fix(layout): order strip before axis title; keep tick styling on spine offset

For strip_placement=outside the strip now clears only the axis ticks and
labels, sitting before the axis title rather than beyond it; the title
shifts out past the strip. The shared band is ordered ticks+labels, strip,
title from the panel outward.

The moved axis is shifted by repositioning its spine outward. This avoids
Spine.set_position's axis.reset_ticks(), which regenerates the ticks and
drops the theme's per-tick styling (tick label colour and font, blanked
minor marks). Instead the existing tick marks are re-pointed at the moved
spine transform; the labels are positioned by the layout.

Author: has2k1

plotnine/_mpl/layout_manager/_plot_layout_items.py

@@ -29,10 +29,11 @@
     )
 
     from matplotlib.axes import Axes
-    from matplotlib.axis import Tick
+    from matplotlib.axis import Axis, Tick
     from matplotlib.figure import Figure
     from matplotlib.lines import Line2D
     from matplotlib.patches import Rectangle
+    from matplotlib.spines import Spine
     from matplotlib.transforms import Bbox, Transform
 
     from plotnine import ggplot
@@ -508,7 +509,7 @@ def _move_artists(self, spaces: PlotSideSpaces):
 
         if self.axis_title_x_top:
             ha = theme.getp(("axis_title_x_top", "ha"), "center")
-            offset = spaces.t.strip_band_offset("axis")
+            offset = spaces.t.strip_band_offset("title")
             self.axis_title_x_top.set_y(spaces.t.y1("axis_title_x") + offset)
             justify.horizontally_about(self.axis_title_x_top, ha, "panel")
 
@@ -519,7 +520,7 @@ def _move_artists(self, spaces: PlotSideSpaces):
 
         if self.axis_title_y_right:
             va = theme.getp(("axis_title_y_right", "va"), "center")
-            offset = spaces.r.strip_band_offset("axis")
+            offset = spaces.r.strip_band_offset("title")
             self.axis_title_y_right.set_x(spaces.r.x1("axis_title_y") + offset)
             justify.vertically_about(self.axis_title_y_right, va, "panel")
 
@@ -662,9 +663,11 @@ def _place_moved_axes(self, spaces: PlotSideSpaces):
         right = spaces.r.strip_band_offset("axis") * fig.bbox.width * to_points
         for ax in self.plot.axs:
             if top:
-                ax.spines["top"].set_position(("outward", top))
+                _spine_set_position_outward(ax.spines["top"], ax.xaxis, top)
             if right:
-                ax.spines["right"].set_position(("outward", right))
+                _spine_set_position_outward(
+                    ax.spines["right"], ax.yaxis, right
+                )
 
     def _strip_breadth_scales(
         self, group: list[StripText], breadth: Literal["height", "width"]
@@ -788,6 +791,26 @@ def _place_strip_text(self, st: StripText):
         st.set_position((x, y))
 
 
+def _spine_set_position_outward(spine: Spine, axis: Axis, distance: float):
+    """
+    Move a spine and its tick marks outward, keeping the theme's tick styling
+
+    This mirrors `Spine.set_position(("outward", distance))` but skips its
+    `axis.reset_ticks()`, which would regenerate the ticks and drop the
+    per-tick styling the theme applied (tick label colour and font, blanked
+    minor tick marks, ...). The reset is avoided by re-pointing the existing
+    tick marks at the moved spine's transform; the tick labels are
+    positioned separately by the layout.
+    """
+    spine._position = ("outward", distance)  # pyright: ignore[reportAttributeAccessIssue]
+    transform = spine.get_spine_transform()
+    spine.set_transform(transform)
+    # The outward-facing marks on a top or right spine are tick2.
+    for tick in (*axis.get_major_ticks(), *axis.get_minor_ticks()):
+        tick.tick2line.set_transform(transform)
+    spine.stale = True
+
+
 def _text_is_visible(text: Text) -> bool:
     """
     Return True if text is visible and is not empty

plotnine/_mpl/layout_manager/_plot_side_space.py

@@ -152,34 +152,43 @@ def _strip_band_extent(self) -> float:
         return 0
 
     @property
-    def _axis_group_extent(self) -> float:
+    def _axis_primary_extent(self) -> float:
         """
-        Outward extent of a moved axis on this side, figure space
+        Outward extent of a moved axis's ticks and tick labels, figure space
 
-        The block is the axis ticks, text and title together. Zero on
-        sides whose axis is in its default position.
+        This is the part of a moved axis that sits next to the panel; the
+        axis title is excluded. Zero on sides whose axis is in its default
+        position.
         """
         return 0
 
-    def strip_band_offset(self, member: Literal["strip", "axis"]) -> float:
+    def strip_band_offset(
+        self, member: Literal["strip", "axis", "title"]
+    ) -> float:
         """
         Outward offset for one member of a shared strip/axis band
 
-        When a moved axis and a facet strip occupy the same side, one of
-        them shifts outward so they do not overlap. `strip_placement`
-        decides which: `"inside"` keeps the strip against the panel and
-        shifts the axis; `"outside"` keeps the axis against the panel and
-        shifts the strip. The offset is zero when the side has no such
-        collision.
+        When a moved axis and a facet strip occupy the same side, the band
+        is ordered, from the panel outward, as the axis ticks and labels,
+        the strip, and the axis title. `strip_placement` decides whether
+        the strip comes before or after the ticks and labels:
+
+        - `"inside"`: panel, strip, ticks and labels, title.
+        - `"outside"`: panel, ticks and labels, strip, title.
+
+        `member` is `"strip"`, `"axis"` (the ticks and labels) or
+        `"title"`. The offset is zero when the side has no such collision.
         """
         strip = self._strip_band_extent
-        axis = self._axis_group_extent
-        if not (strip and axis):
+        primary = self._axis_primary_extent
+        if not (strip and primary):
             return 0
         placement = self.items.plot.theme.getp("strip_placement")
         if placement == "inside":
-            return strip if member == "axis" else 0
-        return axis if member == "strip" else 0
+            return 0 if member == "strip" else strip
+        if member == "axis":
+            return 0
+        return primary if member == "strip" else strip
 
 
 class left_space(_plot_side_space):
@@ -427,8 +436,8 @@ def _strip_band_extent(self) -> float:
         return self.strip_text_y_extra_width
 
     @property
-    def _axis_group_extent(self) -> float:
-        return self.sum_incl("axis_ticks_y") - self.sum_upto("axis_title_y")
+    def _axis_primary_extent(self) -> float:
+        return self.sum_incl("axis_ticks_y") - self.sum_upto("axis_text_y")
 
     @property
     def offset(self):
@@ -583,8 +592,8 @@ def _strip_band_extent(self) -> float:
         return self.strip_text_x_extra_height
 
     @property
-    def _axis_group_extent(self) -> float:
-        return self.sum_incl("axis_ticks_x") - self.sum_upto("axis_title_x")
+    def _axis_primary_extent(self) -> float:
+        return self.sum_incl("axis_ticks_x") - self.sum_upto("axis_text_x")
 
     @property
     def offset(self) -> float: