bpo-37388: Development mode check encoding and errors (GH-14341)

In development mode and in debug build, encoding and errors arguments
are now checked on string encoding and decoding operations. Examples:
open(), str.encode() and bytes.decode().

By default, for best performances, the errors argument is only
checked at the first encoding/decoding error, and the encoding
argument is sometimes ignored for empty strings.

Lib/test/test_io.py

@@ -29,6 +29,7 @@ import random
 import signal
 import sys
 import sysconfig
+import textwrap
 import threading
 import time
 import unittest
@@ -37,7 +38,8 @@ import weakref
 from collections import deque, UserList
 from itertools import cycle, count
 from test import support
-from test.support.script_helper import assert_python_ok, run_python_until_end
+from test.support.script_helper import (
+    assert_python_ok, assert_python_failure, run_python_until_end)
 from test.support import FakePath
 
 import codecs
@@ -4130,6 +4132,51 @@ class MiscIOTest(unittest.TestCase):
         # there used to be a buffer overflow in the parser for rawmode
         self.assertRaises(ValueError, self.open, support.TESTFN, 'rwax+')
 
+    def test_check_encoding_errors(self):
+        # bpo-37388: open() and TextIOWrapper must check encoding and errors
+        # arguments in dev mode
+        mod = self.io.__name__
+        filename = __file__
+        invalid = 'Boom, Shaka Laka, Boom!'
+        code = textwrap.dedent(f'''
+            import sys
+            from {mod} import open, TextIOWrapper
+
+            try:
+                open({filename!r}, encoding={invalid!r})
+            except LookupError:
+                pass
+            else:
+                sys.exit(21)
+
+            try:
+                open({filename!r}, errors={invalid!r})
+            except LookupError:
+                pass
+            else:
+                sys.exit(22)
+
+            fp = open({filename!r}, "rb")
+            with fp:
+                try:
+                    TextIOWrapper(fp, encoding={invalid!r})
+                except LookupError:
+                    pass
+                else:
+                    sys.exit(23)
+
+                try:
+                    TextIOWrapper(fp, errors={invalid!r})
+                except LookupError:
+                    pass
+                else:
+                    sys.exit(24)
+
+            sys.exit(10)
+        ''')
+        proc = assert_python_failure('-X', 'dev', '-c', code)
+        self.assertEqual(proc.rc, 10, proc)
+
 
 class CMiscIOTest(MiscIOTest):
     io = io