Add c-s to pick word under doc cursor to prompt line & search completion (#831)

* Add prompt shourtcut to book
Add completions to search
Add c-s to pick word under doc cursor to prompt line

* limit 20 last items of search completion, update book

* Update book/src/keymap.md

Co-authored-by: Ivan Tham <pickfire@riseup.net>

* limit search completions 200

Co-authored-by: Ivan Tham <pickfire@riseup.net>

4 files changed, 86 insertions, 3 deletions

diff --git a/book/src/keymap.md b/book/src/keymap.md
index a776ee70..4a6f80bb 100644
--- a/book/src/keymap.md
+++ b/book/src/keymap.md
@@ -258,3 +258,25 @@ Keys to use within picker. Remapping currently not supported.
 | `Ctrl-s`                     | Open horizontally |
 | `Ctrl-v`                     | Open vertically   |
 | `Escape`, `Ctrl-c`           | Close picker      |
+
+# Prompt
+Keys to use within prompt, Remapping currently not supported.
+| Key                     | Description                                                             |
+| -----                   | -------------                                                           |
+| `Escape`, `Ctrl-c`      | Close prompt                                                            |
+| `Alt-b`, `Alt-Left`     | Backward a word                                                         |
+| `Ctrl-b`, `Left`        | Backward a char                                                         |
+| `Alt-f`, `Alt-Right`    | Forward a word                                                          |
+| `Ctrl-f`, `Right`       | Forward a char                                                          |
+| `Ctrl-e`, `End`         | move prompt end                                                         |
+| `Ctrl-a`, `Home`        | move prompt start                                                       |
+| `Ctrl-w`                | delete previous word                                                    |
+| `Ctrl-k`                | delete to end of line                                                   |
+| `backspace`             | delete previous char                                                    |
+| `Ctrl-s`                | insert a word under doc cursor, may be changed to Ctrl-r Ctrl-w later   |
+| `Ctrl-p`, `Up`          | select previous history                                                 |
+| `Ctrl-n`, `Down`        | select next history                                                     |
+| `Tab`                   | slect next completion item                                              |
+| `BackTab`               | slect previous completion item                                          |
+| `Enter`                 | Open selected                                                           |
+
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index cc9106eb..6c073fb8 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -1087,6 +1087,7 @@ fn select_regex(cx: &mut Context) {
         cx,
         "select:".into(),
         Some(reg),
+        |_input: &str| Vec::new(),
         move |view, doc, regex, event| {
             if event != PromptEvent::Update {
                 return;
@@ -1109,6 +1110,7 @@ fn split_selection(cx: &mut Context) {
         cx,
         "split:".into(),
         Some(reg),
+        |_input: &str| Vec::new(),
         move |view, doc, regex, event| {
             if event != PromptEvent::Update {
                 return;
@@ -1172,6 +1174,15 @@ fn search_impl(doc: &mut Document, view: &mut View, contents: &str, regex: &Rege
     };
 }
 
+fn search_completions(cx: &mut Context, reg: Option<char>) -> Vec<String> {
+    let mut items = reg
+        .and_then(|reg| cx.editor.registers.get(reg))
+        .map_or(Vec::new(), |reg| reg.read().iter().take(200).collect());
+    items.sort_unstable();
+    items.dedup();
+    items.into_iter().cloned().collect()
+}
+
 // TODO: use one function for search vs extend
 fn search(cx: &mut Context) {
     let reg = cx.register.unwrap_or('/');
@@ -1182,11 +1193,19 @@ fn search(cx: &mut Context) {
     // HAXX: sadly we can't avoid allocating a single string for the whole buffer since we can't
     // feed chunks into the regex yet
     let contents = doc.text().slice(..).to_string();
+    let completions = search_completions(cx, Some(reg));
 
     let prompt = ui::regex_prompt(
         cx,
         "search:".into(),
         Some(reg),
+        move |input: &str| {
+            completions
+                .iter()
+                .filter(|comp| comp.starts_with(input))
+                .map(|comp| (0.., std::borrow::Cow::Owned(comp.clone())))
+                .collect()
+        },
         move |view, doc, regex, event| {
             if event != PromptEvent::Update {
                 return;
@@ -1246,10 +1265,19 @@ fn global_search(cx: &mut Context) {
     let (all_matches_sx, all_matches_rx) =
         tokio::sync::mpsc::unbounded_channel::<(usize, PathBuf)>();
     let smart_case = cx.editor.config.smart_case;
+
+    let completions = search_completions(cx, None);
     let prompt = ui::regex_prompt(
         cx,
         "global search:".into(),
         None,
+        move |input: &str| {
+            completions
+                .iter()
+                .filter(|comp| comp.starts_with(input))
+                .map(|comp| (0.., std::borrow::Cow::Owned(comp.clone())))
+                .collect()
+        },
         move |_view, _doc, regex, event| {
             if event != PromptEvent::Validate {
                 return;
@@ -4086,6 +4114,7 @@ fn keep_selections(cx: &mut Context) {
         cx,
         "keep:".into(),
         Some(reg),
+        |_input: &str| Vec::new(),
         move |view, doc, regex, event| {
             if event != PromptEvent::Update {
                 return;
diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index 30a9ec6b..24eb7acd 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -29,6 +29,7 @@ pub fn regex_prompt(
     cx: &mut crate::commands::Context,
     prompt: std::borrow::Cow<'static, str>,
     history_register: Option<char>,
+    completion_fn: impl FnMut(&str) -> Vec<prompt::Completion> + 'static,
     fun: impl Fn(&mut View, &mut Document, Regex, PromptEvent) + 'static,
 ) -> Prompt {
     let (view, doc) = current!(cx.editor);
@@ -38,7 +39,7 @@ pub fn regex_prompt(
     Prompt::new(
         prompt,
         history_register,
-        |_input: &str| Vec::new(), // this is fine because Vec::new() doesn't allocate
+        completion_fn,
         move |cx: &mut crate::compositor::Context, input: &str, event: PromptEvent| {
             match event {
                 PromptEvent::Abort => {
diff --git a/helix-term/src/ui/prompt.rs b/helix-term/src/ui/prompt.rs
index 853adfc2..c999ba14 100644
--- a/helix-term/src/ui/prompt.rs
+++ b/helix-term/src/ui/prompt.rs
@@ -185,6 +185,11 @@ impl Prompt {
         self.exit_selection();
     }
 
+    pub fn insert_str(&mut self, s: &str) {
+        self.line.insert_str(self.cursor, s);
+        self.cursor += s.len();
+    }
+
     pub fn move_cursor(&mut self, movement: Movement) {
         let pos = self.eval_movement(movement);
         self.cursor = pos
@@ -474,6 +479,26 @@ impl Component for Prompt {
                 (self.callback_fn)(cx, &self.line, PromptEvent::Update);
             }
             KeyEvent {
+                code: KeyCode::Char('s'),
+                modifiers: KeyModifiers::CONTROL,
+            } => {
+                let (view, doc) = current!(cx.editor);
+                let text = doc.text().slice(..);
+
+                use helix_core::textobject;
+                let range = textobject::textobject_word(
+                    text,
+                    doc.selection(view.id).primary(),
+                    textobject::TextObject::Inside,
+                    1,
+                );
+                let line = text.slice(range.from()..range.to()).to_string();
+                if !line.is_empty() {
+                    self.insert_str(line.as_str());
+                    (self.callback_fn)(cx, &self.line, PromptEvent::Update);
+                }
+            }
+            KeyEvent {
                 code: KeyCode::Enter,
                 ..
             } => {
@@ -520,11 +545,17 @@ impl Component for Prompt {
             }
             KeyEvent {
                 code: KeyCode::Tab, ..
-            } => self.change_completion_selection(CompletionDirection::Forward),
+            } => {
+                self.change_completion_selection(CompletionDirection::Forward);
+                (self.callback_fn)(cx, &self.line, PromptEvent::Update)
+            }
             KeyEvent {
                 code: KeyCode::BackTab,
                 ..
-            } => self.change_completion_selection(CompletionDirection::Backward),
+            } => {
+                self.change_completion_selection(CompletionDirection::Backward);
+                (self.callback_fn)(cx, &self.line, PromptEvent::Update)
+            }
             KeyEvent {
                 code: KeyCode::Char('q'),
                 modifiers: KeyModifiers::CONTROL,