Fix #368 - swallow zero-width modifiers

CHANGES.rst

@@ -3,12 +3,13 @@ CHANGE HISTORY
 
 LATEST
 ------
+- Dropped support for Python 2, Python 3.9 or above is now required.
 - Added support for ColouredText titles in MultiColumnLIstBox.
 - Added gutter option to Layout.
 - Added speed option to Sprite.
 - Fixed bug where moving focus between Frames resulted in no current focus.
 - Fixed internal state of RadioButton values to be consistent with selection.
-- Dropped support for Python 2, Python 3.9 or above is now required.
+- Fixed handling of zero width modifiers.
 
 1.14.0
 ------

asciimatics/screen.py

@@ -626,6 +626,11 @@ def print_at(self, text, x, y, colour=7, attr=0, bg=0, transparent=False):
                     if x + i + j + width > self.width:
                         return
 
+                    # Handle modifier glyphs - just delete them for now.
+                    if width == 0:
+                        j -= 1
+                        continue
+
                     # Now handle the update.
                     if c != " " or not transparent:
                         # Fix up orphaned double-width glyphs that we've just bisected.

tests/test_screen.py

@@ -918,6 +918,14 @@ def test_cjk_glyphs_overwrite(self):
         # twice, reflecting their extra width.
         self.assert_line_equals(screen, "x你你確確 ", y=1, length=6)
 
+    def test_zero_width(self):
+        """
+        Check that zero width modifiers are ignored.
+        """
+        screen = Screen.open(unicode_aware=True)
+        screen.print_at("Xx🛡️🍀🍀xX", 0, 0)
+        self.assert_line_equals(screen, "Xx🛡🍀🍀🍀🍀xX", length=9)
+
     def test_save_signal_state(self):
         """Tests that the signal state class works properly.