer.cargo.target#`.
+        checkSingleCrate_enable: bool = "false",
+
         /// Toggles the additional completions that automatically add imports when completed.
         /// Note that your client must specify the `additionalTextEdits` LSP client capability to truly have this feature enabled.
         completion_autoimport_enable: bool       = "true",
@@ -1116,11 +1128,19 @@ impl Config {
                 },
                 extra_args: self.data.checkOnSave_extraArgs.clone(),
                 extra_env: self.check_on_save_extra_env(),
+                single_crate: self.get_crate_for_check(),
             },
         };
         Some(flycheck_config)
     }
 
+    fn get_crate_for_check(&self) -> Option<AbsPathBuf> {
+        match self.data.checkSingleCrate_enable {
+            true => Some(self.root_path().clone()),
+            false => None,
+        }
+    }
+
     pub fn runnables(&self) -> RunnablesConfig {
         RunnablesConfig {
             override_cargo: self.data.runnables_command.clone(),

docs/user/generated_config.adoc

@@ -152,6 +152,20 @@ cargo check --workspace --message-format=json --all-targets
 Check for a specific target. Defaults to
 `#rust-analyzer.cargo.target#`.
 --
+[[rust-analyzer.checkSingleCrate.enable]]rust-analyzer.checkSingleCrate.enable (default: `false`)::
++
+--
+Only check the currently opened crate of a workspace.
+
+Lets Rust analyzer perform less work by only checking the currently
+opened crate when a crate of a workspace is opened alone. This
+means you won't receive diagnostics about the entire workspace, but
+can significantly improve performance when single crates are modified
+as part of a much larger workspace.
+
+ Defaults to
+`#rust-analyzer.cargo.target#`.
+--
 [[rust-analyzer.completion.autoimport.enable]]rust-analyzer.completion.autoimport.enable (default: `true`)::
 +
 --

editors/code/package.json

@@ -573,6 +573,11 @@
                         "string"
                     ]
                 },
+                "rust-analyzer.checkSingleCrate.enable": {
+                    "markdownDescription": "Only check the currently opened crate of a workspace.\n\nLets Rust analyzer perform less work by only checking the currently\nopened crate when a crate of a workspace is opened alone. This\nmeans you won't receive diagnostics about the entire workspace, but\ncan significantly improve performance when single crates are modified\nas part of a much larger workspace.\n\n Defaults to\n`#rust-analyzer.cargo.target#`.",
+                    "default": false,
+                    "type": "boolean"
+                },
                 "rust-analyzer.completion.autoimport.enable": {
                     "markdownDescription": "Toggles the additional completions that automatically add imports when completed.\nNote that your client must specify the `additionalTextEdits` LSP client capability to truly have this feature enabled.",
                     "default": true,