API: re-allow 'datalim' as a valid adjustable with shared axes

This is to allow twinx and twiny to work as expected.
matplotlib · efiring · Jun 12, 2017 · Jun 13, 2017 · Jun 15, 2017 · Jun 15, 2017
commit 7dba6868b10a722b37f7ba0d1fc119d9b8a233de
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -438,7 +438,7 @@ def __init__(self, fig, rect,
          ================   =========================================
          Keyword            Description
          ================   =========================================
-          *adjustable*       [ 'box' | 'datalim' | 'box-forced']
+          *adjustable*       [ 'box' | 'datalim' ]
          *alpha*            float: the alpha transparency (can be None)
          *anchor*           [ 'C', 'SW', 'S', 'SE', 'E', 'NE', 'N',
                               'NW', 'W' ]
@@ -1286,10 +1286,6 @@ def set_adjustable(self, adjustable, share=False):
        """
        # FIXME: add box-forced deprecation
        if adjustable in ('box', 'datalim', 'box-forced'):
-            if self in self._shared_x_axes and self in self._shared_y_axes:
-                if adjustable == 'datalim':
-                    raise ValueError(
-                        'adjustable must be "box" when both axes are shared')
            if share and self in self._shared_x_axes:
                for ax in self._shared_x_axes.get_siblings(self):
                    ax._adjustable = adjustable
@@ -3916,6 +3912,9 @@ def _make_twin_axes(self, *kl, **kwargs):
        make a twinx axes of self. This is used for twinx and twiny.
        """
        ax2 = self.figure.add_axes(self.get_position(True), *kl, **kwargs)
+        # do not touch every thing shared, just this and it's twin.
+        self.set_adjustable('datalim')
+        ax2.set_adjustable('datalim')
        return ax2

    def twinx(self):

diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -4240,8 +4240,6 @@ def test_shared_with_aspect():
    plt.draw()  # Trigger apply_aspect().
    assert axes[0].get_xlim() == axes[1].get_xlim()
    assert axes[0].get_ylim() == axes[1].get_ylim()
-    with pytest.raises(ValueError):
-        axes[0].set_aspect(1, adjustable='datalim', share=True)

    # Different aspect ratios:
    for adjustable in ['box', 'datalim']:
@@ -4262,6 +4260,17 @@ def test_shared_with_aspect():
            assert round(expected, 4) == round(ax.get_aspect(), 4)


+@pytest.mark.parametrize('twin', ('x', 'y'))
+def test_twin_with_aspect(twin):
+    fig, ax = plt.subplots()
+    # test twinx or twiny
+    ax_twin = getattr(ax, 'twin{}'.format(twin))()
+    ax.set_aspect(5)
+    ax_twin.set_aspect(2)
+    assert_array_equal(ax.bbox.extents,
+                       ax_twin.bbox.extents)
+
+
 def test_relim_visible_only():
    x1 = (0., 10.)
    y1 = (0., 10.)