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diff --git a/src/backend/utils/adt/arraysubs.c b/src/backend/utils/adt/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);
+}
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