Rework diff rendering to allow putting the cursor into deleted text, soft-wrapping and scrolling deleted text correctly (#22994)

Closes #12553

* [x] Fix `diff_hunk_before`
* [x] Fix failure to show deleted text when expanding hunk w/ cursor on
second line of the hunk
* [x] Failure to expand diff hunk below the cursor.
* [x] Delete the whole file, and expand the diff. Backspace over the
deleted hunk, panic!
* [x] Go-to-line now counts the diff hunks, but it should not
* [x] backspace at the beginning of a deleted hunk deletes too much text
* [x] Indent guides are rendered incorrectly 
* [ ] Fix randomized multi buffer tests

Maybe:
* [ ] Buffer search should include deleted text (in vim mode it turns
out I use `/x` all the time to jump to the next x I can see).
* [ ] vim: should refuse to switch into insert mode if selection is
fully within a diff.
* [ ] vim `o` command when cursor is on last line of deleted hunk.
* [ ] vim `shift-o` on first line of deleted hunk moves cursor but
doesn't insert line
* [x] `enter` at end of diff hunk inserts a new line but doesn't move
cursor
* [x] (`shift-enter` at start of diff hunk does nothing)
* [ ] Inserting a line just before an expanded hunk collapses it

Release Notes:


- Improved diff rendering, allowing you to navigate with your cursor
inside of deleted text in diff hunks.

---------

Co-authored-by: Conrad <conrad@zed.dev>
Co-authored-by: Cole <cole@zed.dev>
Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: Michael <michael@zed.dev>
Co-authored-by: Agus <agus@zed.dev>
Co-authored-by: João <joao@zed.dev>

crates/editor/src/display_map/wrap_map.rs

@@ -1,11 +1,11 @@
 use super::{
-    fold_map::FoldBufferRows,
+    fold_map::FoldRows,
     tab_map::{self, TabEdit, TabPoint, TabSnapshot},
     Highlights,
 };
 use gpui::{AppContext, Context, Font, LineWrapper, Model, ModelContext, Pixels, Task};
 use language::{Chunk, Point};
-use multi_buffer::MultiBufferSnapshot;
+use multi_buffer::{MultiBufferSnapshot, RowInfo};
 use smol::future::yield_now;
 use std::sync::LazyLock;
 use std::{cmp, collections::VecDeque, mem, ops::Range, time::Duration};
@@ -60,16 +60,16 @@ pub struct WrapChunks<'a> {
 }
 
 #[derive(Clone)]
-pub struct WrapBufferRows<'a> {
-    input_buffer_rows: FoldBufferRows<'a>,
-    input_buffer_row: Option<u32>,
+pub struct WrapRows<'a> {
+    input_buffer_rows: FoldRows<'a>,
+    input_buffer_row: RowInfo,
     output_row: u32,
     soft_wrapped: bool,
     max_output_row: u32,
     transforms: Cursor<'a, Transform, (WrapPoint, TabPoint)>,
 }
 
-impl<'a> WrapBufferRows<'a> {
+impl<'a> WrapRows<'a> {
     pub(crate) fn seek(&mut self, start_row: u32) {
         self.transforms
             .seek(&WrapPoint::new(start_row, 0), Bias::Left, &());
@@ -717,7 +717,7 @@ impl WrapSnapshot {
         self.transforms.summary().output.longest_row
     }
 
-    pub fn buffer_rows(&self, start_row: u32) -> WrapBufferRows {
+    pub fn row_infos(&self, start_row: u32) -> WrapRows {
         let mut transforms = self.transforms.cursor::<(WrapPoint, TabPoint)>(&());
         transforms.seek(&WrapPoint::new(start_row, 0), Bias::Left, &());
         let mut input_row = transforms.start().1.row();
@@ -725,9 +725,9 @@ impl WrapSnapshot {
             input_row += start_row - transforms.start().0.row();
         }
         let soft_wrapped = transforms.item().map_or(false, |t| !t.is_isomorphic());
-        let mut input_buffer_rows = self.tab_snapshot.buffer_rows(input_row);
+        let mut input_buffer_rows = self.tab_snapshot.rows(input_row);
         let input_buffer_row = input_buffer_rows.next().unwrap();
-        WrapBufferRows {
+        WrapRows {
             transforms,
             input_buffer_row,
             input_buffer_rows,
@@ -847,7 +847,7 @@ impl WrapSnapshot {
             }
 
             let text = language::Rope::from(self.text().as_str());
-            let mut input_buffer_rows = self.tab_snapshot.buffer_rows(0);
+            let mut input_buffer_rows = self.tab_snapshot.rows(0);
             let mut expected_buffer_rows = Vec::new();
             let mut prev_tab_row = 0;
             for display_row in 0..=self.max_point().row() {
@@ -855,7 +855,7 @@ impl WrapSnapshot {
                 if tab_point.row() == prev_tab_row && display_row != 0 {
                     expected_buffer_rows.push(None);
                 } else {
-                    expected_buffer_rows.push(input_buffer_rows.next().unwrap());
+                    expected_buffer_rows.push(input_buffer_rows.next().unwrap().buffer_row);
                 }
 
                 prev_tab_row = tab_point.row();
@@ -864,7 +864,8 @@ impl WrapSnapshot {
 
             for start_display_row in 0..expected_buffer_rows.len() {
                 assert_eq!(
-                    self.buffer_rows(start_display_row as u32)
+                    self.row_infos(start_display_row as u32)
+                        .map(|row_info| row_info.buffer_row)
                         .collect::<Vec<_>>(),
                     &expected_buffer_rows[start_display_row..],
                     "invalid buffer_rows({}..)",
@@ -958,8 +959,8 @@ impl<'a> Iterator for WrapChunks<'a> {
     }
 }
 
-impl<'a> Iterator for WrapBufferRows<'a> {
-    type Item = Option<u32>;
+impl<'a> Iterator for WrapRows<'a> {
+    type Item = RowInfo;
 
     fn next(&mut self) -> Option<Self::Item> {
         if self.output_row > self.max_output_row {
@@ -968,6 +969,7 @@ impl<'a> Iterator for WrapBufferRows<'a> {
 
         let buffer_row = self.input_buffer_row;
         let soft_wrapped = self.soft_wrapped;
+        let diff_status = self.input_buffer_row.diff_status;
 
         self.output_row += 1;
         self.transforms
@@ -979,7 +981,15 @@ impl<'a> Iterator for WrapBufferRows<'a> {
             self.soft_wrapped = true;
         }
 
-        Some(if soft_wrapped { None } else { buffer_row })
+        Some(if soft_wrapped {
+            RowInfo {
+                buffer_row: None,
+                multibuffer_row: None,
+                diff_status,
+            }
+        } else {
+            buffer_row
+        })
     }
 }