T22: Collaboration

- presence: avatars ringed in each peer's color with where they are, press to
  follow; a breathing live dot; follow mode frames the view and stops on Escape
- remote cursors and selections painted over a field from its own layout
- comment threads with replies, reactions and resolve; a marker that opens a
  thread in a bubble; a sidebar of open and resolved threads
- annotations washed in their authors' colors, notes on hover
- suggestion mode: edits become suggestions word by word; track changes shows
  them struck and underlined, to accept or reject
- sharing: invite by email with checked chips, roles, the access list and who
  the link lets in, in one dialog
- primitives::hold_focus gives a mode its own focus, shared with ZenMode
- AvatarGroup's tuck and count shared; Avatar::ring_color; TagInput::check;
  TextInput::bounds_for_range; Popover::size
- icons: smile-plus, user-plus, message-square-diff
- gallery: the Collaboration page with scripted states

src/forms/text/element.rs

@@ -358,7 +358,7 @@ fn keep_in_view(
 }
 
 /// Boxes covering display offsets `start..end`, relative to the text origin.
-fn selection_rects(
+pub(super) fn selection_rects(
     lines: &[(usize, WrappedLine)],
     start: usize,
     end: usize,

src/forms/text/geometry.rs

@@ -1,6 +1,8 @@
+use std::ops::Range;
+
 use gpui::{Bounds, Pixels, Point};
 
-use super::TextInput;
+use super::{TextInput, element::selection_rects};
 
 impl TextInput {
     /// The caret's box in window coordinates, once laid out.
@@ -22,6 +24,34 @@ impl TextInput {
         ))
     }
 
+    /// A range's boxes in the window, a line each, from the last layout; later offsets clamp to its end.
+    pub fn bounds_for_range(&self, range: Range<usize>) -> Vec<Bounds<Pixels>> {
+        let Some(layout) = self.layout.as_ref() else {
+            return Vec::new();
+        };
+        if layout.placeholder {
+            return Vec::new();
+        }
+        let laid = layout
+            .lines
+            .last()
+            .map_or(0, |(start, line)| start + line.len());
+        let (start, end) = (
+            self.display_offset(range.start).min(laid),
+            self.display_offset(range.end).min(laid),
+        );
+        selection_rects(
+            &layout.lines,
+            start,
+            end,
+            layout.line_height,
+            layout.bounds.size.width,
+        )
+        .into_iter()
+        .map(|rect| Bounds::new(rect.origin + layout.bounds.origin - self.scroll, rect.size))
+        .collect()
+    }
+
     /// Top-left of a display offset, relative to the text's origin.
     pub(crate) fn position_for(&self, display: usize) -> Option<Point<Pixels>> {
         let layout = self.layout.as_ref()?;