bpo-35062: Fix parsing _io.IncrementalNewlineDecoder's *translate* argument. (GH-10217)

_io.IncrementalNewlineDecoder's initializer possibly assigns out-of-range
value to the bitwise struct field.
(cherry picked from commit b08746b)

Co-authored-by: Xiang Zhang <[email protected]>

Author: miss-islington

Lib/test/test_io.py

@@ -3547,6 +3547,16 @@ def _check(dec):
         dec = self.IncrementalNewlineDecoder(None, translate=True)
         _check(dec)
 
+    def test_translate(self):
+        # issue 35062
+        for translate in (-2, -1, 1, 2):
+            decoder = codecs.getincrementaldecoder("utf-8")()
+            decoder = self.IncrementalNewlineDecoder(decoder, translate)
+            self.check_newline_decoding_utf8(decoder)
+        decoder = codecs.getincrementaldecoder("utf-8")()
+        decoder = self.IncrementalNewlineDecoder(decoder, translate=0)
+        self.assertEqual(decoder.decode(b"\r\r\n"), "\r\r\n")
+
 class CIncrementalNewlineDecoderTest(IncrementalNewlineDecoderTest):
     pass
 

Misc/NEWS.d/next/Library/2018-10-29-23-09-24.bpo-35062.dQS1ng.rst

@@ -0,0 +1,2 @@
+Fix incorrect parsing of :class:`_io.IncrementalNewlineDecoder`'s
+*translate* argument.

Modules/_io/textio.c

@@ -268,7 +268,7 @@ _io_IncrementalNewlineDecoder___init___impl(nldecoder_object *self,
         self->errors = errors;
     }
 
-    self->translate = translate;
+    self->translate = translate ? 1 : 0;
     self->seennl = 0;
     self->pendingcr = 0;