editor: Fix excerpt down scroll behavior to only scroll when there are enough lines (#28231)

Smit Barmase created 8 months ago

Follow up for https://github.com/zed-industries/zed/pull/27058

Improves excerpt down button to only scroll when there exists lines more
than equal to `expand_excerpt_lines`. This prevents weird shift at end
of the file.

Before:


https://github.com/user-attachments/assets/244a3bd6-d813-4cc8-9dcb-3addba2b652f

After:


https://github.com/user-attachments/assets/a9a9ba62-a454-4b56-9c8a-d8e6931b270b


Release Notes:

- N/A

Change summary

crates/editor/src/editor.rs | 31 ++++++++++++++++++++++++++-----
1 file changed, 26 insertions(+), 5 deletions(-)

Detailed changes

crates/editor/src/editor.rs

@@ -183,7 +183,7 @@ use std::{
 };
 pub use sum_tree::Bias;
 use sum_tree::TreeMap;
-use text::{BufferId, OffsetUtf16, Rope};
+use text::{BufferId, FromAnchor, OffsetUtf16, Rope};
 use theme::{
     ActiveTheme, PlayerColor, StatusColors, SyntaxTheme, ThemeColors, ThemeSettings,
     observe_buffer_font_size_adjustment,
@@ -12718,12 +12718,33 @@ impl Editor {
         cx: &mut Context<Self>,
     ) {
         let current_scroll_position = self.scroll_position(cx);
-        let lines = EditorSettings::get_global(cx).expand_excerpt_lines;
+        let lines_to_expand = EditorSettings::get_global(cx).expand_excerpt_lines;
+        let mut should_scroll_up = false;
+
+        if direction == ExpandExcerptDirection::Down {
+            let multi_buffer = self.buffer.read(cx);
+            let snapshot = multi_buffer.snapshot(cx);
+            if let Some(buffer_id) = snapshot.buffer_id_for_excerpt(excerpt) {
+                if let Some(buffer) = multi_buffer.buffer(buffer_id) {
+                    if let Some(excerpt_range) = snapshot.buffer_range_for_excerpt(excerpt) {
+                        let buffer_snapshot = buffer.read(cx).snapshot();
+                        let excerpt_end_row =
+                            Point::from_anchor(&excerpt_range.end, &buffer_snapshot).row;
+                        let last_row = buffer_snapshot.max_point().row;
+                        let lines_below = last_row.saturating_sub(excerpt_end_row);
+                        should_scroll_up = lines_below >= lines_to_expand;
+                    }
+                }
+            }
+        }
+
         self.buffer.update(cx, |buffer, cx| {
-            buffer.expand_excerpts([excerpt], lines, direction, cx)
+            buffer.expand_excerpts([excerpt], lines_to_expand, direction, cx)
         });
-        if direction == ExpandExcerptDirection::Down {
-            let new_scroll_position = current_scroll_position + gpui::Point::new(0.0, lines as f32);
+
+        if should_scroll_up {
+            let new_scroll_position =
+                current_scroll_position + gpui::Point::new(0.0, lines_to_expand as f32);
             self.set_scroll_position(new_scroll_position, window, cx);
         }
     }