fix infinite loop in cropping

Author: willmcgugan

src/textual/strip.py

@@ -372,10 +372,13 @@ def crop(self, start: int, end: int | None = None) -> Strip:
         Returns:
             A new Strip.
         """
+
         start = max(0, start)
         end = self.cell_length if end is None else min(self.cell_length, end)
         if start == 0 and end == self.cell_length:
             return self
+        if end <= start:
+            return Strip([], 0)
         cache_key = (start, end)
         cached = self._crop_cache.get(cache_key)
         if cached is not None:

src/textual/widgets/_text_area.py

@@ -1236,9 +1236,7 @@ def render_line(self, y: int) -> Strip:
 
         # Crop the line to show only the visible part (some may be scrolled out of view)
         if not self.soft_wrap:
-            text_strip = text_strip.crop(
-                scroll_x, scroll_x + virtual_width - gutter_width
-            )
+            text_strip = text_strip.crop(scroll_x, scroll_x + virtual_width)
 
         # Stylize the line the cursor is currently on.
         if cursor_row == line_index:

tests/test_strip.py

@@ -131,7 +131,7 @@ def test_crop():
 
     assert Strip([Segment("foo")]).crop(1, 3) == Strip([Segment("oo")])
     assert Strip([Segment("foo")]).crop(1, 2) == Strip([Segment("o")])
-    assert Strip([Segment("foo")]).crop(1, 1) == Strip([Segment("")])
+    assert Strip([Segment("foo")]).crop(1, 1) == Strip([])
 
     assert Strip([Segment("foo💩"), Segment("b💩ar"), Segment("ba💩z")]).crop(
         1, 6