Add SettingsListener.

docs/source/index.rst

@@ -58,6 +58,13 @@ Region manager
 
 .. autoclass:: sublime_lib.RegionManager
 
+Settings listeners
+------------------
+
+.. autoclass:: sublime_lib.GlobalSettingsListener
+.. autoclass:: sublime_lib.ViewSettingsListener
+.. autofunction:: sublime_lib.on_setting_changed
+
 :mod:`~sublime_lib.encodings` submodule
 ---------------------------------------
 

docs/source/mocks/sublime_plugin.py

@@ -0,0 +1,19 @@
+from sphinx.ext.autodoc.mock import _MockObject
+
+import sys
+
+
+class MockType(_MockObject):
+    def __init__(self, name):
+        self.name = name
+
+    def __repr__(self):
+        return self.name
+
+
+class SublimePluginMock:
+    EventListener = MockType('sublime_plugin.EventListener')
+    ViewEventListener = MockType('sublime_plugin.ViewEventListener')
+
+
+sys.modules[__name__] = SublimePluginMock()

st3/sublime_lib/__init__.py

@@ -7,4 +7,7 @@
 from .view_utils import new_view, close_view, LineEnding  # noqa: F401
 from .activity_indicator import ActivityIndicator  # noqa: F401
 from .window_utils import new_window, close_window  # noqa: F401
+from .settings_listener import (  # noqa: F401
+    GlobalSettingsListener, ViewSettingsListener, on_setting_changed
+)
 from .region_manager import RegionManager  # noqa: F401

st3/sublime_lib/settings_listener.py

@@ -0,0 +1,160 @@
+import sublime
+import sublime_plugin
+
+from collections import namedtuple
+
+from ._util.weak_method import weak_method
+from ._util.collections import get_selector
+
+
+from ._compat.typing import Callable, Any, Iterator, Tuple, TypeVar, Union, Optional
+
+
+__all__ = ['GlobalSettingsListener', 'ViewSettingsListener', 'on_setting_changed']
+
+
+OnChangedOptions = namedtuple('OnChangedOptions', ('selector'))
+OPTIONS_ATTRIBUTE = '_sublime_lib_settings_listener_options'
+
+
+class BaseSettingsListener:
+    def _handlers(self) -> Iterator[Tuple[str, Callable, OnChangedOptions]]:
+        for name in dir(self):
+            value = getattr(self, name)
+            options = getattr(value, OPTIONS_ATTRIBUTE, None)
+
+            if not name.startswith('_') and options is not None:
+                yield name, value, options
+
+    def __init__(self, settings: sublime.Settings, *args: Any, **kwargs: Any) -> None:
+        # Don't complain that object.__init__ doesn't take any args
+        super().__init__(*args, **kwargs)  # type: ignore
+        self.settings = settings
+
+        self.settings.add_on_change(str(id(self)), weak_method(self._on_settings_changed))
+
+        self._last_known_values = {
+            name: options.selector(self.settings)
+            for name, _, options in self._handlers()
+        }
+
+    def __del__(self) -> None:
+        self.settings.clear_on_change(str(id(self)))
+
+    def _on_settings_changed(self) -> None:
+        for name, handler, options in self._handlers():
+            previous_value = self._last_known_values[name]
+            current_value = options.selector(self.settings)
+
+            if current_value != previous_value:
+                self._last_known_values[name] = current_value
+                handler(current_value, previous_value)
+
+
+class GlobalSettingsListener(BaseSettingsListener, sublime_plugin.EventListener):
+    """
+    A subclass of :class:`sublime_plugin.EventListener`
+    that also listens for changes in a global settings object.
+
+    Subclasses must set the `SETTINGS_NAME` class variable to the name of the global settings.
+    Otherwise, :exc:`RuntimeError` is raised.
+
+    Example usage:
+
+    .. code-block:: python
+
+        from sublime_lib import GlobalSettingsListener, on_setting_changed
+
+        class JsCustomConfigurationsListener(GlobalSettingsListener)
+            SETTINGS_NAME = 'JS Custom.sublime-settings'
+
+            @on_setting_changed('configurations')
+            def configurations_changed(self, new_configuration, old_configuration):
+                if self.settings.get('auto_build', False):
+                    sublime.active_window().run_command('build_js_custom_syntaxes')
+    """
+    SETTINGS_NAME = None  # type: Optional[str]
+
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        if type(self) is GlobalSettingsListener:
+            # If someone accidentally exports GlobalSettingsListener itself,
+            # don't attach a listener.
+            return
+        elif self.SETTINGS_NAME is None:
+            listener_name = type(self).__name__
+            raise RuntimeError('Must specify SETTINGS_NAME for listener {}.'.format(listener_name))
+
+        super().__init__(sublime.load_settings(self.SETTINGS_NAME), *args, **kwargs)
+
+    def _on_settings_changed(self) -> None:
+        # Necessary because Sublime keeps EventListener objects alive unnecessarily.
+        # See https://github.com/sublimehq/sublime_text/issues/4078.
+        if self in sublime_plugin.all_callbacks['on_new']:
+            super()._on_settings_changed()
+        else:
+            self.settings.clear_on_change(str(id(self)))
+
+    def on_new(self, view: sublime.View) -> None:
+        pass
+
+
+class ViewSettingsListener(BaseSettingsListener, sublime_plugin.ViewEventListener):
+    """
+    A subclass of :class:`sublime_plugin.ViewEventListener`
+    that also listens for changes in the view settings.
+
+    Example:
+
+    .. code-block:: python
+
+        from sublime_lib import ViewSettingsListener, on_setting_changed
+
+        class TabSizeListener(ViewSettingsListener):
+            @classmethod
+            def is_applicable(cls, settings):
+                return settings.get('translate_tabs_to_spaces', False)
+
+            @classmethod
+            def applies_to_primary_view_only(cls):
+                return True
+
+            @on_setting_changed('tab_size')
+            def tab_size_changed(self, new_value, old_value):
+                self.view.run_command('resize_existing_tabs', {
+                    'new_size': new_value,
+                    'old_size': old_value,
+                })
+    """
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        view = args[0]
+        assert isinstance(view, sublime.View)
+        super().__init__(view.settings(), *args, **kwargs)
+
+
+Selected = TypeVar('Selected')
+OnChangeListener = Callable[[BaseSettingsListener, Selected, Selected], None]
+
+
+def on_setting_changed(
+    selector: Union[str, Callable[[sublime.Settings], Selected]]
+) -> Callable[[OnChangeListener], OnChangeListener]:
+    """
+    A decorator function to mark a method
+    of a :class:`GlobalSettingsListener` or :class:`ViewSettingsListener`
+    as a setting change handler.
+
+    The handler is not called every time the `settings` object changes,
+    but only when the value derived using the `selector` argument changes.
+    If `selector` is callable, then the derived value is ``selector(self)``.
+    If `selector` is a :class:`str`,
+    then the derived value is ``self.get(selector, None)``.
+    Otherwise, the derived value is ``projection(self, selector)``.
+
+    The handler should accept two arguments:
+    the new derived value and the previous derived value.
+    """
+    def decorator(function: OnChangeListener) -> OnChangeListener:
+        setattr(function, OPTIONS_ATTRIBUTE, OnChangedOptions(get_selector(selector)))
+        return function
+
+    return decorator

stubs/sublime_plugin.pyi

@@ -1,6 +1,9 @@
 import sublime
 
-from typing import Callable, Generic, TypeVar, Optional, Union, List, Tuple, overload
+from typing import Callable, Generic, TypeVar, Optional, Union, List, Tuple, Dict, overload
+
+
+all_callbacks: Dict[str, List['EventListener']]
 
 
 InputType = TypeVar('InputType', bound=Union[str, int, float, list, dict, tuple, None])

tests/settings_listener_package/settings_listener_plugin.py

@@ -0,0 +1,24 @@
+import sublime_lib
+from sublime_lib import on_setting_changed, ResourcePath
+
+
+__all__ = ['FooSettingListener', 'GlobalFooSettingListener']
+
+
+PACKAGE_NAME = ResourcePath.from_file_path(__file__).package
+
+
+class FooSettingListener(sublime_lib.ViewSettingsListener):
+    @on_setting_changed('foo')
+    def foo_changed(self, new_value: object, old_value: object):
+        changes = self.settings.get('changes', [])
+        self.settings.set('changes', changes + [[new_value, old_value]])
+
+
+class GlobalFooSettingListener(sublime_lib.GlobalSettingsListener):
+    SETTINGS_NAME = PACKAGE_NAME + '.sublime-settings'
+
+    @on_setting_changed('foo')
+    def foo_changed(self, new_value: object, old_value: object):
+        changes = self.settings.get('changes', [])
+        self.settings.set('changes', changes + [[new_value, old_value]])

tests/test_settings_listener.py

@@ -0,0 +1,88 @@
+import sublime
+from sublime_lib import ResourcePath, new_view, close_view
+from .temporary_package import TemporaryPackage
+
+from unittest import TestCase
+from unittesting import DeferrableTestCase
+
+from sublime_lib import GlobalSettingsListener
+
+
+class TestViewSettingsListener(DeferrableTestCase):
+    def setUp(self):
+        self.view = new_view(sublime.active_window())
+        self.temporary_package = TemporaryPackage(
+            'sublime_lib_settings_listener_test',
+            ResourcePath("Packages/sublime_lib/tests/settings_listener_package")
+        )
+        self.temporary_package.create()
+        yield self.temporary_package.exists
+
+    def tearDown(self):
+        self.temporary_package.destroy()
+        if getattr(self, 'view', None):
+            try:
+                close_view(self.view, force=True)
+            except ValueError:
+                pass
+
+    def test_view_listener(self):
+        self.view.settings().set('foo', 'A')
+        self.view.settings().set('foo', 'B')
+
+        self.temporary_package.destroy()
+        yield lambda: not self.temporary_package.exists()
+
+        self.view.settings().set('foo', 'C')
+
+        self.assertEqual(self.view.settings().get('changes'), [
+            ['A', None],
+            ['B', 'A'],
+        ])
+
+
+class TestGlobalSettingsListener(DeferrableTestCase):
+    def setUp(self):
+        name = 'TestGlobalSettingsListener:{}'.format(str(id(self)))
+        self.settings = sublime.load_settings(name + '.sublime-settings')
+        self.settings.set('changes', [])
+        self.settings.set('foo', None)
+        self.temporary_package = TemporaryPackage(
+            name,
+            ResourcePath("Packages/sublime_lib/tests/settings_listener_package")
+        )
+        self.temporary_package.create()
+        yield self.temporary_package.exists
+
+    def tearDown(self):
+        self.temporary_package.destroy()
+
+    def test_global_listener(self):
+        self.settings.set('foo', 'A')
+        self.settings.set('foo', 'B')
+
+        self.temporary_package.destroy()
+        yield lambda: not self.temporary_package.exists()
+        yield 100
+        import gc
+        gc.collect()
+        yield 100
+
+        self.settings.set('foo', 'C')
+
+        self.assertEqual(self.settings.get('changes'), [
+            ['A', None],
+            ['B', 'A'],
+        ])
+
+
+class TestGlobalSettingsListenerErrors(TestCase):
+    def test_instantiate_base(self):
+        GlobalSettingsListener()
+
+    def test_instantiate_without_name(self):
+        class TestListener(GlobalSettingsListener):
+            pass
+
+        with self.assertRaises(RuntimeError):
+            TestListener()