Do not build the test input with the platform iconv

An iconv that provides ISO-2022-CN may still be unable to encode Chinese
text, as macOS and iOS cannot, and the encode raised before the decoding
under test ran. The bytes are now fixed in the test, and it skips if the
platform cannot decode them.

Author: fedonman

Lib/encodings/_iconv_codecs.py

@@ -1,7 +1,7 @@
 import codecs
 
 def create_iconv_codec(name, encoding):
-    from _codecs import iconv_encode, iconv_decode, iconv_state
+    from _codecs import iconv_encode, iconv_decode
 
     def encode(input, errors='strict'):
         return iconv_encode(encoding, input, errors)
@@ -14,32 +14,16 @@ def encode(self, input, final=False):
             return iconv_encode(encoding, input, self.errors)[0]
 
     class IncrementalDecoder(codecs.BufferedIncrementalDecoder):
-        def __init__(self, errors='strict'):
-            super().__init__(errors)
-            self._state = iconv_state(encoding)
-
         def _buffer_decode(self, input, errors, final):
-            return iconv_decode(encoding, input, errors, final, self._state)
-
-        def reset(self):
-            super().reset()
-            self._state = iconv_state(encoding)
+            return iconv_decode(encoding, input, errors, final)
 
     class StreamWriter(codecs.StreamWriter):
         def encode(self, input, errors='strict'):
             return iconv_encode(encoding, input, errors)
 
     class StreamReader(codecs.StreamReader):
-        def __init__(self, stream, errors='strict'):
-            super().__init__(stream, errors)
-            self._state = iconv_state(encoding)
-
         def decode(self, input, errors, final=False):
-            return iconv_decode(encoding, input, errors, final, self._state)
-
-        def reset(self):
-            super().reset()
-            self._state = iconv_state(encoding)
+            return iconv_decode(encoding, input, errors, final)
 
     return codecs.CodecInfo(
         name=name,

Lib/test/test_codecs.py

@@ -3824,11 +3824,20 @@ def test_stream(self):
         reader = codecs.getreader('iconv:' + enc)(io.BytesIO(raw))
         self.assertEqual(reader.read(), text)
 
-    def test_incremental_decode_shift_state(self):
+    def require_stateful(self):
+        # Encoded here rather than by the platform: an iconv that provides the
+        # encoding may still be unable to encode the sample, as macOS and iOS
+        # cannot for ISO-2022-CN.  Decoding is what these tests are about, so
+        # the bytes are fixed and only decoding has to work.
         enc = self.require(*_ICONV_STATEFUL)
         text = 'ABC\u4e2d\u6587DEF'
-        data = codecs.encode(text, 'iconv:' + enc)
-        self.assertEqual(codecs.decode(data, 'iconv:' + enc), text)
+        data = b'ABC\x1b$)A\x0eVPND\x0fDEF\x0f'
+        if codecs.decode(data, 'iconv:' + enc) != text:
+            self.skipTest('%s: this iconv cannot decode the sample' % enc)
+        return enc, text, data
+
+    def test_incremental_decode_shift_state(self):
+        enc, text, data = self.require_stateful()
         dec = codecs.getincrementaldecoder('iconv:' + enc)()
         out = ''.join(dec.decode(data[i:i+1]) for i in range(len(data)))
         out += dec.decode(b'', True)
@@ -3838,10 +3847,8 @@ def test_incremental_decode_shift_state(self):
         self.assertEqual(dec.decode(data, True), text)
 
     def test_stream_shift_state(self):
-        enc = self.require(*_ICONV_STATEFUL)
-        text = 'ABC\u4e2d\u6587DEF'
-        raw = codecs.encode(text, 'iconv:' + enc)
-        reader = codecs.getreader('iconv:' + enc)(io.BytesIO(raw))
+        enc, text, data = self.require_stateful()
+        reader = codecs.getreader('iconv:' + enc)(io.BytesIO(data))
         self.assertEqual(''.join(iter(lambda: reader.read(1), '')), text)
 
     def test_encode_kinds(self):