gh-129900: Fix SystemExit return codes when the REPL is started from the command line (#129901)

Lib/test/test_sys.py

@@ -285,6 +285,27 @@ class SysModuleTest(unittest.TestCase):
             r'import sys; sys.exit("h\xe9")',
             b"h\xe9", PYTHONIOENCODING='latin-1')
 
+    @support.requires_subprocess()
+    def test_exit_codes_under_repl(self):
+        # GH-129900: SystemExit, or things that raised it, didn't
+        # get their return code propagated by the REPL
+        import tempfile
+
+        exit_ways = [
+            "exit",
+            "__import__('sys').exit",
+            "raise SystemExit"
+        ]
+
+        for exitfunc in exit_ways:
+            for return_code in (0, 123):
+                with self.subTest(exitfunc=exitfunc, return_code=return_code):
+                    with tempfile.TemporaryFile("w+") as stdin:
+                        stdin.write(f"{exitfunc}({return_code})\n")
+                        stdin.seek(0)
+                        proc = subprocess.run([sys.executable], stdin=stdin)
+                        self.assertEqual(proc.returncode, return_code)
+
     def test_getdefaultencoding(self):
         self.assertRaises(TypeError, sys.getdefaultencoding, 42)
         # can't check more than the type, as the user might have changed it