Add language_server_workspace_configuration to extension API (#10212)

This PR adds the ability for extensions to implement
`language_server_workspace_configuration` to provide workspace
configuration to the language server.

We've used the Dart extension as a motivating example for this, pulling
it out into an extension in the process.

Release Notes:

- Removed built-in support for Dart, in favor of making it available as
an extension. The Dart extension will be suggested for download when you
open a `.dart` file.

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/extension_api/Cargo.toml

@@ -15,6 +15,8 @@ workspace = true
 path = "src/extension_api.rs"
 
 [dependencies]
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
 wit-bindgen = "0.22"
 
 [package.metadata.component]

crates/extension_api/src/extension_api.rs

@@ -1,9 +1,13 @@
 //! The Zed Rust Extension API allows you write extensions for [Zed](https://zed.dev/) in Rust.
 
+pub mod settings;
+
 use core::fmt;
 
 use wit::*;
 
+pub use serde_json;
+
 // WIT re-exports.
 //
 // We explicitly enumerate the symbols we want to re-export, as there are some
@@ -62,7 +66,16 @@ pub trait Extension: Send + Sync {
         &mut self,
         _language_server_id: &LanguageServerId,
         _worktree: &Worktree,
-    ) -> Result<Option<String>> {
+    ) -> Result<Option<serde_json::Value>> {
+        Ok(None)
+    }
+
+    /// Returns the workspace configuration options to pass to the language server.
+    fn language_server_workspace_configuration(
+        &mut self,
+        _language_server_id: &LanguageServerId,
+        _worktree: &Worktree,
+    ) -> Result<Option<serde_json::Value>> {
         Ok(None)
     }
 
@@ -142,7 +155,19 @@ impl wit::Guest for Component {
         worktree: &Worktree,
     ) -> Result<Option<String>, String> {
         let language_server_id = LanguageServerId(language_server_id);
-        extension().language_server_initialization_options(&language_server_id, worktree)
+        Ok(extension()
+            .language_server_initialization_options(&language_server_id, worktree)?
+            .and_then(|value| serde_json::to_string(&value).ok()))
+    }
+
+    fn language_server_workspace_configuration(
+        language_server_id: String,
+        worktree: &Worktree,
+    ) -> Result<Option<String>, String> {
+        let language_server_id = LanguageServerId(language_server_id);
+        Ok(extension()
+            .language_server_workspace_configuration(&language_server_id, worktree)?
+            .and_then(|value| serde_json::to_string(&value).ok()))
     }
 
     fn labels_for_completions(

crates/extension_api/src/settings.rs

@@ -0,0 +1,30 @@
+#[path = "../wit/since_v0.0.6/settings.rs"]
+pub mod types;
+
+use crate::{wit, Result, SettingsLocation, Worktree};
+use serde_json;
+pub use types::*;
+
+impl LanguageSettings {
+    pub fn for_worktree(language: Option<&str>, worktree: &Worktree) -> Result<Self> {
+        let location = SettingsLocation {
+            worktree_id: worktree.id(),
+            path: worktree.root_path(),
+        };
+        let settings_json = wit::get_settings(Some(&location), "language", language)?;
+        let settings: Self = serde_json::from_str(&settings_json).map_err(|err| err.to_string())?;
+        Ok(settings)
+    }
+}
+
+impl LspSettings {
+    pub fn for_worktree(language_server_name: &str, worktree: &Worktree) -> Result<Self> {
+        let location = SettingsLocation {
+            worktree_id: worktree.id(),
+            path: worktree.root_path(),
+        };
+        let settings_json = wit::get_settings(Some(&location), "lsp", Some(language_server_name))?;
+        let settings: Self = serde_json::from_str(&settings_json).map_err(|err| err.to_string())?;
+        Ok(settings)
+    }
+}

crates/extension_api/wit/since_v0.0.6/extension.wit

@@ -79,6 +79,13 @@ world extension {
     /// Returns operating system and architecture for the current platform.
     import current-platform: func() -> tuple<os, architecture>;
 
+    record settings-location {
+        worktree-id: u64,
+        path: string,
+    }
+
+    import get-settings: func(path: option<settings-location>, category: string, key: option<string>) -> result<string, string>;
+
     /// Returns the path to the Node binary used by Zed.
     import node-binary-path: func() -> result<string, string>;
 
@@ -121,6 +128,10 @@ world extension {
 
     /// A Zed worktree.
     resource worktree {
+        /// Returns the ID of the worktree.
+        id: func() -> u64;
+        /// Returns the root path of the worktree.
+        root-path: func() -> string;
         /// Returns the textual contents of the specified file in the worktree.
         read-text-file: func(path: string) -> result<string, string>;
         /// Returns the path to the given binary name, if one is present on the `$PATH`.
@@ -137,6 +148,9 @@ world extension {
     /// The initialization options are represented as a JSON string.
     export language-server-initialization-options: func(language-server-id: string, worktree: borrow<worktree>) -> result<option<string>, string>;
 
+    /// Returns the workspace configuration options to pass to the language server.
+    export language-server-workspace-configuration: func(language-server-id: string, worktree: borrow<worktree>) -> result<option<string>, string>;
+
     record code-label {
         /// The source code to parse with Tree-sitter.
         code: string,

crates/extension_api/wit/since_v0.0.6/settings.rs

@@ -0,0 +1,20 @@
+use serde::{Deserialize, Serialize};
+use std::num::NonZeroU32;
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct LanguageSettings {
+    pub tab_size: NonZeroU32,
+}
+
+#[derive(Default, Debug, Serialize, Deserialize)]
+pub struct LspSettings {
+    pub binary: Option<BinarySettings>,
+    pub initialization_options: Option<serde_json::Value>,
+    pub settings: Option<serde_json::Value>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct BinarySettings {
+    pub path: Option<String>,
+    pub arguments: Option<Vec<String>>,
+}