[ceph.git] / ceph / src / civetweb / src / third_party / duktape-1.5.2 / src-separate / duk_hobject_enum.c

/*
 *  Hobject enumeration support.
 *
 *  Creates an internal enumeration state object to be used e.g. with for-in
 *  enumeration.  The state object contains a snapshot of target object keys
 *  and internal control state for enumeration.  Enumerator flags allow caller
 *  to e.g. request internal/non-enumerable properties, and to enumerate only
 *  "own" properties.
 *
 *  Also creates the result value for e.g. Object.keys() based on the same
 *  internal structure.
 *
 *  This snapshot-based enumeration approach is used to simplify enumeration:
 *  non-snapshot-based approaches are difficult to reconcile with mutating
 *  the enumeration target, running multiple long-lived enumerators at the
 *  same time, garbage collection details, etc.  The downside is that the
 *  enumerator object is memory inefficient especially for iterating arrays.
 */

#include "duk_internal.h"

/* XXX: identify enumeration target with an object index (not top of stack) */

/* must match exactly the number of internal properties inserted to enumerator */
#define DUK__ENUM_START_INDEX  2

DUK_LOCAL const duk_uint16_t duk__bufferobject_virtual_props[] = {
        DUK_STRIDX_LENGTH,
        DUK_STRIDX_BYTE_LENGTH,
        DUK_STRIDX_BYTE_OFFSET,
        DUK_STRIDX_BYTES_PER_ELEMENT
};

/*
 *  Helper to sort array index keys.  The keys are in the enumeration object
 *  entry part, starting from DUK__ENUM_START_INDEX, and the entry part is dense.
 *
 *  We use insertion sort because it is simple (leading to compact code,)
 *  works nicely in-place, and minimizes operations if data is already sorted
 *  or nearly sorted (which is a very common case here).  It also minimizes
 *  the use of element comparisons in general.  This is nice because element
 *  comparisons here involve re-parsing the string keys into numbers each
 *  time, which is naturally very expensive.
 *
 *  Note that the entry part values are all "true", e.g.
 *
 *    "1" -> true, "3" -> true, "2" -> true
 *
 *  so it suffices to only work in the key part without exchanging any keys,
 *  simplifying the sort.
 *
 *  http://en.wikipedia.org/wiki/Insertion_sort
 *
 *  (Compiles to about 160 bytes now as a stand-alone function.)
 */

DUK_LOCAL void duk__sort_array_indices(duk_hthread *thr, duk_hobject *h_obj) {
        duk_hstring **keys;
        duk_hstring **p_curr, **p_insert, **p_end;
        duk_hstring *h_curr;
        duk_uarridx_t val_highest, val_curr, val_insert;

        DUK_ASSERT(h_obj != NULL);
        DUK_ASSERT(DUK_HOBJECT_GET_ENEXT(h_obj) >= 2);  /* control props */
        DUK_UNREF(thr);

        if (DUK_HOBJECT_GET_ENEXT(h_obj) <= 1 + DUK__ENUM_START_INDEX) {
                return;
        }

        keys = DUK_HOBJECT_E_GET_KEY_BASE(thr->heap, h_obj);
        p_end = keys + DUK_HOBJECT_GET_ENEXT(h_obj);
        keys += DUK__ENUM_START_INDEX;

        DUK_DDD(DUK_DDDPRINT("keys=%p, p_end=%p (after skipping enum props)",
                             (void *) keys, (void *) p_end));

#ifdef DUK_USE_DDDPRINT
        {
                duk_uint_fast32_t i;
                for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(h_obj); i++) {
                        DUK_DDD(DUK_DDDPRINT("initial: %ld %p -> %!O",
                                             (long) i,
                                             (void *) DUK_HOBJECT_E_GET_KEY_PTR(thr->heap, h_obj, i),
                                             (duk_heaphdr *) DUK_HOBJECT_E_GET_KEY(thr->heap, h_obj, i)));
                }
        }
#endif

        val_highest = DUK_HSTRING_GET_ARRIDX_SLOW(keys[0]);
        for (p_curr = keys + 1; p_curr < p_end; p_curr++) {
                DUK_ASSERT(*p_curr != NULL);
                val_curr = DUK_HSTRING_GET_ARRIDX_SLOW(*p_curr);

                if (val_curr >= val_highest) {
                        DUK_DDD(DUK_DDDPRINT("p_curr=%p, p_end=%p, val_highest=%ld, val_curr=%ld -> "
                                             "already in correct order, next",
                                             (void *) p_curr, (void *) p_end, (long) val_highest, (long) val_curr));
                        val_highest = val_curr;
                        continue;
                }

                DUK_DDD(DUK_DDDPRINT("p_curr=%p, p_end=%p, val_highest=%ld, val_curr=%ld -> "
                                     "needs to be inserted",
                                     (void *) p_curr, (void *) p_end, (long) val_highest, (long) val_curr));

                /* Needs to be inserted; scan backwards, since we optimize
                 * for the case where elements are nearly in order.
                 */

                p_insert = p_curr - 1;
                for (;;) {
                        val_insert = DUK_HSTRING_GET_ARRIDX_SLOW(*p_insert);
                        if (val_insert < val_curr) {
                                DUK_DDD(DUK_DDDPRINT("p_insert=%p, val_insert=%ld, val_curr=%ld -> insert after this",
                                                     (void *) p_insert, (long) val_insert, (long) val_curr));
                                p_insert++;
                                break;
                        }
                        if (p_insert == keys) {
                                DUK_DDD(DUK_DDDPRINT("p_insert=%p -> out of keys, insert to beginning", (void *) p_insert));
                                break;
                        }
                        DUK_DDD(DUK_DDDPRINT("p_insert=%p, val_insert=%ld, val_curr=%ld -> search backwards",
                                             (void *) p_insert, (long) val_insert, (long) val_curr));
                        p_insert--;
                }

                DUK_DDD(DUK_DDDPRINT("final p_insert=%p", (void *) p_insert));

                /*        .-- p_insert   .-- p_curr
                 *        v              v
                 *  | ... | insert | ... | curr
                 */

                h_curr = *p_curr;
                DUK_DDD(DUK_DDDPRINT("memmove: dest=%p, src=%p, size=%ld, h_curr=%p",
                                     (void *) (p_insert + 1), (void *) p_insert,
                                     (long) (p_curr - p_insert), (void *) h_curr));

                DUK_MEMMOVE((void *) (p_insert + 1),
                            (const void *) p_insert,
                            (size_t) ((p_curr - p_insert) * sizeof(duk_hstring *)));
                *p_insert = h_curr;
                /* keep val_highest */
        }

#ifdef DUK_USE_DDDPRINT
        {
                duk_uint_fast32_t i;
                for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(h_obj); i++) {
                        DUK_DDD(DUK_DDDPRINT("final: %ld %p -> %!O",
                                             (long) i,
                                             (void *) DUK_HOBJECT_E_GET_KEY_PTR(thr->heap, h_obj, i),
                                             (duk_heaphdr *) DUK_HOBJECT_E_GET_KEY(thr->heap, h_obj, i)));
                }
        }
#endif
}

/*
 *  Create an internal enumerator object E, which has its keys ordered
 *  to match desired enumeration ordering.  Also initialize internal control
 *  properties for enumeration.
 *
 *  Note: if an array was used to hold enumeration keys instead, an array
 *  scan would be needed to eliminate duplicates found in the prototype chain.
 */

DUK_INTERNAL void duk_hobject_enumerator_create(duk_context *ctx, duk_small_uint_t enum_flags) {
        duk_hthread *thr = (duk_hthread *) ctx;
        duk_hobject *enum_target;
        duk_hobject *curr;
        duk_hobject *res;
#if defined(DUK_USE_ES6_PROXY)
        duk_hobject *h_proxy_target;
        duk_hobject *h_proxy_handler;
        duk_hobject *h_trap_result;
#endif
        duk_uint_fast32_t i, len;  /* used for array, stack, and entry indices */

        DUK_ASSERT(ctx != NULL);

        DUK_DDD(DUK_DDDPRINT("create enumerator, stack top: %ld", (long) duk_get_top(ctx)));

        enum_target = duk_require_hobject(ctx, -1);
        DUK_ASSERT(enum_target != NULL);

        duk_push_object_internal(ctx);
        res = duk_require_hobject(ctx, -1);

        DUK_DDD(DUK_DDDPRINT("created internal object"));

        /* [enum_target res] */

        /* Target must be stored so that we can recheck whether or not
         * keys still exist when we enumerate.  This is not done if the
         * enumeration result comes from a proxy trap as there is no
         * real object to check against.
         */
        duk_push_hobject(ctx, enum_target);
        duk_put_prop_stridx(ctx, -2, DUK_STRIDX_INT_TARGET);

        /* Initialize index so that we skip internal control keys. */
        duk_push_int(ctx, DUK__ENUM_START_INDEX);
        duk_put_prop_stridx(ctx, -2, DUK_STRIDX_INT_NEXT);

        /*
         *  Proxy object handling
         */

#if defined(DUK_USE_ES6_PROXY)
        if (DUK_LIKELY((enum_flags & DUK_ENUM_NO_PROXY_BEHAVIOR) != 0)) {
                goto skip_proxy;
        }
        if (DUK_LIKELY(!duk_hobject_proxy_check(thr,
                                                enum_target,
                                                &h_proxy_target,
                                                &h_proxy_handler))) {
                goto skip_proxy;
        }

        DUK_DDD(DUK_DDDPRINT("proxy enumeration"));
        duk_push_hobject(ctx, h_proxy_handler);
        if (!duk_get_prop_stridx(ctx, -1, DUK_STRIDX_ENUMERATE)) {
                /* No need to replace the 'enum_target' value in stack, only the
                 * enum_target reference.  This also ensures that the original
                 * enum target is reachable, which keeps the proxy and the proxy
                 * target reachable.  We do need to replace the internal _Target.
                 */
                DUK_DDD(DUK_DDDPRINT("no enumerate trap, enumerate proxy target instead"));
                DUK_DDD(DUK_DDDPRINT("h_proxy_target=%!O", (duk_heaphdr *) h_proxy_target));
                enum_target = h_proxy_target;

                duk_push_hobject(ctx, enum_target);  /* -> [ ... enum_target res handler undefined target ] */
                duk_put_prop_stridx(ctx, -4, DUK_STRIDX_INT_TARGET);

                duk_pop_2(ctx);  /* -> [ ... enum_target res ] */
                goto skip_proxy;
        }

        /* [ ... enum_target res handler trap ] */
        duk_insert(ctx, -2);
        duk_push_hobject(ctx, h_proxy_target);    /* -> [ ... enum_target res trap handler target ] */
        duk_call_method(ctx, 1 /*nargs*/);        /* -> [ ... enum_target res trap_result ] */
        h_trap_result = duk_require_hobject(ctx, -1);
        DUK_UNREF(h_trap_result);

        /* Copy trap result keys into the enumerator object. */
        len = (duk_uint_fast32_t) duk_get_length(ctx, -1);
        for (i = 0; i < len; i++) {
                /* XXX: not sure what the correct semantic details are here,
                 * e.g. handling of missing values (gaps), handling of non-array
                 * trap results, etc.
                 *
                 * For keys, we simply skip non-string keys which seems to be
                 * consistent with how e.g. Object.keys() will process proxy trap
                 * results (ES6, Section 19.1.2.14).
                 */
                if (duk_get_prop_index(ctx, -1, i) && duk_is_string(ctx, -1)) {
                        /* [ ... enum_target res trap_result val ] */
                        duk_push_true(ctx);
                        /* [ ... enum_target res trap_result val true ] */
                        duk_put_prop(ctx, -4);
                } else {
                        duk_pop(ctx);
                }
        }
        /* [ ... enum_target res trap_result ] */
        duk_pop(ctx);
        duk_remove(ctx, -2);

        /* [ ... res ] */

        /* The internal _Target property is kept pointing to the original
         * enumeration target (the proxy object), so that the enumerator
         * 'next' operation can read property values if so requested.  The
         * fact that the _Target is a proxy disables key existence check
         * during enumeration.
         */
        DUK_DDD(DUK_DDDPRINT("proxy enumeration, final res: %!O", (duk_heaphdr *) res));
        goto compact_and_return;

 skip_proxy:
#endif  /* DUK_USE_ES6_PROXY */

        curr = enum_target;
        while (curr) {
                /*
                 *  Virtual properties.
                 *
                 *  String and buffer indices are virtual and always enumerable,
                 *  'length' is virtual and non-enumerable.  Array and arguments
                 *  object props have special behavior but are concrete.
                 */

                if (DUK_HOBJECT_HAS_EXOTIC_STRINGOBJ(curr) ||
                    DUK_HOBJECT_IS_BUFFEROBJECT(curr)) {
                        /* String and buffer enumeration behavior is identical now,
                         * so use shared handler.
                         */
                        if (DUK_HOBJECT_HAS_EXOTIC_STRINGOBJ(curr)) {
                                duk_hstring *h_val;
                                h_val = duk_hobject_get_internal_value_string(thr->heap, curr);
                                DUK_ASSERT(h_val != NULL);  /* string objects must not created without internal value */
                                len = (duk_uint_fast32_t) DUK_HSTRING_GET_CHARLEN(h_val);
                        } else {
                                duk_hbufferobject *h_bufobj;
                                DUK_ASSERT(DUK_HOBJECT_IS_BUFFEROBJECT(curr));
                                h_bufobj = (duk_hbufferobject *) curr;
                                if (h_bufobj == NULL) {
                                        /* Neutered buffer, zero length seems
                                         * like good behavior here.
                                         */
                                        len = 0;
                                } else {
                                        /* There's intentionally no check for
                                         * current underlying buffer length.
                                         */
                                        len = (duk_uint_fast32_t) (h_bufobj->length >> h_bufobj->shift);
                                }
                        }

                        for (i = 0; i < len; i++) {
                                duk_hstring *k;

                                k = duk_heap_string_intern_u32_checked(thr, i);
                                DUK_ASSERT(k);
                                duk_push_hstring(ctx, k);
                                duk_push_true(ctx);

                                /* [enum_target res key true] */
                                duk_put_prop(ctx, -3);

                                /* [enum_target res] */
                        }

                        /* 'length' and other virtual properties are not
                         * enumerable, but are included if non-enumerable
                         * properties are requested.
                         */

                        if (enum_flags & DUK_ENUM_INCLUDE_NONENUMERABLE) {
                                duk_uint_fast32_t n;

                                if (DUK_HOBJECT_IS_BUFFEROBJECT(curr)) {
                                        n = sizeof(duk__bufferobject_virtual_props) / sizeof(duk_uint16_t);
                                } else {
                                        DUK_ASSERT(DUK_HOBJECT_HAS_EXOTIC_STRINGOBJ(curr));
                                        DUK_ASSERT(duk__bufferobject_virtual_props[0] == DUK_STRIDX_LENGTH);
                                        n = 1;  /* only 'length' */
                                }

                                for (i = 0; i < n; i++) {
                                        duk_push_hstring_stridx(ctx, duk__bufferobject_virtual_props[i]);
                                        duk_push_true(ctx);
                                        duk_put_prop(ctx, -3);
                                }

                        }
                } else if (DUK_HOBJECT_HAS_EXOTIC_DUKFUNC(curr)) {
                        if (enum_flags & DUK_ENUM_INCLUDE_NONENUMERABLE) {
                                duk_push_hstring_stridx(ctx, DUK_STRIDX_LENGTH);
                                duk_push_true(ctx);
                                duk_put_prop(ctx, -3);
                        }
                }

                /*
                 *  Array part
                 *
                 *  Note: ordering between array and entry part must match 'abandon array'
                 *  behavior in duk_hobject_props.c: key order after an array is abandoned
                 *  must be the same.
                 */

                for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ASIZE(curr); i++) {
                        duk_hstring *k;
                        duk_tval *tv;

                        tv = DUK_HOBJECT_A_GET_VALUE_PTR(thr->heap, curr, i);
                        if (DUK_TVAL_IS_UNUSED(tv)) {
                                continue;
                        }
                        k = duk_heap_string_intern_u32_checked(thr, i);
                        DUK_ASSERT(k);

                        duk_push_hstring(ctx, k);
                        duk_push_true(ctx);

                        /* [enum_target res key true] */
                        duk_put_prop(ctx, -3);

                        /* [enum_target res] */
                }

                /*
                 *  Entries part
                 */

                for (i = 0; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(curr); i++) {
                        duk_hstring *k;

                        k = DUK_HOBJECT_E_GET_KEY(thr->heap, curr, i);
                        if (!k) {
                                continue;
                        }
                        if (!DUK_HOBJECT_E_SLOT_IS_ENUMERABLE(thr->heap, curr, i) &&
                            !(enum_flags & DUK_ENUM_INCLUDE_NONENUMERABLE)) {
                                continue;
                        }
                        if (DUK_HSTRING_HAS_INTERNAL(k) &&
                            !(enum_flags & DUK_ENUM_INCLUDE_INTERNAL)) {
                                continue;
                        }
                        if ((enum_flags & DUK_ENUM_ARRAY_INDICES_ONLY) &&
                            (DUK_HSTRING_GET_ARRIDX_SLOW(k) == DUK_HSTRING_NO_ARRAY_INDEX)) {
                                continue;
                        }

                        DUK_ASSERT(DUK_HOBJECT_E_SLOT_IS_ACCESSOR(thr->heap, curr, i) ||
                                   !DUK_TVAL_IS_UNUSED(&DUK_HOBJECT_E_GET_VALUE_PTR(thr->heap, curr, i)->v));

                        duk_push_hstring(ctx, k);
                        duk_push_true(ctx);

                        /* [enum_target res key true] */
                        duk_put_prop(ctx, -3);

                        /* [enum_target res] */
                }

                if (enum_flags & DUK_ENUM_OWN_PROPERTIES_ONLY) {
                        break;
                }

                curr = DUK_HOBJECT_GET_PROTOTYPE(thr->heap, curr);
        }

        /* [enum_target res] */

        duk_remove(ctx, -2);

        /* [res] */

        if ((enum_flags & (DUK_ENUM_ARRAY_INDICES_ONLY | DUK_ENUM_SORT_ARRAY_INDICES)) ==
                          (DUK_ENUM_ARRAY_INDICES_ONLY | DUK_ENUM_SORT_ARRAY_INDICES)) {
                /*
                 *  Some E5/E5.1 algorithms require that array indices are iterated
                 *  in a strictly ascending order.  This is the case for e.g.
                 *  Array.prototype.forEach() and JSON.stringify() PropertyList
                 *  handling.
                 *
                 *  To ensure this property for arrays with an array part (and
                 *  arbitrary objects too, since e.g. forEach() can be applied
                 *  to an array), the caller can request that we sort the keys
                 *  here.
                 */

                /* XXX: avoid this at least when enum_target is an Array, it has an
                 * array part, and no ancestor properties were included?  Not worth
                 * it for JSON, but maybe worth it for forEach().
                 */

                /* XXX: may need a 'length' filter for forEach()
                 */
                DUK_DDD(DUK_DDDPRINT("sort array indices by caller request"));
                duk__sort_array_indices(thr, res);
        }

#if defined(DUK_USE_ES6_PROXY)
 compact_and_return:
#endif
        /* compact; no need to seal because object is internal */
        duk_hobject_compact_props(thr, res);

        DUK_DDD(DUK_DDDPRINT("created enumerator object: %!iT", (duk_tval *) duk_get_tval(ctx, -1)));
}

/*
 *  Returns non-zero if a key and/or value was enumerated, and:
 *
 *   [enum] -> [key]        (get_value == 0)
 *   [enum] -> [key value]  (get_value == 1)
 *
 *  Returns zero without pushing anything on the stack otherwise.
 */
DUK_INTERNAL duk_bool_t duk_hobject_enumerator_next(duk_context *ctx, duk_bool_t get_value) {
        duk_hthread *thr = (duk_hthread *) ctx;
        duk_hobject *e;
        duk_hobject *enum_target;
        duk_hstring *res = NULL;
        duk_uint_fast32_t idx;
        duk_bool_t check_existence;

        DUK_ASSERT(ctx != NULL);

        /* [... enum] */

        e = duk_require_hobject(ctx, -1);

        /* XXX use get tval ptr, more efficient */
        duk_get_prop_stridx(ctx, -1, DUK_STRIDX_INT_NEXT);
        idx = (duk_uint_fast32_t) duk_require_uint(ctx, -1);
        duk_pop(ctx);
        DUK_DDD(DUK_DDDPRINT("enumeration: index is: %ld", (long) idx));

        /* Enumeration keys are checked against the enumeration target (to see
         * that they still exist).  In the proxy enumeration case _Target will
         * be the proxy, and checking key existence against the proxy is not
         * required (or sensible, as the keys may be fully virtual).
         */
        duk_get_prop_stridx(ctx, -1, DUK_STRIDX_INT_TARGET);
        enum_target = duk_require_hobject(ctx, -1);
        DUK_ASSERT(enum_target != NULL);
#if defined(DUK_USE_ES6_PROXY)
        check_existence = (!DUK_HOBJECT_HAS_EXOTIC_PROXYOBJ(enum_target));
#else
        check_existence = 1;
#endif
        duk_pop(ctx);  /* still reachable */

        DUK_DDD(DUK_DDDPRINT("getting next enum value, enum_target=%!iO, enumerator=%!iT",
                             (duk_heaphdr *) enum_target, (duk_tval *) duk_get_tval(ctx, -1)));

        /* no array part */
        for (;;) {
                duk_hstring *k;

                if (idx >= DUK_HOBJECT_GET_ENEXT(e)) {
                        DUK_DDD(DUK_DDDPRINT("enumeration: ran out of elements"));
                        break;
                }

                /* we know these because enum objects are internally created */
                k = DUK_HOBJECT_E_GET_KEY(thr->heap, e, idx);
                DUK_ASSERT(k != NULL);
                DUK_ASSERT(!DUK_HOBJECT_E_SLOT_IS_ACCESSOR(thr->heap, e, idx));
                DUK_ASSERT(!DUK_TVAL_IS_UNUSED(&DUK_HOBJECT_E_GET_VALUE(thr->heap, e, idx).v));

                idx++;

                /* recheck that the property still exists */
                if (check_existence && !duk_hobject_hasprop_raw(thr, enum_target, k)) {
                        DUK_DDD(DUK_DDDPRINT("property deleted during enumeration, skip"));
                        continue;
                }

                DUK_DDD(DUK_DDDPRINT("enumeration: found element, key: %!O", (duk_heaphdr *) k));
                res = k;
                break;
        }

        DUK_DDD(DUK_DDDPRINT("enumeration: updating next index to %ld", (long) idx));

        duk_push_u32(ctx, (duk_uint32_t) idx);
        duk_put_prop_stridx(ctx, -2, DUK_STRIDX_INT_NEXT);

        /* [... enum] */

        if (res) {
                duk_push_hstring(ctx, res);
                if (get_value) {
                        duk_push_hobject(ctx, enum_target);
                        duk_dup(ctx, -2);      /* -> [... enum key enum_target key] */
                        duk_get_prop(ctx, -2); /* -> [... enum key enum_target val] */
                        duk_remove(ctx, -2);   /* -> [... enum key val] */
                        duk_remove(ctx, -3);   /* -> [... key val] */
                } else {
                        duk_remove(ctx, -2);   /* -> [... key] */
                }
                return 1;
        } else {
                duk_pop(ctx);  /* -> [...] */
                return 0;
        }
}

/*
 *  Get enumerated keys in an Ecmascript array.  Matches Object.keys() behavior
 *  described in E5 Section 15.2.3.14.
 */

DUK_INTERNAL duk_ret_t duk_hobject_get_enumerated_keys(duk_context *ctx, duk_small_uint_t enum_flags) {
        duk_hthread *thr = (duk_hthread *) ctx;
        duk_hobject *e;
        duk_uint_fast32_t i;
        duk_uint_fast32_t idx;

        DUK_ASSERT(ctx != NULL);
        DUK_ASSERT(duk_get_hobject(ctx, -1) != NULL);
        DUK_UNREF(thr);

        /* Create a temporary enumerator to get the (non-duplicated) key list;
         * the enumerator state is initialized without being needed, but that
         * has little impact.
         */

        duk_hobject_enumerator_create(ctx, enum_flags);
        duk_push_array(ctx);

        /* [enum_target enum res] */

        e = duk_require_hobject(ctx, -2);
        DUK_ASSERT(e != NULL);

        idx = 0;
        for (i = DUK__ENUM_START_INDEX; i < (duk_uint_fast32_t) DUK_HOBJECT_GET_ENEXT(e); i++) {
                duk_hstring *k;

                k = DUK_HOBJECT_E_GET_KEY(thr->heap, e, i);
                DUK_ASSERT(k);  /* enumerator must have no keys deleted */

                /* [enum_target enum res] */
                duk_push_hstring(ctx, k);
                duk_put_prop_index(ctx, -2, idx);
                idx++;
        }

        /* [enum_target enum res] */
        duk_remove(ctx, -2);

        /* [enum_target res] */

        return 1;  /* return 1 to allow callers to tail call */
}