snapshot

src/textual/_compositor.py

@@ -912,7 +912,7 @@ def get_widget_and_offset_at(
         offset_x2 = 0
 
         for segment in lines[0]:
-            end += segment.cell_length
+            end += len(segment.text)
             style = segment.style
             if style is not None and style._meta is not None:
                 meta = style.meta
@@ -921,10 +921,11 @@ def get_widget_and_offset_at(
                     offset_x2 = offset_x + len(segment.text)
 
                     if x <= end and x >= start:
+                        first, _ = segment.split_cells(x - start)
                         return widget, (
                             None
                             if offset_y is None
-                            else Offset(offset_x + (x - start), offset_y)
+                            else Offset(offset_x + len(first.text), offset_y)
                         )
             start = end
 

tests/snapshot_tests/test_snapshots.py

@@ -3330,3 +3330,21 @@ def compose(self) -> ComposeResult:
             yield Label("This does not allow [bold]markup[/bold]", markup=False)
 
     snap_compare(LabelApp())
+
+
+def test_arbitrary_selection_double_cell(snap_compare):
+    """Check that selection understands double width cells.
+
+    You should see a smiley face followed by 'Hello World!', where Hello is highlighted."""
+
+    class LApp(App):
+        def compose(self) -> ComposeResult:
+            yield Label("😃Hello World!")
+
+    async def run_before(pilot: Pilot) -> None:
+        await pilot.pause()
+        await pilot.mouse_down(Label, offset=(2, 0))
+        await pilot.mouse_up(Label, offset=(7, 0))
+        await pilot.pause()
+
+    assert snap_compare(LApp(), run_before=run_before)