Fix inset locator renderer fallback (swev-id: matplotlib__matplotlib-26291)

lib/mpl_toolkits/axes_grid1/inset_locator.py

@@ -69,6 +69,8 @@ def draw(self, renderer):
         raise RuntimeError("No draw method should be called")
 
     def __call__(self, ax, renderer):
+        if renderer is None:
+            renderer = ax.figure._get_renderer()
         self.axes = ax
         bbox = self.get_window_extent(renderer)
         px, py = self.get_offset(bbox.width, bbox.height, 0, 0, renderer)

lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py

@@ -1,3 +1,4 @@
+from io import BytesIO
 from itertools import product
 import platform
 
@@ -119,6 +120,17 @@ def test_inset_colorbar_tight_layout_smoketest():
         plt.tight_layout()
 
 
+def test_inset_axes_tight_bbox_smoketest():
+    fig, (ax, ax2) = plt.subplots(1, 2, figsize=(5.5, 2.8))
+    try:
+        inset_axes(ax, width=1.3, height=0.9)
+        buffer = BytesIO()
+        fig.savefig(buffer, format="png", bbox_inches="tight")
+        assert buffer.getbuffer().nbytes > 0
+    finally:
+        plt.close(fig)
+
+
 @image_comparison(['inset_locator.png'], style='default', remove_text=True)
 def test_inset_locator():
     fig, ax = plt.subplots(figsize=[5, 4])