arraysubs.c

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/*-------------------------------------------------------------------------
 *
 * arraysubs.c
 *    Subscripting support functions for arrays.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/arraysubs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "executor/execExpr.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/subscripting.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"


/* SubscriptingRefState.workspace for array subscripting execution */
typedef struct ArraySubWorkspace
{
    /* Values determined during expression compilation */
    Oid         refelemtype;    /* OID of the array element type */
    int16       refattrlength;  /* typlen of array type */
    int16       refelemlength;  /* typlen of the array element type */
    bool        refelembyval;   /* is the element type pass-by-value? */
    char        refelemalign;   /* typalign of the element type */

    /*
     * Subscript values converted to integers.  Note that these arrays must be
     * of length MAXDIM even when dealing with fewer subscripts, because
     * array_get/set_slice may scribble on the extra entries.
     */
    int         upperindex[MAXDIM];
    int         lowerindex[MAXDIM];
} ArraySubWorkspace;


/*
 * Finish parse analysis of a SubscriptingRef expression for an array.
 *
 * Transform the subscript expressions, coerce them to integers,
 * and determine the result type of the SubscriptingRef node.
 */
static void
array_subscript_transform(SubscriptingRef *sbsref,
                          List *indirection,
                          ParseState *pstate,
                          bool isSlice,
                          bool isAssignment)
{
    List       *upperIndexpr = NIL;
    List       *lowerIndexpr = NIL;
    ListCell   *idx;

    /*
     * Transform the subscript expressions, and separate upper and lower
     * bounds into two lists.
     *
     * If we have a container slice expression, we convert any non-slice
     * indirection items to slices by treating the single subscript as the
     * upper bound and supplying an assumed lower bound of 1.
     */
    foreach(idx, indirection)
    {
        A_Indices  *ai = lfirst_node(A_Indices, idx);
        Node       *subexpr;

        if (isSlice)
        {
            if (ai->lidx)
            {
                subexpr = transformExpr(pstate, ai->lidx, pstate->p_expr_kind);
                /* If it's not int4 already, try to coerce */
                subexpr = coerce_to_target_type(pstate,
                                                subexpr, exprType(subexpr),
                                                INT4OID, -1,
                                                COERCION_ASSIGNMENT,
                                                COERCE_IMPLICIT_CAST,
                                                -1);
                if (subexpr == NULL)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                             errmsg("array subscript must have type integer"),
                             parser_errposition(pstate, exprLocation(ai->lidx))));
            }
            else if (!ai->is_slice)
            {
                /* Make a constant 1 */
                subexpr = (Node *) makeConst(INT4OID,
                                             -1,
                                             InvalidOid,
                                             sizeof(int32),
                                             Int32GetDatum(1),
                                             false,
                                             true); /* pass by value */
            }
            else
            {
                /* Slice with omitted lower bound, put NULL into the list */
                subexpr = NULL;
            }
            lowerIndexpr = lappend(lowerIndexpr, subexpr);
        }
        else
            Assert(ai->lidx == NULL && !ai->is_slice);

        if (ai->uidx)
        {
            subexpr = transformExpr(pstate, ai->uidx, pstate->p_expr_kind);
            /* If it's not int4 already, try to coerce */
            subexpr = coerce_to_target_type(pstate,
                                            subexpr, exprType(subexpr),
                                            INT4OID, -1,
                                            COERCION_ASSIGNMENT,
                                            COERCE_IMPLICIT_CAST,
                                            -1);
            if (subexpr == NULL)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("array subscript must have type integer"),
                         parser_errposition(pstate, exprLocation(ai->uidx))));
        }
        else
        {
            /* Slice with omitted upper bound, put NULL into the list */
            Assert(isSlice && ai->is_slice);
            subexpr = NULL;
        }
        upperIndexpr = lappend(upperIndexpr, subexpr);
    }

    /* ... and store the transformed lists into the SubscriptRef node */
    sbsref->refupperindexpr = upperIndexpr;
    sbsref->reflowerindexpr = lowerIndexpr;

    /* Verify subscript list lengths are within implementation limit */
    if (list_length(upperIndexpr) > MAXDIM)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("number of array dimensions (%d) exceeds the maximum allowed (%d)",
                        list_length(upperIndexpr), MAXDIM)));
    /* We need not check lowerIndexpr separately */

    /*
     * Determine the result type of the subscripting operation.  It's the same
     * as the array type if we're slicing, else it's the element type.  In
     * either case, the typmod is the same as the array's, so we need not
     * change reftypmod.
     */
    if (isSlice)
        sbsref->refrestype = sbsref->refcontainertype;
    else
        sbsref->refrestype = sbsref->refelemtype;
}

/*
 * During execution, process the subscripts in a SubscriptingRef expression.
 *
 * The subscript expressions are already evaluated in Datum form in the
 * SubscriptingRefState's arrays.  Check and convert them as necessary.
 *
 * If any subscript is NULL, we throw error in assignment cases, or in fetch
 * cases set result to NULL and return false (instructing caller to skip the
 * rest of the SubscriptingRef sequence).
 *
 * We convert all the subscripts to plain integers and save them in the
 * sbsrefstate->workspace arrays.
 */
static bool
array_subscript_check_subscripts(ExprState *state,
                                 ExprEvalStep *op,
                                 ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref_subscript.state;
    ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;

    /* Process upper subscripts */
    for (int i = 0; i < sbsrefstate->numupper; i++)
    {
        if (sbsrefstate->upperprovided[i])
        {
            /* If any index expr yields NULL, result is NULL or error */
            if (sbsrefstate->upperindexnull[i])
            {
                if (sbsrefstate->isassignment)
                    ereport(ERROR,
                            (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                             errmsg("array subscript in assignment must not be null")));
                *op->resnull = true;
                return false;
            }
            workspace->upperindex[i] = DatumGetInt32(sbsrefstate->upperindex[i]);
        }
    }

    /* Likewise for lower subscripts */
    for (int i = 0; i < sbsrefstate->numlower; i++)
    {
        if (sbsrefstate->lowerprovided[i])
        {
            /* If any index expr yields NULL, result is NULL or error */
            if (sbsrefstate->lowerindexnull[i])
            {
                if (sbsrefstate->isassignment)
                    ereport(ERROR,
                            (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                             errmsg("array subscript in assignment must not be null")));
                *op->resnull = true;
                return false;
            }
            workspace->lowerindex[i] = DatumGetInt32(sbsrefstate->lowerindex[i]);
        }
    }

    return true;
}

/*
 * Evaluate SubscriptingRef fetch for an array element.
 *
 * Source container is in step's result variable (it's known not NULL, since
 * we set fetch_strict to true), and indexes have already been evaluated into
 * workspace array.
 */
static void
array_subscript_fetch(ExprState *state,
                      ExprEvalStep *op,
                      ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;

    /* Should not get here if source array (or any subscript) is null */
    Assert(!(*op->resnull));

    *op->resvalue = array_get_element(*op->resvalue,
                                      sbsrefstate->numupper,
                                      workspace->upperindex,
                                      workspace->refattrlength,
                                      workspace->refelemlength,
                                      workspace->refelembyval,
                                      workspace->refelemalign,
                                      op->resnull);
}

/*
 * Evaluate SubscriptingRef fetch for an array slice.
 *
 * Source container is in step's result variable (it's known not NULL, since
 * we set fetch_strict to true), and indexes have already been evaluated into
 * workspace array.
 */
static void
array_subscript_fetch_slice(ExprState *state,
                            ExprEvalStep *op,
                            ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;

    /* Should not get here if source array (or any subscript) is null */
    Assert(!(*op->resnull));

    *op->resvalue = array_get_slice(*op->resvalue,
                                    sbsrefstate->numupper,
                                    workspace->upperindex,
                                    workspace->lowerindex,
                                    sbsrefstate->upperprovided,
                                    sbsrefstate->lowerprovided,
                                    workspace->refattrlength,
                                    workspace->refelemlength,
                                    workspace->refelembyval,
                                    workspace->refelemalign);
    /* The slice is never NULL, so no need to change *op->resnull */
}

/*
 * Evaluate SubscriptingRef assignment for an array element assignment.
 *
 * Input container (possibly null) is in result area, replacement value is in
 * SubscriptingRefState's replacevalue/replacenull.
 */
static void
array_subscript_assign(ExprState *state,
                       ExprEvalStep *op,
                       ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;
    Datum       arraySource = *op->resvalue;

    /*
     * For an assignment to a fixed-length array type, both the original array
     * and the value to be assigned into it must be non-NULL, else we punt and
     * return the original array.
     */
    if (workspace->refattrlength > 0)
    {
        if (*op->resnull || sbsrefstate->replacenull)
            return;
    }

    /*
     * For assignment to varlena arrays, we handle a NULL original array by
     * substituting an empty (zero-dimensional) array; insertion of the new
     * element will result in a singleton array value.  It does not matter
     * whether the new element is NULL.
     */
    if (*op->resnull)
    {
        arraySource = PointerGetDatum(construct_empty_array(workspace->refelemtype));
        *op->resnull = false;
    }

    *op->resvalue = array_set_element(arraySource,
                                      sbsrefstate->numupper,
                                      workspace->upperindex,
                                      sbsrefstate->replacevalue,
                                      sbsrefstate->replacenull,
                                      workspace->refattrlength,
                                      workspace->refelemlength,
                                      workspace->refelembyval,
                                      workspace->refelemalign);
    /* The result is never NULL, so no need to change *op->resnull */
}

/*
 * Evaluate SubscriptingRef assignment for an array slice assignment.
 *
 * Input container (possibly null) is in result area, replacement value is in
 * SubscriptingRefState's replacevalue/replacenull.
 */
static void
array_subscript_assign_slice(ExprState *state,
                             ExprEvalStep *op,
                             ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;
    Datum       arraySource = *op->resvalue;

    /*
     * For an assignment to a fixed-length array type, both the original array
     * and the value to be assigned into it must be non-NULL, else we punt and
     * return the original array.
     */
    if (workspace->refattrlength > 0)
    {
        if (*op->resnull || sbsrefstate->replacenull)
            return;
    }

    /*
     * For assignment to varlena arrays, we handle a NULL original array by
     * substituting an empty (zero-dimensional) array; insertion of the new
     * element will result in a singleton array value.  It does not matter
     * whether the new element is NULL.
     */
    if (*op->resnull)
    {
        arraySource = PointerGetDatum(construct_empty_array(workspace->refelemtype));
        *op->resnull = false;
    }

    *op->resvalue = array_set_slice(arraySource,
                                    sbsrefstate->numupper,
                                    workspace->upperindex,
                                    workspace->lowerindex,
                                    sbsrefstate->upperprovided,
                                    sbsrefstate->lowerprovided,
                                    sbsrefstate->replacevalue,
                                    sbsrefstate->replacenull,
                                    workspace->refattrlength,
                                    workspace->refelemlength,
                                    workspace->refelembyval,
                                    workspace->refelemalign);
    /* The result is never NULL, so no need to change *op->resnull */
}

/*
 * Compute old array element value for a SubscriptingRef assignment
 * expression.  Will only be called if the new-value subexpression
 * contains SubscriptingRef or FieldStore.  This is the same as the
 * regular fetch case, except that we have to handle a null array,
 * and the value should be stored into the SubscriptingRefState's
 * prevvalue/prevnull fields.
 */
static void
array_subscript_fetch_old(ExprState *state,
                          ExprEvalStep *op,
                          ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;

    if (*op->resnull)
    {
        /* whole array is null, so any element is too */
        sbsrefstate->prevvalue = (Datum) 0;
        sbsrefstate->prevnull = true;
    }
    else
        sbsrefstate->prevvalue = array_get_element(*op->resvalue,
                                                   sbsrefstate->numupper,
                                                   workspace->upperindex,
                                                   workspace->refattrlength,
                                                   workspace->refelemlength,
                                                   workspace->refelembyval,
                                                   workspace->refelemalign,
                                                   &sbsrefstate->prevnull);
}

/*
 * Compute old array slice value for a SubscriptingRef assignment
 * expression.  Will only be called if the new-value subexpression
 * contains SubscriptingRef or FieldStore.  This is the same as the
 * regular fetch case, except that we have to handle a null array,
 * and the value should be stored into the SubscriptingRefState's
 * prevvalue/prevnull fields.
 *
 * Note: this is presently dead code, because the new value for a
 * slice would have to be an array, so it couldn't directly contain a
 * FieldStore; nor could it contain a SubscriptingRef assignment, since
 * we consider adjacent subscripts to index one multidimensional array
 * not nested array types.  Future generalizations might make this
 * reachable, however.
 */
static void
array_subscript_fetch_old_slice(ExprState *state,
                                ExprEvalStep *op,
                                ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;

    if (*op->resnull)
    {
        /* whole array is null, so any slice is too */
        sbsrefstate->prevvalue = (Datum) 0;
        sbsrefstate->prevnull = true;
    }
    else
    {
        sbsrefstate->prevvalue = array_get_slice(*op->resvalue,
                                                 sbsrefstate->numupper,
                                                 workspace->upperindex,
                                                 workspace->lowerindex,
                                                 sbsrefstate->upperprovided,
                                                 sbsrefstate->lowerprovided,
                                                 workspace->refattrlength,
                                                 workspace->refelemlength,
                                                 workspace->refelembyval,
                                                 workspace->refelemalign);
        /* slices of non-null arrays are never null */
        sbsrefstate->prevnull = false;
    }
}

/*
 * Set up execution state for an array subscript operation.
 */
static void
array_exec_setup(const SubscriptingRef *sbsref,
                 SubscriptingRefState *sbsrefstate,
                 SubscriptExecSteps *methods)
{
    bool        is_slice = (sbsrefstate->numlower != 0);
    ArraySubWorkspace *workspace;

    /*
     * Enforce the implementation limit on number of array subscripts.  This
     * check isn't entirely redundant with checking at parse time; conceivably
     * the expression was stored by a backend with a different MAXDIM value.
     */
    if (sbsrefstate->numupper > MAXDIM)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("number of array dimensions (%d) exceeds the maximum allowed (%d)",
                        sbsrefstate->numupper, MAXDIM)));

    /* Should be impossible if parser is sane, but check anyway: */
    if (sbsrefstate->numlower != 0 &&
        sbsrefstate->numupper != sbsrefstate->numlower)
        elog(ERROR, "upper and lower index lists are not same length");

    /*
     * Allocate type-specific workspace.
     */
    workspace = (ArraySubWorkspace *) palloc(sizeof(ArraySubWorkspace));
    sbsrefstate->workspace = workspace;

    /*
     * Collect datatype details we'll need at execution.
     */
    workspace->refelemtype = sbsref->refelemtype;
    workspace->refattrlength = get_typlen(sbsref->refcontainertype);
    get_typlenbyvalalign(sbsref->refelemtype,
                         &workspace->refelemlength,
                         &workspace->refelembyval,
                         &workspace->refelemalign);

    /*
     * Pass back pointers to appropriate step execution functions.
     */
    methods->sbs_check_subscripts = array_subscript_check_subscripts;
    if (is_slice)
    {
        methods->sbs_fetch = array_subscript_fetch_slice;
        methods->sbs_assign = array_subscript_assign_slice;
        methods->sbs_fetch_old = array_subscript_fetch_old_slice;
    }
    else
    {
        methods->sbs_fetch = array_subscript_fetch;
        methods->sbs_assign = array_subscript_assign;
        methods->sbs_fetch_old = array_subscript_fetch_old;
    }
}

/*
 * array_subscript_handler
 *      Subscripting handler for standard varlena arrays.
 *
 * This should be used only for "true" array types, which have array headers
 * as understood by the varlena array routines, and are referenced by the
 * element type's pg_type.typarray field.
 */
Datum
array_subscript_handler(PG_FUNCTION_ARGS)
{
    static const SubscriptRoutines sbsroutines = {
        .transform = array_subscript_transform,
        .exec_setup = array_exec_setup,
        .fetch_strict = true,   /* fetch returns NULL for NULL inputs */
        .fetch_leakproof = true,    /* fetch returns NULL for bad subscript */
        .store_leakproof = false    /* ... but assignment throws error */
    };

    PG_RETURN_POINTER(&sbsroutines);
}

/*
 * raw_array_subscript_handler
 *      Subscripting handler for "raw" arrays.
 *
 * A "raw" array just contains N independent instances of the element type.
 * Currently we require both the element type and the array type to be fixed
 * length, but it wouldn't be too hard to relax that for the array type.
 *
 * As of now, all the support code is shared with standard varlena arrays.
 * We may split those into separate code paths, but probably that would yield
 * only marginal speedups.  The main point of having a separate handler is
 * so that pg_type.typsubscript clearly indicates the type's semantics.
 */
Datum
raw_array_subscript_handler(PG_FUNCTION_ARGS)
{
    static const SubscriptRoutines sbsroutines = {
        .transform = array_subscript_transform,
        .exec_setup = array_exec_setup,
        .fetch_strict = true,   /* fetch returns NULL for NULL inputs */
        .fetch_leakproof = true,    /* fetch returns NULL for bad subscript */
        .store_leakproof = false    /* ... but assignment throws error */
    };

    PG_RETURN_POINTER(&sbsroutines);
}