[3.14] gh-159739: Reject the minimum dynamic formatting width (GH-159780) (#159931)

Adapt the str formatting fix to Objects/unicodeobject.c and use the error wording already present in the 3.14 formatters.

(cherry picked from commit 95f94d0)

Author: jelle-openai

Lib/test/test_format.py

@@ -287,6 +287,8 @@ def test_common_format(self):
                         "%i format: a real number is required, not str")
         test_exc_common('%i', b'1', TypeError,
                         "%i format: a real number is required, not bytes")
+        test_exc_common('%*r', (-maxsize - 1, 1), OverflowError,
+                        "width too big")
 
     def test_str_format(self):
         testformat("%r", "\u0378", "'\\u0378'")  # non printable

Misc/NEWS.d/next/Core_and_Builtins/2026-10-19-20-38-17.gh-issue-159739.78e530.rst

@@ -0,0 +1,2 @@
+Raise :exc:`OverflowError` when the absolute value of a dynamic printf-style
+formatting width is too large.

Objects/bytesobject.c

@@ -752,6 +752,10 @@ _PyBytes_FormatEx(const char *format, Py_ssize_t format_len,
                 if (width == -1 && PyErr_Occurred())
                     goto error;
                 if (width < 0) {
+                    if (width == PY_SSIZE_T_MIN) {
+                        PyErr_SetString(PyExc_OverflowError, "width too big");
+                        goto error;
+                    }
                     flags |= F_LJUST;
                     width = -width;
                 }

Objects/unicodeobject.c

@@ -15150,6 +15150,10 @@ unicode_format_arg_parse(struct unicode_formatter_t *ctx,
         if (arg->width == -1 && PyErr_Occurred())
             return -1;
         if (arg->width < 0) {
+            if (arg->width == PY_SSIZE_T_MIN) {
+                PyErr_SetString(PyExc_OverflowError, "width too big");
+                return -1;
+            }
             arg->flags |= F_LJUST;
             arg->width = -arg->width;
         }