Highlight matching text in file picker suggestions (#1635)

* Highlight matching text in file picker suggestions

* Remove cache, specialize highlighting code

* Fix outdated comments

3 files changed, 84 insertions, 30 deletions

diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index 064c74ee..b6aaf9e0 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -688,12 +688,12 @@ impl EditorView {
         surface.set_string_truncated(
             viewport.x + 8, // 8: 1 space + 3 char mode string + 1 space + 1 spinner + 1 space
             viewport.y,
-            title,
+            &title,
             viewport
                 .width
                 .saturating_sub(6)
                 .saturating_sub(right_side_text.width() as u16 + 1) as usize, // "+ 1": a space between the title and the selection info
-            base_style,
+            |_| base_style,
             true,
             true,
         );
diff --git a/helix-term/src/ui/picker.rs b/helix-term/src/ui/picker.rs
index 34709e8b..06e50f51 100644
--- a/helix-term/src/ui/picker.rs
+++ b/helix-term/src/ui/picker.rs
@@ -24,7 +24,7 @@ use crate::ui::{Prompt, PromptEvent};
 use helix_core::{movement::Direction, Position};
 use helix_view::{
     editor::Action,
-    graphics::{Color, CursorKind, Margin, Rect, Style},
+    graphics::{Color, CursorKind, Margin, Modifier, Rect, Style},
     Document, Editor,
 };
 
@@ -343,7 +343,7 @@ impl<T> Picker<T> {
                     }
                     // TODO: maybe using format_fn isn't the best idea here
                     let text = (self.format_fn)(option);
-                    // TODO: using fuzzy_indices could give us the char idx for match highlighting
+                    // Highlight indices are computed lazily in the render function
                     self.matcher
                         .fuzzy_match(&text, pattern)
                         .map(|score| (index, score))
@@ -483,6 +483,8 @@ impl<T: 'static> Component for Picker<T> {
 
     fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
         let text_style = cx.editor.theme.get("ui.text");
+        let selected = cx.editor.theme.get("ui.text.focus");
+        let highlighted = cx.editor.theme.get("special").add_modifier(Modifier::BOLD);
 
         // -- Render the frame:
         // clear area
@@ -525,29 +527,41 @@ impl<T: 'static> Component for Picker<T> {
         // subtract area of prompt from top and current item marker " > " from left
         let inner = inner.clip_top(2).clip_left(3);
 
-        let selected = cx.editor.theme.get("ui.text.focus");
-
         let rows = inner.height;
         let offset = self.cursor - (self.cursor % std::cmp::max(1, rows as usize));
 
-        let files = self.matches.iter().skip(offset).map(|(index, _score)| {
-            (index, self.options.get(*index).unwrap()) // get_unchecked
-        });
+        let files = self
+            .matches
+            .iter_mut()
+            .skip(offset)
+            .map(|(index, _score)| (*index, self.options.get(*index).unwrap()));
 
         for (i, (_index, option)) in files.take(rows as usize).enumerate() {
-            if i == (self.cursor - offset) {
+            let is_active = i == (self.cursor - offset);
+            if is_active {
                 surface.set_string(inner.x.saturating_sub(2), inner.y + i as u16, ">", selected);
             }
 
+            let formatted = (self.format_fn)(option);
+
+            let (_score, highlights) = self
+                .matcher
+                .fuzzy_indices(&formatted, &self.prompt.line)
+                .unwrap_or_default();
+
             surface.set_string_truncated(
                 inner.x,
                 inner.y + i as u16,
-                (self.format_fn)(option),
+                &formatted,
                 inner.width as usize,
-                if i == (self.cursor - offset) {
-                    selected
-                } else {
-                    text_style
+                |idx| {
+                    if highlights.contains(&idx) {
+                        highlighted
+                    } else if is_active {
+                        selected
+                    } else {
+                        text_style
+                    }
                 },
                 true,
                 self.truncate_start,
diff --git a/helix-tui/src/buffer.rs b/helix-tui/src/buffer.rs
index f8673e43..22956b04 100644
--- a/helix-tui/src/buffer.rs
+++ b/helix-tui/src/buffer.rs
@@ -287,7 +287,7 @@ impl Buffer {
     where
         S: AsRef<str>,
     {
-        self.set_string_truncated(x, y, string, width, style, false, false)
+        self.set_string_truncated_at_end(x, y, string.as_ref(), width, style)
     }
 
     /// Print at most the first `width` characters of a string if enough space is available
@@ -295,19 +295,16 @@ impl Buffer {
     /// truncated lines. If `truncate_start` is `true`, truncate the beginning of the string
     /// instead of the end.
     #[allow(clippy::too_many_arguments)]
-    pub fn set_string_truncated<S>(
+    pub fn set_string_truncated(
         &mut self,
         x: u16,
         y: u16,
-        string: S,
+        string: &str,
         width: usize,
-        style: Style,
+        style: impl Fn(usize) -> Style, // Map a grapheme's string offset to a style
         ellipsis: bool,
         truncate_start: bool,
-    ) -> (u16, u16)
-    where
-        S: AsRef<str>,
-    {
+    ) -> (u16, u16) {
         // prevent panic if out of range
         if !self.in_bounds(x, y) || width == 0 {
             return (x, y);
@@ -316,10 +313,10 @@ impl Buffer {
         let mut index = self.index_of(x, y);
         let mut x_offset = x as usize;
         let width = if ellipsis { width - 1 } else { width };
-        let graphemes = UnicodeSegmentation::graphemes(string.as_ref(), true);
+        let graphemes = string.grapheme_indices(true);
         let max_offset = min(self.area.right() as usize, width.saturating_add(x as usize));
         if !truncate_start {
-            for s in graphemes {
+            for (byte_offset, s) in graphemes {
                 let width = s.width();
                 if width == 0 {
                     continue;
@@ -331,7 +328,7 @@ impl Buffer {
                 }
 
                 self.content[index].set_symbol(s);
-                self.content[index].set_style(style);
+                self.content[index].set_style(style(byte_offset));
                 // Reset following cells if multi-width (they would be hidden by the grapheme),
                 for i in index + 1..index + width {
                     self.content[i].reset();
@@ -339,14 +336,14 @@ impl Buffer {
                 index += width;
                 x_offset += width;
             }
-            if ellipsis && x_offset - (x as usize) < string.as_ref().width() {
+            if ellipsis && x_offset - (x as usize) < string.width() {
                 self.content[index].set_symbol("…");
             }
         } else {
             let mut start_index = self.index_of(x, y);
             let mut index = self.index_of(max_offset as u16, y);
 
-            let total_width = string.as_ref().width();
+            let total_width = string.width();
             let truncated = total_width > width;
             if ellipsis && truncated {
                 self.content[start_index].set_symbol("…");
@@ -355,7 +352,7 @@ impl Buffer {
             if !truncated {
                 index -= width - total_width;
             }
-            for s in graphemes.rev() {
+            for (byte_offset, s) in graphemes.rev() {
                 let width = s.width();
                 if width == 0 {
                     continue;
@@ -365,7 +362,7 @@ impl Buffer {
                     break;
                 }
                 self.content[start].set_symbol(s);
-                self.content[start].set_style(style);
+                self.content[start].set_style(style(byte_offset));
                 for i in start + 1..index {
                     self.content[i].reset();
                 }
@@ -375,6 +372,49 @@ impl Buffer {
         (x_offset as u16, y)
     }
 
+    /// Print at most the first `width` characters of a string if enough space is available
+    /// until the end of the line.
+    pub fn set_string_truncated_at_end(
+        &mut self,
+        x: u16,
+        y: u16,
+        string: &str,
+        width: usize,
+        style: Style,
+    ) -> (u16, u16) {
+        // prevent panic if out of range
+        if !self.in_bounds(x, y) {
+            return (x, y);
+        }
+
+        let mut index = self.index_of(x, y);
+        let mut x_offset = x as usize;
+        let max_x_offset = min(self.area.right() as usize, width.saturating_add(x as usize));
+
+        for s in string.graphemes(true) {
+            let width = s.width();
+            if width == 0 {
+                continue;
+            }
+            // `x_offset + width > max_offset` could be integer overflow on 32-bit machines if we
+            // change dimensions to usize or u32 and someone resizes the terminal to 1x2^32.
+            if width > max_x_offset.saturating_sub(x_offset) {
+                break;
+            }
+
+            self.content[index].set_symbol(s);
+            self.content[index].set_style(style);
+            // Reset following cells if multi-width (they would be hidden by the grapheme),
+            for i in index + 1..index + width {
+                self.content[i].reset();
+            }
+            index += width;
+            x_offset += width;
+        }
+
+        (x_offset as u16, y)
+    }
+
     pub fn set_spans<'a>(&mut self, x: u16, y: u16, spans: &Spans<'a>, width: u16) -> (u16, u16) {
         let mut remaining_width = width;
         let mut x = x;