gh-114563: C decimal falls back to pydecimal for unsupported format strings

Lib/test/test_decimal.py

@@ -1110,6 +1110,13 @@ def test_formatting(self):
  ('z>z6.1f', '-0.', 'zzz0.0'),
  ('x>z6.1f', '-0.', 'xxx0.0'),
  ('🖤>z6.1f', '-0.', '🖤🖤🖤0.0'), # multi-byte fill char
+ ('\x00>z6.1f', '-0.', '\x00\x00\x000.0'), # null fill char
+
+ # issue 114563 ('z' format on F type in cdecimal)
+ ('z3,.10F', '-6.24E-323', '0.0000000000'),
+
+ # issue 91060 ('#' format in cdecimal)
+ ('#', '0', '0.'),
 
  # issue 6850
  ('a=-7.0', '0.12345', 'aaaa0.1'),
@@ -5726,6 +5733,21 @@ def test_c_signaldict_segfault(self):
  with self.assertRaisesRegex(ValueError, err_msg):
  sd.copy()
 
+ def test_format_fallback_capitals(self):
+ # Fallback to _pydecimal formatting (triggered by `#` format which
+ # is unsupported by mpdecimal) should honor the current context.
+ x = C.Decimal('6.09e+23')
+ self.assertEqual(format(x, '#'), '6.09E+23')
+ with C.localcontext(capitals=0):
+ self.assertEqual(format(x, '#'), '6.09e+23')
+
+ def test_format_fallback_rounding(self):
+ y = C.Decimal('6.09')
+ self.assertEqual(format(y, '#.1f'), '6.1')
+ with C.localcontext(rounding=C.ROUND_DOWN):
+ self.assertEqual(format(y, '#.1f'), '6.0')
+
+
 @requires_docstrings
 @requires_cdecimal
 class SignatureTest(unittest.TestCase):

Misc/NEWS.d/next/Library/2024-02-11-20-23-36.gh-issue-114563.RzxNYT.rst

@@ -0,0 +1,4 @@
+Fix several :func:`format()` bugs when using the C implementation of :class:`~decimal.Decimal`:
+* memory leak in some rare cases when using the ``z`` format option (coerce negative 0)
+* incorrect output when applying the ``z`` format option to type ``F`` (fixed-point with capital ``NAN`` / ``INF``)
+* incorrect output when applying the ``#`` format option (alternate form)

Modules/_decimal/_decimal.c

@@ -82,6 +82,9 @@ typedef struct {
  /* Convert rationals for comparison */
  PyObject *Rational;
 
+ /* Invariant: NULL or pointer to _pydecimal.Decimal */
+ PyObject *PyDecimal;
+
  PyObject *SignalTuple;
 
  struct DecCondMap *signal_map;
@@ -3336,56 +3339,6 @@ dotsep_as_utf8(const char *s)
  return utf8;
 }
 
-/* copy of libmpdec _mpd_round() */
-static void
-_mpd_round(mpd_t *result, const mpd_t *a, mpd_ssize_t prec,
- const mpd_context_t *ctx, uint32_t *status)
-{
- mpd_ssize_t exp = a->exp + a->digits - prec;
-
- if (prec <= 0) {
- mpd_seterror(result, MPD_Invalid_operation, status);
- return;
- }
- if (mpd_isspecial(a) || mpd_iszero(a)) {
- mpd_qcopy(result, a, status);
- return;
- }
-
- mpd_qrescale_fmt(result, a, exp, ctx, status);
- if (result->digits > prec) {
- mpd_qrescale_fmt(result, result, exp+1, ctx, status);
- }
-}
-
-/* Locate negative zero "z" option within a UTF-8 format spec string.
- * Returns pointer to "z", else NULL.
- * The portion of the spec we're working with is [[fill]align][sign][z] */
-static const char *
-format_spec_z_search(char const *fmt, Py_ssize_t size) {
- char const *pos = fmt;
- char const *fmt_end = fmt + size;
- /* skip over [[fill]align] (fill may be multi-byte character) */
- pos += 1;
- while (pos < fmt_end && *pos & 0x80) {
- pos += 1;
- }
- if (pos < fmt_end && strchr("<>=^", *pos) != NULL) {
- pos += 1;
- } else {
- /* fill not present-- skip over [align] */
- pos = fmt;
- if (pos < fmt_end && strchr("<>=^", *pos) != NULL) {
- pos += 1;
- }
- }
- /* skip over [sign] */
- if (pos < fmt_end && strchr("+- ", *pos) != NULL) {
- pos += 1;
- }
- return pos < fmt_end && *pos == 'z' ? pos : NULL;
-}
-
 static int
 dict_get_item_string(PyObject *dict, const char *key, PyObject **valueobj, const char **valuestr)
 {
@@ -3411,6 +3364,48 @@ dict_get_item_string(PyObject *dict, const char *key, PyObject **valueobj, const
  return 0;
 }
 
+/*
+ * Fallback _pydecimal formatting for new format specifiers that mpdecimal does
+ * not yet support. As documented, libmpdec follows the PEP-3101 format language:
+ * https://www.bytereef.org/mpdecimal/doc/libmpdec/assign-convert.html#to-string
+ */
+static PyObject *
+pydec_format(PyObject *dec, PyObject *context, PyObject *fmt, decimal_state *state)
+{
+ PyObject *result;
+ PyObject *pydec;
+ PyObject *u;
+
+ if (state->PyDecimal == NULL) {
+ state->PyDecimal = _PyImport_GetModuleAttrString("_pydecimal", "Decimal");
+ if (state->PyDecimal == NULL) {
+ return NULL;
+ }
+ }
+
+ u = dec_str(dec);
+ if (u == NULL) {
+ return NULL;
+ }
+
+ pydec = PyObject_CallOneArg(state->PyDecimal, u);
+ Py_DECREF(u);
+ if (pydec == NULL) {
+ return NULL;
+ }
+
+ result = PyObject_CallMethod(pydec, "__format__", "(OO)", fmt, context);
+ Py_DECREF(pydec);
+
+ if (result == NULL && PyErr_ExceptionMatches(PyExc_ValueError)) {
+ /* Do not confuse users with the _pydecimal exception */
+ PyErr_Clear();
+ PyErr_SetString(PyExc_ValueError, "invalid format string");
+ }
+
+ return result;
+}
+
 /* Formatted representation of a PyDecObject. */
 static PyObject *
 dec_format(PyObject *dec, PyObject *args)
@@ -3423,16 +3418,11 @@ dec_format(PyObject *dec, PyObject *args)
  PyObject *fmtarg;
  PyObject *context;
  mpd_spec_t spec;
- char const *fmt;
- char *fmt_copy = NULL;
+ char *fmt;
  char *decstring = NULL;
  uint32_t status = 0;
  int replace_fillchar = 0;
- int no_neg_0 = 0;
  Py_ssize_t size;
- mpd_t *mpd = MPD(dec);
- mpd_uint_t dt[MPD_MINALLOC_MAX];
- mpd_t tmp = {MPD_STATIC|MPD_STATIC_DATA,0,0,0,MPD_MINALLOC_MAX,dt};
 
 
  decimal_state *state = get_module_state_by_def(Py_TYPE(dec));
@@ -3442,7 +3432,7 @@ dec_format(PyObject *dec, PyObject *args)
  }
 
  if (PyUnicode_Check(fmtarg)) {
- fmt = PyUnicode_AsUTF8AndSize(fmtarg, &size);
+ fmt = (char *)PyUnicode_AsUTF8AndSize(fmtarg, &size);
  if (fmt == NULL) {
  return NULL;
  }
@@ -3454,35 +3444,15 @@ dec_format(PyObject *dec, PyObject *args)
  }
  }
 
- /* NOTE: If https://github.com/python/cpython/pull/29438 lands, the
- * format string manipulation below can be eliminated by enhancing
- * the forked mpd_parse_fmt_str(). */
  if (size > 0 && fmt[0] == '\0') {
  /* NUL fill character: must be replaced with a valid UTF-8 char
  before calling mpd_parse_fmt_str(). */
  replace_fillchar = 1;
- fmt = fmt_copy = dec_strdup(fmt, size);
- if (fmt_copy == NULL) {
+ fmt = dec_strdup(fmt, size);
+ if (fmt == NULL) {
  return NULL;
  }
- fmt_copy[0] = '_';
- }
- /* Strip 'z' option, which isn't understood by mpd_parse_fmt_str().
- * NOTE: fmt is always null terminated by PyUnicode_AsUTF8AndSize() */
- char const *z_position = format_spec_z_search(fmt, size);
- if (z_position != NULL) {
- no_neg_0 = 1;
- size_t z_index = z_position - fmt;
- if (fmt_copy == NULL) {
- fmt = fmt_copy = dec_strdup(fmt, size);
- if (fmt_copy == NULL) {
- return NULL;
- }
- }
- /* Shift characters (including null terminator) left,
- overwriting the 'z' option. */
- memmove(fmt_copy + z_index, fmt_copy + z_index + 1, size - z_index);
- size -= 1;
+ fmt[0] = '_';
  }
  }
  else {
@@ -3492,10 +3462,13 @@ dec_format(PyObject *dec, PyObject *args)
  }
 
  if (!mpd_parse_fmt_str(&spec, fmt, CtxCaps(context))) {
- PyErr_SetString(PyExc_ValueError,
- "invalid format string");
- goto finish;
+ if (replace_fillchar) {
+ PyMem_Free(fmt);
+ }
+
+ return pydec_format(dec, context, fmtarg, state);
  }
+
  if (replace_fillchar) {
  /* In order to avoid clobbering parts of UTF-8 thousands separators or
  decimal points when the substitution is reversed later, the actual
@@ -3548,45 +3521,8 @@ dec_format(PyObject *dec, PyObject *args)
  }
  }
 
- if (no_neg_0 && mpd_isnegative(mpd) && !mpd_isspecial(mpd)) {
- /* Round into a temporary (carefully mirroring the rounding
- of mpd_qformat_spec()), and check if the result is negative zero.
- If so, clear the sign and format the resulting positive zero. */
- mpd_ssize_t prec;
- mpd_qcopy(&tmp, mpd, &status);
- if (spec.prec >= 0) {
- switch (spec.type) {
- case 'f':
- mpd_qrescale(&tmp, &tmp, -spec.prec, CTX(context), &status);
- break;
- case '%':
- tmp.exp += 2;
- mpd_qrescale(&tmp, &tmp, -spec.prec, CTX(context), &status);
- break;
- case 'g':
- prec = (spec.prec == 0) ? 1 : spec.prec;
- if (tmp.digits > prec) {
- _mpd_round(&tmp, &tmp, prec, CTX(context), &status);
- }
- break;
- case 'e':
- if (!mpd_iszero(&tmp)) {
- _mpd_round(&tmp, &tmp, spec.prec+1, CTX(context), &status);
- }
- break;
- }
- }
- if (status & MPD_Errors) {
- PyErr_SetString(PyExc_ValueError, "unexpected error when rounding");
- goto finish;
- }
- if (mpd_iszero(&tmp)) {
- mpd_set_positive(&tmp);
- mpd = &tmp;
- }
- }
 
- decstring = mpd_qformat_spec(mpd, &spec, CTX(context), &status);
+ decstring = mpd_qformat_spec(MPD(dec), &spec, CTX(context), &status);
  if (decstring == NULL) {
  if (status & MPD_Malloc_error) {
  PyErr_NoMemory();
@@ -3609,7 +3545,7 @@ dec_format(PyObject *dec, PyObject *args)
  Py_XDECREF(grouping);
  Py_XDECREF(sep);
  Py_XDECREF(dot);
- if (fmt_copy) PyMem_Free(fmt_copy);
+ if (replace_fillchar) PyMem_Free(fmt);
  if (decstring) mpd_free(decstring);
  return result;
 }
@@ -5987,6 +5923,9 @@ _decimal_exec(PyObject *m)
  Py_CLEAR(collections_abc);
  Py_CLEAR(MutableMapping);
 
+ /* For format specifiers not yet supported by libmpdec */
+ state->PyDecimal = NULL;
+
  /* Add types to the module */
  CHECK_INT(PyModule_AddType(m, state->PyDec_Type));
  CHECK_INT(PyModule_AddType(m, state->PyDecContext_Type));
@@ -6192,6 +6131,7 @@ decimal_clear(PyObject *module)
  Py_CLEAR(state->extended_context_template);
  Py_CLEAR(state->Rational);
  Py_CLEAR(state->SignalTuple);
+ Py_CLEAR(state->PyDecimal);
 
  PyMem_Free(state->signal_map);
  PyMem_Free(state->cond_map);