T21a round 3 fix, after the cap

- TextInput records the selection each edit replaces, where every edit passes;
  the block editor's undo goes back to it, for typing, delete, cut and paste
- TextInput's layout geometry moves to forms/text/geometry.rs
- Reviews: T21a done, fixed after the cap, no fourth review

src/forms/text/geometry.rs

@@ -0,0 +1,68 @@
+use gpui::{Bounds, Pixels, Point};
+
+use super::TextInput;
+
+impl TextInput {
+    /// The caret's box in window coordinates, once laid out.
+    pub fn caret_bounds(&self) -> Option<Bounds<Pixels>> {
+        self.bounds_for(self.cursor())
+    }
+
+    /// An offset's box in the window, from the last layout; later offsets clamp to its end.
+    pub fn bounds_for(&self, offset: usize) -> Option<Bounds<Pixels>> {
+        let layout = self.layout.as_ref()?;
+        let laid = layout
+            .lines
+            .last()
+            .map_or(0, |(start, line)| start + line.len());
+        let at = self.position_for(self.display_offset(offset).min(laid))?;
+        Some(Bounds::new(
+            layout.bounds.origin + at - self.scroll,
+            gpui::size(Pixels::ZERO, layout.line_height),
+        ))
+    }
+
+    /// 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()?;
+        if layout.placeholder {
+            return Some(Point::default());
+        }
+        let mut top = Pixels::ZERO;
+        for (start, line) in &layout.lines {
+            if display <= start + line.len() {
+                let at = line.position_for_index(display - start, layout.line_height)?;
+                return Some(gpui::point(at.x, at.y + top));
+            }
+            top += line.size(layout.line_height).height;
+        }
+        None
+    }
+
+    /// The content offset nearest a window position.
+    pub(crate) fn offset_for_point(&self, point: Point<Pixels>) -> usize {
+        let Some(layout) = self.layout.as_ref() else {
+            return 0;
+        };
+        if layout.placeholder {
+            return 0;
+        }
+        let local = point - layout.bounds.origin + self.scroll;
+        if local.y < Pixels::ZERO {
+            return 0;
+        }
+        let mut top = Pixels::ZERO;
+        for (start, line) in &layout.lines {
+            let height = line.size(layout.line_height).height;
+            if local.y < top + height {
+                let inside = gpui::point(local.x.max(Pixels::ZERO), local.y - top);
+                let index = match line.closest_index_for_position(inside, layout.line_height) {
+                    Ok(index) | Err(index) => index,
+                };
+                return self.content_offset(start + index.min(line.len()));
+            }
+            top += height;
+        }
+        self.text.len()
+    }
+}

src/forms/text/mod.rs

@@ -1,6 +1,7 @@
 mod actions;
 mod edit;
 mod element;
+mod geometry;
 mod highlight;
 mod ime;
 
@@ -61,6 +62,8 @@ pub struct TextInput {
     highlighter: Option<Highlighter>,
     disabled: bool,
     history: History<Snapshot>,
+    /// The selection the last edit replaced.
+    edited_from: Range<usize>,
     pub(crate) layout: Option<Layout>,
     pub(crate) scroll: Point<Pixels>,
     selecting: bool,
@@ -109,6 +112,7 @@ impl TextInput {
             highlighter: None,
             disabled: false,
             history: History::default(),
+            edited_from: 0..0,
             layout: None,
             scroll: Point::default(),
             selecting: false,
@@ -250,25 +254,6 @@ impl TextInput {
         self.restart_blink(cx);
     }
 
-    /// The caret's box in window coordinates, once laid out.
-    pub fn caret_bounds(&self) -> Option<Bounds<Pixels>> {
-        self.bounds_for(self.cursor())
-    }
-
-    /// An offset's box in the window, from the last layout; later offsets clamp to its end.
-    pub fn bounds_for(&self, offset: usize) -> Option<Bounds<Pixels>> {
-        let layout = self.layout.as_ref()?;
-        let laid = layout
-            .lines
-            .last()
-            .map_or(0, |(start, line)| start + line.len());
-        let at = self.position_for(self.display_offset(offset).min(laid))?;
-        Some(Bounds::new(
-            layout.bounds.origin + at - self.scroll,
-            gpui::size(Pixels::ZERO, layout.line_height),
-        ))
-    }
-
     /// Keeps what `filter` and `max_len` allow of `incoming`.
     fn admit(&self, incoming: &str, keep: usize) -> String {
         let allowed: String = incoming
@@ -281,6 +266,11 @@ impl TextInput {
         }
     }
 
+    /// The selection the last edit replaced, for an owner's undo to go back to.
+    pub(crate) fn edited_from(&self) -> Range<usize> {
+        self.edited_from.clone()
+    }
+
     pub(crate) fn replace(
         &mut self,
         range: Range<usize>,
@@ -291,6 +281,7 @@ impl TextInput {
         if self.disabled {
             return;
         }
+        self.edited_from = self.selection.clone();
         let incoming = if self.rows.is_none() {
             incoming.replace(['\n', '\r'], " ")
         } else {
@@ -423,50 +414,6 @@ impl TextInput {
         }
     }
 
-    /// 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()?;
-        if layout.placeholder {
-            return Some(Point::default());
-        }
-        let mut top = Pixels::ZERO;
-        for (start, line) in &layout.lines {
-            if display <= start + line.len() {
-                let at = line.position_for_index(display - start, layout.line_height)?;
-                return Some(gpui::point(at.x, at.y + top));
-            }
-            top += line.size(layout.line_height).height;
-        }
-        None
-    }
-
-    /// The content offset nearest a window position.
-    pub(crate) fn offset_for_point(&self, point: Point<Pixels>) -> usize {
-        let Some(layout) = self.layout.as_ref() else {
-            return 0;
-        };
-        if layout.placeholder {
-            return 0;
-        }
-        let local = point - layout.bounds.origin + self.scroll;
-        if local.y < Pixels::ZERO {
-            return 0;
-        }
-        let mut top = Pixels::ZERO;
-        for (start, line) in &layout.lines {
-            let height = line.size(layout.line_height).height;
-            if local.y < top + height {
-                let inside = gpui::point(local.x.max(Pixels::ZERO), local.y - top);
-                let index = match line.closest_index_for_position(inside, layout.line_height) {
-                    Ok(index) | Err(index) => index,
-                };
-                return self.content_offset(start + index.min(line.len()));
-            }
-            top += height;
-        }
-        self.text.len()
-    }
-
     pub(crate) fn highlights(&self, cx: &App) -> Vec<(Range<usize>, Highlight)> {
         match (&self.highlighter, self.masked) {
             (Some(highlight), false) => highlight(&self.text, cx),