Unfold buffers in multibuffers when editing them (#25677)

Release Notes:

- Multibuffers: Unfold excerpts when editing their contents.

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/editor/src/editor_tests.rs

@@ -15644,7 +15644,7 @@ async fn test_find_enclosing_node_with_task(cx: &mut TestAppContext) {
 }
 
 #[gpui::test]
-async fn test_multi_buffer_folding(cx: &mut TestAppContext) {
+async fn test_folding_buffers(cx: &mut TestAppContext) {
     init_test(cx, |_| {});
 
     let sample_text_1 = "aaaa\nbbbb\ncccc\ndddd\neeee\nffff\ngggg\nhhhh\niiii\njjjj".to_string();
@@ -15751,7 +15751,7 @@ async fn test_multi_buffer_folding(cx: &mut TestAppContext) {
     let multi_buffer_editor = cx.new_window_entity(|window, cx| {
         Editor::new(
             EditorMode::Full,
-            multi_buffer,
+            multi_buffer.clone(),
             Some(project.clone()),
             true,
             window,
@@ -15759,10 +15759,9 @@ async fn test_multi_buffer_folding(cx: &mut TestAppContext) {
         )
     });
 
-    let full_text = "\n\n\naaaa\nbbbb\ncccc\n\n\n\nffff\ngggg\n\n\n\njjjj\n\n\n\n\nllll\nmmmm\nnnnn\n\n\n\nqqqq\nrrrr\n\n\n\nuuuu\n\n\n\n\nvvvv\nwwww\nxxxx\n\n\n\n1111\n2222\n\n\n\n5555\n";
     assert_eq!(
         multi_buffer_editor.update(cx, |editor, cx| editor.display_text(cx)),
-        full_text,
+        "\n\n\naaaa\nbbbb\ncccc\n\n\n\nffff\ngggg\n\n\n\njjjj\n\n\n\n\nllll\nmmmm\nnnnn\n\n\n\nqqqq\nrrrr\n\n\n\nuuuu\n\n\n\n\nvvvv\nwwww\nxxxx\n\n\n\n1111\n2222\n\n\n\n5555\n",
     );
 
     multi_buffer_editor.update(cx, |editor, cx| {
@@ -15808,12 +15807,25 @@ async fn test_multi_buffer_folding(cx: &mut TestAppContext) {
         "After unfolding the second buffer, its text should be displayed"
     );
 
-    multi_buffer_editor.update(cx, |editor, cx| {
-        editor.unfold_buffer(buffer_1.read(cx).remote_id(), cx)
+    // Typing inside of buffer 1 causes that buffer to be unfolded.
+    multi_buffer_editor.update_in(cx, |editor, window, cx| {
+        assert_eq!(
+            multi_buffer
+                .read(cx)
+                .snapshot(cx)
+                .text_for_range(Point::new(1, 0)..Point::new(1, 4))
+                .collect::<String>(),
+            "bbbb"
+        );
+        editor.change_selections(None, window, cx, |selections| {
+            selections.select_ranges(vec![Point::new(1, 0)..Point::new(1, 0)]);
+        });
+        editor.handle_input("B", window, cx);
     });
+
     assert_eq!(
         multi_buffer_editor.update(cx, |editor, cx| editor.display_text(cx)),
-        "\n\n\naaaa\nbbbb\ncccc\n\n\n\nffff\ngggg\n\n\n\njjjj\n\n\n\n\nllll\nmmmm\nnnnn\n\n\n\nqqqq\nrrrr\n\n\n\nuuuu\n\n\n",
+        "\n\n\nB\n\n\n\n\n\n\n\n\n\n\nllll\nmmmm\nnnnn\n\n\n\nqqqq\nrrrr\n\n\n\nuuuu\n\n\n",
         "After unfolding the first buffer, its and 2nd buffer's text should be displayed"
     );
 
@@ -15822,13 +15834,13 @@ async fn test_multi_buffer_folding(cx: &mut TestAppContext) {
     });
     assert_eq!(
         multi_buffer_editor.update(cx, |editor, cx| editor.display_text(cx)),
-        full_text,
+        "\n\n\nB\n\n\n\n\n\n\n\n\n\n\nllll\nmmmm\nnnnn\n\n\n\nqqqq\nrrrr\n\n\n\nuuuu\n\n\n\n\nvvvv\nwwww\nxxxx\n\n\n\n1111\n2222\n\n\n\n5555\n",
         "After unfolding the all buffers, all original text should be displayed"
     );
 }
 
 #[gpui::test]
-async fn test_multi_buffer_single_excerpts_folding(cx: &mut TestAppContext) {
+async fn test_folding_buffers_with_one_excerpt(cx: &mut TestAppContext) {
     init_test(cx, |_| {});
 
     let sample_text_1 = "1111\n2222\n3333".to_string();
@@ -15977,7 +15989,7 @@ async fn test_multi_buffer_single_excerpts_folding(cx: &mut TestAppContext) {
 }
 
 #[gpui::test]
-async fn test_multi_buffer_with_single_excerpt_folding(cx: &mut TestAppContext) {
+async fn test_folding_buffer_when_multibuffer_has_only_one_excerpt(cx: &mut TestAppContext) {
     init_test(cx, |_| {});
 
     let sample_text = "aaaa\nbbbb\ncccc\ndddd\neeee\nffff\ngggg\nhhhh\niiii\njjjj".to_string();