Move label hiding rectilinear-only check into _label_outer_{x,y}axis.

This allows having it both in subplots() (which had that check before)
and in subplot_mosaic (which didn't, see test).  (All Axes returned by
subplots() have the same projection, so `all(ax.name == "rectilinear")`
can be replaced by independently checking each Axes.)

Also improve the rectilinearity check by testing the shape of the axes
patch instead (so that e.g. skewT also participates in
outer-only-labels), and add an escape hatch so that Axes.label_outer
always does "what it says on, the tin".

Author: anntzer

lib/matplotlib/axes/_subplots.py

@@ -1,3 +1,4 @@
+import matplotlib as mpl
 from matplotlib import _api, cbook
 from matplotlib.axes._axes import Axes
 from matplotlib.gridspec import GridSpec, SubplotSpec
@@ -109,10 +110,13 @@ def label_outer(self):
         labels are on the top side); y-labels only for subplots on the first
         column (or last column, if labels are on the right side).
         """
-        self._label_outer_xaxis()
-        self._label_outer_yaxis()
+        self._label_outer_xaxis(check_patch=False)
+        self._label_outer_yaxis(check_patch=False)
 
-    def _label_outer_xaxis(self):
+    def _label_outer_xaxis(self, *, check_patch):
+        # see documentation in label_outer.
+        if check_patch and not isinstance(self.patch, mpl.patches.Rectangle):
+            return
         ss = self.get_subplotspec()
         label_position = self.xaxis.get_label_position()
         if not ss.is_first_row():  # Remove top label/ticklabels/offsettext.
@@ -128,7 +132,10 @@ def _label_outer_xaxis(self):
             if self.xaxis.offsetText.get_position()[1] == 0:
                 self.xaxis.offsetText.set_visible(False)
 
-    def _label_outer_yaxis(self):
+    def _label_outer_yaxis(self, *, check_patch):
+        # see documentation in label_outer.
+        if check_patch and not isinstance(self.patch, mpl.patches.Rectangle):
+            return
         ss = self.get_subplotspec()
         label_position = self.yaxis.get_label_position()
         if not ss.is_first_col():  # Remove left label/ticklabels/offsettext.

lib/matplotlib/figure.py

@@ -1910,10 +1910,10 @@ def _do_layout(gs, mosaic, unique_ids, nested):
         for ax in ret.values():
             if sharex:
                 ax.sharex(ax0)
-                ax._label_outer_xaxis()
+                ax._label_outer_xaxis(check_patch=True)
             if sharey:
                 ax.sharey(ax0)
-                ax._label_outer_yaxis()
+                ax._label_outer_yaxis(check_patch=True)
         for k, ax in ret.items():
             if isinstance(k, str):
                 ax.set_label(k)

lib/matplotlib/gridspec.py

@@ -306,13 +306,12 @@ def subplots(self, *, sharex=False, sharey=False, squeeze=True,
                     self[row, col], **subplot_kw)
 
         # turn off redundant tick labeling
-        if all(ax.name == "rectilinear" for ax in axarr.flat):
-            if sharex in ["col", "all"]:
-                for ax in axarr.flat:
-                    ax._label_outer_xaxis()
-            if sharey in ["row", "all"]:
-                for ax in axarr.flat:
-                    ax._label_outer_yaxis()
+        if sharex in ["col", "all"]:
+            for ax in axarr.flat:
+                ax._label_outer_xaxis(check_patch=True)
+        if sharey in ["row", "all"]:
+            for ax in axarr.flat:
+                ax._label_outer_yaxis(check_patch=True)
 
         if squeeze:
             # Discarding unneeded dimensions that equal 1.  If we only have one

lib/matplotlib/tests/test_polar.py

@@ -396,10 +396,15 @@ def test_remove_shared_polar(fig_ref, fig_test):
 
 def test_shared_polar_keeps_ticklabels():
     fig, axs = plt.subplots(
-        2, 2, subplot_kw=dict(projection="polar"), sharex=True, sharey=True)
+        2, 2, subplot_kw={"projection": "polar"}, sharex=True, sharey=True)
     fig.canvas.draw()
     assert axs[0, 1].xaxis.majorTicks[0].get_visible()
     assert axs[0, 1].yaxis.majorTicks[0].get_visible()
+    fig, axs = plt.subplot_mosaic(
+        "ab\ncd", subplot_kw={"projection": "polar"}, sharex=True, sharey=True)
+    fig.canvas.draw()
+    assert axs["b"].xaxis.majorTicks[0].get_visible()
+    assert axs["b"].yaxis.majorTicks[0].get_visible()
 
 
 def test_axvline_axvspan_do_not_modify_rlims():