Suppress the "non-GUI backend" warning from the .. plot:: directive...

anntzer · anntzer · commit 13239b56c931 · 2018-08-25T10:34:16.000+02:00
... when the example file contains a call to `show()` (the
examples are always run with the agg backend).  To do so, patch
FigureManagerBase.show to be a no-op when running the example.

Also modified a test to check for this behavior.
diff --git a/lib/matplotlib/sphinxext/plot_directive.py b/lib/matplotlib/sphinxext/plot_directive.py
@@ -156,6 +156,7 @@
 import jinja2  # Sphinx dependency.
 
 import matplotlib
+from matplotlib.backend_bases import FigureManagerBase
 try:
     with warnings.catch_warnings(record=True):
         warnings.simplefilter("error", UserWarning)
@@ -491,9 +492,13 @@ def run_code(code, code_path, ns=None, function_name=None):
                     exec(str(setup.config.plot_pre_code), ns)
             if "__main__" in code:
                 ns['__name__'] = '__main__'
-            exec(code, ns)
-            if function_name is not None:
-                exec(function_name + "()", ns)
+
+            # Patch out non-interactive show() to avoid triggering a warning.
+            with cbook._setattr_cm(FigureManagerBase, show=lambda self: None):
+                exec(code, ns)
+                if function_name is not None:
+                    exec(function_name + "()", ns)
+
         except (Exception, SystemExit) as err:
             raise PlotError(traceback.format_exc())
         finally:
diff --git a/lib/matplotlib/sphinxext/tests/test_tinypages.py b/lib/matplotlib/sphinxext/tests/test_tinypages.py
@@ -19,11 +19,13 @@ def test_tinypages(tmpdir):
     # Build the pages with warnings turned into errors
     cmd = [sys.executable, '-msphinx', '-W', '-b', 'html', '-d', doctree_dir,
            pjoin(dirname(__file__), 'tinypages'), html_dir]
-    proc = Popen(cmd, stdout=PIPE, stderr=PIPE)
+    proc = Popen(cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True)
     out, err = proc.communicate()
     assert proc.returncode == 0, \
-        "'{} -msphinx' failed with stdout:\n{}\nstderr:\n{}\n".format(
-            sys.executable, out, err)
+        "sphinx build failed with stdout:\n{}\nstderr:\n{}\n".format(out, err)
+    if err:
+        pytest.fail("sphinx build emitted the following warnings:\n{}"
+                    .format(err))
 
     assert isdir(html_dir)
 
