MNT: raise when silently dropping user input

tacaswell · tacaswell · commit 629592928d46 · 2020-02-29T19:28:56.000-05:00
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -2754,6 +2754,9 @@ def add_gridspec(self, nrows, ncols, **kwargs):
         """
 
         _ = kwargs.pop('figure', None)  # pop in case user has added this...
+        if _ and _ is not self:
+            raise ValueError(f"you passed the figure {_} which is going to"
+                             "be over-ridden by this method with self")
         gs = GridSpec(nrows=nrows, ncols=ncols, figure=self, **kwargs)
         self._gridspecs.append(gs)
         return gs
