Refactor websettings and save/restore defaults.

This makes qutebrowser.config.websettings much easier to understand, and saves
all defaults so it can restore them properly when a setting is set to an empty
string.

Before, when we set the fonts to empty strings instead of the true default, in
some cases anti-aliasing was broken.

Fixes #549.

qutebrowser/config/websettings.py

@@ -22,176 +22,345 @@
 Module attributes:
     ATTRIBUTES: A mapping from internal setting names to QWebSetting enum
                 constants.
-    SETTERS: A mapping from setting names to QWebSetting setter method names.
-    settings: The global QWebSettings singleton instance.
 """
 
 import os.path
 
 from PyQt5.QtWebKit import QWebSettings
-from PyQt5.QtCore import QUrl
 
 from qutebrowser.config import config
-from qutebrowser.utils import usertypes, standarddir, objreg, log
+from qutebrowser.utils import standarddir, objreg, log, utils, debug
 
-MapType = usertypes.enum('MapType', ['attribute', 'setter', 'static_setter'])
+UNSET = object()
+
+
+class Base:
+
+    """Base class for QWebSetting wrappers.
+
+    Attributes:
+        _default: The default value of this setting.
+    """
+
+    def __init__(self):
+        self._default = UNSET
+
+    def _get_qws(self, qws):
+        """Get the QWebSettings object to use.
+
+        Args:
+            qws: The QWebSettings instance to use, or None to use the global
+                 instance.
+        """
+        if qws is None:
+            return QWebSettings.globalSettings()
+        else:
+            return qws
+
+    def save_default(self, qws=None):
+        """Save the default value based on the currently set one.
+
+        This does nothing if no getter is configured for this setting.
+
+        Args:
+            qws: The QWebSettings instance to use, or None to use the global
+                 instance.
+        """
+        try:
+            self._default = self.get(qws)
+        except AttributeError:
+            pass
+
+    def restore_default(self, qws=None):
+        """Restore the default value from the saved one.
+
+        This does nothing if the default has never been set.
+
+        Args:
+            qws: The QWebSettings instance to use, or None to use the global
+                 instance.
+        """
+        if self._default is not UNSET:
+            self._set(self._default, qws=qws)
+
+    def get(self, qws=None):
+        """Get the value of this setting.
+
+        Must be overridden by subclasses.
+
+        Args:
+            qws: The QWebSettings instance to use, or None to use the global
+                 instance.
+        """
+        raise NotImplementedError
+
+    def set(self, value, qws=None):
+        """Set the value of this setting.
+
+        Args:
+            value: The value to set.
+            qws: The QWebSettings instance to use, or None to use the global
+                 instance.
+        """
+        if value is None:
+            self.restore_default(qws)
+        else:
+            self._set(value, qws=qws)
+
+    def _set(self, value, qws):
+        """Inner function to set the value of this setting.
+
+        Must be overridden by subclasses.
+
+        Args:
+            value: The value to set.
+            qws: The QWebSettings instance to use, or None to use the global
+                 instance.
+        """
+        raise NotImplementedError
+
+
+class Attribute(Base):
+
+    """A setting set via QWebSettings::setAttribute.
+
+    Attributes:
+        self._attribute: A QWebSettings::WebAttribute instance.
+    """
+
+    def __init__(self, attribute):
+        super().__init__()
+        self._attribute = attribute
+
+    def __repr__(self):
+        return utils.get_repr(
+            self, attribute=debug.qenum_key(QWebSettings, self._attribute),
+            constructor=True)
+
+    def get(self, qws=None):
+        return self._get_qws(qws).attribute(self._attribute)
+
+    def _set(self, value, qws=None):
+        self._get_qws(qws).setAttribute(self._attribute, value)
+
+
+class Setter(Base):
+
+    """A setting set via QWebSettings getter/setter methods.
+
+    This will pass the QWebSettings instance ("self") as first argument to the
+    methods, so self._getter/self._setter are the *unbound* methods.
+
+    Attributes:
+        _getter: The unbound QWebSettings method to get this value, or None.
+        _setter: The unbound QWebSettings method to set this value.
+        _args: An iterable of the arguments to pass to the setter/getter
+               (before the value, for the setter).
+        _unpack: Whether to unpack args (True) or pass them directly (False).
+    """
+
+    def __init__(self, getter, setter, args=(), unpack=False):
+        super().__init__()
+        self._getter = getter
+        self._setter = setter
+        self._args = args
+        self._unpack = unpack
+
+    def __repr__(self):
+        return utils.get_repr(self, getter=self._getter, setter=self._setter,
+                              args=self._args, unpack=self._unpack,
+                              constructor=True)
+
+    def get(self, qws=None):
+        if self._getter is None:
+            raise AttributeError("No getter set!")
+        return self._getter(self._get_qws(qws), *self._args)
+
+    def _set(self, value, qws=None):
+        args = [self._get_qws(qws)]
+        args.extend(self._args)
+        if self._unpack:
+            args.extend(value)
+        else:
+            args.append(value)
+        self._setter(*args)
+
+
+class NullStringSetter(Setter):
+
+    """A setter for settings requiring a null QString as default.
+
+    This overrides save_default so None is saved for an empty string. This is
+    needed for the CSS media type, because it returns an empty Python string
+    when getting the value, but setting it to the default requires passing None
+    (a null QString) instead of an empty string.
+    """
+
+    def save_default(self, qws=None):
+        try:
+            val = self.get(qws)
+        except AttributeError:
+            pass
+        if val == '':
+            self._set(None, qws=qws)
+        else:
+            self._set(val, qws=qws)
+
+
+class GlobalSetter(Setter):
+
+    """A setting set via static QWebSettings getter/setter methods.
+
+    self._getter/self._setter are the *bound* methods.
+    """
+
+    def get(self, qws=None):
+        if qws is not None:
+            raise ValueError("qws may not be set with GlobalSetters!")
+        if self._getter is None:
+            raise AttributeError("No getter set!")
+        return self._getter(*self._args)
+
+    def _set(self, value, qws=None):
+        if qws is not None:
+            raise ValueError("qws may not be set with GlobalSetters!")
+        args = list(self._args)
+        if self._unpack:
+            args.extend(value)
+        else:
+            args.append(value)
+        self._setter(*args)
 
 
 MAPPINGS = {
     'content': {
         'allow-images':
-            (MapType.attribute, QWebSettings.AutoLoadImages),
+            Attribute(QWebSettings.AutoLoadImages),
         'allow-javascript':
-            (MapType.attribute, QWebSettings.JavascriptEnabled),
+            Attribute(QWebSettings.JavascriptEnabled),
         'javascript-can-open-windows':
-            (MapType.attribute, QWebSettings.JavascriptCanOpenWindows),
+            Attribute(QWebSettings.JavascriptCanOpenWindows),
         'javascript-can-close-windows':
-            (MapType.attribute, QWebSettings.JavascriptCanCloseWindows),
+            Attribute(QWebSettings.JavascriptCanCloseWindows),
         'javascript-can-access-clipboard':
-            (MapType.attribute, QWebSettings.JavascriptCanAccessClipboard),
+            Attribute(QWebSettings.JavascriptCanAccessClipboard),
         #'allow-java':
-        #   (MapType.attribute, QWebSettings.JavaEnabled),
+        #   Attribute(QWebSettings.JavaEnabled),
         'allow-plugins':
-            (MapType.attribute, QWebSettings.PluginsEnabled),
+            Attribute(QWebSettings.PluginsEnabled),
         'local-content-can-access-remote-urls':
-            (MapType.attribute, QWebSettings.LocalContentCanAccessRemoteUrls),
+            Attribute(QWebSettings.LocalContentCanAccessRemoteUrls),
         'local-content-can-access-file-urls':
-            (MapType.attribute, QWebSettings.LocalContentCanAccessFileUrls),
+            Attribute(QWebSettings.LocalContentCanAccessFileUrls),
     },
     'network': {
         'dns-prefetch':
-            (MapType.attribute, QWebSettings.DnsPrefetchEnabled),
+            Attribute(QWebSettings.DnsPrefetchEnabled),
     },
     'input': {
         'spatial-navigation':
-            (MapType.attribute, QWebSettings.SpatialNavigationEnabled),
+            Attribute(QWebSettings.SpatialNavigationEnabled),
         'links-included-in-focus-chain':
-            (MapType.attribute, QWebSettings.LinksIncludedInFocusChain),
+            Attribute(QWebSettings.LinksIncludedInFocusChain),
     },
     'fonts': {
         'web-family-standard':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontFamily,
-             qws.setFontFamily(QWebSettings.StandardFont, v),
+                   setter=QWebSettings.setFontFamily,
-             ""),
+                   args=[QWebSettings.StandardFont]),
         'web-family-fixed':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontFamily,
-             qws.setFontFamily(QWebSettings.FixedFont, v),
+                   setter=QWebSettings.setFontFamily,
-             ""),
+                   args=[QWebSettings.FixedFont]),
         'web-family-serif':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontFamily,
-             qws.setFontFamily(QWebSettings.SerifFont, v),
+                   setter=QWebSettings.setFontFamily,
-             ""),
+                   args=[QWebSettings.SerifFont]),
         'web-family-sans-serif':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontFamily,
-             qws.setFontFamily(QWebSettings.SansSerifFont, v),
+                   setter=QWebSettings.setFontFamily,
-             ""),
+                   args=[QWebSettings.SansSerifFont]),
         'web-family-cursive':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontFamily,
-             qws.setFontFamily(QWebSettings.CursiveFont, v),
+                   setter=QWebSettings.setFontFamily,
-             ""),
+                   args=[QWebSettings.CursiveFont]),
         'web-family-fantasy':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontFamily,
-             qws.setFontFamily(QWebSettings.FantasyFont, v),
+                   setter=QWebSettings.setFontFamily,
-             ""),
+                   args=[QWebSettings.FantasyFont]),
         'web-size-minimum':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontSize,
-             qws.setFontSize(QWebSettings.MinimumFontSize, v)),
+                   setter=QWebSettings.setFontSize,
+                   args=[QWebSettings.MinimumFontSize]),
         'web-size-minimum-logical':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontSize,
-             qws.setFontSize(QWebSettings.MinimumLogicalFontSize, v)),
+                   setter=QWebSettings.setFontSize,
+                   args=[QWebSettings.MinimumLogicalFontSize]),
         'web-size-default':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontSize,
-             qws.setFontSize(QWebSettings.DefaultFontSize, v)),
+                   setter=QWebSettings.setFontSize,
+                   args=[QWebSettings.DefaultFontSize]),
         'web-size-default-fixed':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.fontSize,
-             qws.setFontSize(QWebSettings.DefaultFixedFontSize, v)),
+                   setter=QWebSettings.setFontSize,
+                   args=[QWebSettings.DefaultFixedFontSize]),
     },
     'ui': {
         'zoom-text-only':
-            (MapType.attribute, QWebSettings.ZoomTextOnly),
+            Attribute(QWebSettings.ZoomTextOnly),
         'frame-flattening':
-            (MapType.attribute, QWebSettings.FrameFlatteningEnabled),
+            Attribute(QWebSettings.FrameFlatteningEnabled),
         'user-stylesheet':
-            (MapType.setter, lambda qws, v:
+            Setter(getter=QWebSettings.userStyleSheetUrl,
-             qws.setUserStyleSheetUrl(v),
+                   setter=QWebSettings.setUserStyleSheetUrl),
-             QUrl()),
         'css-media-type':
-            (MapType.setter, lambda qws, v:
+            NullStringSetter(getter=QWebSettings.cssMediaType,
-             qws.setCSSMediaType(v)),
+                             setter=QWebSettings.setCSSMediaType),
         #'accelerated-compositing':
-        #   (MapType.attribute, QWebSettings.AcceleratedCompositingEnabled),
+        #   Attribute(QWebSettings.AcceleratedCompositingEnabled),
         #'tiled-backing-store':
-        #   (MapType.attribute, QWebSettings.TiledBackingStoreEnabled),
+        #   Attribute(QWebSettings.TiledBackingStoreEnabled),
     },
     'storage': {
         'offline-storage-database':
-            (MapType.attribute, QWebSettings.OfflineStorageDatabaseEnabled),
+            Attribute(QWebSettings.OfflineStorageDatabaseEnabled),
         'offline-web-application-storage':
-            (MapType.attribute,
+            Attribute(QWebSettings.OfflineWebApplicationCacheEnabled),
-             QWebSettings.OfflineWebApplicationCacheEnabled),
         'local-storage':
-            (MapType.attribute, QWebSettings.LocalStorageEnabled),
+            Attribute(QWebSettings.LocalStorageEnabled),
         'maximum-pages-in-cache':
-            (MapType.static_setter, lambda v:
+            GlobalSetter(getter=QWebSettings.maximumPagesInCache,
-             QWebSettings.setMaximumPagesInCache(v)),
+                         setter=QWebSettings.setMaximumPagesInCache),
         'object-cache-capacities':
-            (MapType.static_setter, lambda v:
+            GlobalSetter(getter=None,
-             QWebSettings.setObjectCacheCapacities(*v)),
+                         setter=QWebSettings.setObjectCacheCapacities,
+                         unpack=True),
         'offline-storage-default-quota':
-            (MapType.static_setter, lambda v:
+            GlobalSetter(getter=QWebSettings.offlineStorageDefaultQuota,
-             QWebSettings.setOfflineStorageDefaultQuota(v)),
+                         setter=QWebSettings.setOfflineStorageDefaultQuota),
         'offline-web-application-cache-quota':
-            (MapType.static_setter, lambda v:
+            GlobalSetter(
-             QWebSettings.setOfflineWebApplicationCacheQuota(v)),
+                getter=QWebSettings.offlineWebApplicationCacheQuota,
+                setter=QWebSettings.setOfflineWebApplicationCacheQuota),
     },
     'general': {
         'private-browsing':
-            (MapType.attribute, QWebSettings.PrivateBrowsingEnabled),
+            Attribute(QWebSettings.PrivateBrowsingEnabled),
         'developer-extras':
-            (MapType.attribute, QWebSettings.DeveloperExtrasEnabled),
+            Attribute(QWebSettings.DeveloperExtrasEnabled),
         'print-element-backgrounds':
-            (MapType.attribute, QWebSettings.PrintElementBackgrounds),
+            Attribute(QWebSettings.PrintElementBackgrounds),
         'xss-auditing':
-            (MapType.attribute, QWebSettings.XSSAuditingEnabled),
+            Attribute(QWebSettings.XSSAuditingEnabled),
         'site-specific-quirks':
-            (MapType.attribute, QWebSettings.SiteSpecificQuirksEnabled),
+            Attribute(QWebSettings.SiteSpecificQuirksEnabled),
         'default-encoding':
-            (MapType.setter, lambda qws, v: qws.setDefaultTextEncoding(v), ""),
+            Setter(getter=QWebSettings.defaultTextEncoding,
+                   setter=QWebSettings.setDefaultTextEncoding),
     }
 }
 
 
-settings = None
-UNSET = object()
-
-
-def _set_setting(typ, arg, default=UNSET, value=UNSET):
-    """Set a QWebSettings setting.
-
-    Args:
-        typ: The type of the item.
-        arg: The argument (attribute/handler)
-        default: The value to use if the user set an empty string.
-        value: The value to set.
-    """
-    if not isinstance(typ, MapType):
-        raise TypeError("Type {} is no MapType member!".format(typ))
-    if value is UNSET:
-        raise TypeError("No value given!")
-    if value is None:
-        if default is UNSET:
-            return
-        else:
-            value = default
-
-    if typ == MapType.attribute:
-        settings.setAttribute(arg, value)
-    elif typ == MapType.setter:
-        arg(settings, value)
-    elif typ == MapType.static_setter:
-        arg(value)
-
-
 def init():
     """Initialize the global QWebSettings."""
     QWebSettings.setIconDatabasePath(standarddir.cache())
@@ -202,14 +371,13 @@ def init():
     QWebSettings.setOfflineStoragePath(
         os.path.join(standarddir.data(), 'offline-storage'))
 
-    global settings
-    settings = QWebSettings.globalSettings()
     for sectname, section in MAPPINGS.items():
         for optname, mapping in section.items():
+            mapping.save_default()
             value = config.get(sectname, optname)
             log.misc.debug("Setting {} -> {} to {!r}".format(sectname, optname,
                                                              value))
-            _set_setting(*mapping, value=value)
+            mapping.set(value)
     objreg.get('config').changed.connect(update_settings)
 
 
@@ -220,4 +388,4 @@ def update_settings(section, option):
     except KeyError:
         return
     value = config.get(section, option)
-    _set_setting(*mapping, value=value)
+    mapping.set(value)