Fix ordering of tex font usepackages.

anntzer · anntzer · commit e77bd0b7384e · 2021-05-21T11:26:51.000+02:00
Sets do not maintain insertion order even with recent pythons (try e.g.
`for _ in $(seq 10); do python -c 'print({"a", "b"})'; done`), but we
have `cbook._OrderedSet` for that.

Keeping usepackage order can matter for caching purposes.
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook/__init__.py
@@ -2014,8 +2014,9 @@ def _setattr_cm(obj, **kwargs):
 
 
 class _OrderedSet(collections.abc.MutableSet):
-    def __init__(self):
+    def __init__(self, iterable=()):
         self._od = collections.OrderedDict()
+        self |= iterable
 
     def __contains__(self, key):
         return key in self._od
diff --git a/lib/matplotlib/texmanager.py b/lib/matplotlib/texmanager.py
@@ -110,8 +110,9 @@ def get_font_config(self):
 
         # The following packages and commands need to be included in the latex
         # file's preamble:
-        cmd = {fonts[family][1]
-               for family in ['serif', 'sans-serif', 'monospace']}
+        cmd = cbook._OrderedSet(
+            fonts[family][1]
+            for family in ['serif', 'sans-serif', 'monospace'])
         if self.font_family == 'cursive':
             cmd.add(fonts['cursive'][1])
         cmd.add(r'\usepackage{type1cm}')
