Minor joinplot user-friendliness

- Warn/ignore when `ax` is passed as kwarg (closes #2666)
- Set the joint axes to be active (closes #2511)

seaborn/axisgrid.py

@@ -2137,12 +2137,9 @@ def jointplot(
     from .regression import regplot, residplot
     from .distributions import histplot, kdeplot, _freedman_diaconis_bins
 
-    # Handle deprecations
-    if "size" in kwargs:
-        height = kwargs.pop("size")
-        msg = ("The `size` parameter has been renamed to `height`; "
-               "please update your code.")
-        warnings.warn(msg, UserWarning)
+    if kwargs.pop("ax", None) is not None:
+        msg = "Ignoring `ax`; jointplot is a figure-level function."
+        warnings.warn(msg, UserWarning, stacklevel=2)
 
     # Set up empty default kwarg dicts
     joint_kws = {} if joint_kws is None else joint_kws.copy()
@@ -2285,6 +2282,9 @@ def jointplot(
         histplot(x=x, hue=hue, ax=grid.ax_marg_x, **marginal_kws)
         histplot(y=y, hue=hue, ax=grid.ax_marg_y, **marginal_kws)
 
+    # Make the main axes active in the matplotlib state machine
+    plt.sca(grid.ax_joint)
+
     return grid
 
 

tests/test_axisgrid.py

@@ -1788,4 +1788,11 @@ def test_distplot_kwarg_warning(self, long_df):
 
         with pytest.warns(UserWarning):
             g = ag.jointplot(data=long_df, x="x", y="y", marginal_kws=dict(rug=True))
-            assert g.ax_marg_x.patches
+        assert g.ax_marg_x.patches
+
+    def test_ax_warning(self, long_df):
+
+        ax = plt.gca()
+        with pytest.warns(UserWarning):
+            g = ag.jointplot(data=long_df, x="x", y="y", ax=ax)
+        assert g.ax_joint.collections