Adds support for multiple language servers per language.

Language Servers are now configured in a separate table in `languages.toml`:

```toml
[langauge-server.mylang-lsp]
command = "mylang-lsp"
args = ["--stdio"]
config = { provideFormatter = true }

[language-server.efm-lsp-prettier]
command = "efm-langserver"

[language-server.efm-lsp-prettier.config]
documentFormatting = true
languages = { typescript = [ { formatCommand ="prettier --stdin-filepath ${INPUT}", formatStdin = true } ] }
```

The language server for a language is configured like this (`typescript-language-server` is configured by default):

```toml
[[language]]
name = "typescript"
language-servers = [ { name = "efm-lsp-prettier", only-features = [ "format" ] }, "typescript-language-server" ]
```

or equivalent:

```toml
[[language]]
name = "typescript"
language-servers = [ { name = "typescript-language-server", except-features = [ "format" ] }, "efm-lsp-prettier" ]
```

Each requested LSP feature is priorized in the order of the `language-servers` array.
For example the first `goto-definition` supported language server (in this case `typescript-language-server`) will be taken for the relevant LSP request (command `goto_definition`).

If no `except-features` or `only-features` is given all features for the language server are enabled, as long as the language server supports these. If it doesn't the next language server which supports the feature is tried.

The list of supported features are:

- `format`
- `goto-definition`
- `goto-declaration`
- `goto-type-definition`
- `goto-reference`
- `goto-implementation`
- `signature-help`
- `hover`
- `document-highlight`
- `completion`
- `code-action`
- `workspace-command`
- `document-symbols`
- `workspace-symbols`
- `diagnostics`
- `rename-symbol`
- `inlay-hints`

Another side-effect/difference that comes with this PR, is that only one language server instance is started if different languages use the same language server.

3 files changed, 163 insertions, 116 deletions

diff --git a/helix-lsp/src/client.rs b/helix-lsp/src/client.rs
index 840e7382..c0f3adb8 100644
--- a/helix-lsp/src/client.rs
+++ b/helix-lsp/src/client.rs
@@ -44,6 +44,7 @@ fn workspace_for_uri(uri: lsp::Url) -> WorkspaceFolder {
 #[derive(Debug)]
 pub struct Client {
     id: usize,
+    name: String,
     _process: Child,
     server_tx: UnboundedSender<Payload>,
     request_counter: AtomicU64,
@@ -166,8 +167,7 @@ impl Client {
         tokio::spawn(self.did_change_workspace(vec![workspace_for_uri(root_uri)], Vec::new()));
     }
 
-    #[allow(clippy::type_complexity)]
-    #[allow(clippy::too_many_arguments)]
+    #[allow(clippy::type_complexity, clippy::too_many_arguments)]
     pub fn start(
         cmd: &str,
         args: &[String],
@@ -176,6 +176,7 @@ impl Client {
         root_markers: &[String],
         manual_roots: &[PathBuf],
         id: usize,
+        name: String,
         req_timeout: u64,
         doc_path: Option<&std::path::PathBuf>,
     ) -> Result<(Self, UnboundedReceiver<(usize, Call)>, Arc<Notify>)> {
@@ -200,7 +201,7 @@ impl Client {
         let stderr = BufReader::new(process.stderr.take().expect("Failed to open stderr"));
 
         let (server_rx, server_tx, initialize_notify) =
-            Transport::start(reader, writer, stderr, id);
+            Transport::start(reader, writer, stderr, id, name.clone());
         let (workspace, workspace_is_cwd) = find_workspace();
         let workspace = path::get_normalized_path(&workspace);
         let root = find_lsp_workspace(
@@ -225,6 +226,7 @@ impl Client {
 
         let client = Self {
             id,
+            name,
             _process: process,
             server_tx,
             request_counter: AtomicU64::new(0),
@@ -240,6 +242,10 @@ impl Client {
         Ok((client, server_rx, initialize_notify))
     }
 
+    pub fn name(&self) -> &String {
+        &self.name
+    }
+
     pub fn id(&self) -> usize {
         self.id
     }
diff --git a/helix-lsp/src/lib.rs b/helix-lsp/src/lib.rs
index 31ee1d75..12e63255 100644
--- a/helix-lsp/src/lib.rs
+++ b/helix-lsp/src/lib.rs
@@ -17,19 +17,16 @@ use helix_core::{
 use tokio::sync::mpsc::UnboundedReceiver;
 
 use std::{
-    collections::{hash_map::Entry, HashMap},
+    collections::HashMap,
     path::{Path, PathBuf},
-    sync::{
-        atomic::{AtomicUsize, Ordering},
-        Arc,
-    },
+    sync::Arc,
 };
 
 use thiserror::Error;
 use tokio_stream::wrappers::UnboundedReceiverStream;
 
 pub type Result<T> = core::result::Result<T, Error>;
-type LanguageId = String;
+type LanguageServerName = String;
 
 #[derive(Error, Debug)]
 pub enum Error {
@@ -49,7 +46,7 @@ pub enum Error {
     Other(#[from] anyhow::Error),
 }
 
-#[derive(Clone, Copy, Debug, Default)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
 pub enum OffsetEncoding {
     /// UTF-8 code units aka bytes
     Utf8,
@@ -624,23 +621,18 @@ impl Notification {
 
 #[derive(Debug)]
 pub struct Registry {
-    inner: HashMap<LanguageId, Vec<(usize, Arc<Client>)>>,
-
-    counter: AtomicUsize,
+    inner: HashMap<LanguageServerName, Vec<Arc<Client>>>,
+    syn_loader: Arc<helix_core::syntax::Loader>,
+    counter: usize,
     pub incoming: SelectAll<UnboundedReceiverStream<(usize, Call)>>,
 }
 
-impl Default for Registry {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
 impl Registry {
-    pub fn new() -> Self {
+    pub fn new(syn_loader: Arc<helix_core::syntax::Loader>) -> Self {
         Self {
             inner: HashMap::new(),
-            counter: AtomicUsize::new(0),
+            syn_loader,
+            counter: 0,
             incoming: SelectAll::new(),
         }
     }
@@ -649,15 +641,43 @@ impl Registry {
         self.inner
             .values()
             .flatten()
-            .find(|(client_id, _)| client_id == &id)
-            .map(|(_, client)| client.as_ref())
+            .find(|client| client.id() == id)
+            .map(|client| &**client)
     }
 
     pub fn remove_by_id(&mut self, id: usize) {
-        self.inner.retain(|_, clients| {
-            clients.retain(|&(client_id, _)| client_id != id);
-            !clients.is_empty()
-        })
+        self.inner.retain(|_, language_servers| {
+            language_servers.retain(|ls| id != ls.id());
+            !language_servers.is_empty()
+        });
+    }
+
+    fn start_client(
+        &mut self,
+        name: String,
+        ls_config: &LanguageConfiguration,
+        doc_path: Option<&std::path::PathBuf>,
+        root_dirs: &[PathBuf],
+        enable_snippets: bool,
+    ) -> Result<Arc<Client>> {
+        let config = self
+            .syn_loader
+            .language_server_configs()
+            .get(&name)
+            .ok_or_else(|| anyhow::anyhow!("Language server '{name}' not defined"))?;
+        self.counter += 1;
+        let id = self.counter;
+        let NewClient(client, incoming) = start_client(
+            id,
+            name,
+            ls_config,
+            config,
+            doc_path,
+            root_dirs,
+            enable_snippets,
+        )?;
+        self.incoming.push(UnboundedReceiverStream::new(incoming));
+        Ok(client)
     }
 
     pub fn restart(
@@ -666,48 +686,46 @@ impl Registry {
         doc_path: Option<&std::path::PathBuf>,
         root_dirs: &[PathBuf],
         enable_snippets: bool,
-    ) -> Result<Option<Arc<Client>>> {
-        let config = match &language_config.language_server {
-            Some(config) => config,
-            None => return Ok(None),
-        };
-
-        let scope = language_config.scope.clone();
-
-        match self.inner.entry(scope) {
-            Entry::Vacant(_) => Ok(None),
-            Entry::Occupied(mut entry) => {
-                // initialize a new client
-                let id = self.counter.fetch_add(1, Ordering::Relaxed);
-
-                let NewClientResult(client, incoming) = start_client(
-                    id,
-                    language_config,
-                    config,
-                    doc_path,
-                    root_dirs,
-                    enable_snippets,
-                )?;
-                self.incoming.push(UnboundedReceiverStream::new(incoming));
+    ) -> Result<Vec<Arc<Client>>> {
+        language_config
+            .language_servers
+            .iter()
+            .filter_map(|config| {
+                let name = config.name().clone();
+
+                #[allow(clippy::map_entry)]
+                if self.inner.contains_key(&name) {
+                    let client = match self.start_client(
+                        name.clone(),
+                        language_config,
+                        doc_path,
+                        root_dirs,
+                        enable_snippets,
+                    ) {
+                        Ok(client) => client,
+                        error => return Some(error),
+                    };
+                    let old_clients = self.inner.insert(name, vec![client.clone()]).unwrap();
 
-                let old_clients = entry.insert(vec![(id, client.clone())]);
+                    // TODO what if there are different language servers for different workspaces,
+                    // I think the language servers will be stopped without being restarted, which is not intended
+                    for old_client in old_clients {
+                        tokio::spawn(async move {
+                            let _ = old_client.force_shutdown().await;
+                        });
+                    }
 
-                for (_, old_client) in old_clients {
-                    tokio::spawn(async move {
-                        let _ = old_client.force_shutdown().await;
-                    });
+                    Some(Ok(client))
+                } else {
+                    None
                 }
-
-                Ok(Some(client))
-            }
-        }
+            })
+            .collect()
     }
 
-    pub fn stop(&mut self, language_config: &LanguageConfiguration) {
-        let scope = language_config.scope.clone();
-
-        if let Some(clients) = self.inner.remove(&scope) {
-            for (_, client) in clients {
+    pub fn stop(&mut self, name: &str) {
+        if let Some(clients) = self.inner.remove(name) {
+            for client in clients {
                 tokio::spawn(async move {
                     let _ = client.force_shutdown().await;
                 });
@@ -721,37 +739,35 @@ impl Registry {
         doc_path: Option<&std::path::PathBuf>,
         root_dirs: &[PathBuf],
         enable_snippets: bool,
-    ) -> Result<Option<Arc<Client>>> {
-        let config = match &language_config.language_server {
-            Some(config) => config,
-            None => return Ok(None),
-        };
-
-        let clients = self.inner.entry(language_config.scope.clone()).or_default();
-        // check if we already have a client for this documents root that we can reuse
-        if let Some((_, client)) = clients.iter_mut().enumerate().find(|(i, (_, client))| {
-            client.try_add_doc(&language_config.roots, root_dirs, doc_path, *i == 0)
-        }) {
-            return Ok(Some(client.1.clone()));
-        }
-        // initialize a new client
-        let id = self.counter.fetch_add(1, Ordering::Relaxed);
-
-        let NewClientResult(client, incoming) = start_client(
-            id,
-            language_config,
-            config,
-            doc_path,
-            root_dirs,
-            enable_snippets,
-        )?;
-        clients.push((id, client.clone()));
-        self.incoming.push(UnboundedReceiverStream::new(incoming));
-        Ok(Some(client))
+    ) -> Result<Vec<Arc<Client>>> {
+        language_config
+            .language_servers
+            .iter()
+            .map(|features| {
+                let name = features.name();
+                if let Some(clients) = self.inner.get_mut(name) {
+                    if let Some((_, client)) = clients.iter_mut().enumerate().find(|(i, client)| {
+                        client.try_add_doc(&language_config.roots, root_dirs, doc_path, *i == 0)
+                    }) {
+                        return Ok(client.clone());
+                    }
+                }
+                let client = self.start_client(
+                    name.clone(),
+                    language_config,
+                    doc_path,
+                    root_dirs,
+                    enable_snippets,
+                )?;
+                let clients = self.inner.entry(features.name().clone()).or_default();
+                clients.push(client.clone());
+                Ok(client)
+            })
+            .collect()
     }
 
     pub fn iter_clients(&self) -> impl Iterator<Item = &Arc<Client>> {
-        self.inner.values().flatten().map(|(_, client)| client)
+        self.inner.values().flatten()
     }
 }
 
@@ -833,26 +849,28 @@ impl LspProgressMap {
     }
 }
 
-struct NewClientResult(Arc<Client>, UnboundedReceiver<(usize, Call)>);
+struct NewClient(Arc<Client>, UnboundedReceiver<(usize, Call)>);
 
 /// start_client takes both a LanguageConfiguration and a LanguageServerConfiguration to ensure that
 /// it is only called when it makes sense.
 fn start_client(
     id: usize,
+    name: String,
     config: &LanguageConfiguration,
     ls_config: &LanguageServerConfiguration,
     doc_path: Option<&std::path::PathBuf>,
     root_dirs: &[PathBuf],
     enable_snippets: bool,
-) -> Result<NewClientResult> {
+) -> Result<NewClient> {
     let (client, incoming, initialize_notify) = Client::start(
         &ls_config.command,
         &ls_config.args,
-        config.config.clone(),
+        ls_config.config.clone(),
         ls_config.environment.clone(),
         &config.roots,
         config.workspace_lsp_roots.as_deref().unwrap_or(root_dirs),
         id,
+        name,
         ls_config.timeout,
         doc_path,
     )?;
@@ -886,7 +904,7 @@ fn start_client(
         initialize_notify.notify_one();
     });
 
-    Ok(NewClientResult(client, incoming))
+    Ok(NewClient(client, incoming))
 }
 
 /// Find an LSP workspace of a file using the following mechanism:
diff --git a/helix-lsp/src/transport.rs b/helix-lsp/src/transport.rs
index 3e3e06ee..8c38c177 100644
--- a/helix-lsp/src/transport.rs
+++ b/helix-lsp/src/transport.rs
@@ -38,6 +38,7 @@ enum ServerMessage {
 #[derive(Debug)]
 pub struct Transport {
     id: usize,
+    name: String,
     pending_requests: Mutex<HashMap<jsonrpc::Id, Sender<Result<Value>>>>,
 }
 
@@ -47,6 +48,7 @@ impl Transport {
         server_stdin: BufWriter<ChildStdin>,
         server_stderr: BufReader<ChildStderr>,
         id: usize,
+        name: String,
     ) -> (
         UnboundedReceiver<(usize, jsonrpc::Call)>,
         UnboundedSender<Payload>,
@@ -58,6 +60,7 @@ impl Transport {
 
         let transport = Self {
             id,
+            name,
             pending_requests: Mutex::new(HashMap::default()),
         };
 
@@ -83,6 +86,7 @@ impl Transport {
     async fn recv_server_message(
         reader: &mut (impl AsyncBufRead + Unpin + Send),
         buffer: &mut String,
+        language_server_name: &str,
     ) -> Result<ServerMessage> {
         let mut content_length = None;
         loop {
@@ -124,7 +128,7 @@ impl Transport {
         reader.read_exact(&mut content).await?;
         let msg = std::str::from_utf8(&content).context("invalid utf8 from server")?;
 
-        info!("<- {}", msg);
+        info!("{language_server_name} <- {msg}");
 
         // try parsing as output (server response) or call (server request)
         let output: serde_json::Result<ServerMessage> = serde_json::from_str(msg);
@@ -135,12 +139,13 @@ impl Transport {
     async fn recv_server_error(
         err: &mut (impl AsyncBufRead + Unpin + Send),
         buffer: &mut String,
+        language_server_name: &str,
     ) -> Result<()> {
         buffer.truncate(0);
         if err.read_line(buffer).await? == 0 {
             return Err(Error::StreamClosed);
         };
-        error!("err <- {:?}", buffer);
+        error!("{language_server_name} err <- {buffer:?}");
 
         Ok(())
     }
@@ -162,15 +167,17 @@ impl Transport {
             Payload::Notification(value) => serde_json::to_string(&value)?,
             Payload::Response(error) => serde_json::to_string(&error)?,
         };
-        self.send_string_to_server(server_stdin, json).await
+        self.send_string_to_server(server_stdin, json, &self.name)
+            .await
     }
 
     async fn send_string_to_server(
         &self,
         server_stdin: &mut BufWriter<ChildStdin>,
         request: String,
+        language_server_name: &str,
     ) -> Result<()> {
-        info!("-> {}", request);
+        info!("{language_server_name} -> {request}");
 
         // send the headers
         server_stdin
@@ -189,9 +196,13 @@ impl Transport {
         &self,
         client_tx: &UnboundedSender<(usize, jsonrpc::Call)>,
         msg: ServerMessage,
+        language_server_name: &str,
     ) -> Result<()> {
         match msg {
-            ServerMessage::Output(output) => self.process_request_response(output).await?,
+            ServerMessage::Output(output) => {
+                self.process_request_response(output, language_server_name)
+                    .await?
+            }
             ServerMessage::Call(call) => {
                 client_tx
                     .send((self.id, call))
@@ -202,14 +213,18 @@ impl Transport {
         Ok(())
     }
 
-    async fn process_request_response(&self, output: jsonrpc::Output) -> Result<()> {
+    async fn process_request_response(
+        &self,
+        output: jsonrpc::Output,
+        language_server_name: &str,
+    ) -> Result<()> {
         let (id, result) = match output {
             jsonrpc::Output::Success(jsonrpc::Success { id, result, .. }) => {
-                info!("<- {}", result);
+                info!("{language_server_name} <- {}", result);
                 (id, Ok(result))
             }
             jsonrpc::Output::Failure(jsonrpc::Failure { id, error, .. }) => {
-                error!("<- {}", error);
+                error!("{language_server_name} <- {error}");
                 (id, Err(error.into()))
             }
         };
@@ -240,12 +255,17 @@ impl Transport {
     ) {
         let mut recv_buffer = String::new();
         loop {
-            match Self::recv_server_message(&mut server_stdout, &mut recv_buffer).await {
+            match Self::recv_server_message(&mut server_stdout, &mut recv_buffer, &transport.name)
+                .await
+            {
                 Ok(msg) => {
-                    match transport.process_server_message(&client_tx, msg).await {
+                    match transport
+                        .process_server_message(&client_tx, msg, &transport.name)
+                        .await
+                    {
                         Ok(_) => {}
                         Err(err) => {
-                            error!("err: <- {:?}", err);
+                            error!("{} err: <- {err:?}", transport.name);
                             break;
                         }
                     };
@@ -270,7 +290,7 @@ impl Transport {
                             params: jsonrpc::Params::None,
                         }));
                     match transport
-                        .process_server_message(&client_tx, notification)
+                        .process_server_message(&client_tx, notification, &transport.name)
                         .await
                     {
                         Ok(_) => {}
@@ -281,20 +301,22 @@ impl Transport {
                     break;
                 }
                 Err(err) => {
-                    error!("err: <- {:?}", err);
+                    error!("{} err: <- {err:?}", transport.name);
                     break;
                 }
             }
         }
     }
 
-    async fn err(_transport: Arc<Self>, mut server_stderr: BufReader<ChildStderr>) {
+    async fn err(transport: Arc<Self>, mut server_stderr: BufReader<ChildStderr>) {
         let mut recv_buffer = String::new();
         loop {
-            match Self::recv_server_error(&mut server_stderr, &mut recv_buffer).await {
+            match Self::recv_server_error(&mut server_stderr, &mut recv_buffer, &transport.name)
+                .await
+            {
                 Ok(_) => {}
                 Err(err) => {
-                    error!("err: <- {:?}", err);
+                    error!("{} err: <- {err:?}", transport.name);
                     break;
                 }
             }
@@ -348,10 +370,11 @@ impl Transport {
                         method: lsp_types::notification::Initialized::METHOD.to_string(),
                         params: jsonrpc::Params::None,
                     }));
-                    match transport.process_server_message(&client_tx, notification).await {
+                    let language_server_name = &transport.name;
+                    match transport.process_server_message(&client_tx, notification, language_server_name).await {
                         Ok(_) => {}
                         Err(err) => {
-                            error!("err: <- {:?}", err);
+                            error!("{language_server_name} err: <- {err:?}");
                         }
                     }
 
@@ -361,7 +384,7 @@ impl Transport {
                         match transport.send_payload_to_server(&mut server_stdin, msg).await {
                             Ok(_) => {}
                             Err(err) => {
-                                error!("err: <- {:?}", err);
+                                error!("{language_server_name} err: <- {err:?}");
                             }
                         }
                     }
@@ -380,7 +403,7 @@ impl Transport {
                             match transport.send_payload_to_server(&mut server_stdin, msg).await {
                                 Ok(_) => {}
                                 Err(err) => {
-                                    error!("err: <- {:?}", err);
+                                    error!("{} err: <- {err:?}", transport.name);
                                 }
                             }
                         }