Add register_theme_update_callback function to rich_utils.py

Also:
- Moved code for updating lexers when theme is updated to pt_utils.py and this now registers with the above callback
- Update unit tests to cover new/modified code

Author: tleonhardt

cmd2/pt_utils.py

@@ -266,6 +266,15 @@ def clear(self) -> None:
 _lexers: "weakref.WeakSet[Cmd2Lexer]" = weakref.WeakSet()
 
 
+def _update_lexer_colors() -> None:
+    """Update colors for all active lexers."""
+    for lexer in _lexers:
+        lexer.set_colors()
+
+
+ru.register_theme_update_callback(_update_lexer_colors)
+
+
 class Cmd2Lexer(Lexer):
     """Lexer that highlights cmd2 command names, aliases, and macros."""
 

cmd2/rich_utils.py

@@ -4,6 +4,7 @@
 import re
 import sys
 from collections.abc import (
+    Callable,
     Iterator,
     Mapping,
 )
@@ -309,6 +310,15 @@ def __cmd2_argparse_help__(self, formatter: Cmd2HelpFormatter) -> Group:
 # The application-wide theme. Use get_theme() and set_theme() to access it.
 _APP_THEME: Theme | None = None
 
+# Callbacks to be executed when the theme is updated
+_theme_update_callbacks: list[Callable[[], None]] = []
+
+
+def register_theme_update_callback(callback: Callable[[], None]) -> None:
+    """Register a callback to be executed when the theme is updated."""
+    if callback not in _theme_update_callbacks:
+        _theme_update_callbacks.append(callback)
+
 
 def get_theme() -> Theme:
     """Get the application-wide theme. Initializes it on the first call."""
@@ -351,11 +361,9 @@ def set_theme(styles: Mapping[str, StyleType] | None = None) -> None:
     for name in Cmd2HelpFormatter.styles.keys() & theme.styles.keys():
         Cmd2HelpFormatter.styles[name] = theme.styles[name]
 
-    # Update colors in active prompt-toolkit lexers
-    from . import pt_utils
-
-    for lexer in pt_utils._lexers:
-        lexer.set_colors()
+    # Notify callbacks that the theme has been updated
+    for callback in _theme_update_callbacks:
+        callback()
 
 
 def _create_default_theme() -> Theme:

tests/test_pt_utils.py

@@ -803,3 +803,12 @@ def test_rich_to_pt_style_nohidden_conceal(self):
         style = Style(conceal=False)
         pt_style = pt_utils.rich_to_pt_style(style)
         assert "nohidden" in pt_style
+
+
+def test_update_lexer_colors() -> None:
+    mock_lexer = Mock()
+    pt_utils._lexers.add(mock_lexer)
+
+    pt_utils._update_lexer_colors()
+
+    mock_lexer.set_colors.assert_called_once()

tests/test_rich_utils.py

@@ -349,3 +349,26 @@ def side_effect(color: bool, **kwargs: Any) -> None:
     assert mock_set_color.call_count == 2
     mock_set_color.assert_any_call(True, file=sys.stdout)
     mock_set_color.assert_any_call(True)
+
+
+def test_register_theme_update_callback() -> None:
+    # Clear callbacks for a clean state
+    ru._theme_update_callbacks.clear()
+
+    # Define a dummy callback
+    def my_callback() -> None:
+        pass
+
+    ru.register_theme_update_callback(my_callback)
+    assert my_callback in ru._theme_update_callbacks
+
+    # Test that registering the same callback again doesn't duplicate it
+    ru.register_theme_update_callback(my_callback)
+    assert len(ru._theme_update_callbacks) == 1
+
+    # Test that set_theme calls the callback
+    mock_callback = mock.Mock()
+    ru.register_theme_update_callback(mock_callback)
+
+    ru.set_theme()
+    mock_callback.assert_called_once()