Fix mouse multi cursor placement for wrapped lines (#61590)

Closes https://github.com/zed-industries/zed/issues/25237


https://github.com/user-attachments/assets/0f1d54a0-c8f1-4b49-8327-73375a2e1f4e


Release Notes:

- Fixed mouse multi cursor placement for wrapped lines

---------

Co-authored-by: Finn Evers <finn@zed.dev>

crates/editor/src/editor_tests.rs

@@ -42108,6 +42108,87 @@ async fn test_columnar_selection_past_end_of_line(cx: &mut TestAppContext) {
     "});
 }
 
+#[gpui::test]
+async fn test_columnar_selection_with_soft_wrap(cx: &mut TestAppContext) {
+    init_test(cx, |_| {});
+
+    let mut cx = EditorTestContext::new(cx).await;
+
+    cx.set_state(indoc! {"
+        ˇ1. Very long line to show how a wrapped line would look
+        2. Very long line to show how a wrapped line would look
+    "});
+
+    let soft_wrap_second_line_row = |editor: &mut Editor, cx: &mut Context<Editor>| {
+        editor.set_wrap_width(Some(100.0.into()), cx);
+        let snapshot = editor.display_snapshot(cx);
+        let second_line_row = Point::new(1, 0).to_display_point(&snapshot).row();
+        assert!(
+            second_line_row.0 > 1,
+            "expected the first line to be soft wrapped"
+        );
+        second_line_row
+    };
+
+    // Dragging a columnar selection across the soft-wrapped rows of the first
+    // line must produce one selection per buffer line, not one per display row.
+    cx.update_editor(|editor, window, cx| {
+        let second_line_row = soft_wrap_second_line_row(editor, cx);
+        editor.select(
+            SelectPhase::BeginColumnar {
+                position: DisplayPoint::new(DisplayRow(0), 0),
+                goal_column: 0,
+                reset: true,
+                mode: ColumnarMode::FromMouse,
+            },
+            window,
+            cx,
+        );
+        editor.select(
+            SelectPhase::Update {
+                position: DisplayPoint::new(second_line_row, 1),
+                goal_column: 1,
+                scroll_delta: gpui::Point::default(),
+            },
+            window,
+            cx,
+        );
+    });
+
+    cx.assert_editor_state(indoc! {"
+        «1ˇ». Very long line to show how a wrapped line would look
+        «2ˇ». Very long line to show how a wrapped line would look
+    "});
+
+    cx.update_editor(|editor, window, cx| {
+        let second_line_row = soft_wrap_second_line_row(editor, cx);
+        editor.select(
+            SelectPhase::BeginColumnar {
+                position: DisplayPoint::new(DisplayRow(0), 0),
+                goal_column: 0,
+                reset: true,
+                mode: ColumnarMode::FromMouse,
+            },
+            window,
+            cx,
+        );
+        editor.select(
+            SelectPhase::Update {
+                position: DisplayPoint::new(second_line_row, 0),
+                goal_column: 0,
+                scroll_delta: gpui::Point::default(),
+            },
+            window,
+            cx,
+        );
+    });
+
+    cx.assert_editor_state(indoc! {"
+        ˇ1. Very long line to show how a wrapped line would look
+        ˇ2. Very long line to show how a wrapped line would look
+    "});
+}
+
 #[gpui::test]
 async fn test_toggle_markdown_block_quote(cx: &mut TestAppContext) {
     init_test(cx, |_| {});

crates/editor/src/selection.rs

@@ -1809,6 +1809,7 @@ impl Editor {
         let end_x = tail_x.max(head_x);
         let reversed = head_x < tail_x;
 
+        let mut last_buffer_row = None;
         let selection_ranges = (start_row.0..=end_row.0)
             .map(DisplayRow)
             .filter_map(|row| {
@@ -1816,6 +1817,12 @@ impl Editor {
                     return None;
                 }
 
+                let buffer_row = row.as_display_point().to_point(display_map).row;
+                if last_buffer_row == Some(buffer_row) {
+                    return None;
+                }
+                last_buffer_row = Some(buffer_row);
+
                 let layout = display_map.layout_row(row, &text_layout_details);
                 if matches!(columnar_state, ColumnarSelectionState::FromSelection { .. })
                     && start_x > layout.width