Handle prompt completions with AsyncHook.

This change allows prompt completions to be calculated in the
background, to avoid blocking the UI on slow file IO such as over a
networked FS.

helix-term/src/commands/typed.rs

@@ -12,7 +12,7 @@ use helix_core::{line_ending, shellwords::Shellwords};
 use helix_view::document::{read_to_string, DEFAULT_LANGUAGE_NAME};
 use helix_view::editor::{CloseError, ConfigEvent};
 use serde_json::Value;
-use ui::completers::{self, Completer};
+use ui::completers::{self, Completer, CompletionResult};
 
 #[derive(Clone)]
 pub struct TypableCommand {
@@ -3187,19 +3187,22 @@ pub(super) fn command_mode(cx: &mut Context) {
                     .get(&words[0] as &str)
                     .map(|tc| tc.completer_for_argument_number(argument_number))
                 {
-                    completer(editor, word)
-                        .into_iter()
-                        .map(|(range, file)| {
-                            let file = shellwords::escape(file);
-
-                            // offset ranges to input
-                            let offset = input.len() - word_len;
-                            let range = (range.start + offset)..;
-                            (range, file)
-                        })
-                        .collect()
+                    let input = String::from(input);
+                    completer(editor, word).map(move |completion| {
+                        completion
+                            .into_iter()
+                            .map(|(range, file)| {
+                                let file = shellwords::escape(file);
+
+                                // offset ranges to input
+                                let offset = input.len() - word_len;
+                                let range = (range.start + offset)..;
+                                (range, file)
+                            })
+                            .collect()
+                    })
                 } else {
-                    Vec::new()
+                    CompletionResult::Immediate(Vec::new())
                 }
             }
         }, // completion

helix-term/src/ui/mod.rs

@@ -17,6 +17,7 @@ mod text_decorations;
 use crate::compositor::Compositor;
 use crate::filter_picker_entry;
 use crate::job::{self, Callback};
+use crate::ui::completers::CompletionResult;
 pub use completion::{Completion, CompletionItem};
 pub use editor::EditorView;
 use helix_stdx::rope;
@@ -36,7 +37,7 @@ pub fn prompt(
     cx: &mut crate::commands::Context,
     prompt: std::borrow::Cow<'static, str>,
     history_register: Option<char>,
-    completion_fn: impl FnMut(&Editor, &str) -> Vec<prompt::Completion> + 'static,
+    completion_fn: impl FnMut(&Editor, &str) -> CompletionResult + 'static,
     callback_fn: impl FnMut(&mut crate::compositor::Context, &str, PromptEvent) + 'static,
 ) {
     let mut prompt = Prompt::new(prompt, history_register, completion_fn, callback_fn);
@@ -45,24 +46,11 @@ pub fn prompt(
     cx.push_layer(Box::new(prompt));
 }
 
-pub fn prompt_with_input(
-    cx: &mut crate::commands::Context,
-    prompt: std::borrow::Cow<'static, str>,
-    input: String,
-    history_register: Option<char>,
-    completion_fn: impl FnMut(&Editor, &str) -> Vec<prompt::Completion> + 'static,
-    callback_fn: impl FnMut(&mut crate::compositor::Context, &str, PromptEvent) + 'static,
-) {
-    let prompt = Prompt::new(prompt, history_register, completion_fn, callback_fn)
-        .with_line(input, cx.editor);
-    cx.push_layer(Box::new(prompt));
-}
-
 pub fn regex_prompt(
     cx: &mut crate::commands::Context,
     prompt: std::borrow::Cow<'static, str>,
     history_register: Option<char>,
-    completion_fn: impl FnMut(&Editor, &str) -> Vec<prompt::Completion> + 'static,
+    completion_fn: impl FnMut(&Editor, &str) -> CompletionResult + 'static,
     fun: impl Fn(&mut crate::compositor::Context, rope::Regex, PromptEvent) + 'static,
 ) {
     raw_regex_prompt(
@@ -77,7 +65,7 @@ pub fn raw_regex_prompt(
     cx: &mut crate::commands::Context,
     prompt: std::borrow::Cow<'static, str>,
     history_register: Option<char>,
-    completion_fn: impl FnMut(&Editor, &str) -> Vec<prompt::Completion> + 'static,
+    completion_fn: impl FnMut(&Editor, &str) -> CompletionResult + 'static,
     fun: impl Fn(&mut crate::compositor::Context, rope::Regex, &str, PromptEvent) + 'static,
 ) {
     let (view, doc) = current!(cx.editor);
@@ -275,13 +263,40 @@ pub mod completers {
     use once_cell::sync::Lazy;
     use std::borrow::Cow;
 
-    pub type Completer = fn(&Editor, &str) -> Vec<Completion>;
+    pub enum CompletionResult {
+        Immediate(Vec<Completion>),
+        Callback(Box<dyn FnOnce() -> Vec<Completion> + Send + Sync>),
+    }
+
+    fn callback(f: impl FnOnce() -> Vec<Completion> + Send + Sync + 'static) -> CompletionResult {
+        CompletionResult::Callback(Box::new(f))
+    }
+
+    impl CompletionResult {
+        pub fn map(
+            self,
+            f: impl FnOnce(Vec<Completion>) -> Vec<Completion> + Send + Sync + 'static,
+        ) -> CompletionResult {
+            match self {
+                CompletionResult::Immediate(v) => CompletionResult::Immediate(f(v)),
+                CompletionResult::Callback(v) => callback(move || f(v())),
+            }
+        }
+    }
 
-    pub fn none(_editor: &Editor, _input: &str) -> Vec<Completion> {
-        Vec::new()
+    impl FromIterator<Completion> for CompletionResult {
+        fn from_iter<T: IntoIterator<Item = Completion>>(items: T) -> Self {
+            Self::Immediate(items.into_iter().collect())
+        }
     }
 
-    pub fn buffer(editor: &Editor, input: &str) -> Vec<Completion> {
+    pub type Completer = fn(&Editor, &str) -> CompletionResult;
+
+    pub fn none(_editor: &Editor, _input: &str) -> CompletionResult {
+        CompletionResult::Immediate(Vec::new())
+    }
+
+    pub fn buffer(editor: &Editor, input: &str) -> CompletionResult {
         let names = editor.documents.values().map(|doc| {
             doc.relative_path()
                 .map(|p| p.display().to_string().into())
@@ -294,20 +309,23 @@ pub mod completers {
             .collect()
     }
 
-    pub fn theme(_editor: &Editor, input: &str) -> Vec<Completion> {
-        let mut names = theme::Loader::read_names(&helix_loader::config_dir().join("themes"));
-        for rt_dir in helix_loader::runtime_dirs() {
-            names.extend(theme::Loader::read_names(&rt_dir.join("themes")));
-        }
-        names.push("default".into());
-        names.push("base16_default".into());
-        names.sort();
-        names.dedup();
+    pub fn theme(_editor: &Editor, input: &str) -> CompletionResult {
+        let input = String::from(input);
+        callback(move || {
+            let mut names = theme::Loader::read_names(&helix_loader::config_dir().join("themes"));
+            for rt_dir in helix_loader::runtime_dirs() {
+                names.extend(theme::Loader::read_names(&rt_dir.join("themes")));
+            }
+            names.push("default".into());
+            names.push("base16_default".into());
+            names.sort();
+            names.dedup();
 
-        fuzzy_match(input, names, false)
-            .into_iter()
-            .map(|(name, _)| ((0..), name.into()))
-            .collect()
+            fuzzy_match(&input, names, false)
+                .into_iter()
+                .map(|(name, _)| ((0..), name.into()))
+                .collect()
+        })
     }
 
     /// Recursive function to get all keys from this value and add them to vec
@@ -326,7 +344,7 @@ pub mod completers {
         }
     }
 
-    pub fn setting(_editor: &Editor, input: &str) -> Vec<Completion> {
+    pub fn setting(_editor: &Editor, input: &str) -> CompletionResult {
         static KEYS: Lazy<Vec<String>> = Lazy::new(|| {
             let mut keys = Vec::new();
             let json = serde_json::json!(Config::default());
@@ -340,27 +358,30 @@ pub mod completers {
             .collect()
     }
 
-    pub fn filename(editor: &Editor, input: &str) -> Vec<Completion> {
+    pub fn filename(editor: &Editor, input: &str) -> CompletionResult {
         filename_with_git_ignore(editor, input, true)
     }
 
     pub fn filename_with_git_ignore(
-        editor: &Editor,
+        _editor: &Editor,
         input: &str,
         git_ignore: bool,
-    ) -> Vec<Completion> {
-        filename_impl(editor, input, git_ignore, |entry| {
-            let is_dir = entry.file_type().map_or(false, |entry| entry.is_dir());
-
-            if is_dir {
-                FileMatch::AcceptIncomplete
-            } else {
-                FileMatch::Accept
-            }
+    ) -> CompletionResult {
+        let input = String::from(input);
+        callback(move || {
+            filename_impl(&input, git_ignore, |entry| {
+                let is_dir = entry.file_type().map_or(false, |entry| entry.is_dir());
+
+                if is_dir {
+                    FileMatch::AcceptIncomplete
+                } else {
+                    FileMatch::Accept
+                }
+            })
         })
     }
 
-    pub fn language(editor: &Editor, input: &str) -> Vec<Completion> {
+    pub fn language(editor: &Editor, input: &str) -> CompletionResult {
         let text: String = "text".into();
 
         let loader = editor.syn_loader.load();
@@ -375,7 +396,7 @@ pub mod completers {
             .collect()
     }
 
-    pub fn lsp_workspace_command(editor: &Editor, input: &str) -> Vec<Completion> {
+    pub fn lsp_workspace_command(editor: &Editor, input: &str) -> CompletionResult {
         let commands = doc!(editor)
             .language_servers_with_feature(LanguageServerFeature::WorkspaceCommand)
             .flat_map(|ls| {
@@ -391,23 +412,26 @@ pub mod completers {
             .collect()
     }
 
-    pub fn directory(editor: &Editor, input: &str) -> Vec<Completion> {
+    pub fn directory(editor: &Editor, input: &str) -> CompletionResult {
         directory_with_git_ignore(editor, input, true)
     }
 
     pub fn directory_with_git_ignore(
-        editor: &Editor,
+        _editor: &Editor,
         input: &str,
         git_ignore: bool,
-    ) -> Vec<Completion> {
-        filename_impl(editor, input, git_ignore, |entry| {
-            let is_dir = entry.file_type().map_or(false, |entry| entry.is_dir());
-
-            if is_dir {
-                FileMatch::Accept
-            } else {
-                FileMatch::Reject
-            }
+    ) -> CompletionResult {
+        let input = String::from(input);
+        callback(move || {
+            filename_impl(&input, git_ignore, |entry| {
+                let is_dir = entry.file_type().map_or(false, |entry| entry.is_dir());
+
+                if is_dir {
+                    FileMatch::Accept
+                } else {
+                    FileMatch::Reject
+                }
+            })
         })
     }
 
@@ -423,12 +447,7 @@ pub mod completers {
     }
 
     // TODO: we could return an iter/lazy thing so it can fetch as many as it needs.
-    fn filename_impl<F>(
-        _editor: &Editor,
-        input: &str,
-        git_ignore: bool,
-        filter_fn: F,
-    ) -> Vec<Completion>
+    fn filename_impl<F>(input: &str, git_ignore: bool, filter_fn: F) -> Vec<Completion>
     where
         F: Fn(&ignore::DirEntry) -> FileMatch,
     {
@@ -522,7 +541,7 @@ pub mod completers {
         }
     }
 
-    pub fn register(editor: &Editor, input: &str) -> Vec<Completion> {
+    pub fn register(editor: &Editor, input: &str) -> CompletionResult {
         let iter = editor
             .registers
             .iter_preview()

helix-term/src/ui/prompt.rs

@@ -1,12 +1,16 @@
 use crate::compositor::{Component, Compositor, Context, Event, EventResult};
-use crate::{alt, ctrl, key, shift, ui};
+use crate::ui::completers::CompletionResult;
+use crate::{alt, ctrl, job, key, shift, ui};
 use arc_swap::ArcSwap;
 use helix_core::syntax;
+use helix_event::{AsyncHook, CancelRx, CancelTx};
 use helix_view::document::Mode;
 use helix_view::input::KeyEvent;
 use helix_view::keyboard::KeyCode;
 use std::sync::Arc;
+use std::time::Duration;
 use std::{borrow::Cow, ops::RangeFrom};
+use tokio::time::Instant;
 use tui::buffer::Buffer as Surface;
 use tui::widgets::{Block, Widget};
 
@@ -18,9 +22,39 @@ use helix_view::{
     Editor,
 };
 
-type PromptCharHandler = Box<dyn Fn(&mut Prompt, char, &Context)>;
 pub type Completion = (RangeFrom<usize>, Cow<'static, str>);
-type CompletionFn = Box<dyn FnMut(&Editor, &str) -> Vec<Completion>>;
+struct CompletionEvent {
+    cancel: CancelRx,
+    callback: Box<dyn FnOnce() -> Vec<Completion> + Send + Sync>,
+    send: std::sync::mpsc::SyncSender<Vec<Completion>>,
+}
+
+struct CompletionHandler {}
+
+impl helix_event::AsyncHook for CompletionHandler {
+    type Event = CompletionEvent;
+
+    fn handle_event(&mut self, mut event: CompletionEvent, _: Option<Instant>) -> Option<Instant> {
+        let Err(tokio::sync::oneshot::error::TryRecvError::Empty) = event.cancel.try_recv() else {
+            return None;
+        };
+        let completion = (event.callback)();
+        if event.send.send(completion).is_err() {
+            return None;
+        }
+        job::dispatch_blocking(move |_editor, compositor| {
+            if let Some(prompt) = compositor.find::<Prompt>() {
+                prompt.process_async_completion();
+            }
+        });
+        None
+    }
+
+    fn finish_debounce(&mut self) {}
+}
+
+type PromptCharHandler = Box<dyn Fn(&mut Prompt, char, &Context)>;
+type CompletionFn = Box<dyn FnMut(&Editor, &str) -> CompletionResult>;
 type CallbackFn = Box<dyn FnMut(&mut Context, &str, PromptEvent)>;
 pub type DocFn = Box<dyn Fn(&str) -> Option<Cow<str>>>;
 
@@ -28,11 +62,14 @@ pub struct Prompt {
     prompt: Cow<'static, str>,
     line: String,
     cursor: usize,
+    completion_fn: CompletionFn,
+    completion_hook: tokio::sync::mpsc::Sender<CompletionEvent>,
+    completion_ctx: Option<CancelTx>,
+    receive_completion: Option<std::sync::mpsc::Receiver<Vec<Completion>>>,
     completion: Vec<Completion>,
     selection: Option<usize>,
     history_register: Option<char>,
     history_pos: Option<usize>,
-    completion_fn: CompletionFn,
     callback_fn: CallbackFn,
     pub doc_fn: DocFn,
     next_char_handler: Option<PromptCharHandler>,
@@ -73,18 +110,21 @@ impl Prompt {
     pub fn new(
         prompt: Cow<'static, str>,
         history_register: Option<char>,
-        completion_fn: impl FnMut(&Editor, &str) -> Vec<Completion> + 'static,
+        completion_fn: impl FnMut(&Editor, &str) -> CompletionResult + 'static,
         callback_fn: impl FnMut(&mut Context, &str, PromptEvent) + 'static,
     ) -> Self {
         Self {
             prompt,
             line: String::new(),
             cursor: 0,
+            completion_fn: Box::new(completion_fn),
+            completion_hook: CompletionHandler {}.spawn(),
+            completion_ctx: None,
+            receive_completion: None,
             completion: Vec::new(),
             selection: None,
             history_register,
             history_pos: None,
-            completion_fn: Box::new(completion_fn),
             callback_fn: Box::new(callback_fn),
             doc_fn: Box::new(|_| None),
             next_char_handler: None,
@@ -141,8 +181,35 @@ impl Prompt {
     }
 
     pub fn recalculate_completion(&mut self, editor: &Editor) {
+        // Cancel any pending async completions.
+        self.completion_ctx = None;
+        self.receive_completion = None;
+
         self.exit_selection();
-        self.completion = (self.completion_fn)(editor, &self.line);
+        match (self.completion_fn)(editor, &self.line) {
+            CompletionResult::Immediate(completion) => self.completion = completion,
+            CompletionResult::Callback(f) => {
+                let (cancel_tx, cancel_rx) = helix_event::cancelation();
+                let (send_completion, recv_completion) = std::sync::mpsc::sync_channel(1);
+                helix_event::send_blocking(
+                    &self.completion_hook,
+                    CompletionEvent {
+                        cancel: cancel_rx,
+                        callback: f,
+                        send: send_completion,
+                    },
+                );
+                // To avoid flicker, give the completion handler a small timeout to
+                // complete immediately.
+                if let Ok(completion) = recv_completion.recv_timeout(Duration::from_millis(100)) {
+                    self.completion = completion;
+                    return;
+                }
+                self.completion.clear();
+                self.completion_ctx = Some(cancel_tx);
+                self.receive_completion = Some(recv_completion);
+            }
+        }
     }
 
     /// Compute the cursor position after applying movement
@@ -390,6 +457,16 @@ impl Prompt {
     pub fn exit_selection(&mut self) {
         self.selection = None;
     }
+
+    fn process_async_completion(&mut self) {
+        let Some(receive_completion) = &self.receive_completion else {
+            return;
+        };
+        if let Ok(completion) = receive_completion.try_recv() {
+            self.completion = completion;
+            helix_event::request_redraw();
+        }
+    }
 }
 
 const BASE_WIDTH: u16 = 30;
@@ -402,7 +479,6 @@ impl Prompt {
         let selected_color = theme.get("ui.menu.selected");
         let suggestion_color = theme.get("ui.text.inactive");
         let background = theme.get("ui.background");
-        // completion
 
         let max_len = self
             .completion