Consider --preview flag for server subcommand (#12208)

## Summary

This PR removes the requirement of `--preview` flag to run the `ruff
server` and instead considers it to be an indicator to turn on preview
mode for the linter and the formatter.

resolves: #12161 

## Test Plan

Add test cases to assert the `preview` value is updated accordingly.

In an editor context, I used the local `ruff` executable in Neovim with
the `--preview` flag and verified that the preview-only violations are
being highlighted.

Running with:
```lua
require('lspconfig').ruff.setup({
  cmd = {
    '/Users/dhruv/work/astral/ruff/target/debug/ruff',
    'server',
    '--preview',
  },
})
```
The screenshot shows that `E502` is highlighted with the below config in
`pyproject.toml`:

<img width="877" alt="Screenshot 2024-07-17 at 16 43 09"
src="https://github.com/user-attachments/assets/c7016ef3-55b1-4a14-bbd3-a07b1bcdd323">

crates/ruff/src/args.rs

@@ -494,9 +494,20 @@ pub struct FormatCommand {
 
 #[derive(Copy, Clone, Debug, clap::Parser)]
 pub struct ServerCommand {
-    /// Enable preview mode; required for regular operation
-    #[arg(long)]
-    pub(crate) preview: bool,
+    /// Enable preview mode. Use `--no-preview` to disable.
+    ///
+    /// This enables unstable server features and turns on the preview mode for the linter
+    /// and the formatter.
+    #[arg(long, overrides_with("no_preview"))]
+    preview: bool,
+    #[clap(long, overrides_with("preview"), hide = true)]
+    no_preview: bool,
+}
+
+impl ServerCommand {
+    pub(crate) fn resolve_preview(self) -> Option<bool> {
+        resolve_bool_arg(self.preview, self.no_preview)
+    }
 }
 
 #[derive(Debug, Clone, Copy, clap::ValueEnum)]

crates/ruff/src/commands/server.rs

@@ -4,13 +4,11 @@ use crate::ExitStatus;
 use anyhow::Result;
 use ruff_server::Server;
 
-pub(crate) fn run_server(preview: bool, worker_threads: NonZeroUsize) -> Result<ExitStatus> {
-    if !preview {
-        tracing::error!("--preview needs to be provided as a command line argument while the server is still unstable.\nFor example: `ruff server --preview`");
-        return Ok(ExitStatus::Error);
-    }
-
-    let server = Server::new(worker_threads)?;
+pub(crate) fn run_server(
+    worker_threads: NonZeroUsize,
+    preview: Option<bool>,
+) -> Result<ExitStatus> {
+    let server = Server::new(worker_threads, preview)?;
 
     server.run().map(|()| ExitStatus::Success)
 }

crates/ruff/src/lib.rs

@@ -200,15 +200,13 @@ fn format(args: FormatCommand, global_options: GlobalConfigArgs) -> Result<ExitS
 }
 
 fn server(args: ServerCommand) -> Result<ExitStatus> {
-    let ServerCommand { preview } = args;
-
     let four = NonZeroUsize::new(4).unwrap();
 
     // by default, we set the number of worker threads to `num_cpus`, with a maximum of 4.
     let worker_threads = std::thread::available_parallelism()
         .unwrap_or(four)
         .max(four);
-    commands::server::run_server(preview, worker_threads)
+    commands::server::run_server(worker_threads, args.resolve_preview())
 }
 
 pub fn check(args: CheckCommand, global_options: GlobalConfigArgs) -> Result<ExitStatus> {

crates/ruff_server/resources/test/fixtures/settings/empty_multiple_workspace.json

@@ -0,0 +1,16 @@
+{
+    "settings": [
+        {
+            "cwd": "/Users/test/projects/first",
+            "workspace": "file:///Users/test/projects/first"
+        },
+        {
+            "cwd": "/Users/test/projects/second",
+            "workspace": "file:///Users/test/projects/second"
+        }
+    ],
+    "globalSettings": {
+        "cwd": "/",
+        "workspace": "/"
+    }
+}

crates/ruff_server/resources/test/fixtures/settings/vs_code_initialization_options.json

@@ -1,7 +1,7 @@
 {
     "settings": [
         {
-            "experimentalServer": true,
+            "nativeServer": "on",
             "cwd": "/Users/test/projects/pandas",
             "workspace": "file:///Users/test/projects/pandas",
             "path": [],
@@ -21,20 +21,19 @@
             "lint": {
                 "enable": true,
                 "run": "onType",
-                "args": [
-                    "--preview"
-                ]
+                "args": []
             },
             "format": {
                 "args": []
             },
             "enable": true,
             "organizeImports": true,
             "fixAll": true,
-            "showNotifications": "off"
+            "showNotifications": "off",
+            "showSyntaxErrors": true
         },
         {
-            "experimentalServer": true,
+            "nativeServer": "on",
             "cwd": "/Users/test/projects/scipy",
             "workspace": "file:///Users/test/projects/scipy",
             "path": [],
@@ -55,21 +54,20 @@
                 "enable": true,
                 "preview": false,
                 "run": "onType",
-                "args": [
-                    "--preview"
-                ]
+                "args": []
             },
             "format": {
                 "args": []
             },
             "enable": true,
             "organizeImports": true,
             "fixAll": true,
-            "showNotifications": "off"
+            "showNotifications": "off",
+            "showSyntaxErrors": true
         }
     ],
     "globalSettings": {
-        "experimentalServer": true,
+        "nativeServer": "on",
         "cwd": "/",
         "workspace": "/",
         "path": [],
@@ -89,16 +87,15 @@
             "preview": true,
             "select": ["F", "I"],
             "run": "onType",
-            "args": [
-                "--preview"
-            ]
+            "args": []
         },
         "format": {
             "args": []
         },
         "enable": true,
         "organizeImports": true,
         "fixAll": false,
-        "showNotifications": "off"
+        "showNotifications": "off",
+        "showSyntaxErrors": true
     }
 }

crates/ruff_server/src/server.rs

@@ -48,7 +48,7 @@ pub struct Server {
 }
 
 impl Server {
-    pub fn new(worker_threads: NonZeroUsize) -> crate::Result<Self> {
+    pub fn new(worker_threads: NonZeroUsize, preview: Option<bool>) -> crate::Result<Self> {
         let connection = ConnectionInitializer::stdio();
 
         let (id, init_params) = connection.initialize_start()?;
@@ -70,14 +70,18 @@ impl Server {
 
         crate::message::init_messenger(connection.make_sender());
 
-        let AllSettings {
-            global_settings,
-            mut workspace_settings,
-        } = AllSettings::from_value(
+        let mut all_settings = AllSettings::from_value(
             init_params
                 .initialization_options
                 .unwrap_or_else(|| serde_json::Value::Object(serde_json::Map::default())),
         );
+        if let Some(preview) = preview {
+            all_settings.set_preview(preview);
+        }
+        let AllSettings {
+            global_settings,
+            mut workspace_settings,
+        } = all_settings;
 
         crate::trace::init_tracing(
             connection.make_sender(),

crates/ruff_server/src/session/settings.rs

@@ -84,6 +84,20 @@ pub struct ClientSettings {
     pub(crate) tracing: TracingSettings,
 }
 
+impl ClientSettings {
+    /// Update the preview flag for the linter and the formatter with the given value.
+    pub(crate) fn set_preview(&mut self, preview: bool) {
+        match self.lint.as_mut() {
+            None => self.lint = Some(LintOptions::default().with_preview(preview)),
+            Some(lint) => lint.set_preview(preview),
+        }
+        match self.format.as_mut() {
+            None => self.format = Some(FormatOptions::default().with_preview(preview)),
+            Some(format) => format.set_preview(preview),
+        }
+    }
+}
+
 /// Settings needed to initialize tracing. These will only be
 /// read from the global configuration.
 #[derive(Debug, Deserialize, Default)]
@@ -107,7 +121,7 @@ struct WorkspaceSettings {
     workspace: Url,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Default, Deserialize)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[serde(rename_all = "camelCase")]
 struct LintOptions {
@@ -118,13 +132,35 @@ struct LintOptions {
     ignore: Option<Vec<String>>,
 }
 
+impl LintOptions {
+    fn with_preview(mut self, preview: bool) -> LintOptions {
+        self.preview = Some(preview);
+        self
+    }
+
+    fn set_preview(&mut self, preview: bool) {
+        self.preview = Some(preview);
+    }
+}
+
 #[derive(Debug, Default, Deserialize)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[serde(rename_all = "camelCase")]
 struct FormatOptions {
     preview: Option<bool>,
 }
 
+impl FormatOptions {
+    fn with_preview(mut self, preview: bool) -> FormatOptions {
+        self.preview = Some(preview);
+        self
+    }
+
+    fn set_preview(&mut self, preview: bool) {
+        self.preview = Some(preview);
+    }
+}
+
 #[derive(Debug, Default, Deserialize)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[serde(rename_all = "camelCase")]
@@ -159,6 +195,7 @@ enum InitializationOptions {
 }
 
 /// Built from the initialization options provided by the client.
+#[derive(Debug)]
 pub(crate) struct AllSettings {
     pub(crate) global_settings: ClientSettings,
     /// If this is `None`, the client only passed in global settings.
@@ -179,6 +216,16 @@ impl AllSettings {
         )
     }
 
+    /// Update the preview flag for both the global and all workspace settings.
+    pub(crate) fn set_preview(&mut self, preview: bool) {
+        self.global_settings.set_preview(preview);
+        if let Some(workspace_settings) = self.workspace_settings.as_mut() {
+            for settings in workspace_settings.values_mut() {
+                settings.set_preview(preview);
+            }
+        }
+    }
+
     fn from_init_options(options: InitializationOptions) -> Self {
         let (global_settings, workspace_settings) = match options {
             InitializationOptions::GlobalOnly { settings } => (settings, None),
@@ -393,6 +440,11 @@ mod tests {
     const EMPTY_INIT_OPTIONS_FIXTURE: &str =
         include_str!("../../resources/test/fixtures/settings/empty.json");
 
+    // This fixture contains multiple workspaces with empty initialization options. It only sets
+    // the `cwd` and the `workspace` value.
+    const EMPTY_MULTIPLE_WORKSPACE_INIT_OPTIONS_FIXTURE: &str =
+        include_str!("../../resources/test/fixtures/settings/empty_multiple_workspace.json");
+
     fn deserialize_fixture<T: DeserializeOwned>(content: &str) -> T {
         serde_json::from_str(content).expect("test fixture JSON should deserialize")
     }
@@ -456,7 +508,9 @@ mod tests {
                 exclude: None,
                 line_length: None,
                 configuration_preference: None,
-                show_syntax_errors: None,
+                show_syntax_errors: Some(
+                    true,
+                ),
                 tracing: TracingSettings {
                     log_level: None,
                     log_file: None,
@@ -509,7 +563,9 @@ mod tests {
                         exclude: None,
                         line_length: None,
                         configuration_preference: None,
-                        show_syntax_errors: None,
+                        show_syntax_errors: Some(
+                            true,
+                        ),
                         tracing: TracingSettings {
                             log_level: None,
                             log_file: None,
@@ -575,7 +631,9 @@ mod tests {
                         exclude: None,
                         line_length: None,
                         configuration_preference: None,
-                        show_syntax_errors: None,
+                        show_syntax_errors: Some(
+                            true,
+                        ),
                         tracing: TracingSettings {
                             log_level: None,
                             log_file: None,
@@ -771,4 +829,30 @@ mod tests {
 
         assert_eq!(options, InitializationOptions::default());
     }
+
+    fn assert_preview_client_settings(settings: &ClientSettings, preview: bool) {
+        assert_eq!(settings.lint.as_ref().unwrap().preview.unwrap(), preview);
+        assert_eq!(settings.format.as_ref().unwrap().preview.unwrap(), preview);
+    }
+
+    fn assert_preview_all_settings(all_settings: &AllSettings, preview: bool) {
+        assert_preview_client_settings(&all_settings.global_settings, preview);
+        if let Some(workspace_settings) = all_settings.workspace_settings.as_ref() {
+            for settings in workspace_settings.values() {
+                assert_preview_client_settings(settings, preview);
+            }
+        }
+    }
+
+    #[test]
+    fn test_preview_flag() {
+        let options = deserialize_fixture(EMPTY_MULTIPLE_WORKSPACE_INIT_OPTIONS_FIXTURE);
+        let mut all_settings = AllSettings::from_init_options(options);
+
+        all_settings.set_preview(false);
+        assert_preview_all_settings(&all_settings, false);
+
+        all_settings.set_preview(true);
+        assert_preview_all_settings(&all_settings, true);
+    }
 }