Move getting default system font to configutils

For easier testability, as a preparation for #5663.

2 files changed, 56 insertions, 42 deletions

diff --git a/qutebrowser/config/configtypes.py b/qutebrowser/config/configtypes.py
index 0b4ed4d3b..6328c3140 100644
--- a/qutebrowser/config/configtypes.py
+++ b/qutebrowser/config/configtypes.py
@@ -56,8 +56,8 @@ from typing import (Any, Callable, Dict as DictType, Iterable, Iterator,
 import attr
 import yaml
 from PyQt5.QtCore import QUrl, Qt
-from PyQt5.QtGui import QColor, QFontDatabase
-from PyQt5.QtWidgets import QTabWidget, QTabBar, QApplication
+from PyQt5.QtGui import QColor
+from PyQt5.QtWidgets import QTabWidget, QTabBar
 from PyQt5.QtNetwork import QNetworkProxy
 
 from qutebrowser.misc import objects, debugcachestats
@@ -1159,50 +1159,11 @@ class FontBase(BaseType):
 
         If the given family value (fonts.default_family in the config) is
         unset, a system-specific default monospace font is used.
-
-        Note that (at least) three ways of getting the default monospace font
-        exist:
-
-        1) f = QFont()
-           f.setStyleHint(QFont.Monospace)
-           print(f.defaultFamily())
-
-        2) f = QFont()
-           f.setStyleHint(QFont.TypeWriter)
-           print(f.defaultFamily())
-
-        3) f = QFontDatabase.systemFont(QFontDatabase.FixedFont)
-           print(f.family())
-
-        They yield different results depending on the OS:
-
-                   QFont.Monospace  | QFont.TypeWriter    | QFontDatabase
-                   ------------------------------------------------------
-        Windows:   Courier New      | Courier New         | Courier New
-        Linux:     DejaVu Sans Mono | DejaVu Sans Mono    | monospace
-        macOS:     Menlo            | American Typewriter | Monaco
-
-        Test script: https://p.cmpl.cc/d4dfe573
-
-        On Linux, it seems like both actually resolve to the same font.
-
-        On macOS, "American Typewriter" looks like it indeed tries to imitate a
-        typewriter, so it's not really a suitable UI font.
-
-        Looking at those Wikipedia articles:
-
-        https://en.wikipedia.org/wiki/Monaco_(typeface)
-        https://en.wikipedia.org/wiki/Menlo_(typeface)
-
-        the "right" choice isn't really obvious. Thus, let's go for the
-        QFontDatabase approach here, since it's by far the simplest one.
         """
         if default_family:
             families = configutils.FontFamilies(default_family)
         else:
-            assert QApplication.instance() is not None
-            font = QFontDatabase.systemFont(QFontDatabase.FixedFont)
-            families = configutils.FontFamilies([font.family()])
+            families = configutils.FontFamilies.from_system_default()
 
         cls.default_family = families.to_str(quote=True)
         cls.default_size = default_size
diff --git a/qutebrowser/config/configutils.py b/qutebrowser/config/configutils.py
index 1d98db3e7..b4eb004c2 100644
--- a/qutebrowser/config/configutils.py
+++ b/qutebrowser/config/configutils.py
@@ -29,6 +29,8 @@ from typing import (
     MutableMapping)
 
 from PyQt5.QtCore import QUrl
+from PyQt5.QtGui import QFontDatabase
+from PyQt5.QtWidgets import QApplication
 
 from qutebrowser.utils import utils, urlmatch, usertypes, qtutils
 from qutebrowser.config import configexc
@@ -296,6 +298,57 @@ class FontFamilies:
         return ', '.join(families)
 
     @classmethod
+    def from_system_default(
+            cls,
+            font_type: QFontDatabase.SystemFont = QFontDatabase.FixedFont,
+    ) -> 'FontFamilies':
+        """Get a FontFamilies object for the default system font.
+
+        By default, the monospace font is returned, though via the "font_type" argument,
+        other types can be requested as well.
+
+        Note that (at least) three ways of getting the default monospace font
+        exist:
+
+        1) f = QFont()
+           f.setStyleHint(QFont.Monospace)
+           print(f.defaultFamily())
+
+        2) f = QFont()
+           f.setStyleHint(QFont.TypeWriter)
+           print(f.defaultFamily())
+
+        3) f = QFontDatabase.systemFont(QFontDatabase.FixedFont)
+           print(f.family())
+
+        They yield different results depending on the OS:
+
+                   QFont.Monospace  | QFont.TypeWriter    | QFontDatabase
+                   ------------------------------------------------------
+        Windows:   Courier New      | Courier New         | Courier New
+        Linux:     DejaVu Sans Mono | DejaVu Sans Mono    | monospace
+        macOS:     Menlo            | American Typewriter | Monaco
+
+        Test script: https://p.cmpl.cc/d4dfe573
+
+        On Linux, it seems like both actually resolve to the same font.
+
+        On macOS, "American Typewriter" looks like it indeed tries to imitate a
+        typewriter, so it's not really a suitable UI font.
+
+        Looking at those Wikipedia articles:
+
+        https://en.wikipedia.org/wiki/Monaco_(typeface)
+        https://en.wikipedia.org/wiki/Menlo_(typeface)
+
+        the "right" choice isn't really obvious. Thus, let's go for the
+        QFontDatabase approach here, since it's by far the simplest one.
+        """
+        assert QApplication.instance() is not None
+        font = QFontDatabase.systemFont(font_type)
+        return cls([font.family()])
+
+    @classmethod
     def from_str(cls, family_str: str) -> 'FontFamilies':
         """Parse a CSS-like string of font families."""
         families = []