Rewrite PyBytes_FromFormatV() using _PyBytesWriter API

* Add much more unit tests on PyBytes_FromFormatV()
* Remove the first loop to compute the length of the output string
* Use _PyBytesWriter to handle the bytes buffer, use overallocation
* Cleanup the code to make simpler and easier to review

Lib/test/test_bytes.py

@@ -783,25 +783,93 @@ class BytesTest(BaseBytesTest, unittest.TestCase):
     # Test PyBytes_FromFormat()
     def test_from_format(self):
         test.support.import_module('ctypes')
-        from ctypes import pythonapi, py_object, c_int, c_char_p
+        _testcapi = test.support.import_module('_testcapi')
+        from ctypes import pythonapi, py_object
+        from ctypes import (
+            c_int, c_uint,
+            c_long, c_ulong,
+            c_size_t, c_ssize_t,
+            c_char_p)
+
         PyBytes_FromFormat = pythonapi.PyBytes_FromFormat
         PyBytes_FromFormat.restype = py_object
 
+        # basic tests
         self.assertEqual(PyBytes_FromFormat(b'format'),
                          b'format')
-
+        self.assertEqual(PyBytes_FromFormat(b'Hello %s !', b'world'),
+                         b'Hello world !')
+
+        # test formatters
+        self.assertEqual(PyBytes_FromFormat(b'c=%c', c_int(0)),
+                         b'c=\0')
+        self.assertEqual(PyBytes_FromFormat(b'c=%c', c_int(ord('@'))),
+                         b'c=@')
+        self.assertEqual(PyBytes_FromFormat(b'c=%c', c_int(255)),
+                         b'c=\xff')
+        self.assertEqual(PyBytes_FromFormat(b'd=%d ld=%ld zd=%zd',
+                                            c_int(1), c_long(2),
+                                            c_size_t(3)),
+                         b'd=1 ld=2 zd=3')
+        self.assertEqual(PyBytes_FromFormat(b'd=%d ld=%ld zd=%zd',
+                                            c_int(-1), c_long(-2),
+                                            c_size_t(-3)),
+                         b'd=-1 ld=-2 zd=-3')
+        self.assertEqual(PyBytes_FromFormat(b'u=%u lu=%lu zu=%zu',
+                                            c_uint(123), c_ulong(456),
+                                            c_size_t(789)),
+                         b'u=123 lu=456 zu=789')
+        self.assertEqual(PyBytes_FromFormat(b'i=%i', c_int(123)),
+                         b'i=123')
+        self.assertEqual(PyBytes_FromFormat(b'i=%i', c_int(-123)),
+                         b'i=-123')
+        self.assertEqual(PyBytes_FromFormat(b'x=%x', c_int(0xabc)),
+                         b'x=abc')
+        self.assertEqual(PyBytes_FromFormat(b'ptr=%p',
+                                            c_char_p(0xabcdef)),
+                         b'ptr=0xabcdef')
+        self.assertEqual(PyBytes_FromFormat(b's=%s', c_char_p(b'cstr')),
+                         b's=cstr')
+
+        # test minimum and maximum integer values
+        size_max = c_size_t(-1).value
+        for formatstr, ctypes_type, value, py_formatter in (
+            (b'%d', c_int, _testcapi.INT_MIN, str),
+            (b'%d', c_int, _testcapi.INT_MAX, str),
+            (b'%ld', c_long, _testcapi.LONG_MIN, str),
+            (b'%ld', c_long, _testcapi.LONG_MAX, str),
+            (b'%lu', c_ulong, _testcapi.ULONG_MAX, str),
+            (b'%zd', c_ssize_t, _testcapi.PY_SSIZE_T_MIN, str),
+            (b'%zd', c_ssize_t, _testcapi.PY_SSIZE_T_MAX, str),
+            (b'%zu', c_size_t, size_max, str),
+            (b'%p', c_char_p, size_max, lambda value: '%#x' % value),
+        ):
+            self.assertEqual(PyBytes_FromFormat(formatstr, ctypes_type(value)),
+                             py_formatter(value).encode('ascii')),
+
+        # width and precision (width is currently ignored)
+        self.assertEqual(PyBytes_FromFormat(b'%5s', b'a'),
+                         b'a')
+        self.assertEqual(PyBytes_FromFormat(b'%.3s', b'abcdef'),
+                         b'abc')
+
+        # '%%' formatter
+        self.assertEqual(PyBytes_FromFormat(b'%%'),
+                         b'%')
+        self.assertEqual(PyBytes_FromFormat(b'[%%]'),
+                         b'[%]')
+        self.assertEqual(PyBytes_FromFormat(b'%%%c', c_int(ord('_'))),
+                         b'%_')
+        self.assertEqual(PyBytes_FromFormat(b'%%s'),
+                         b'%s')
+
+        # Invalid formats and partial formatting
         self.assertEqual(PyBytes_FromFormat(b'%'), b'%')
-        self.assertEqual(PyBytes_FromFormat(b'%%'), b'%')
-        self.assertEqual(PyBytes_FromFormat(b'%%s'), b'%s')
-        self.assertEqual(PyBytes_FromFormat(b'[%%]'), b'[%]')
-        self.assertEqual(PyBytes_FromFormat(b'%%%c', c_int(ord('_'))), b'%_')
-
-        self.assertEqual(PyBytes_FromFormat(b'c:%c', c_int(255)),
-                         b'c:\xff')
-        self.assertEqual(PyBytes_FromFormat(b's:%s', c_char_p(b'cstr')),
-                         b's:cstr')
+        self.assertEqual(PyBytes_FromFormat(b'x=%i y=%', c_int(2), c_int(3)),
+                         b'x=2 y=%')
 
-        # Issue #19969
+        # Issue #19969: %c must raise OverflowError for values
+        # not in the range [0; 255]
         self.assertRaises(OverflowError,
                           PyBytes_FromFormat, b'%c', c_int(-1))
         self.assertRaises(OverflowError,