Enable clangd's dot-to-arrow feature (#21142)

Closes #20815


![dot2arrow1127](https://github.com/user-attachments/assets/d825f9bf-52ae-47ee-b3a3-5f952b6e8979)

Release Notes:
- Enabled clangd's dot-to-arrow feature

crates/language/src/language.rs

@@ -30,7 +30,10 @@ use gpui::{AppContext, AsyncAppContext, Model, SharedString, Task};
 pub use highlight_map::HighlightMap;
 use http_client::HttpClient;
 pub use language_registry::{LanguageName, LoadedLanguage};
-use lsp::{CodeActionKind, LanguageServerBinary, LanguageServerBinaryOptions, LanguageServerName};
+use lsp::{
+    CodeActionKind, InitializeParams, LanguageServerBinary, LanguageServerBinaryOptions,
+    LanguageServerName,
+};
 use parking_lot::Mutex;
 use regex::Regex;
 use schemars::{
@@ -484,6 +487,11 @@ pub trait LspAdapter: 'static + Send + Sync {
     fn language_ids(&self) -> HashMap<String, String> {
         Default::default()
     }
+
+    /// Support custom initialize params.
+    fn prepare_initialize_params(&self, original: InitializeParams) -> Result<InitializeParams> {
+        Ok(original)
+    }
 }
 
 async fn try_fetch_server_binary<L: LspAdapter + 'static + Send + Sync + ?Sized>(

crates/languages/src/c.rs

@@ -4,10 +4,11 @@ use futures::StreamExt;
 use gpui::AsyncAppContext;
 use http_client::github::{latest_github_release, GitHubLspBinaryVersion};
 pub use language::*;
-use lsp::{LanguageServerBinary, LanguageServerName};
+use lsp::{InitializeParams, LanguageServerBinary, LanguageServerName};
+use serde_json::json;
 use smol::fs::{self, File};
 use std::{any::Any, env::consts, path::PathBuf, sync::Arc};
-use util::{fs::remove_matching, maybe, ResultExt};
+use util::{fs::remove_matching, maybe, merge_json_value_into, ResultExt};
 
 pub struct CLspAdapter;
 
@@ -257,6 +258,26 @@ impl super::LspAdapter for CLspAdapter {
             filter_range,
         })
     }
+
+    fn prepare_initialize_params(
+        &self,
+        mut original: InitializeParams,
+    ) -> Result<InitializeParams> {
+        // enable clangd's dot-to-arrow feature.
+        let experimental = json!({
+            "textDocument": {
+                "completion" : {
+                    "editsNearCursor": true
+                }
+            }
+        });
+        if let Some(ref mut original_experimental) = original.capabilities.experimental {
+            merge_json_value_into(experimental, original_experimental);
+        } else {
+            original.capabilities.experimental = Some(experimental);
+        }
+        Ok(original)
+    }
 }
 
 async fn get_cached_server_binary(container_dir: PathBuf) -> Option<LanguageServerBinary> {

crates/lsp/src/lsp.rs

@@ -599,22 +599,14 @@ impl LanguageServer {
         Ok(())
     }
 
-    /// Initializes a language server by sending the `Initialize` request.
-    /// Note that `options` is used directly to construct [`InitializeParams`], which is why it is owned.
-    ///
-    /// [LSP Specification](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialize)
-    pub fn initialize(
-        mut self,
-        options: Option<Value>,
-        cx: &AppContext,
-    ) -> Task<Result<Arc<Self>>> {
+    pub fn default_initialize_params(&self, cx: &AppContext) -> InitializeParams {
         let root_uri = Url::from_file_path(&self.working_dir).unwrap();
         #[allow(deprecated)]
-        let params = InitializeParams {
+        InitializeParams {
             process_id: None,
             root_path: None,
             root_uri: Some(root_uri.clone()),
-            initialization_options: options,
+            initialization_options: None,
             capabilities: ClientCapabilities {
                 workspace: Some(WorkspaceClientCapabilities {
                     configuration: Some(true),
@@ -779,6 +771,22 @@ impl LanguageServer {
             }),
             locale: None,
             ..Default::default()
+        }
+    }
+
+    /// Initializes a language server by sending the `Initialize` request.
+    /// Note that `options` is used directly to construct [`InitializeParams`], which is why it is owned.
+    ///
+    /// [LSP Specification](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialize)
+    pub fn initialize(
+        mut self,
+        initialize_params: Option<InitializeParams>,
+        cx: &AppContext,
+    ) -> Task<Result<Arc<Self>>> {
+        let params = if let Some(params) = initialize_params {
+            params
+        } else {
+            self.default_initialize_params(cx)
         };
 
         cx.spawn(|_| async move {

crates/project/src/lsp_store.rs

@@ -5673,8 +5673,6 @@ impl LspStore {
                             .initialization_options(&(delegate))
                             .await?;
 
-                        Self::setup_lsp_messages(this.clone(), &language_server, delegate, adapter);
-
                         match (&mut initialization_options, override_options) {
                             (Some(initialization_options), Some(override_options)) => {
                                 merge_json_value_into(override_options, initialization_options);
@@ -5683,8 +5681,18 @@ impl LspStore {
                             _ => {}
                         }
 
+                        let initialization_params = cx.update(|cx| {
+                            let mut params = language_server.default_initialize_params(cx);
+                            params.initialization_options = initialization_options;
+                            adapter.adapter.prepare_initialize_params(params)
+                        })??;
+
+                        Self::setup_lsp_messages(this.clone(), &language_server, delegate, adapter);
+
                         let language_server = cx
-                            .update(|cx| language_server.initialize(initialization_options, cx))?
+                            .update(|cx| {
+                                language_server.initialize(Some(initialization_params), cx)
+                            })?
                             .await
                             .inspect_err(|_| {
                                 if let Some(this) = this.upgrade() {