Draft Highlighter API

core/src/renderer/null.rs

@@ -149,6 +149,17 @@ impl text::Editor for () {
         _new_font: Self::Font,
         _new_size: Pixels,
         _new_line_height: text::LineHeight,
+        _new_highlighter: &mut impl text::Highlighter,
+    ) {
+    }
+
+    fn highlight<H: text::Highlighter>(
+        &mut self,
+        _font: Self::Font,
+        _highlighter: &mut H,
+        _format_highlight: impl Fn(
+            &H::Highlight,
+        ) -> text::highlighter::Format<Self::Font>,
     ) {
     }
 }

core/src/text.rs

@@ -2,8 +2,10 @@
 mod paragraph;
 
 pub mod editor;
+pub mod highlighter;
 
 pub use editor::Editor;
+pub use highlighter::Highlighter;
 pub use paragraph::Paragraph;
 
 use crate::alignment;

core/src/text/editor.rs

@@ -1,3 +1,4 @@
+use crate::text::highlighter::{self, Highlighter};
 use crate::text::LineHeight;
 use crate::{Pixels, Point, Rectangle, Size};
 
@@ -29,6 +30,14 @@ pub trait Editor: Sized + Default {
         new_font: Self::Font,
         new_size: Pixels,
         new_line_height: LineHeight,
+        new_highlighter: &mut impl Highlighter,
+    );
+
+    fn highlight<H: Highlighter>(
+        &mut self,
+        font: Self::Font,
+        highlighter: &mut H,
+        format_highlight: impl Fn(&H::Highlight) -> highlighter::Format<Self::Font>,
     );
 }
 

core/src/text/highlighter.rs

@@ -0,0 +1,56 @@
+use crate::Color;
+
+use std::hash::Hash;
+use std::ops::Range;
+
+pub trait Highlighter: Clone + 'static {
+    type Settings: Hash;
+    type Highlight;
+
+    type Iterator<'a>: Iterator<Item = (Range<usize>, Self::Highlight)>
+    where
+        Self: 'a;
+
+    fn new(settings: &Self::Settings) -> Self;
+
+    fn change_line(&mut self, line: usize);
+
+    fn highlight_line(&mut self, line: &str) -> Self::Iterator<'_>;
+
+    fn current_line(&self) -> usize;
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Style {
+    pub color: Color,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct PlainText;
+
+impl Highlighter for PlainText {
+    type Settings = ();
+    type Highlight = ();
+
+    type Iterator<'a> = std::iter::Empty<(Range<usize>, Self::Highlight)>;
+
+    fn new(_settings: &Self::Settings) -> Self {
+        Self
+    }
+
+    fn change_line(&mut self, _line: usize) {}
+
+    fn highlight_line(&mut self, _line: &str) -> Self::Iterator<'_> {
+        std::iter::empty()
+    }
+
+    fn current_line(&self) -> usize {
+        usize::MAX
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Format<Font> {
+    pub color: Option<Color>,
+    pub font: Option<Font>,
+}

graphics/src/text.rs

@@ -10,7 +10,7 @@ pub use cosmic_text;
 
 use crate::core::font::{self, Font};
 use crate::core::text::Shaping;
-use crate::core::Size;
+use crate::core::{Color, Size};
 
 use once_cell::sync::OnceCell;
 use std::borrow::Cow;
@@ -129,3 +129,9 @@ pub fn to_shaping(shaping: Shaping) -> cosmic_text::Shaping {
         Shaping::Advanced => cosmic_text::Shaping::Advanced,
     }
 }
+
+pub fn to_color(color: Color) -> cosmic_text::Color {
+    let [r, g, b, a] = color.into_rgba8();
+
+    cosmic_text::Color::rgba(r, g, b, a)
+}

graphics/src/text/editor.rs

@@ -1,4 +1,5 @@
 use crate::core::text::editor::{self, Action, Cursor, Direction, Motion};
+use crate::core::text::highlighter::{self, Highlighter};
 use crate::core::text::LineHeight;
 use crate::core::{Font, Pixels, Point, Rectangle, Size};
 use crate::text;
@@ -15,6 +16,7 @@ struct Internal {
     editor: cosmic_text::Editor,
     font: Font,
     bounds: Size,
+    topmost_line_changed: Option<usize>,
     version: text::Version,
 }
 
@@ -433,6 +435,7 @@ impl editor::Editor for Editor {
         new_font: Font,
         new_size: Pixels,
         new_line_height: LineHeight,
+        new_highlighter: &mut impl Highlighter,
     ) {
         let editor =
             self.0.take().expect("editor should always be initialized");
@@ -479,6 +482,69 @@ impl editor::Editor for Editor {
             internal.bounds = new_bounds;
         }
 
+        if let Some(topmost_line_changed) = internal.topmost_line_changed.take()
+        {
+            new_highlighter.change_line(topmost_line_changed);
+        }
+
+        self.0 = Some(Arc::new(internal));
+    }
+
+    fn highlight<H: Highlighter>(
+        &mut self,
+        font: Self::Font,
+        highlighter: &mut H,
+        format_highlight: impl Fn(&H::Highlight) -> highlighter::Format<Self::Font>,
+    ) {
+        let internal = self.internal();
+
+        let scroll = internal.editor.buffer().scroll();
+        let visible_lines = internal.editor.buffer().visible_lines();
+        let last_visible_line = (scroll + visible_lines - 1) as usize;
+
+        let current_line = highlighter.current_line();
+
+        if current_line > last_visible_line {
+            return;
+        }
+
+        let editor =
+            self.0.take().expect("editor should always be initialized");
+
+        let mut internal = Arc::try_unwrap(editor)
+            .expect("Editor cannot have multiple strong references");
+
+        let mut font_system =
+            text::font_system().write().expect("Write font system");
+
+        let attributes = text::to_attributes(font);
+
+        for line in &mut internal.editor.buffer_mut().lines
+            [current_line..=last_visible_line]
+        {
+            let mut list = cosmic_text::AttrsList::new(attributes);
+
+            for (range, highlight) in highlighter.highlight_line(line.text()) {
+                let format = format_highlight(&highlight);
+
+                list.add_span(
+                    range,
+                    cosmic_text::Attrs {
+                        color_opt: format.color.map(text::to_color),
+                        ..if let Some(font) = format.font {
+                            text::to_attributes(font)
+                        } else {
+                            attributes
+                        }
+                    },
+                );
+            }
+
+            let _ = line.set_attrs_list(list);
+        }
+
+        internal.editor.shape_as_needed(font_system.raw());
+
         self.0 = Some(Arc::new(internal));
     }
 }
@@ -508,6 +574,7 @@ impl Default for Internal {
             )),
             font: Font::default(),
             bounds: Size::ZERO,
+            topmost_line_changed: None,
             version: text::Version::default(),
         }
     }

style/src/lib.rs

@@ -15,7 +15,7 @@
     clippy::needless_borrow,
     clippy::new_without_default,
     clippy::useless_conversion,
-    missing_docs,
+    // missing_docs,
     unused_results,
     rustdoc::broken_intra_doc_links
 )]

style/src/text_editor.rs

@@ -1,5 +1,6 @@
 //! Change the appearance of a text editor.
-use iced_core::{Background, BorderRadius, Color};
+use crate::core::text::highlighter;
+use crate::core::{self, Background, BorderRadius, Color};
 
 /// The appearance of a text input.
 #[derive(Debug, Clone, Copy)]
@@ -45,3 +46,16 @@ pub trait StyleSheet {
     /// Produces the style of a disabled text input.
     fn disabled(&self, style: &Self::Style) -> Appearance;
 }
+
+pub trait Highlight<Font = core::Font, Theme = crate::Theme> {
+    fn format(&self, theme: &Theme) -> highlighter::Format<Font>;
+}
+
+impl<Font, Theme> Highlight<Font, Theme> for () {
+    fn format(&self, _theme: &Theme) -> highlighter::Format<Font> {
+        highlighter::Format {
+            color: None,
+            font: None,
+        }
+    }
+}

widget/src/helpers.rs

@@ -212,7 +212,7 @@ where
 /// [`TextEditor`]: crate::TextEditor
 pub fn text_editor<Message, Renderer>(
     content: &text_editor::Content<Renderer>,
-) -> TextEditor<'_, Message, Renderer>
+) -> TextEditor<'_, core::text::highlighter::PlainText, Message, Renderer>
 where
     Message: Clone,
     Renderer: core::text::Renderer,

widget/src/text_editor.rs

@@ -4,6 +4,7 @@ use crate::core::layout::{self, Layout};
 use crate::core::mouse;
 use crate::core::renderer;
 use crate::core::text::editor::{Cursor, Editor as _};
+use crate::core::text::highlighter::{self, Highlighter};
 use crate::core::text::{self, LineHeight};
 use crate::core::widget::{self, Widget};
 use crate::core::{
@@ -12,13 +13,15 @@ use crate::core::{
 };
 
 use std::cell::RefCell;
+use std::ops::DerefMut;
 use std::sync::Arc;
 
-pub use crate::style::text_editor::{Appearance, StyleSheet};
+pub use crate::style::text_editor::{Appearance, Highlight, StyleSheet};
 pub use text::editor::{Action, Motion};
 
-pub struct TextEditor<'a, Message, Renderer = crate::Renderer>
+pub struct TextEditor<'a, Highlighter, Message, Renderer = crate::Renderer>
 where
+    Highlighter: text::Highlighter,
     Renderer: text::Renderer,
     Renderer::Theme: StyleSheet,
 {
@@ -31,9 +34,11 @@ where
     padding: Padding,
     style: <Renderer::Theme as StyleSheet>::Style,
     on_edit: Option<Box<dyn Fn(Action) -> Message + 'a>>,
+    highlighter_settings: Highlighter::Settings,
 }
 
-impl<'a, Message, Renderer> TextEditor<'a, Message, Renderer>
+impl<'a, Message, Renderer>
+    TextEditor<'a, highlighter::PlainText, Message, Renderer>
 where
     Renderer: text::Renderer,
     Renderer::Theme: StyleSheet,
@@ -49,9 +54,19 @@ where
             padding: Padding::new(5.0),
             style: Default::default(),
             on_edit: None,
+            highlighter_settings: (),
         }
     }
+}
 
+impl<'a, Highlighter, Message, Renderer>
+    TextEditor<'a, Highlighter, Message, Renderer>
+where
+    Highlighter: text::Highlighter,
+    Highlighter::Highlight: Highlight<Renderer::Font, Renderer::Theme>,
+    Renderer: text::Renderer,
+    Renderer::Theme: StyleSheet,
+{
     pub fn on_edit(mut self, on_edit: impl Fn(Action) -> Message + 'a) -> Self {
         self.on_edit = Some(Box::new(on_edit));
         self
@@ -160,20 +175,23 @@ where
     }
 }
 
-struct State {
+struct State<Highlighter> {
     is_focused: bool,
     last_click: Option<mouse::Click>,
     drag_click: Option<mouse::click::Kind>,
+    highlighter: RefCell<Highlighter>,
 }
 
-impl<'a, Message, Renderer> Widget<Message, Renderer>
+impl<'a, Highlighter, Message, Renderer> Widget<Message, Renderer>
-    for TextEditor<'a, Message, Renderer>
+    for TextEditor<'a, Highlighter, Message, Renderer>
 where
+    Highlighter: text::Highlighter,
+    Highlighter::Highlight: Highlight<Renderer::Font, Renderer::Theme>,
     Renderer: text::Renderer,
     Renderer::Theme: StyleSheet,
 {
     fn tag(&self) -> widget::tree::Tag {
-        widget::tree::Tag::of::<State>()
+        widget::tree::Tag::of::<State<Highlighter>>()
     }
 
     fn state(&self) -> widget::tree::State {
@@ -181,6 +199,9 @@ where
             is_focused: false,
             last_click: None,
             drag_click: None,
+            highlighter: RefCell::new(Highlighter::new(
+                &self.highlighter_settings,
+            )),
         })
     }
 
@@ -194,17 +215,19 @@ where
 
     fn layout(
         &self,
-        _tree: &mut widget::Tree,
+        tree: &mut widget::Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> iced_renderer::core::layout::Node {
         let mut internal = self.content.0.borrow_mut();
+        let state = tree.state.downcast_mut::<State<Highlighter>>();
 
         internal.editor.update(
             limits.pad(self.padding).max(),
             self.font.unwrap_or_else(|| renderer.default_font()),
             self.text_size.unwrap_or_else(|| renderer.default_size()),
             self.line_height,
+            state.highlighter.borrow_mut().deref_mut(),
         );
 
         layout::Node::new(limits.max())
@@ -225,7 +248,7 @@ where
             return event::Status::Ignored;
         };
 
-        let state = tree.state.downcast_mut::<State>();
+        let state = tree.state.downcast_mut::<State<Highlighter>>();
 
         let Some(update) = Update::from_event(
             event,
@@ -290,8 +313,14 @@ where
     ) {
         let bounds = layout.bounds();
 
-        let internal = self.content.0.borrow();
+        let mut internal = self.content.0.borrow_mut();
-        let state = tree.state.downcast_ref::<State>();
+        let state = tree.state.downcast_ref::<State<Highlighter>>();
+
+        internal.editor.highlight(
+            self.font.unwrap_or_else(|| renderer.default_font()),
+            state.highlighter.borrow_mut().deref_mut(),
+            |highlight| highlight.format(theme),
+        );
 
         let is_disabled = self.on_edit.is_none();
         let is_mouse_over = cursor.is_over(bounds);
@@ -389,14 +418,19 @@ where
     }
 }
 
-impl<'a, Message, Renderer> From<TextEditor<'a, Message, Renderer>>
+impl<'a, Highlighter, Message, Renderer>
+    From<TextEditor<'a, Highlighter, Message, Renderer>>
     for Element<'a, Message, Renderer>
 where
+    Highlighter: text::Highlighter,
+    Highlighter::Highlight: Highlight<Renderer::Font, Renderer::Theme>,
     Message: 'a,
     Renderer: text::Renderer,
     Renderer::Theme: StyleSheet,
 {
-    fn from(text_editor: TextEditor<'a, Message, Renderer>) -> Self {
+    fn from(
+        text_editor: TextEditor<'a, Highlighter, Message, Renderer>,
+    ) -> Self {
         Self::new(text_editor)
     }
 }
@@ -411,9 +445,9 @@ enum Update {
 }
 
 impl Update {
-    fn from_event(
+    fn from_event<H: Highlighter>(
         event: Event,
-        state: &State,
+        state: &State<H>,
         bounds: Rectangle,
         padding: Padding,
         cursor: mouse::Cursor,