Improve findfont cache invalidation.

Resolution of fontproperties also depends on the default values of
FontProperties attributes.  This fix is tested by the new
test_fontproperty_default_cache_invalidation.

test_mutable_fontproperty_cache_invalidation is a separate test (which
was already passing before), but also checks a useful property:
mutating a FontProperty instance should invalidate its corresponding
cache.

Author: anntzer

lib/matplotlib/font_manager.py

@@ -1344,9 +1344,11 @@ def findfont(self, prop, fontext='ttf', directory=None,
         # Pass the relevant rcParams (and the font manager, as `self`) to
         # _findfont_cached so to prevent using a stale cache entry after an
         # rcParam was changed.
-        rc_params = tuple(tuple(mpl.rcParams[key]) for key in [
-            "font.serif", "font.sans-serif", "font.cursive", "font.fantasy",
-            "font.monospace"])
+        rc_params = [mpl.rcParams[f"font.{key}"] for key in [
+            "family", "style", "variant", "weight", "stretch", "size",
+            "serif", "sans-serif", "cursive", "fantasy", "monospace"]]
+        rc_params = tuple(tuple(e) if isinstance(e, list) else e
+                          for e in rc_params)  # Make this hashable.
         ret = self._findfont_cached(
             prop, fontext, directory, fallback_to_default, rebuild_if_missing,
             rc_params)

lib/matplotlib/tests/test_font_manager.py

@@ -434,3 +434,17 @@ def test_font_match_warning(caplog):
     findfont(FontProperties(family=["DejaVu Sans"], weight=750))
     logs = [rec.message for rec in caplog.records]
     assert 'findfont: Failed to find font weight 750, now using 700.' in logs
+
+
+def test_mutable_fontproperty_cache_invalidation():
+    fp = FontProperties()
+    assert findfont(fp).endswith("DejaVuSans.ttf")
+    fp.set_weight("bold")
+    assert findfont(fp).endswith("DejaVuSans-Bold.ttf")
+
+
+def test_fontproperty_default_cache_invalidation():
+    mpl.rcParams["font.weight"] = "normal"
+    assert findfont("DejaVu Sans").endswith("DejaVuSans.ttf")
+    mpl.rcParams["font.weight"] = "bold"
+    assert findfont("DejaVu Sans").endswith("DejaVuSans-Bold.ttf")