array_userfuncs.c

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/*-------------------------------------------------------------------------
 *
 * array_userfuncs.c
 *    Misc user-visible array support functions
 *
 * Copyright (c) 2003-2018, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/array_userfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_type.h"
#include "common/int.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/typcache.h"


static Datum array_position_common(FunctionCallInfo fcinfo);


/*
 * fetch_array_arg_replace_nulls
 *
 * Fetch an array-valued argument in expanded form; if it's null, construct an
 * empty array value of the proper data type.  Also cache basic element type
 * information in fn_extra.
 *
 * Caution: if the input is a read/write pointer, this returns the input
 * argument; so callers must be sure that their changes are "safe", that is
 * they cannot leave the array in a corrupt state.
 *
 * If we're being called as an aggregate function, make sure any newly-made
 * expanded array is allocated in the aggregate state context, so as to save
 * copying operations.
 */
static ExpandedArrayHeader *
fetch_array_arg_replace_nulls(FunctionCallInfo fcinfo, int argno)
{
    ExpandedArrayHeader *eah;
    Oid         element_type;
    ArrayMetaState *my_extra;
    MemoryContext resultcxt;

    /* If first time through, create datatype cache struct */
    my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
    if (my_extra == NULL)
    {
        my_extra = (ArrayMetaState *)
            MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
                               sizeof(ArrayMetaState));
        my_extra->element_type = InvalidOid;
        fcinfo->flinfo->fn_extra = my_extra;
    }

    /* Figure out which context we want the result in */
    if (!AggCheckCallContext(fcinfo, &resultcxt))
        resultcxt = CurrentMemoryContext;

    /* Now collect the array value */
    if (!PG_ARGISNULL(argno))
    {
        MemoryContext oldcxt = MemoryContextSwitchTo(resultcxt);

        eah = PG_GETARG_EXPANDED_ARRAYX(argno, my_extra);
        MemoryContextSwitchTo(oldcxt);
    }
    else
    {
        /* We have to look up the array type and element type */
        Oid         arr_typeid = get_fn_expr_argtype(fcinfo->flinfo, argno);

        if (!OidIsValid(arr_typeid))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not determine input data type")));
        element_type = get_element_type(arr_typeid);
        if (!OidIsValid(element_type))
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("input data type is not an array")));

        eah = construct_empty_expanded_array(element_type,
                                             resultcxt,
                                             my_extra);
    }

    return eah;
}

/*-----------------------------------------------------------------------------
 * array_append :
 *      push an element onto the end of a one-dimensional array
 *----------------------------------------------------------------------------
 */
Datum
array_append(PG_FUNCTION_ARGS)
{
    ExpandedArrayHeader *eah;
    Datum       newelem;
    bool        isNull;
    Datum       result;
    int        *dimv,
               *lb;
    int         indx;
    ArrayMetaState *my_extra;

    eah = fetch_array_arg_replace_nulls(fcinfo, 0);
    isNull = PG_ARGISNULL(1);
    if (isNull)
        newelem = (Datum) 0;
    else
        newelem = PG_GETARG_DATUM(1);

    if (eah->ndims == 1)
    {
        /* append newelem */
        lb = eah->lbound;
        dimv = eah->dims;

        /* index of added elem is at lb[0] + (dimv[0] - 1) + 1 */
        if (pg_add_s32_overflow(lb[0], dimv[0], &indx))
            ereport(ERROR,
                    (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                     errmsg("integer out of range")));
    }
    else if (eah->ndims == 0)
        indx = 1;
    else
        ereport(ERROR,
                (errcode(ERRCODE_DATA_EXCEPTION),
                 errmsg("argument must be empty or one-dimensional array")));

    /* Perform element insertion */
    my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;

    result = array_set_element(EOHPGetRWDatum(&eah->hdr),
                               1, &indx, newelem, isNull,
                               -1, my_extra->typlen, my_extra->typbyval, my_extra->typalign);

    PG_RETURN_DATUM(result);
}

/*-----------------------------------------------------------------------------
 * array_prepend :
 *      push an element onto the front of a one-dimensional array
 *----------------------------------------------------------------------------
 */
Datum
array_prepend(PG_FUNCTION_ARGS)
{
    ExpandedArrayHeader *eah;
    Datum       newelem;
    bool        isNull;
    Datum       result;
    int        *lb;
    int         indx;
    int         lb0;
    ArrayMetaState *my_extra;

    isNull = PG_ARGISNULL(0);
    if (isNull)
        newelem = (Datum) 0;
    else
        newelem = PG_GETARG_DATUM(0);
    eah = fetch_array_arg_replace_nulls(fcinfo, 1);

    if (eah->ndims == 1)
    {
        /* prepend newelem */
        lb = eah->lbound;
        lb0 = lb[0];

        if (pg_sub_s32_overflow(lb0, 1, &indx))
            ereport(ERROR,
                    (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                     errmsg("integer out of range")));
    }
    else if (eah->ndims == 0)
    {
        indx = 1;
        lb0 = 1;
    }
    else
        ereport(ERROR,
                (errcode(ERRCODE_DATA_EXCEPTION),
                 errmsg("argument must be empty or one-dimensional array")));

    /* Perform element insertion */
    my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;

    result = array_set_element(EOHPGetRWDatum(&eah->hdr),
                               1, &indx, newelem, isNull,
                               -1, my_extra->typlen, my_extra->typbyval, my_extra->typalign);

    /* Readjust result's LB to match the input's, as expected for prepend */
    Assert(result == EOHPGetRWDatum(&eah->hdr));
    if (eah->ndims == 1)
    {
        /* This is ok whether we've deconstructed or not */
        eah->lbound[0] = lb0;
    }

    PG_RETURN_DATUM(result);
}

/*-----------------------------------------------------------------------------
 * array_cat :
 *      concatenate two nD arrays to form an nD array, or
 *      push an (n-1)D array onto the end of an nD array
 *----------------------------------------------------------------------------
 */
Datum
array_cat(PG_FUNCTION_ARGS)
{
    ArrayType  *v1,
               *v2;
    ArrayType  *result;
    int        *dims,
               *lbs,
                ndims,
                nitems,
                ndatabytes,
                nbytes;
    int        *dims1,
               *lbs1,
                ndims1,
                nitems1,
                ndatabytes1;
    int        *dims2,
               *lbs2,
                ndims2,
                nitems2,
                ndatabytes2;
    int         i;
    char       *dat1,
               *dat2;
    bits8      *bitmap1,
               *bitmap2;
    Oid         element_type;
    Oid         element_type1;
    Oid         element_type2;
    int32       dataoffset;

    /* Concatenating a null array is a no-op, just return the other input */
    if (PG_ARGISNULL(0))
    {
        if (PG_ARGISNULL(1))
            PG_RETURN_NULL();
        result = PG_GETARG_ARRAYTYPE_P(1);
        PG_RETURN_ARRAYTYPE_P(result);
    }
    if (PG_ARGISNULL(1))
    {
        result = PG_GETARG_ARRAYTYPE_P(0);
        PG_RETURN_ARRAYTYPE_P(result);
    }

    v1 = PG_GETARG_ARRAYTYPE_P(0);
    v2 = PG_GETARG_ARRAYTYPE_P(1);

    element_type1 = ARR_ELEMTYPE(v1);
    element_type2 = ARR_ELEMTYPE(v2);

    /* Check we have matching element types */
    if (element_type1 != element_type2)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("cannot concatenate incompatible arrays"),
                 errdetail("Arrays with element types %s and %s are not "
                           "compatible for concatenation.",
                           format_type_be(element_type1),
                           format_type_be(element_type2))));

    /* OK, use it */
    element_type = element_type1;

    /*----------
     * We must have one of the following combinations of inputs:
     * 1) one empty array, and one non-empty array
     * 2) both arrays empty
     * 3) two arrays with ndims1 == ndims2
     * 4) ndims1 == ndims2 - 1
     * 5) ndims1 == ndims2 + 1
     *----------
     */
    ndims1 = ARR_NDIM(v1);
    ndims2 = ARR_NDIM(v2);

    /*
     * short circuit - if one input array is empty, and the other is not, we
     * return the non-empty one as the result
     *
     * if both are empty, return the first one
     */
    if (ndims1 == 0 && ndims2 > 0)
        PG_RETURN_ARRAYTYPE_P(v2);

    if (ndims2 == 0)
        PG_RETURN_ARRAYTYPE_P(v1);

    /* the rest fall under rule 3, 4, or 5 */
    if (ndims1 != ndims2 &&
        ndims1 != ndims2 - 1 &&
        ndims1 != ndims2 + 1)
        ereport(ERROR,
                (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                 errmsg("cannot concatenate incompatible arrays"),
                 errdetail("Arrays of %d and %d dimensions are not "
                           "compatible for concatenation.",
                           ndims1, ndims2)));

    /* get argument array details */
    lbs1 = ARR_LBOUND(v1);
    lbs2 = ARR_LBOUND(v2);
    dims1 = ARR_DIMS(v1);
    dims2 = ARR_DIMS(v2);
    dat1 = ARR_DATA_PTR(v1);
    dat2 = ARR_DATA_PTR(v2);
    bitmap1 = ARR_NULLBITMAP(v1);
    bitmap2 = ARR_NULLBITMAP(v2);
    nitems1 = ArrayGetNItems(ndims1, dims1);
    nitems2 = ArrayGetNItems(ndims2, dims2);
    ndatabytes1 = ARR_SIZE(v1) - ARR_DATA_OFFSET(v1);
    ndatabytes2 = ARR_SIZE(v2) - ARR_DATA_OFFSET(v2);

    if (ndims1 == ndims2)
    {
        /*
         * resulting array is made up of the elements (possibly arrays
         * themselves) of the input argument arrays
         */
        ndims = ndims1;
        dims = (int *) palloc(ndims * sizeof(int));
        lbs = (int *) palloc(ndims * sizeof(int));

        dims[0] = dims1[0] + dims2[0];
        lbs[0] = lbs1[0];

        for (i = 1; i < ndims; i++)
        {
            if (dims1[i] != dims2[i] || lbs1[i] != lbs2[i])
                ereport(ERROR,
                        (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                         errmsg("cannot concatenate incompatible arrays"),
                         errdetail("Arrays with differing element dimensions are "
                                   "not compatible for concatenation.")));

            dims[i] = dims1[i];
            lbs[i] = lbs1[i];
        }
    }
    else if (ndims1 == ndims2 - 1)
    {
        /*
         * resulting array has the second argument as the outer array, with
         * the first argument inserted at the front of the outer dimension
         */
        ndims = ndims2;
        dims = (int *) palloc(ndims * sizeof(int));
        lbs = (int *) palloc(ndims * sizeof(int));
        memcpy(dims, dims2, ndims * sizeof(int));
        memcpy(lbs, lbs2, ndims * sizeof(int));

        /* increment number of elements in outer array */
        dims[0] += 1;

        /* make sure the added element matches our existing elements */
        for (i = 0; i < ndims1; i++)
        {
            if (dims1[i] != dims[i + 1] || lbs1[i] != lbs[i + 1])
                ereport(ERROR,
                        (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                         errmsg("cannot concatenate incompatible arrays"),
                         errdetail("Arrays with differing dimensions are not "
                                   "compatible for concatenation.")));
        }
    }
    else
    {
        /*
         * (ndims1 == ndims2 + 1)
         *
         * resulting array has the first argument as the outer array, with the
         * second argument appended to the end of the outer dimension
         */
        ndims = ndims1;
        dims = (int *) palloc(ndims * sizeof(int));
        lbs = (int *) palloc(ndims * sizeof(int));
        memcpy(dims, dims1, ndims * sizeof(int));
        memcpy(lbs, lbs1, ndims * sizeof(int));

        /* increment number of elements in outer array */
        dims[0] += 1;

        /* make sure the added element matches our existing elements */
        for (i = 0; i < ndims2; i++)
        {
            if (dims2[i] != dims[i + 1] || lbs2[i] != lbs[i + 1])
                ereport(ERROR,
                        (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                         errmsg("cannot concatenate incompatible arrays"),
                         errdetail("Arrays with differing dimensions are not "
                                   "compatible for concatenation.")));
        }
    }

    /* Do this mainly for overflow checking */
    nitems = ArrayGetNItems(ndims, dims);

    /* build the result array */
    ndatabytes = ndatabytes1 + ndatabytes2;
    if (ARR_HASNULL(v1) || ARR_HASNULL(v2))
    {
        dataoffset = ARR_OVERHEAD_WITHNULLS(ndims, nitems);
        nbytes = ndatabytes + dataoffset;
    }
    else
    {
        dataoffset = 0;         /* marker for no null bitmap */
        nbytes = ndatabytes + ARR_OVERHEAD_NONULLS(ndims);
    }
    result = (ArrayType *) palloc0(nbytes);
    SET_VARSIZE(result, nbytes);
    result->ndim = ndims;
    result->dataoffset = dataoffset;
    result->elemtype = element_type;
    memcpy(ARR_DIMS(result), dims, ndims * sizeof(int));
    memcpy(ARR_LBOUND(result), lbs, ndims * sizeof(int));
    /* data area is arg1 then arg2 */
    memcpy(ARR_DATA_PTR(result), dat1, ndatabytes1);
    memcpy(ARR_DATA_PTR(result) + ndatabytes1, dat2, ndatabytes2);
    /* handle the null bitmap if needed */
    if (ARR_HASNULL(result))
    {
        array_bitmap_copy(ARR_NULLBITMAP(result), 0,
                          bitmap1, 0,
                          nitems1);
        array_bitmap_copy(ARR_NULLBITMAP(result), nitems1,
                          bitmap2, 0,
                          nitems2);
    }

    PG_RETURN_ARRAYTYPE_P(result);
}


/*
 * ARRAY_AGG(anynonarray) aggregate function
 */
Datum
array_agg_transfn(PG_FUNCTION_ARGS)
{
    Oid         arg1_typeid = get_fn_expr_argtype(fcinfo->flinfo, 1);
    MemoryContext aggcontext;
    ArrayBuildState *state;
    Datum       elem;

    if (arg1_typeid == InvalidOid)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not determine input data type")));

    /*
     * Note: we do not need a run-time check about whether arg1_typeid is a
     * valid array element type, because the parser would have verified that
     * while resolving the input/result types of this polymorphic aggregate.
     */

    if (!AggCheckCallContext(fcinfo, &aggcontext))
    {
        /* cannot be called directly because of internal-type argument */
        elog(ERROR, "array_agg_transfn called in non-aggregate context");
    }

    if (PG_ARGISNULL(0))
        state = initArrayResult(arg1_typeid, aggcontext, false);
    else
        state = (ArrayBuildState *) PG_GETARG_POINTER(0);

    elem = PG_ARGISNULL(1) ? (Datum) 0 : PG_GETARG_DATUM(1);

    state = accumArrayResult(state,
                             elem,
                             PG_ARGISNULL(1),
                             arg1_typeid,
                             aggcontext);

    /*
     * The transition type for array_agg() is declared to be "internal", which
     * is a pass-by-value type the same size as a pointer.  So we can safely
     * pass the ArrayBuildState pointer through nodeAgg.c's machinations.
     */
    PG_RETURN_POINTER(state);
}

Datum
array_agg_finalfn(PG_FUNCTION_ARGS)
{
    Datum       result;
    ArrayBuildState *state;
    int         dims[1];
    int         lbs[1];

    /* cannot be called directly because of internal-type argument */
    Assert(AggCheckCallContext(fcinfo, NULL));

    state = PG_ARGISNULL(0) ? NULL : (ArrayBuildState *) PG_GETARG_POINTER(0);

    if (state == NULL)
        PG_RETURN_NULL();       /* returns null iff no input values */

    dims[0] = state->nelems;
    lbs[0] = 1;

    /*
     * Make the result.  We cannot release the ArrayBuildState because
     * sometimes aggregate final functions are re-executed.  Rather, it is
     * nodeAgg.c's responsibility to reset the aggcontext when it's safe to do
     * so.
     */
    result = makeMdArrayResult(state, 1, dims, lbs,
                               CurrentMemoryContext,
                               false);

    PG_RETURN_DATUM(result);
}

/*
 * ARRAY_AGG(anyarray) aggregate function
 */
Datum
array_agg_array_transfn(PG_FUNCTION_ARGS)
{
    Oid         arg1_typeid = get_fn_expr_argtype(fcinfo->flinfo, 1);
    MemoryContext aggcontext;
    ArrayBuildStateArr *state;

    if (arg1_typeid == InvalidOid)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not determine input data type")));

    /*
     * Note: we do not need a run-time check about whether arg1_typeid is a
     * valid array type, because the parser would have verified that while
     * resolving the input/result types of this polymorphic aggregate.
     */

    if (!AggCheckCallContext(fcinfo, &aggcontext))
    {
        /* cannot be called directly because of internal-type argument */
        elog(ERROR, "array_agg_array_transfn called in non-aggregate context");
    }


    if (PG_ARGISNULL(0))
        state = initArrayResultArr(arg1_typeid, InvalidOid, aggcontext, false);
    else
        state = (ArrayBuildStateArr *) PG_GETARG_POINTER(0);

    state = accumArrayResultArr(state,
                                PG_GETARG_DATUM(1),
                                PG_ARGISNULL(1),
                                arg1_typeid,
                                aggcontext);

    /*
     * The transition type for array_agg() is declared to be "internal", which
     * is a pass-by-value type the same size as a pointer.  So we can safely
     * pass the ArrayBuildStateArr pointer through nodeAgg.c's machinations.
     */
    PG_RETURN_POINTER(state);
}

Datum
array_agg_array_finalfn(PG_FUNCTION_ARGS)
{
    Datum       result;
    ArrayBuildStateArr *state;

    /* cannot be called directly because of internal-type argument */
    Assert(AggCheckCallContext(fcinfo, NULL));

    state = PG_ARGISNULL(0) ? NULL : (ArrayBuildStateArr *) PG_GETARG_POINTER(0);

    if (state == NULL)
        PG_RETURN_NULL();       /* returns null iff no input values */

    /*
     * Make the result.  We cannot release the ArrayBuildStateArr because
     * sometimes aggregate final functions are re-executed.  Rather, it is
     * nodeAgg.c's responsibility to reset the aggcontext when it's safe to do
     * so.
     */
    result = makeArrayResultArr(state, CurrentMemoryContext, false);

    PG_RETURN_DATUM(result);
}

/*-----------------------------------------------------------------------------
 * array_position, array_position_start :
 *          return the offset of a value in an array.
 *
 * IS NOT DISTINCT FROM semantics are used for comparisons.  Return NULL when
 * the value is not found.
 *-----------------------------------------------------------------------------
 */
Datum
array_position(PG_FUNCTION_ARGS)
{
    return array_position_common(fcinfo);
}

Datum
array_position_start(PG_FUNCTION_ARGS)
{
    return array_position_common(fcinfo);
}

/*
 * array_position_common
 *      Common code for array_position and array_position_start
 *
 * These are separate wrappers for the sake of opr_sanity regression test.
 * They are not strict so we have to test for null inputs explicitly.
 */
static Datum
array_position_common(FunctionCallInfo fcinfo)
{
    ArrayType  *array;
    Oid         collation = PG_GET_COLLATION();
    Oid         element_type;
    Datum       searched_element,
                value;
    bool        isnull;
    int         position,
                position_min;
    bool        found = false;
    TypeCacheEntry *typentry;
    ArrayMetaState *my_extra;
    bool        null_search;
    ArrayIterator array_iterator;

    if (PG_ARGISNULL(0))
        PG_RETURN_NULL();

    array = PG_GETARG_ARRAYTYPE_P(0);
    element_type = ARR_ELEMTYPE(array);

    /*
     * We refuse to search for elements in multi-dimensional arrays, since we
     * have no good way to report the element's location in the array.
     */
    if (ARR_NDIM(array) > 1)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("searching for elements in multidimensional arrays is not supported")));

    if (PG_ARGISNULL(1))
    {
        /* fast return when the array doesn't have nulls */
        if (!array_contains_nulls(array))
            PG_RETURN_NULL();
        searched_element = (Datum) 0;
        null_search = true;
    }
    else
    {
        searched_element = PG_GETARG_DATUM(1);
        null_search = false;
    }

    position = (ARR_LBOUND(array))[0] - 1;

    /* figure out where to start */
    if (PG_NARGS() == 3)
    {
        if (PG_ARGISNULL(2))
            ereport(ERROR,
                    (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                     errmsg("initial position must not be null")));

        position_min = PG_GETARG_INT32(2);
    }
    else
        position_min = (ARR_LBOUND(array))[0];

    /*
     * We arrange to look up type info for array_create_iterator only once per
     * series of calls, assuming the element type doesn't change underneath
     * us.
     */
    my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
    if (my_extra == NULL)
    {
        fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
                                                      sizeof(ArrayMetaState));
        my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
        my_extra->element_type = ~element_type;
    }

    if (my_extra->element_type != element_type)
    {
        get_typlenbyvalalign(element_type,
                             &my_extra->typlen,
                             &my_extra->typbyval,
                             &my_extra->typalign);

        typentry = lookup_type_cache(element_type, TYPECACHE_EQ_OPR_FINFO);

        if (!OidIsValid(typentry->eq_opr_finfo.fn_oid))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_FUNCTION),
                     errmsg("could not identify an equality operator for type %s",
                            format_type_be(element_type))));

        my_extra->element_type = element_type;
        fmgr_info_cxt(typentry->eq_opr_finfo.fn_oid, &my_extra->proc,
                      fcinfo->flinfo->fn_mcxt);
    }

    /* Examine each array element until we find a match. */
    array_iterator = array_create_iterator(array, 0, my_extra);
    while (array_iterate(array_iterator, &value, &isnull))
    {
        position++;

        /* skip initial elements if caller requested so */
        if (position < position_min)
            continue;

        /*
         * Can't look at the array element's value if it's null; but if we
         * search for null, we have a hit and are done.
         */
        if (isnull || null_search)
        {
            if (isnull && null_search)
            {
                found = true;
                break;
            }
            else
                continue;
        }

        /* not nulls, so run the operator */
        if (DatumGetBool(FunctionCall2Coll(&my_extra->proc, collation,
                                           searched_element, value)))
        {
            found = true;
            break;
        }
    }

    array_free_iterator(array_iterator);

    /* Avoid leaking memory when handed toasted input */
    PG_FREE_IF_COPY(array, 0);

    if (!found)
        PG_RETURN_NULL();

    PG_RETURN_INT32(position);
}

/*-----------------------------------------------------------------------------
 * array_positions :
 *          return an array of positions of a value in an array.
 *
 * IS NOT DISTINCT FROM semantics are used for comparisons.  Returns NULL when
 * the input array is NULL.  When the value is not found in the array, returns
 * an empty array.
 *
 * This is not strict so we have to test for null inputs explicitly.
 *-----------------------------------------------------------------------------
 */
Datum
array_positions(PG_FUNCTION_ARGS)
{
    ArrayType  *array;
    Oid         collation = PG_GET_COLLATION();
    Oid         element_type;
    Datum       searched_element,
                value;
    bool        isnull;
    int         position;
    TypeCacheEntry *typentry;
    ArrayMetaState *my_extra;
    bool        null_search;
    ArrayIterator array_iterator;
    ArrayBuildState *astate = NULL;

    if (PG_ARGISNULL(0))
        PG_RETURN_NULL();

    array = PG_GETARG_ARRAYTYPE_P(0);
    element_type = ARR_ELEMTYPE(array);

    position = (ARR_LBOUND(array))[0] - 1;

    /*
     * We refuse to search for elements in multi-dimensional arrays, since we
     * have no good way to report the element's location in the array.
     */
    if (ARR_NDIM(array) > 1)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("searching for elements in multidimensional arrays is not supported")));

    astate = initArrayResult(INT4OID, CurrentMemoryContext, false);

    if (PG_ARGISNULL(1))
    {
        /* fast return when the array doesn't have nulls */
        if (!array_contains_nulls(array))
            PG_RETURN_DATUM(makeArrayResult(astate, CurrentMemoryContext));
        searched_element = (Datum) 0;
        null_search = true;
    }
    else
    {
        searched_element = PG_GETARG_DATUM(1);
        null_search = false;
    }

    /*
     * We arrange to look up type info for array_create_iterator only once per
     * series of calls, assuming the element type doesn't change underneath
     * us.
     */
    my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
    if (my_extra == NULL)
    {
        fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
                                                      sizeof(ArrayMetaState));
        my_extra = (ArrayMetaState *) fcinfo->flinfo->fn_extra;
        my_extra->element_type = ~element_type;
    }

    if (my_extra->element_type != element_type)
    {
        get_typlenbyvalalign(element_type,
                             &my_extra->typlen,
                             &my_extra->typbyval,
                             &my_extra->typalign);

        typentry = lookup_type_cache(element_type, TYPECACHE_EQ_OPR_FINFO);

        if (!OidIsValid(typentry->eq_opr_finfo.fn_oid))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_FUNCTION),
                     errmsg("could not identify an equality operator for type %s",
                            format_type_be(element_type))));

        my_extra->element_type = element_type;
        fmgr_info_cxt(typentry->eq_opr_finfo.fn_oid, &my_extra->proc,
                      fcinfo->flinfo->fn_mcxt);
    }

    /*
     * Accumulate each array position iff the element matches the given
     * element.
     */
    array_iterator = array_create_iterator(array, 0, my_extra);
    while (array_iterate(array_iterator, &value, &isnull))
    {
        position += 1;

        /*
         * Can't look at the array element's value if it's null; but if we
         * search for null, we have a hit.
         */
        if (isnull || null_search)
        {
            if (isnull && null_search)
                astate =
                    accumArrayResult(astate, Int32GetDatum(position), false,
                                     INT4OID, CurrentMemoryContext);

            continue;
        }

        /* not nulls, so run the operator */
        if (DatumGetBool(FunctionCall2Coll(&my_extra->proc, collation,
                                           searched_element, value)))
            astate =
                accumArrayResult(astate, Int32GetDatum(position), false,
                                 INT4OID, CurrentMemoryContext);
    }

    array_free_iterator(array_iterator);

    /* Avoid leaking memory when handed toasted input */
    PG_FREE_IF_COPY(array, 0);

    PG_RETURN_DATUM(makeArrayResult(astate, CurrentMemoryContext));
}