Add support for LSP DidChangeWatchedFiles (#7665)

* Add initial support for LSP DidChangeWatchedFiles

* Move file event Handler to helix-lsp

* Simplify file event handling

* Refactor file event handling

* Block on future within LSP file event handler

* Fully qualify uses of the file_event::Handler type

* Rename ops field to options

* Revert newline removal from helix-view/Cargo.toml

* Ensure file event Handler is cleaned up when lsp client is shutdown

3 files changed, 217 insertions, 0 deletions

diff --git a/helix-lsp/src/client.rs b/helix-lsp/src/client.rs
index 92ab03db..ed9a2f83 100644
--- a/helix-lsp/src/client.rs
+++ b/helix-lsp/src/client.rs
@@ -544,6 +544,10 @@ impl Client {
                         normalizes_line_endings: Some(false),
                         change_annotation_support: None,
                     }),
+                    did_change_watched_files: Some(lsp::DidChangeWatchedFilesClientCapabilities {
+                        dynamic_registration: Some(true),
+                        relative_pattern_support: Some(false),
+                    }),
                     ..Default::default()
                 }),
                 text_document: Some(lsp::TextDocumentClientCapabilities {
@@ -1453,4 +1457,13 @@ impl Client {
 
         Some(self.call::<lsp::request::ExecuteCommand>(params))
     }
+
+    pub fn did_change_watched_files(
+        &self,
+        changes: Vec<lsp::FileEvent>,
+    ) -> impl Future<Output = std::result::Result<(), Error>> {
+        self.notify::<lsp::notification::DidChangeWatchedFiles>(lsp::DidChangeWatchedFilesParams {
+            changes,
+        })
+    }
 }
diff --git a/helix-lsp/src/file_event.rs b/helix-lsp/src/file_event.rs
new file mode 100644
index 00000000..26a27c98
--- /dev/null
+++ b/helix-lsp/src/file_event.rs
@@ -0,0 +1,193 @@
+use std::{collections::HashMap, path::PathBuf, sync::Weak};
+
+use globset::{GlobBuilder, GlobSetBuilder};
+use tokio::sync::mpsc;
+
+use crate::{lsp, Client};
+
+enum Event {
+    FileChanged {
+        path: PathBuf,
+    },
+    Register {
+        client_id: usize,
+        client: Weak<Client>,
+        registration_id: String,
+        options: lsp::DidChangeWatchedFilesRegistrationOptions,
+    },
+    Unregister {
+        client_id: usize,
+        registration_id: String,
+    },
+    RemoveClient {
+        client_id: usize,
+    },
+}
+
+#[derive(Default)]
+struct ClientState {
+    client: Weak<Client>,
+    registered: HashMap<String, globset::GlobSet>,
+}
+
+/// The Handler uses a dedicated tokio task to respond to file change events by
+/// forwarding changes to LSPs that have registered for notifications with a
+/// matching glob.
+///
+/// When an LSP registers for the DidChangeWatchedFiles notification, the
+/// Handler is notified by sending the registration details in addition to a
+/// weak reference to the LSP client. This is done so that the Handler can have
+/// access to the client without preventing the client from being dropped if it
+/// is closed and the Handler isn't properly notified.
+#[derive(Clone, Debug)]
+pub struct Handler {
+    tx: mpsc::UnboundedSender<Event>,
+}
+
+impl Default for Handler {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Handler {
+    pub fn new() -> Self {
+        let (tx, rx) = mpsc::unbounded_channel();
+        tokio::spawn(Self::run(rx));
+        Self { tx }
+    }
+
+    pub fn register(
+        &self,
+        client_id: usize,
+        client: Weak<Client>,
+        registration_id: String,
+        options: lsp::DidChangeWatchedFilesRegistrationOptions,
+    ) {
+        let _ = self.tx.send(Event::Register {
+            client_id,
+            client,
+            registration_id,
+            options,
+        });
+    }
+
+    pub fn unregister(&self, client_id: usize, registration_id: String) {
+        let _ = self.tx.send(Event::Unregister {
+            client_id,
+            registration_id,
+        });
+    }
+
+    pub fn file_changed(&self, path: PathBuf) {
+        let _ = self.tx.send(Event::FileChanged { path });
+    }
+
+    pub fn remove_client(&self, client_id: usize) {
+        let _ = self.tx.send(Event::RemoveClient { client_id });
+    }
+
+    async fn run(mut rx: mpsc::UnboundedReceiver<Event>) {
+        let mut state: HashMap<usize, ClientState> = HashMap::new();
+        while let Some(event) = rx.recv().await {
+            match event {
+                Event::FileChanged { path } => {
+                    log::debug!("Received file event for {:?}", &path);
+
+                    state.retain(|id, client_state| {
+                        if !client_state
+                            .registered
+                            .values()
+                            .any(|glob| glob.is_match(&path))
+                        {
+                            return true;
+                        }
+                        let Some(client) = client_state.client.upgrade() else {
+                            log::warn!("LSP client was dropped: {id}");
+                            return false;
+                        };
+                        let Ok(uri) = lsp::Url::from_file_path(&path) else {
+                            return true;
+                        };
+                        log::debug!(
+                            "Sending didChangeWatchedFiles notification to client '{}'",
+                            client.name()
+                        );
+                        if let Err(err) = crate::block_on(client
+                            .did_change_watched_files(vec![lsp::FileEvent {
+                                uri,
+                                // We currently always send the CHANGED state
+                                // since we don't actually have more context at
+                                // the moment.
+                                typ: lsp::FileChangeType::CHANGED,
+                            }]))
+                        {
+                            log::warn!("Failed to send didChangeWatchedFiles notification to client: {err}");
+                        }
+                        true
+                    });
+                }
+                Event::Register {
+                    client_id,
+                    client,
+                    registration_id,
+                    options: ops,
+                } => {
+                    log::debug!(
+                        "Registering didChangeWatchedFiles for client '{}' with id '{}'",
+                        client_id,
+                        registration_id
+                    );
+
+                    let mut entry = state.entry(client_id).or_insert_with(ClientState::default);
+                    entry.client = client;
+
+                    let mut builder = GlobSetBuilder::new();
+                    for watcher in ops.watchers {
+                        if let lsp::GlobPattern::String(pattern) = watcher.glob_pattern {
+                            if let Ok(glob) = GlobBuilder::new(&pattern).build() {
+                                builder.add(glob);
+                            }
+                        }
+                    }
+                    match builder.build() {
+                        Ok(globset) => {
+                            entry.registered.insert(registration_id, globset);
+                        }
+                        Err(err) => {
+                            // Remove any old state for that registration id and
+                            // remove the entire client if it's now empty.
+                            entry.registered.remove(&registration_id);
+                            if entry.registered.is_empty() {
+                                state.remove(&client_id);
+                            }
+                            log::warn!(
+                                "Unable to build globset for LSP didChangeWatchedFiles {err}"
+                            )
+                        }
+                    }
+                }
+                Event::Unregister {
+                    client_id,
+                    registration_id,
+                } => {
+                    log::debug!(
+                        "Unregistering didChangeWatchedFiles with id '{}' for client '{}'",
+                        registration_id,
+                        client_id
+                    );
+                    if let Some(client_state) = state.get_mut(&client_id) {
+                        client_state.registered.remove(&registration_id);
+                        if client_state.registered.is_empty() {
+                            state.remove(&client_id);
+                        }
+                    }
+                }
+                Event::RemoveClient { client_id } => {
+                    log::debug!("Removing LSP client: {client_id}");
+                    state.remove(&client_id);
+                }
+            }
+        }
+    }
+}
diff --git a/helix-lsp/src/lib.rs b/helix-lsp/src/lib.rs
index 95c61086..90f0c3fd 100644
--- a/helix-lsp/src/lib.rs
+++ b/helix-lsp/src/lib.rs
@@ -1,4 +1,5 @@
 mod client;
+pub mod file_event;
 pub mod jsonrpc;
 pub mod snippet;
 mod transport;
@@ -547,6 +548,7 @@ pub enum MethodCall {
     WorkspaceFolders,
     WorkspaceConfiguration(lsp::ConfigurationParams),
     RegisterCapability(lsp::RegistrationParams),
+    UnregisterCapability(lsp::UnregistrationParams),
 }
 
 impl MethodCall {
@@ -570,6 +572,10 @@ impl MethodCall {
                 let params: lsp::RegistrationParams = params.parse()?;
                 Self::RegisterCapability(params)
             }
+            lsp::request::UnregisterCapability::METHOD => {
+                let params: lsp::UnregistrationParams = params.parse()?;
+                Self::UnregisterCapability(params)
+            }
             _ => {
                 return Err(Error::Unhandled);
             }
@@ -629,6 +635,7 @@ pub struct Registry {
     syn_loader: Arc<helix_core::syntax::Loader>,
     counter: usize,
     pub incoming: SelectAll<UnboundedReceiverStream<(usize, Call)>>,
+    pub file_event_handler: file_event::Handler,
 }
 
 impl Registry {
@@ -638,6 +645,7 @@ impl Registry {
             syn_loader,
             counter: 0,
             incoming: SelectAll::new(),
+            file_event_handler: file_event::Handler::new(),
         }
     }
 
@@ -650,6 +658,7 @@ impl Registry {
     }
 
     pub fn remove_by_id(&mut self, id: usize) {
+        self.file_event_handler.remove_client(id);
         self.inner.retain(|_, language_servers| {
             language_servers.retain(|ls| id != ls.id());
             !language_servers.is_empty()
@@ -715,6 +724,7 @@ impl Registry {
                         .unwrap();
 
                     for old_client in old_clients {
+                        self.file_event_handler.remove_client(old_client.id());
                         tokio::spawn(async move {
                             let _ = old_client.force_shutdown().await;
                         });
@@ -731,6 +741,7 @@ impl Registry {
     pub fn stop(&mut self, name: &str) {
         if let Some(clients) = self.inner.remove(name) {
             for client in clients {
+                self.file_event_handler.remove_client(client.id());
                 tokio::spawn(async move {
                     let _ = client.force_shutdown().await;
                 });