bpo-45644: Make json.tool read infile before writing to outfile (GH-29273) (GH-29446)

so that

$ python -m json.tool foo.json foo.json

doesn't result in an empty foo.json.

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
(cherry picked from commit 815dad42d53fc40a6dc057e067f4a8a885c3b858)

Co-authored-by: Chris Wesseling <chris.wesseling@protonmail.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/Lib/test/test_json/test_tool.py b/Lib/test/test_json/test_tool.py
index fc2a7a4..d441bb1 100644
--- a/Lib/test/test_json/test_tool.py
+++ b/Lib/test/test_json/test_tool.py
@@ -130,6 +130,15 @@ class TestTool(unittest.TestCase):
         self.assertEqual(out, b'')
         self.assertEqual(err, b'')
 
+    def test_writing_in_place(self):
+        infile = self._create_infile()
+        rc, out, err = assert_python_ok('-m', 'json.tool', infile, infile)
+        with open(infile, "r", encoding="utf-8") as fp:
+            self.assertEqual(fp.read(), self.expect)
+        self.assertEqual(rc, 0)
+        self.assertEqual(out, b'')
+        self.assertEqual(err, b'')
+
     def test_jsonlines(self):
         args = sys.executable, '-m', 'json.tool', '--json-lines'
         process = subprocess.run(args, input=self.jsonlines_raw, capture_output=True, text=True, check=True)