Fix InsideStrokedRectangle to inset stroke under any transform

plotnine/_mpl/patches.py

@@ -111,16 +111,41 @@ def draw(self, renderer):
 
 class InsideStrokedRectangle(Rectangle):
     """
-    A rectangle whose stroked is fully contained within it
+    A rectangle whose stroke is fully contained within it
     """
 
     @artist.allow_rasterization
     def draw(self, renderer):
         """
-        Draw with the bounds of the rectangle adjusted to contain the stroke
+        Draw stroking at 2·lw and clipping to the rectangle's own boundary
+
+        The outer half of the stroke is removed by the clip, leaving exactly
+        `lw` of stroke fully inside the rectangle, with the visible outer edge
+        of the stroke on the original boundary. This is transform-agnostic
+        (works under data, axes, identity, and DrawingArea transforms) and
+        idempotent across redraws.
         """
-        x, y = self.xy
-        w, h = self.get_width(), self.get_height()
         lw = self.get_linewidth()
-        self.set_bounds((x + lw / 2), (y + lw / 2), (w - lw), (h - lw))
-        super().draw(renderer)
+        if lw <= 0:
+            return super().draw(renderer)
+
+        saved_clip_path = self.get_clip_path()
+        saved_clip_on = self.get_clip_on()
+
+        # Dash lengths track the linewidth: matplotlib stores the dash
+        # pattern as multipliers and scales them whenever set_linewidth is
+        # called. Doubling lw below would therefore stretch the dashes 2x.
+        # Snapshot the pattern at the user's lw now and write it back after
+        # the doubling so the dashes render at their requested length.
+        original_dash_pattern = self._dash_pattern
+        try:
+            self.set_linewidth(2 * lw)
+            self._dash_pattern = original_dash_pattern
+            self.set_clip_path(self.get_path(), self.get_transform())
+            self.set_clip_on(True)
+            self.set_snap(False)
+            super().draw(renderer)
+        finally:
+            self.set_linewidth(lw)
+            self.set_clip_path(saved_clip_path)
+            self.set_clip_on(saved_clip_on)