Start language servers based on buffers' languages

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/language/src/language.rs

@@ -1,6 +1,7 @@
 use crate::HighlightMap;
 use anyhow::Result;
-use gpui::AppContext;
+use gpui::{executor::Background, AppContext};
+use lsp::LanguageServer;
 use parking_lot::Mutex;
 use serde::Deserialize;
 use std::{collections::HashSet, path::Path, str, sync::Arc};
@@ -16,10 +17,13 @@ pub struct LanguageConfig {
     pub language_server: Option<LanguageServerConfig>,
 }
 
-#[derive(Deserialize)]
+#[derive(Default, Deserialize)]
 pub struct LanguageServerConfig {
     pub binary: String,
     pub disk_based_diagnostic_sources: HashSet<String>,
+    #[cfg(any(test, feature = "test-support"))]
+    #[serde(skip)]
+    pub fake_server: Option<(Arc<LanguageServer>, Arc<std::sync::atomic::AtomicBool>)>,
 }
 
 #[derive(Clone, Debug, Deserialize)]
@@ -117,6 +121,12 @@ impl Language {
         cx: &AppContext,
     ) -> Result<Option<Arc<lsp::LanguageServer>>> {
         if let Some(config) = &self.config.language_server {
+            #[cfg(any(test, feature = "test-support"))]
+            if let Some((server, started)) = &config.fake_server {
+                started.store(true, std::sync::atomic::Ordering::SeqCst);
+                return Ok(Some(server.clone()));
+            }
+
             const ZED_BUNDLE: Option<&'static str> = option_env!("ZED_BUNDLE");
             let binary_path = if ZED_BUNDLE.map_or(Ok(false), |b| b.parse())? {
                 cx.platform()
@@ -151,6 +161,23 @@ impl Language {
     }
 }
 
+#[cfg(any(test, feature = "test-support"))]
+impl LanguageServerConfig {
+    pub async fn fake(executor: Arc<Background>) -> (Self, lsp::FakeLanguageServer) {
+        let (server, fake) = lsp::LanguageServer::fake(executor).await;
+        fake.started
+            .store(false, std::sync::atomic::Ordering::SeqCst);
+        let started = fake.started.clone();
+        (
+            Self {
+                fake_server: Some((server, started)),
+                ..Default::default()
+            },
+            fake,
+        )
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/language/src/lib.rs

@@ -6,7 +6,7 @@ mod tests;
 
 pub use self::{
     highlight_map::{HighlightId, HighlightMap},
-    language::{BracketPair, Language, LanguageConfig, LanguageRegistry},
+    language::{BracketPair, Language, LanguageConfig, LanguageRegistry, LanguageServerConfig},
 };
 use anyhow::{anyhow, Result};
 pub use buffer::{Buffer as TextBuffer, Operation as _, *};
@@ -37,6 +37,9 @@ use std::{
 use tree_sitter::{InputEdit, Parser, QueryCursor, Tree};
 use util::{post_inc, TryFutureExt as _};
 
+#[cfg(any(test, feature = "test-support"))]
+pub use tree_sitter_rust;
+
 pub use lsp::DiagnosticSeverity;
 
 thread_local! {

crates/language/src/tests.rs

@@ -1,7 +1,6 @@
 use super::*;
-use crate::language::LanguageServerConfig;
 use gpui::{ModelHandle, MutableAppContext};
-use std::{iter::FromIterator, rc::Rc};
+use std::rc::Rc;
 use unindent::Unindent as _;
 
 #[gpui::test]
@@ -676,10 +675,7 @@ fn rust_lang() -> Option<Arc<Language>> {
             LanguageConfig {
                 name: "Rust".to_string(),
                 path_suffixes: vec!["rs".to_string()],
-                language_server: Some(LanguageServerConfig {
-                    binary: "rust-analyzer".to_string(),
-                    disk_based_diagnostic_sources: HashSet::from_iter(vec!["rustc".to_string()]),
-                }),
+                language_server: None,
                 ..Default::default()
             },
             tree_sitter_rust::language(),