Function format_lean_io_error

LeanPy/native/python_bridge.c:844–873

Convert an `IO.Error` payload into a printable C string. The bridge's * own errors are `userError String`; for others we fall back to the * underlying field-0 if it looks like a string, else a generic tag. */

static PyObject *g_lean_callable_type    = NULL;
static PyObject *g_lean_callable_kw_type = NULL;

static PyObject *leancallable_call(PyObject *self_, PyObject *args, PyObject *kwds);
static void      leancallable_dealloc(PyObject *self_);
static PyObject *leancallable_repr(PyObject *self_);

/* Convert an `IO.Error` payload into a printable C string. The bridge's
 * own errors are `userError String`; for others we fall back to the
 * underlying field-0 if it looks like a string, else a generic tag. */
static void format_lean_io_error(lean_object *err, char *buf, size_t bufsz) {
    if (!err) {
        snprintf(buf, bufsz, "Lean error (no payload)");
        return;
    }
    /* Most IO.Error variants (e.g. userError) carry a String at field 0. */
    if (lean_is_scalar(err)) {
        snprintf(buf, bufsz, "Lean IO.Error (tag %u, no payload)",
                 (unsigned)lean_unbox(err));
        return;
    }
    unsigned tag = lean_ptr_tag(err);
    /* lean_ctor_get returns a borrowed pointer */
    lean_object *fld = lean_ctor_get(err, 0);
    if (fld && !lean_is_scalar(fld) && lean_is_string(fld)) {
        snprintf(buf, bufsz, "%s", lean_string_cstr(fld));
        return;
    }
    /* userError-shaped: even if the tag detection above fails, just try
     * to read field 0 as a string. */
    if (fld && !lean_is_scalar(fld)) {
        const char *cs = lean_string_cstr(fld);
        if (cs && cs[0]) {
            snprintf(buf, bufsz, "%s", cs);