Deprecate evaluating Python 2 syntax in configuration files

tests/test_util_pycompat.py

@@ -0,0 +1,43 @@
+# -*- coding: utf-8 -*-
+"""
+    test_util_pycompat
+    ~~~~~~~~~~~~~~~~~~
+
+    Tests sphinx.util.pycompat functions.
+
+    :copyright: Copyright 2007-2018 by the Sphinx team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+
+import tempfile
+
+from sphinx.testing.util import strip_escseq
+from sphinx.util import logging
+from sphinx.util.pycompat import execfile_
+
+
+def test_execfile_python2(capsys, app, status, warning):
+    logging.setup(app, status, warning)
+
+    ns = {}
+    with tempfile.NamedTemporaryFile() as tmp:
+        tmp.write(b'print "hello"\n')
+        tmp.flush()
+        execfile_(tmp.name, ns)
+    msg = (
+        'Support for evaluating Python 2 syntax is deprecated '
+        'and will be removed in Sphinx 4.0. '
+        'Convert %s to Python 3 syntax.\n' % tmp.name)
+    assert msg in strip_escseq(warning.getvalue())
+    captured = capsys.readouterr()
+    assert captured.out == 'hello\n'
+
+
+def test_execfile(capsys):
+    ns = {}
+    with tempfile.NamedTemporaryFile() as tmp:
+        tmp.write(b'print("hello")\n')
+        tmp.flush()
+        execfile_(tmp.name, ns)
+    captured = capsys.readouterr()
+    assert captured.out == 'hello\n'