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[pgsql.git] / src / backend / executor / functions.c

/*-------------------------------------------------------------------------
 *
 * functions.c
 *        Execution of SQL-language functions
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        src/backend/executor/functions.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "executor/functions.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
#include "parser/parse_func.h"
#include "rewrite/rewriteHandler.h"
#include "storage/proc.h"
#include "tcop/utility.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"


/*
 * Specialized DestReceiver for collecting query output in a SQL function
 */
typedef struct
{
        DestReceiver pub;                       /* publicly-known function pointers */
        Tuplestorestate *tstore;        /* where to put result tuples */
        MemoryContext cxt;                      /* context containing tstore */
        JunkFilter *filter;                     /* filter to convert tuple type */
} DR_sqlfunction;

/*
 * We have an execution_state record for each query in a function.  Each
 * record contains a plantree for its query.  If the query is currently in
 * F_EXEC_RUN state then there's a QueryDesc too.
 *
 * The "next" fields chain together all the execution_state records generated
 * from a single original parsetree.  (There will only be more than one in
 * case of rule expansion of the original parsetree.)
 */
typedef enum
{
        F_EXEC_START, F_EXEC_RUN, F_EXEC_DONE,
} ExecStatus;

typedef struct execution_state
{
        struct execution_state *next;
        ExecStatus      status;
        bool            setsResult;             /* true if this query produces func's result */
        bool            lazyEval;               /* true if should fetch one row at a time */
        PlannedStmt *stmt;                      /* plan for this query */
        QueryDesc  *qd;                         /* null unless status == RUN */
} execution_state;


/*
 * An SQLFunctionCache record is built during the first call,
 * and linked to from the fn_extra field of the FmgrInfo struct.
 *
 * Note that currently this has only the lifespan of the calling query.
 * Someday we should rewrite this code to use plancache.c to save parse/plan
 * results for longer than that.
 *
 * Physically, though, the data has the lifespan of the FmgrInfo that's used
 * to call the function, and there are cases (particularly with indexes)
 * where the FmgrInfo might survive across transactions.  We cannot assume
 * that the parse/plan trees are good for longer than the (sub)transaction in
 * which parsing was done, so we must mark the record with the LXID/subxid of
 * its creation time, and regenerate everything if that's obsolete.  To avoid
 * memory leakage when we do have to regenerate things, all the data is kept
 * in a sub-context of the FmgrInfo's fn_mcxt.
 */
typedef struct
{
        char       *fname;                      /* function name (for error msgs) */
        char       *src;                        /* function body text (for error msgs) */

        SQLFunctionParseInfoPtr pinfo;  /* data for parser callback hooks */

        Oid                     rettype;                /* actual return type */
        int16           typlen;                 /* length of the return type */
        bool            typbyval;               /* true if return type is pass by value */
        bool            returnsSet;             /* true if returning multiple rows */
        bool            returnsTuple;   /* true if returning whole tuple result */
        bool            shutdown_reg;   /* true if registered shutdown callback */
        bool            readonly_func;  /* true to run in "read only" mode */
        bool            lazyEval;               /* true if using lazyEval for result query */

        ParamListInfo paramLI;          /* Param list representing current args */

        Tuplestorestate *tstore;        /* where we accumulate result tuples */

        JunkFilter *junkFilter;         /* will be NULL if function returns VOID */

        /*
         * func_state is a List of execution_state records, each of which is the
         * first for its original parsetree, with any additional records chained
         * to it via the "next" fields.  This sublist structure is needed to keep
         * track of where the original query boundaries are.
         */
        List       *func_state;

        MemoryContext fcontext;         /* memory context holding this struct and all
                                                                 * subsidiary data */

        LocalTransactionId lxid;        /* lxid in which cache was made */
        SubTransactionId subxid;        /* subxid in which cache was made */
} SQLFunctionCache;

typedef SQLFunctionCache *SQLFunctionCachePtr;


/* non-export function prototypes */
static Node *sql_fn_param_ref(ParseState *pstate, ParamRef *pref);
static Node *sql_fn_post_column_ref(ParseState *pstate,
                                                                        ColumnRef *cref, Node *var);
static Node *sql_fn_make_param(SQLFunctionParseInfoPtr pinfo,
                                                           int paramno, int location);
static Node *sql_fn_resolve_param_name(SQLFunctionParseInfoPtr pinfo,
                                                                           const char *paramname, int location);
static List *init_execution_state(List *queryTree_list,
                                                                  SQLFunctionCachePtr fcache,
                                                                  bool lazyEvalOK);
static void init_sql_fcache(FunctionCallInfo fcinfo, Oid collation, bool lazyEvalOK);
static void postquel_start(execution_state *es, SQLFunctionCachePtr fcache);
static bool postquel_getnext(execution_state *es, SQLFunctionCachePtr fcache);
static void postquel_end(execution_state *es);
static void postquel_sub_params(SQLFunctionCachePtr fcache,
                                                                FunctionCallInfo fcinfo);
static Datum postquel_get_single_result(TupleTableSlot *slot,
                                                                                FunctionCallInfo fcinfo,
                                                                                SQLFunctionCachePtr fcache,
                                                                                MemoryContext resultcontext);
static void sql_exec_error_callback(void *arg);
static void ShutdownSQLFunction(Datum arg);
static bool coerce_fn_result_column(TargetEntry *src_tle,
                                                                        Oid res_type, int32 res_typmod,
                                                                        bool tlist_is_modifiable,
                                                                        List **upper_tlist,
                                                                        bool *upper_tlist_nontrivial);
static void sqlfunction_startup(DestReceiver *self, int operation, TupleDesc typeinfo);
static bool sqlfunction_receive(TupleTableSlot *slot, DestReceiver *self);
static void sqlfunction_shutdown(DestReceiver *self);
static void sqlfunction_destroy(DestReceiver *self);


/*
 * Prepare the SQLFunctionParseInfo struct for parsing a SQL function body
 *
 * This includes resolving actual types of polymorphic arguments.
 *
 * call_expr can be passed as NULL, but then we will fail if there are any
 * polymorphic arguments.
 */
SQLFunctionParseInfoPtr
prepare_sql_fn_parse_info(HeapTuple procedureTuple,
                                                  Node *call_expr,
                                                  Oid inputCollation)
{
        SQLFunctionParseInfoPtr pinfo;
        Form_pg_proc procedureStruct = (Form_pg_proc) GETSTRUCT(procedureTuple);
        int                     nargs;

        pinfo = (SQLFunctionParseInfoPtr) palloc0(sizeof(SQLFunctionParseInfo));

        /* Function's name (only) can be used to qualify argument names */
        pinfo->fname = pstrdup(NameStr(procedureStruct->proname));

        /* Save the function's input collation */
        pinfo->collation = inputCollation;

        /*
         * Copy input argument types from the pg_proc entry, then resolve any
         * polymorphic types.
         */
        pinfo->nargs = nargs = procedureStruct->pronargs;
        if (nargs > 0)
        {
                Oid                *argOidVect;
                int                     argnum;

                argOidVect = (Oid *) palloc(nargs * sizeof(Oid));
                memcpy(argOidVect,
                           procedureStruct->proargtypes.values,
                           nargs * sizeof(Oid));

                for (argnum = 0; argnum < nargs; argnum++)
                {
                        Oid                     argtype = argOidVect[argnum];

                        if (IsPolymorphicType(argtype))
                        {
                                argtype = get_call_expr_argtype(call_expr, argnum);
                                if (argtype == InvalidOid)
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                                                         errmsg("could not determine actual type of argument declared %s",
                                                                        format_type_be(argOidVect[argnum]))));
                                argOidVect[argnum] = argtype;
                        }
                }

                pinfo->argtypes = argOidVect;
        }

        /*
         * Collect names of arguments, too, if any
         */
        if (nargs > 0)
        {
                Datum           proargnames;
                Datum           proargmodes;
                int                     n_arg_names;
                bool            isNull;

                proargnames = SysCacheGetAttr(PROCNAMEARGSNSP, procedureTuple,
                                                                          Anum_pg_proc_proargnames,
                                                                          &isNull);
                if (isNull)
                        proargnames = PointerGetDatum(NULL);    /* just to be sure */

                proargmodes = SysCacheGetAttr(PROCNAMEARGSNSP, procedureTuple,
                                                                          Anum_pg_proc_proargmodes,
                                                                          &isNull);
                if (isNull)
                        proargmodes = PointerGetDatum(NULL);    /* just to be sure */

                n_arg_names = get_func_input_arg_names(proargnames, proargmodes,
                                                                                           &pinfo->argnames);

                /* Paranoia: ignore the result if too few array entries */
                if (n_arg_names < nargs)
                        pinfo->argnames = NULL;
        }
        else
                pinfo->argnames = NULL;

        return pinfo;
}

/*
 * Parser setup hook for parsing a SQL function body.
 */
void
sql_fn_parser_setup(struct ParseState *pstate, SQLFunctionParseInfoPtr pinfo)
{
        pstate->p_pre_columnref_hook = NULL;
        pstate->p_post_columnref_hook = sql_fn_post_column_ref;
        pstate->p_paramref_hook = sql_fn_param_ref;
        /* no need to use p_coerce_param_hook */
        pstate->p_ref_hook_state = pinfo;
}

/*
 * sql_fn_post_column_ref               parser callback for ColumnRefs
 */
static Node *
sql_fn_post_column_ref(ParseState *pstate, ColumnRef *cref, Node *var)
{
        SQLFunctionParseInfoPtr pinfo = (SQLFunctionParseInfoPtr) pstate->p_ref_hook_state;
        int                     nnames;
        Node       *field1;
        Node       *subfield = NULL;
        const char *name1;
        const char *name2 = NULL;
        Node       *param;

        /*
         * Never override a table-column reference.  This corresponds to
         * considering the parameter names to appear in a scope outside the
         * individual SQL commands, which is what we want.
         */
        if (var != NULL)
                return NULL;

        /*----------
         * The allowed syntaxes are:
         *
         * A            A = parameter name
         * A.B          A = function name, B = parameter name
         *                      OR: A = record-typed parameter name, B = field name
         *                      (the first possibility takes precedence)
         * A.B.C        A = function name, B = record-typed parameter name,
         *                      C = field name
         * A.*          Whole-row reference to composite parameter A.
         * A.B.*        Same, with A = function name, B = parameter name
         *
         * Here, it's sufficient to ignore the "*" in the last two cases --- the
         * main parser will take care of expanding the whole-row reference.
         *----------
         */
        nnames = list_length(cref->fields);

        if (nnames > 3)
                return NULL;

        if (IsA(llast(cref->fields), A_Star))
                nnames--;

        field1 = (Node *) linitial(cref->fields);
        name1 = strVal(field1);
        if (nnames > 1)
        {
                subfield = (Node *) lsecond(cref->fields);
                name2 = strVal(subfield);
        }

        if (nnames == 3)
        {
                /*
                 * Three-part name: if the first part doesn't match the function name,
                 * we can fail immediately. Otherwise, look up the second part, and
                 * take the third part to be a field reference.
                 */
                if (strcmp(name1, pinfo->fname) != 0)
                        return NULL;

                param = sql_fn_resolve_param_name(pinfo, name2, cref->location);

                subfield = (Node *) lthird(cref->fields);
                Assert(IsA(subfield, String));
        }
        else if (nnames == 2 && strcmp(name1, pinfo->fname) == 0)
        {
                /*
                 * Two-part name with first part matching function name: first see if
                 * second part matches any parameter name.
                 */
                param = sql_fn_resolve_param_name(pinfo, name2, cref->location);

                if (param)
                {
                        /* Yes, so this is a parameter reference, no subfield */
                        subfield = NULL;
                }
                else
                {
                        /* No, so try to match as parameter name and subfield */
                        param = sql_fn_resolve_param_name(pinfo, name1, cref->location);
                }
        }
        else
        {
                /* Single name, or parameter name followed by subfield */
                param = sql_fn_resolve_param_name(pinfo, name1, cref->location);
        }

        if (!param)
                return NULL;                    /* No match */

        if (subfield)
        {
                /*
                 * Must be a reference to a field of a composite parameter; otherwise
                 * ParseFuncOrColumn will return NULL, and we'll fail back at the
                 * caller.
                 */
                param = ParseFuncOrColumn(pstate,
                                                                  list_make1(subfield),
                                                                  list_make1(param),
                                                                  pstate->p_last_srf,
                                                                  NULL,
                                                                  false,
                                                                  cref->location);
        }

        return param;
}

/*
 * sql_fn_param_ref             parser callback for ParamRefs ($n symbols)
 */
static Node *
sql_fn_param_ref(ParseState *pstate, ParamRef *pref)
{
        SQLFunctionParseInfoPtr pinfo = (SQLFunctionParseInfoPtr) pstate->p_ref_hook_state;
        int                     paramno = pref->number;

        /* Check parameter number is valid */
        if (paramno <= 0 || paramno > pinfo->nargs)
                return NULL;                    /* unknown parameter number */

        return sql_fn_make_param(pinfo, paramno, pref->location);
}

/*
 * sql_fn_make_param            construct a Param node for the given paramno
 */
static Node *
sql_fn_make_param(SQLFunctionParseInfoPtr pinfo,
                                  int paramno, int location)
{
        Param      *param;

        param = makeNode(Param);
        param->paramkind = PARAM_EXTERN;
        param->paramid = paramno;
        param->paramtype = pinfo->argtypes[paramno - 1];
        param->paramtypmod = -1;
        param->paramcollid = get_typcollation(param->paramtype);
        param->location = location;

        /*
         * If we have a function input collation, allow it to override the
         * type-derived collation for parameter symbols.  (XXX perhaps this should
         * not happen if the type collation is not default?)
         */
        if (OidIsValid(pinfo->collation) && OidIsValid(param->paramcollid))
                param->paramcollid = pinfo->collation;

        return (Node *) param;
}

/*
 * Search for a function parameter of the given name; if there is one,
 * construct and return a Param node for it.  If not, return NULL.
 * Helper function for sql_fn_post_column_ref.
 */
static Node *
sql_fn_resolve_param_name(SQLFunctionParseInfoPtr pinfo,
                                                  const char *paramname, int location)
{
        int                     i;

        if (pinfo->argnames == NULL)
                return NULL;

        for (i = 0; i < pinfo->nargs; i++)
        {
                if (pinfo->argnames[i] && strcmp(pinfo->argnames[i], paramname) == 0)
                        return sql_fn_make_param(pinfo, i + 1, location);
        }

        return NULL;
}

/*
 * Set up the per-query execution_state records for a SQL function.
 *
 * The input is a List of Lists of parsed and rewritten, but not planned,
 * querytrees.  The sublist structure denotes the original query boundaries.
 */
static List *
init_execution_state(List *queryTree_list,
                                         SQLFunctionCachePtr fcache,
                                         bool lazyEvalOK)
{
        List       *eslist = NIL;
        execution_state *lasttages = NULL;
        ListCell   *lc1;

        foreach(lc1, queryTree_list)
        {
                List       *qtlist = lfirst_node(List, lc1);
                execution_state *firstes = NULL;
                execution_state *preves = NULL;
                ListCell   *lc2;

                foreach(lc2, qtlist)
                {
                        Query      *queryTree = lfirst_node(Query, lc2);
                        PlannedStmt *stmt;
                        execution_state *newes;

                        /* Plan the query if needed */
                        if (queryTree->commandType == CMD_UTILITY)
                        {
                                /* Utility commands require no planning. */
                                stmt = makeNode(PlannedStmt);
                                stmt->commandType = CMD_UTILITY;
                                stmt->canSetTag = queryTree->canSetTag;
                                stmt->utilityStmt = queryTree->utilityStmt;
                                stmt->stmt_location = queryTree->stmt_location;
                                stmt->stmt_len = queryTree->stmt_len;
                                stmt->queryId = queryTree->queryId;
                        }
                        else
                                stmt = pg_plan_query(queryTree,
                                                                         fcache->src,
                                                                         CURSOR_OPT_PARALLEL_OK,
                                                                         NULL);

                        /*
                         * Precheck all commands for validity in a function.  This should
                         * generally match the restrictions spi.c applies.
                         */
                        if (stmt->commandType == CMD_UTILITY)
                        {
                                if (IsA(stmt->utilityStmt, CopyStmt) &&
                                        ((CopyStmt *) stmt->utilityStmt)->filename == NULL)
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                                         errmsg("cannot COPY to/from client in an SQL function")));

                                if (IsA(stmt->utilityStmt, TransactionStmt))
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                        /* translator: %s is a SQL statement name */
                                                         errmsg("%s is not allowed in an SQL function",
                                                                        CreateCommandName(stmt->utilityStmt))));
                        }

                        if (fcache->readonly_func && !CommandIsReadOnly(stmt))
                                ereport(ERROR,
                                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                /* translator: %s is a SQL statement name */
                                                 errmsg("%s is not allowed in a non-volatile function",
                                                                CreateCommandName((Node *) stmt))));

                        /* OK, build the execution_state for this query */
                        newes = (execution_state *) palloc(sizeof(execution_state));
                        if (preves)
                                preves->next = newes;
                        else
                                firstes = newes;

                        newes->next = NULL;
                        newes->status = F_EXEC_START;
                        newes->setsResult = false;      /* might change below */
                        newes->lazyEval = false;        /* might change below */
                        newes->stmt = stmt;
                        newes->qd = NULL;

                        if (queryTree->canSetTag)
                                lasttages = newes;

                        preves = newes;
                }

                eslist = lappend(eslist, firstes);
        }

        /*
         * Mark the last canSetTag query as delivering the function result; then,
         * if it is a plain SELECT, mark it for lazy evaluation. If it's not a
         * SELECT we must always run it to completion.
         *
         * Note: at some point we might add additional criteria for whether to use
         * lazy eval.  However, we should prefer to use it whenever the function
         * doesn't return set, since fetching more than one row is useless in that
         * case.
         *
         * Note: don't set setsResult if the function returns VOID, as evidenced
         * by not having made a junkfilter.  This ensures we'll throw away any
         * output from the last statement in such a function.
         */
        if (lasttages && fcache->junkFilter)
        {
                lasttages->setsResult = true;
                if (lazyEvalOK &&
                        lasttages->stmt->commandType == CMD_SELECT &&
                        !lasttages->stmt->hasModifyingCTE)
                        fcache->lazyEval = lasttages->lazyEval = true;
        }

        return eslist;
}

/*
 * Initialize the SQLFunctionCache for a SQL function
 */
static void
init_sql_fcache(FunctionCallInfo fcinfo, Oid collation, bool lazyEvalOK)
{
        FmgrInfo   *finfo = fcinfo->flinfo;
        Oid                     foid = finfo->fn_oid;
        MemoryContext fcontext;
        MemoryContext oldcontext;
        Oid                     rettype;
        TupleDesc       rettupdesc;
        HeapTuple       procedureTuple;
        Form_pg_proc procedureStruct;
        SQLFunctionCachePtr fcache;
        List       *queryTree_list;
        List       *resulttlist;
        ListCell   *lc;
        Datum           tmp;
        bool            isNull;

        /*
         * Create memory context that holds all the SQLFunctionCache data.  It
         * must be a child of whatever context holds the FmgrInfo.
         */
        fcontext = AllocSetContextCreate(finfo->fn_mcxt,
                                                                         "SQL function",
                                                                         ALLOCSET_DEFAULT_SIZES);

        oldcontext = MemoryContextSwitchTo(fcontext);

        /*
         * Create the struct proper, link it to fcontext and fn_extra.  Once this
         * is done, we'll be able to recover the memory after failure, even if the
         * FmgrInfo is long-lived.
         */
        fcache = (SQLFunctionCachePtr) palloc0(sizeof(SQLFunctionCache));
        fcache->fcontext = fcontext;
        finfo->fn_extra = fcache;

        /*
         * get the procedure tuple corresponding to the given function Oid
         */
        procedureTuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(foid));
        if (!HeapTupleIsValid(procedureTuple))
                elog(ERROR, "cache lookup failed for function %u", foid);
        procedureStruct = (Form_pg_proc) GETSTRUCT(procedureTuple);

        /*
         * copy function name immediately for use by error reporting callback, and
         * for use as memory context identifier
         */
        fcache->fname = pstrdup(NameStr(procedureStruct->proname));
        MemoryContextSetIdentifier(fcontext, fcache->fname);

        /*
         * Resolve any polymorphism, obtaining the actual result type, and the
         * corresponding tupdesc if it's a rowtype.
         */
        (void) get_call_result_type(fcinfo, &rettype, &rettupdesc);

        fcache->rettype = rettype;

        /* Fetch the typlen and byval info for the result type */
        get_typlenbyval(rettype, &fcache->typlen, &fcache->typbyval);

        /* Remember whether we're returning setof something */
        fcache->returnsSet = procedureStruct->proretset;

        /* Remember if function is STABLE/IMMUTABLE */
        fcache->readonly_func =
                (procedureStruct->provolatile != PROVOLATILE_VOLATILE);

        /*
         * We need the actual argument types to pass to the parser.  Also make
         * sure that parameter symbols are considered to have the function's
         * resolved input collation.
         */
        fcache->pinfo = prepare_sql_fn_parse_info(procedureTuple,
                                                                                          finfo->fn_expr,
                                                                                          collation);

        /*
         * And of course we need the function body text.
         */
        tmp = SysCacheGetAttrNotNull(PROCOID, procedureTuple, Anum_pg_proc_prosrc);
        fcache->src = TextDatumGetCString(tmp);

        /* If we have prosqlbody, pay attention to that not prosrc. */
        tmp = SysCacheGetAttr(PROCOID,
                                                  procedureTuple,
                                                  Anum_pg_proc_prosqlbody,
                                                  &isNull);

        /*
         * Parse and rewrite the queries in the function text.  Use sublists to
         * keep track of the original query boundaries.
         *
         * Note: since parsing and planning is done in fcontext, we will generate
         * a lot of cruft that lives as long as the fcache does.  This is annoying
         * but we'll not worry about it until the module is rewritten to use
         * plancache.c.
         */
        queryTree_list = NIL;
        if (!isNull)
        {
                Node       *n;
                List       *stored_query_list;

                n = stringToNode(TextDatumGetCString(tmp));
                if (IsA(n, List))
                        stored_query_list = linitial_node(List, castNode(List, n));
                else
                        stored_query_list = list_make1(n);

                foreach(lc, stored_query_list)
                {
                        Query      *parsetree = lfirst_node(Query, lc);
                        List       *queryTree_sublist;

                        AcquireRewriteLocks(parsetree, true, false);
                        queryTree_sublist = pg_rewrite_query(parsetree);
                        queryTree_list = lappend(queryTree_list, queryTree_sublist);
                }
        }
        else
        {
                List       *raw_parsetree_list;

                raw_parsetree_list = pg_parse_query(fcache->src);

                foreach(lc, raw_parsetree_list)
                {
                        RawStmt    *parsetree = lfirst_node(RawStmt, lc);
                        List       *queryTree_sublist;

                        queryTree_sublist = pg_analyze_and_rewrite_withcb(parsetree,
                                                                                                                          fcache->src,
                                                                                                                          (ParserSetupHook) sql_fn_parser_setup,
                                                                                                                          fcache->pinfo,
                                                                                                                          NULL);
                        queryTree_list = lappend(queryTree_list, queryTree_sublist);
                }
        }

        /*
         * Check that there are no statements we don't want to allow.
         */
        check_sql_fn_statements(queryTree_list);

        /*
         * Check that the function returns the type it claims to.  Although in
         * simple cases this was already done when the function was defined, we
         * have to recheck because database objects used in the function's queries
         * might have changed type.  We'd have to recheck anyway if the function
         * had any polymorphic arguments.  Moreover, check_sql_fn_retval takes
         * care of injecting any required column type coercions.  (But we don't
         * ask it to insert nulls for dropped columns; the junkfilter handles
         * that.)
         *
         * Note: we set fcache->returnsTuple according to whether we are returning
         * the whole tuple result or just a single column.  In the latter case we
         * clear returnsTuple because we need not act different from the scalar
         * result case, even if it's a rowtype column.  (However, we have to force
         * lazy eval mode in that case; otherwise we'd need extra code to expand
         * the rowtype column into multiple columns, since we have no way to
         * notify the caller that it should do that.)
         */
        fcache->returnsTuple = check_sql_fn_retval(queryTree_list,
                                                                                           rettype,
                                                                                           rettupdesc,
                                                                                           procedureStruct->prokind,
                                                                                           false,
                                                                                           &resulttlist);

        /*
         * Construct a JunkFilter we can use to coerce the returned rowtype to the
         * desired form, unless the result type is VOID, in which case there's
         * nothing to coerce to.  (XXX Frequently, the JunkFilter isn't doing
         * anything very interesting, but much of this module expects it to be
         * there anyway.)
         */
        if (rettype != VOIDOID)
        {
                TupleTableSlot *slot = MakeSingleTupleTableSlot(NULL,
                                                                                                                &TTSOpsMinimalTuple);

                /*
                 * If the result is composite, *and* we are returning the whole tuple
                 * result, we need to insert nulls for any dropped columns.  In the
                 * single-column-result case, there might be dropped columns within
                 * the composite column value, but it's not our problem here.  There
                 * should be no resjunk entries in resulttlist, so in the second case
                 * the JunkFilter is certainly a no-op.
                 */
                if (rettupdesc && fcache->returnsTuple)
                        fcache->junkFilter = ExecInitJunkFilterConversion(resulttlist,
                                                                                                                          rettupdesc,
                                                                                                                          slot);
                else
                        fcache->junkFilter = ExecInitJunkFilter(resulttlist, slot);
        }

        if (fcache->returnsTuple)
        {
                /* Make sure output rowtype is properly blessed */
                BlessTupleDesc(fcache->junkFilter->jf_resultSlot->tts_tupleDescriptor);
        }
        else if (fcache->returnsSet && type_is_rowtype(fcache->rettype))
        {
                /*
                 * Returning rowtype as if it were scalar --- materialize won't work.
                 * Right now it's sufficient to override any caller preference for
                 * materialize mode, but to add more smarts in init_execution_state
                 * about this, we'd probably need a three-way flag instead of bool.
                 */
                lazyEvalOK = true;
        }

        /* Finally, plan the queries */
        fcache->func_state = init_execution_state(queryTree_list,
                                                                                          fcache,
                                                                                          lazyEvalOK);

        /* Mark fcache with time of creation to show it's valid */
        fcache->lxid = MyProc->vxid.lxid;
        fcache->subxid = GetCurrentSubTransactionId();

        ReleaseSysCache(procedureTuple);

        MemoryContextSwitchTo(oldcontext);
}

/* Start up execution of one execution_state node */
static void
postquel_start(execution_state *es, SQLFunctionCachePtr fcache)
{
        DestReceiver *dest;

        Assert(es->qd == NULL);

        /* Caller should have ensured a suitable snapshot is active */
        Assert(ActiveSnapshotSet());

        /*
         * If this query produces the function result, send its output to the
         * tuplestore; else discard any output.
         */
        if (es->setsResult)
        {
                DR_sqlfunction *myState;

                dest = CreateDestReceiver(DestSQLFunction);
                /* pass down the needed info to the dest receiver routines */
                myState = (DR_sqlfunction *) dest;
                Assert(myState->pub.mydest == DestSQLFunction);
                myState->tstore = fcache->tstore;
                myState->cxt = CurrentMemoryContext;
                myState->filter = fcache->junkFilter;
        }
        else
                dest = None_Receiver;

        es->qd = CreateQueryDesc(es->stmt,
                                                         fcache->src,
                                                         GetActiveSnapshot(),
                                                         InvalidSnapshot,
                                                         dest,
                                                         fcache->paramLI,
                                                         es->qd ? es->qd->queryEnv : NULL,
                                                         0);

        /* Utility commands don't need Executor. */
        if (es->qd->operation != CMD_UTILITY)
        {
                /*
                 * In lazyEval mode, do not let the executor set up an AfterTrigger
                 * context.  This is necessary not just an optimization, because we
                 * mustn't exit from the function execution with a stacked
                 * AfterTrigger level still active.  We are careful not to select
                 * lazyEval mode for any statement that could possibly queue triggers.
                 */
                int                     eflags;

                if (es->lazyEval)
                        eflags = EXEC_FLAG_SKIP_TRIGGERS;
                else
                        eflags = 0;                     /* default run-to-completion flags */
                ExecutorStart(es->qd, eflags);
        }

        es->status = F_EXEC_RUN;
}

/* Run one execution_state; either to completion or to first result row */
/* Returns true if we ran to completion */
static bool
postquel_getnext(execution_state *es, SQLFunctionCachePtr fcache)
{
        bool            result;

        if (es->qd->operation == CMD_UTILITY)
        {
                ProcessUtility(es->qd->plannedstmt,
                                           fcache->src,
                                           true,        /* protect function cache's parsetree */
                                           PROCESS_UTILITY_QUERY,
                                           es->qd->params,
                                           es->qd->queryEnv,
                                           es->qd->dest,
                                           NULL);
                result = true;                  /* never stops early */
        }
        else
        {
                /* Run regular commands to completion unless lazyEval */
                uint64          count = (es->lazyEval) ? 1 : 0;

                ExecutorRun(es->qd, ForwardScanDirection, count);

                /*
                 * If we requested run to completion OR there was no tuple returned,
                 * command must be complete.
                 */
                result = (count == 0 || es->qd->estate->es_processed == 0);
        }

        return result;
}

/* Shut down execution of one execution_state node */
static void
postquel_end(execution_state *es)
{
        /* mark status done to ensure we don't do ExecutorEnd twice */
        es->status = F_EXEC_DONE;

        /* Utility commands don't need Executor. */
        if (es->qd->operation != CMD_UTILITY)
        {
                ExecutorFinish(es->qd);
                ExecutorEnd(es->qd);
        }

        es->qd->dest->rDestroy(es->qd->dest);

        FreeQueryDesc(es->qd);
        es->qd = NULL;
}

/* Build ParamListInfo array representing current arguments */
static void
postquel_sub_params(SQLFunctionCachePtr fcache,
                                        FunctionCallInfo fcinfo)
{
        int                     nargs = fcinfo->nargs;

        if (nargs > 0)
        {
                ParamListInfo paramLI;
                Oid                *argtypes = fcache->pinfo->argtypes;

                if (fcache->paramLI == NULL)
                {
                        paramLI = makeParamList(nargs);
                        fcache->paramLI = paramLI;
                }
                else
                {
                        paramLI = fcache->paramLI;
                        Assert(paramLI->numParams == nargs);
                }

                for (int i = 0; i < nargs; i++)
                {
                        ParamExternData *prm = &paramLI->params[i];

                        /*
                         * If an incoming parameter value is a R/W expanded datum, we
                         * force it to R/O.  We'd be perfectly entitled to scribble on it,
                         * but the problem is that if the parameter is referenced more
                         * than once in the function, earlier references might mutate the
                         * value seen by later references, which won't do at all.  We
                         * could do better if we could be sure of the number of Param
                         * nodes in the function's plans; but we might not have planned
                         * all the statements yet, nor do we have plan tree walker
                         * infrastructure.  (Examining the parse trees is not good enough,
                         * because of possible function inlining during planning.)
                         */
                        prm->isnull = fcinfo->args[i].isnull;
                        prm->value = MakeExpandedObjectReadOnly(fcinfo->args[i].value,
                                                                                                        prm->isnull,
                                                                                                        get_typlen(argtypes[i]));
                        prm->pflags = 0;
                        prm->ptype = argtypes[i];
                }
        }
        else
                fcache->paramLI = NULL;
}

/*
 * Extract the SQL function's value from a single result row.  This is used
 * both for scalar (non-set) functions and for each row of a lazy-eval set
 * result.
 */
static Datum
postquel_get_single_result(TupleTableSlot *slot,
                                                   FunctionCallInfo fcinfo,
                                                   SQLFunctionCachePtr fcache,
                                                   MemoryContext resultcontext)
{
        Datum           value;
        MemoryContext oldcontext;

        /*
         * Set up to return the function value.  For pass-by-reference datatypes,
         * be sure to allocate the result in resultcontext, not the current memory
         * context (which has query lifespan).  We can't leave the data in the
         * TupleTableSlot because we intend to clear the slot before returning.
         */
        oldcontext = MemoryContextSwitchTo(resultcontext);

        if (fcache->returnsTuple)
        {
                /* We must return the whole tuple as a Datum. */
                fcinfo->isnull = false;
                value = ExecFetchSlotHeapTupleDatum(slot);
        }
        else
        {
                /*
                 * Returning a scalar, which we have to extract from the first column
                 * of the SELECT result, and then copy into result context if needed.
                 */
                value = slot_getattr(slot, 1, &(fcinfo->isnull));

                if (!fcinfo->isnull)
                        value = datumCopy(value, fcache->typbyval, fcache->typlen);
        }

        MemoryContextSwitchTo(oldcontext);

        return value;
}

/*
 * fmgr_sql: function call manager for SQL functions
 */
Datum
fmgr_sql(PG_FUNCTION_ARGS)
{
        SQLFunctionCachePtr fcache;
        ErrorContextCallback sqlerrcontext;
        MemoryContext oldcontext;
        bool            randomAccess;
        bool            lazyEvalOK;
        bool            is_first;
        bool            pushed_snapshot;
        execution_state *es;
        TupleTableSlot *slot;
        Datum           result;
        List       *eslist;
        ListCell   *eslc;

        /*
         * Setup error traceback support for ereport()
         */
        sqlerrcontext.callback = sql_exec_error_callback;
        sqlerrcontext.arg = fcinfo->flinfo;
        sqlerrcontext.previous = error_context_stack;
        error_context_stack = &sqlerrcontext;

        /* Check call context */
        if (fcinfo->flinfo->fn_retset)
        {
                ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;

                /*
                 * For simplicity, we require callers to support both set eval modes.
                 * There are cases where we must use one or must use the other, and
                 * it's not really worthwhile to postpone the check till we know. But
                 * note we do not require caller to provide an expectedDesc.
                 */
                if (!rsi || !IsA(rsi, ReturnSetInfo) ||
                        (rsi->allowedModes & SFRM_ValuePerCall) == 0 ||
                        (rsi->allowedModes & SFRM_Materialize) == 0)
                        ereport(ERROR,
                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                         errmsg("set-valued function called in context that cannot accept a set")));
                randomAccess = rsi->allowedModes & SFRM_Materialize_Random;
                lazyEvalOK = !(rsi->allowedModes & SFRM_Materialize_Preferred);
        }
        else
        {
                randomAccess = false;
                lazyEvalOK = true;
        }

        /*
         * Initialize fcache (build plans) if first time through; or re-initialize
         * if the cache is stale.
         */
        fcache = (SQLFunctionCachePtr) fcinfo->flinfo->fn_extra;

        if (fcache != NULL)
        {
                if (fcache->lxid != MyProc->vxid.lxid ||
                        !SubTransactionIsActive(fcache->subxid))
                {
                        /* It's stale; unlink and delete */
                        fcinfo->flinfo->fn_extra = NULL;
                        MemoryContextDelete(fcache->fcontext);
                        fcache = NULL;
                }
        }

        if (fcache == NULL)
        {
                init_sql_fcache(fcinfo, PG_GET_COLLATION(), lazyEvalOK);
                fcache = (SQLFunctionCachePtr) fcinfo->flinfo->fn_extra;
        }

        /*
         * Switch to context in which the fcache lives.  This ensures that our
         * tuplestore etc will have sufficient lifetime.  The sub-executor is
         * responsible for deleting per-tuple information.  (XXX in the case of a
         * long-lived FmgrInfo, this policy represents more memory leakage, but
         * it's not entirely clear where to keep stuff instead.)
         */
        oldcontext = MemoryContextSwitchTo(fcache->fcontext);

        /*
         * Find first unfinished query in function, and note whether it's the
         * first query.
         */
        eslist = fcache->func_state;
        es = NULL;
        is_first = true;
        foreach(eslc, eslist)
        {
                es = (execution_state *) lfirst(eslc);

                while (es && es->status == F_EXEC_DONE)
                {
                        is_first = false;
                        es = es->next;
                }

                if (es)
                        break;
        }

        /*
         * Convert params to appropriate format if starting a fresh execution. (If
         * continuing execution, we can re-use prior params.)
         */
        if (is_first && es && es->status == F_EXEC_START)
                postquel_sub_params(fcache, fcinfo);

        /*
         * Build tuplestore to hold results, if we don't have one already. Note
         * it's in the query-lifespan context.
         */
        if (!fcache->tstore)
                fcache->tstore = tuplestore_begin_heap(randomAccess, false, work_mem);

        /*
         * Execute each command in the function one after another until we either
         * run out of commands or get a result row from a lazily-evaluated SELECT.
         *
         * Notes about snapshot management:
         *
         * In a read-only function, we just use the surrounding query's snapshot.
         *
         * In a non-read-only function, we rely on the fact that we'll never
         * suspend execution between queries of the function: the only reason to
         * suspend execution before completion is if we are returning a row from a
         * lazily-evaluated SELECT.  So, when first entering this loop, we'll
         * either start a new query (and push a fresh snapshot) or re-establish
         * the active snapshot from the existing query descriptor.  If we need to
         * start a new query in a subsequent execution of the loop, either we need
         * a fresh snapshot (and pushed_snapshot is false) or the existing
         * snapshot is on the active stack and we can just bump its command ID.
         */
        pushed_snapshot = false;
        while (es)
        {
                bool            completed;

                if (es->status == F_EXEC_START)
                {
                        /*
                         * If not read-only, be sure to advance the command counter for
                         * each command, so that all work to date in this transaction is
                         * visible.  Take a new snapshot if we don't have one yet,
                         * otherwise just bump the command ID in the existing snapshot.
                         */
                        if (!fcache->readonly_func)
                        {
                                CommandCounterIncrement();
                                if (!pushed_snapshot)
                                {
                                        PushActiveSnapshot(GetTransactionSnapshot());
                                        pushed_snapshot = true;
                                }
                                else
                                        UpdateActiveSnapshotCommandId();
                        }

                        postquel_start(es, fcache);
                }
                else if (!fcache->readonly_func && !pushed_snapshot)
                {
                        /* Re-establish active snapshot when re-entering function */
                        PushActiveSnapshot(es->qd->snapshot);
                        pushed_snapshot = true;
                }

                completed = postquel_getnext(es, fcache);

                /*
                 * If we ran the command to completion, we can shut it down now. Any
                 * row(s) we need to return are safely stashed in the tuplestore, and
                 * we want to be sure that, for example, AFTER triggers get fired
                 * before we return anything.  Also, if the function doesn't return
                 * set, we can shut it down anyway because it must be a SELECT and we
                 * don't care about fetching any more result rows.
                 */
                if (completed || !fcache->returnsSet)
                        postquel_end(es);

                /*
                 * Break from loop if we didn't shut down (implying we got a
                 * lazily-evaluated row).  Otherwise we'll press on till the whole
                 * function is done, relying on the tuplestore to keep hold of the
                 * data to eventually be returned.  This is necessary since an
                 * INSERT/UPDATE/DELETE RETURNING that sets the result might be
                 * followed by additional rule-inserted commands, and we want to
                 * finish doing all those commands before we return anything.
                 */
                if (es->status != F_EXEC_DONE)
                        break;

                /*
                 * Advance to next execution_state, which might be in the next list.
                 */
                es = es->next;
                while (!es)
                {
                        eslc = lnext(eslist, eslc);
                        if (!eslc)
                                break;                  /* end of function */

                        es = (execution_state *) lfirst(eslc);

                        /*
                         * Flush the current snapshot so that we will take a new one for
                         * the new query list.  This ensures that new snaps are taken at
                         * original-query boundaries, matching the behavior of interactive
                         * execution.
                         */
                        if (pushed_snapshot)
                        {
                                PopActiveSnapshot();
                                pushed_snapshot = false;
                        }
                }
        }

        /*
         * The tuplestore now contains whatever row(s) we are supposed to return.
         */
        if (fcache->returnsSet)
        {
                ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;

                if (es)
                {
                        /*
                         * If we stopped short of being done, we must have a lazy-eval
                         * row.
                         */
                        Assert(es->lazyEval);
                        /* Re-use the junkfilter's output slot to fetch back the tuple */
                        Assert(fcache->junkFilter);
                        slot = fcache->junkFilter->jf_resultSlot;
                        if (!tuplestore_gettupleslot(fcache->tstore, true, false, slot))
                                elog(ERROR, "failed to fetch lazy-eval tuple");
                        /* Extract the result as a datum, and copy out from the slot */
                        result = postquel_get_single_result(slot, fcinfo,
                                                                                                fcache, oldcontext);
                        /* Clear the tuplestore, but keep it for next time */
                        /* NB: this might delete the slot's content, but we don't care */
                        tuplestore_clear(fcache->tstore);

                        /*
                         * Let caller know we're not finished.
                         */
                        rsi->isDone = ExprMultipleResult;

                        /*
                         * Ensure we will get shut down cleanly if the exprcontext is not
                         * run to completion.
                         */
                        if (!fcache->shutdown_reg)
                        {
                                RegisterExprContextCallback(rsi->econtext,
                                                                                        ShutdownSQLFunction,
                                                                                        PointerGetDatum(fcache));
                                fcache->shutdown_reg = true;
                        }
                }
                else if (fcache->lazyEval)
                {
                        /*
                         * We are done with a lazy evaluation.  Clean up.
                         */
                        tuplestore_clear(fcache->tstore);

                        /*
                         * Let caller know we're finished.
                         */
                        rsi->isDone = ExprEndResult;

                        fcinfo->isnull = true;
                        result = (Datum) 0;

                        /* Deregister shutdown callback, if we made one */
                        if (fcache->shutdown_reg)
                        {
                                UnregisterExprContextCallback(rsi->econtext,
                                                                                          ShutdownSQLFunction,
                                                                                          PointerGetDatum(fcache));
                                fcache->shutdown_reg = false;
                        }
                }
                else
                {
                        /*
                         * We are done with a non-lazy evaluation.  Return whatever is in
                         * the tuplestore.  (It is now caller's responsibility to free the
                         * tuplestore when done.)
                         */
                        rsi->returnMode = SFRM_Materialize;
                        rsi->setResult = fcache->tstore;
                        fcache->tstore = NULL;
                        /* must copy desc because execSRF.c will free it */
                        if (fcache->junkFilter)
                                rsi->setDesc = CreateTupleDescCopy(fcache->junkFilter->jf_cleanTupType);

                        fcinfo->isnull = true;
                        result = (Datum) 0;

                        /* Deregister shutdown callback, if we made one */
                        if (fcache->shutdown_reg)
                        {
                                UnregisterExprContextCallback(rsi->econtext,
                                                                                          ShutdownSQLFunction,
                                                                                          PointerGetDatum(fcache));
                                fcache->shutdown_reg = false;
                        }
                }
        }
        else
        {
                /*
                 * Non-set function.  If we got a row, return it; else return NULL.
                 */
                if (fcache->junkFilter)
                {
                        /* Re-use the junkfilter's output slot to fetch back the tuple */
                        slot = fcache->junkFilter->jf_resultSlot;
                        if (tuplestore_gettupleslot(fcache->tstore, true, false, slot))
                                result = postquel_get_single_result(slot, fcinfo,
                                                                                                        fcache, oldcontext);
                        else
                        {
                                fcinfo->isnull = true;
                                result = (Datum) 0;
                        }
                }
                else
                {
                        /* Should only get here for VOID functions and procedures */
                        Assert(fcache->rettype == VOIDOID);
                        fcinfo->isnull = true;
                        result = (Datum) 0;
                }

                /* Clear the tuplestore, but keep it for next time */
                tuplestore_clear(fcache->tstore);
        }

        /* Pop snapshot if we have pushed one */
        if (pushed_snapshot)
                PopActiveSnapshot();

        /*
         * If we've gone through every command in the function, we are done. Reset
         * the execution states to start over again on next call.
         */
        if (es == NULL)
        {
                foreach(eslc, fcache->func_state)
                {
                        es = (execution_state *) lfirst(eslc);
                        while (es)
                        {
                                es->status = F_EXEC_START;
                                es = es->next;
                        }
                }
        }

        error_context_stack = sqlerrcontext.previous;

        MemoryContextSwitchTo(oldcontext);

        return result;
}


/*
 * error context callback to let us supply a call-stack traceback
 */
static void
sql_exec_error_callback(void *arg)
{
        FmgrInfo   *flinfo = (FmgrInfo *) arg;
        SQLFunctionCachePtr fcache = (SQLFunctionCachePtr) flinfo->fn_extra;
        int                     syntaxerrposition;

        /*
         * We can do nothing useful if init_sql_fcache() didn't get as far as
         * saving the function name
         */
        if (fcache == NULL || fcache->fname == NULL)
                return;

        /*
         * If there is a syntax error position, convert to internal syntax error
         */
        syntaxerrposition = geterrposition();
        if (syntaxerrposition > 0 && fcache->src != NULL)
        {
                errposition(0);
                internalerrposition(syntaxerrposition);
                internalerrquery(fcache->src);
        }

        /*
         * Try to determine where in the function we failed.  If there is a query
         * with non-null QueryDesc, finger it.  (We check this rather than looking
         * for F_EXEC_RUN state, so that errors during ExecutorStart or
         * ExecutorEnd are blamed on the appropriate query; see postquel_start and
         * postquel_end.)
         */
        if (fcache->func_state)
        {
                execution_state *es;
                int                     query_num;
                ListCell   *lc;

                es = NULL;
                query_num = 1;
                foreach(lc, fcache->func_state)
                {
                        es = (execution_state *) lfirst(lc);
                        while (es)
                        {
                                if (es->qd)
                                {
                                        errcontext("SQL function \"%s\" statement %d",
                                                           fcache->fname, query_num);
                                        break;
                                }
                                es = es->next;
                        }
                        if (es)
                                break;
                        query_num++;
                }
                if (es == NULL)
                {
                        /*
                         * couldn't identify a running query; might be function entry,
                         * function exit, or between queries.
                         */
                        errcontext("SQL function \"%s\"", fcache->fname);
                }
        }
        else
        {
                /*
                 * Assume we failed during init_sql_fcache().  (It's possible that the
                 * function actually has an empty body, but in that case we may as
                 * well report all errors as being "during startup".)
                 */
                errcontext("SQL function \"%s\" during startup", fcache->fname);
        }
}


/*
 * callback function in case a function-returning-set needs to be shut down
 * before it has been run to completion
 */
static void
ShutdownSQLFunction(Datum arg)
{
        SQLFunctionCachePtr fcache = (SQLFunctionCachePtr) DatumGetPointer(arg);
        execution_state *es;
        ListCell   *lc;

        foreach(lc, fcache->func_state)
        {
                es = (execution_state *) lfirst(lc);
                while (es)
                {
                        /* Shut down anything still running */
                        if (es->status == F_EXEC_RUN)
                        {
                                /* Re-establish active snapshot for any called functions */
                                if (!fcache->readonly_func)
                                        PushActiveSnapshot(es->qd->snapshot);

                                postquel_end(es);

                                if (!fcache->readonly_func)
                                        PopActiveSnapshot();
                        }

                        /* Reset states to START in case we're called again */
                        es->status = F_EXEC_START;
                        es = es->next;
                }
        }

        /* Release tuplestore if we have one */
        if (fcache->tstore)
                tuplestore_end(fcache->tstore);
        fcache->tstore = NULL;

        /* execUtils will deregister the callback... */
        fcache->shutdown_reg = false;
}

/*
 * check_sql_fn_statements
 *
 * Check statements in an SQL function.  Error out if there is anything that
 * is not acceptable.
 */
void
check_sql_fn_statements(List *queryTreeLists)
{
        ListCell   *lc;

        /* We are given a list of sublists of Queries */
        foreach(lc, queryTreeLists)
        {
                List       *sublist = lfirst_node(List, lc);
                ListCell   *lc2;

                foreach(lc2, sublist)
                {
                        Query      *query = lfirst_node(Query, lc2);

                        /*
                         * Disallow calling procedures with output arguments.  The current
                         * implementation would just throw the output values away, unless
                         * the statement is the last one.  Per SQL standard, we should
                         * assign the output values by name.  By disallowing this here, we
                         * preserve an opportunity for future improvement.
                         */
                        if (query->commandType == CMD_UTILITY &&
                                IsA(query->utilityStmt, CallStmt))
                        {
                                CallStmt   *stmt = (CallStmt *) query->utilityStmt;

                                if (stmt->outargs != NIL)
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                                         errmsg("calling procedures with output arguments is not supported in SQL functions")));
                        }
                }
        }
}

/*
 * check_sql_fn_retval()
 *              Check return value of a list of lists of sql parse trees.
 *
 * The return value of a sql function is the value returned by the last
 * canSetTag query in the function.  We do some ad-hoc type checking and
 * coercion here to ensure that the function returns what it's supposed to.
 * Note that we may actually modify the last query to make it match!
 *
 * This function returns true if the sql function returns the entire tuple
 * result of its final statement, or false if it returns just the first column
 * result of that statement.  It throws an error if the final statement doesn't
 * return the right type at all.
 *
 * Note that because we allow "SELECT rowtype_expression", the result can be
 * false even when the declared function return type is a rowtype.
 *
 * For a polymorphic function the passed rettype must be the actual resolved
 * output type of the function.  (This means we can't check the type during
 * function definition of a polymorphic function.)  If we do see a polymorphic
 * rettype we'll throw an error, saying it is not a supported rettype.
 *
 * If the function returns composite, the passed rettupdesc should describe
 * the expected output.  If rettupdesc is NULL, we can't verify that the
 * output matches; that should only happen in fmgr_sql_validator(), or when
 * the function returns RECORD and the caller doesn't actually care which
 * composite type it is.
 *
 * (Typically, rettype and rettupdesc are computed by get_call_result_type
 * or a sibling function.)
 *
 * In addition to coercing individual output columns, we can modify the
 * output to include dummy NULL columns for any dropped columns appearing
 * in rettupdesc.  This is done only if the caller asks for it.
 *
 * If resultTargetList isn't NULL, then *resultTargetList is set to the
 * targetlist that defines the final statement's result.  Exception: if the
 * function is defined to return VOID then *resultTargetList is set to NIL.
 */
bool
check_sql_fn_retval(List *queryTreeLists,
                                        Oid rettype, TupleDesc rettupdesc,
                                        char prokind,
                                        bool insertDroppedCols,
                                        List **resultTargetList)
{
        bool            is_tuple_result = false;
        Query      *parse;
        ListCell   *parse_cell;
        List       *tlist;
        int                     tlistlen;
        bool            tlist_is_modifiable;
        char            fn_typtype;
        List       *upper_tlist = NIL;
        bool            upper_tlist_nontrivial = false;
        ListCell   *lc;

        if (resultTargetList)
                *resultTargetList = NIL;        /* initialize in case of VOID result */

        /*
         * If it's declared to return VOID, we don't care what's in the function.
         * (This takes care of procedures with no output parameters, as well.)
         */
        if (rettype == VOIDOID)
                return false;

        /*
         * Find the last canSetTag query in the function body (which is presented
         * to us as a list of sublists of Query nodes).  This isn't necessarily
         * the last parsetree, because rule rewriting can insert queries after
         * what the user wrote.  Note that it might not even be in the last
         * sublist, for example if the last query rewrites to DO INSTEAD NOTHING.
         * (It might not be unreasonable to throw an error in such a case, but
         * this is the historical behavior and it doesn't seem worth changing.)
         */
        parse = NULL;
        parse_cell = NULL;
        foreach(lc, queryTreeLists)
        {
                List       *sublist = lfirst_node(List, lc);
                ListCell   *lc2;

                foreach(lc2, sublist)
                {
                        Query      *q = lfirst_node(Query, lc2);

                        if (q->canSetTag)
                        {
                                parse = q;
                                parse_cell = lc2;
                        }
                }
        }

        /*
         * If it's a plain SELECT, it returns whatever the targetlist says.
         * Otherwise, if it's INSERT/UPDATE/DELETE/MERGE with RETURNING, it
         * returns that. Otherwise, the function return type must be VOID.
         *
         * Note: eventually replace this test with QueryReturnsTuples?  We'd need
         * a more general method of determining the output type, though.  Also, it
         * seems too dangerous to consider FETCH or EXECUTE as returning a
         * determinable rowtype, since they depend on relatively short-lived
         * entities.
         */
        if (parse &&
                parse->commandType == CMD_SELECT)
        {
                tlist = parse->targetList;
                /* tlist is modifiable unless it's a dummy in a setop query */
                tlist_is_modifiable = (parse->setOperations == NULL);
        }
        else if (parse &&
                         (parse->commandType == CMD_INSERT ||
                          parse->commandType == CMD_UPDATE ||
                          parse->commandType == CMD_DELETE ||
                          parse->commandType == CMD_MERGE) &&
                         parse->returningList)
        {
                tlist = parse->returningList;
                /* returningList can always be modified */
                tlist_is_modifiable = true;
        }
        else
        {
                /* Empty function body, or last statement is a utility command */
                ereport(ERROR,
                                (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                                 errmsg("return type mismatch in function declared to return %s",
                                                format_type_be(rettype)),
                                 errdetail("Function's final statement must be SELECT or INSERT/UPDATE/DELETE/MERGE RETURNING.")));
                return false;                   /* keep compiler quiet */
        }

        /*
         * OK, check that the targetlist returns something matching the declared
         * type, and modify it if necessary.  If possible, we insert any coercion
         * steps right into the final statement's targetlist.  However, that might
         * risk changes in the statement's semantics --- we can't safely change
         * the output type of a grouping column, for instance.  In such cases we
         * handle coercions by inserting an extra level of Query that effectively
         * just does a projection.
         */

        /*
         * Count the non-junk entries in the result targetlist.
         */
        tlistlen = ExecCleanTargetListLength(tlist);

        fn_typtype = get_typtype(rettype);

        if (fn_typtype == TYPTYPE_BASE ||
                fn_typtype == TYPTYPE_DOMAIN ||
                fn_typtype == TYPTYPE_ENUM ||
                fn_typtype == TYPTYPE_RANGE ||
                fn_typtype == TYPTYPE_MULTIRANGE)
        {
                /*
                 * For scalar-type returns, the target list must have exactly one
                 * non-junk entry, and its type must be coercible to rettype.
                 */
                TargetEntry *tle;

                if (tlistlen != 1)
                        ereport(ERROR,
                                        (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                                         errmsg("return type mismatch in function declared to return %s",
                                                        format_type_be(rettype)),
                                         errdetail("Final statement must return exactly one column.")));

                /* We assume here that non-junk TLEs must come first in tlists */
                tle = (TargetEntry *) linitial(tlist);
                Assert(!tle->resjunk);

                if (!coerce_fn_result_column(tle, rettype, -1,
                                                                         tlist_is_modifiable,
                                                                         &upper_tlist,
                                                                         &upper_tlist_nontrivial))
                        ereport(ERROR,
                                        (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                                         errmsg("return type mismatch in function declared to return %s",
                                                        format_type_be(rettype)),
                                         errdetail("Actual return type is %s.",
                                                           format_type_be(exprType((Node *) tle->expr)))));
        }
        else if (fn_typtype == TYPTYPE_COMPOSITE || rettype == RECORDOID)
        {
                /*
                 * Returns a rowtype.
                 *
                 * Note that we will not consider a domain over composite to be a
                 * "rowtype" return type; it goes through the scalar case above.  This
                 * is because we only provide column-by-column implicit casting, and
                 * will not cast the complete record result.  So the only way to
                 * produce a domain-over-composite result is to compute it as an
                 * explicit single-column result.  The single-composite-column code
                 * path just below could handle such cases, but it won't be reached.
                 */
                int                     tupnatts;       /* physical number of columns in tuple */
                int                     tuplogcols; /* # of nondeleted columns in tuple */
                int                     colindex;       /* physical column index */

                /*
                 * If the target list has one non-junk entry, and that expression has
                 * or can be coerced to the declared return type, take it as the
                 * result.  This allows, for example, 'SELECT func2()', where func2
                 * has the same composite return type as the function that's calling
                 * it.  This provision creates some ambiguity --- maybe the expression
                 * was meant to be the lone field of the composite result --- but it
                 * works well enough as long as we don't get too enthusiastic about
                 * inventing coercions from scalar to composite types.
                 *
                 * XXX Note that if rettype is RECORD and the expression is of a named
                 * composite type, or vice versa, this coercion will succeed, whether
                 * or not the record type really matches.  For the moment we rely on
                 * runtime type checking to catch any discrepancy, but it'd be nice to
                 * do better at parse time.
                 *
                 * We must *not* do this for a procedure, however.  Procedures with
                 * output parameter(s) have rettype RECORD, and the CALL code expects
                 * to get results corresponding to the list of output parameters, even
                 * when there's just one parameter that's composite.
                 */
                if (tlistlen == 1 && prokind != PROKIND_PROCEDURE)
                {
                        TargetEntry *tle = (TargetEntry *) linitial(tlist);

                        Assert(!tle->resjunk);
                        if (coerce_fn_result_column(tle, rettype, -1,
                                                                                tlist_is_modifiable,
                                                                                &upper_tlist,
                                                                                &upper_tlist_nontrivial))
                        {
                                /* Note that we're NOT setting is_tuple_result */
                                goto tlist_coercion_finished;
                        }
                }

                /*
                 * If the caller didn't provide an expected tupdesc, we can't do any
                 * further checking.  Assume we're returning the whole tuple.
                 */
                if (rettupdesc == NULL)
                {
                        /* Return tlist if requested */
                        if (resultTargetList)
                                *resultTargetList = tlist;
                        return true;
                }

                /*
                 * Verify that the targetlist matches the return tuple type.  We scan
                 * the non-resjunk columns, and coerce them if necessary to match the
                 * datatypes of the non-deleted attributes.  For deleted attributes,
                 * insert NULL result columns if the caller asked for that.
                 */
                tupnatts = rettupdesc->natts;
                tuplogcols = 0;                 /* we'll count nondeleted cols as we go */
                colindex = 0;

                foreach(lc, tlist)
                {
                        TargetEntry *tle = (TargetEntry *) lfirst(lc);
                        Form_pg_attribute attr;

                        /* resjunk columns can simply be ignored */
                        if (tle->resjunk)
                                continue;

                        do
                        {
                                colindex++;
                                if (colindex > tupnatts)
                                        ereport(ERROR,
                                                        (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                                                         errmsg("return type mismatch in function declared to return %s",
                                                                        format_type_be(rettype)),
                                                         errdetail("Final statement returns too many columns.")));
                                attr = TupleDescAttr(rettupdesc, colindex - 1);
                                if (attr->attisdropped && insertDroppedCols)
                                {
                                        Expr       *null_expr;

                                        /* The type of the null we insert isn't important */
                                        null_expr = (Expr *) makeConst(INT4OID,
                                                                                                   -1,
                                                                                                   InvalidOid,
                                                                                                   sizeof(int32),
                                                                                                   (Datum) 0,
                                                                                                   true,        /* isnull */
                                                                                                   true /* byval */ );
                                        upper_tlist = lappend(upper_tlist,
                                                                                  makeTargetEntry(null_expr,
                                                                                                                  list_length(upper_tlist) + 1,
                                                                                                                  NULL,
                                                                                                                  false));
                                        upper_tlist_nontrivial = true;
                                }
                        } while (attr->attisdropped);
                        tuplogcols++;

                        if (!coerce_fn_result_column(tle,
                                                                                 attr->atttypid, attr->atttypmod,
                                                                                 tlist_is_modifiable,
                                                                                 &upper_tlist,
                                                                                 &upper_tlist_nontrivial))
                                ereport(ERROR,
                                                (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                                                 errmsg("return type mismatch in function declared to return %s",
                                                                format_type_be(rettype)),
                                                 errdetail("Final statement returns %s instead of %s at column %d.",
                                                                   format_type_be(exprType((Node *) tle->expr)),
                                                                   format_type_be(attr->atttypid),
                                                                   tuplogcols)));
                }

                /* remaining columns in rettupdesc had better all be dropped */
                for (colindex++; colindex <= tupnatts; colindex++)
                {
                        if (!TupleDescCompactAttr(rettupdesc, colindex - 1)->attisdropped)
                                ereport(ERROR,
                                                (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                                                 errmsg("return type mismatch in function declared to return %s",
                                                                format_type_be(rettype)),
                                                 errdetail("Final statement returns too few columns.")));
                        if (insertDroppedCols)
                        {
                                Expr       *null_expr;

                                /* The type of the null we insert isn't important */
                                null_expr = (Expr *) makeConst(INT4OID,
                                                                                           -1,
                                                                                           InvalidOid,
                                                                                           sizeof(int32),
                                                                                           (Datum) 0,
                                                                                           true,        /* isnull */
                                                                                           true /* byval */ );
                                upper_tlist = lappend(upper_tlist,
                                                                          makeTargetEntry(null_expr,
                                                                                                          list_length(upper_tlist) + 1,
                                                                                                          NULL,
                                                                                                          false));
                                upper_tlist_nontrivial = true;
                        }
                }

                /* Report that we are returning entire tuple result */
                is_tuple_result = true;
        }
        else
                ereport(ERROR,
                                (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                                 errmsg("return type %s is not supported for SQL functions",
                                                format_type_be(rettype))));

tlist_coercion_finished:

        /*
         * If necessary, modify the final Query by injecting an extra Query level
         * that just performs a projection.  (It'd be dubious to do this to a
         * non-SELECT query, but we never have to; RETURNING lists can always be
         * modified in-place.)
         */
        if (upper_tlist_nontrivial)
        {
                Query      *newquery;
                List       *colnames;
                RangeTblEntry *rte;
                RangeTblRef *rtr;

                Assert(parse->commandType == CMD_SELECT);

                /* Most of the upper Query struct can be left as zeroes/nulls */
                newquery = makeNode(Query);
                newquery->commandType = CMD_SELECT;
                newquery->querySource = parse->querySource;
                newquery->canSetTag = true;
                newquery->targetList = upper_tlist;

                /* We need a moderately realistic colnames list for the subquery RTE */
                colnames = NIL;
                foreach(lc, parse->targetList)
                {
                        TargetEntry *tle = (TargetEntry *) lfirst(lc);

                        if (tle->resjunk)
                                continue;
                        colnames = lappend(colnames,
                                                           makeString(tle->resname ? tle->resname : ""));
                }

                /* Build a suitable RTE for the subquery */
                rte = makeNode(RangeTblEntry);
                rte->rtekind = RTE_SUBQUERY;
                rte->subquery = parse;
                rte->eref = rte->alias = makeAlias("*SELECT*", colnames);
                rte->lateral = false;
                rte->inh = false;
                rte->inFromCl = true;
                newquery->rtable = list_make1(rte);

                rtr = makeNode(RangeTblRef);
                rtr->rtindex = 1;
                newquery->jointree = makeFromExpr(list_make1(rtr), NULL);

                /*
                 * Make sure the new query is marked as having row security if the
                 * original one does.
                 */
                newquery->hasRowSecurity = parse->hasRowSecurity;

                /* Replace original query in the correct element of the query list */
                lfirst(parse_cell) = newquery;
        }

        /* Return tlist (possibly modified) if requested */
        if (resultTargetList)
                *resultTargetList = upper_tlist;

        return is_tuple_result;
}

/*
 * Process one function result column for check_sql_fn_retval
 *
 * Coerce the output value to the required type/typmod, and add a column
 * to *upper_tlist for it.  Set *upper_tlist_nontrivial to true if we
 * add an upper tlist item that's not just a Var.
 *
 * Returns true if OK, false if could not coerce to required type
 * (in which case, no changes have been made)
 */
static bool
coerce_fn_result_column(TargetEntry *src_tle,
                                                Oid res_type,
                                                int32 res_typmod,
                                                bool tlist_is_modifiable,
                                                List **upper_tlist,
                                                bool *upper_tlist_nontrivial)
{
        TargetEntry *new_tle;
        Expr       *new_tle_expr;
        Node       *cast_result;

        /*
         * If the TLE has a sortgroupref marking, don't change it, as it probably
         * is referenced by ORDER BY, DISTINCT, etc, and changing its type would
         * break query semantics.  Otherwise, it's safe to modify in-place unless
         * the query as a whole has issues with that.
         */
        if (tlist_is_modifiable && src_tle->ressortgroupref == 0)
        {
                /* OK to modify src_tle in place, if necessary */
                cast_result = coerce_to_target_type(NULL,
                                                                                        (Node *) src_tle->expr,
                                                                                        exprType((Node *) src_tle->expr),
                                                                                        res_type, res_typmod,
                                                                                        COERCION_ASSIGNMENT,
                                                                                        COERCE_IMPLICIT_CAST,
                                                                                        -1);
                if (cast_result == NULL)
                        return false;
                assign_expr_collations(NULL, cast_result);
                src_tle->expr = (Expr *) cast_result;
                /* Make a Var referencing the possibly-modified TLE */
                new_tle_expr = (Expr *) makeVarFromTargetEntry(1, src_tle);
        }
        else
        {
                /* Any casting must happen in the upper tlist */
                Var                *var = makeVarFromTargetEntry(1, src_tle);

                cast_result = coerce_to_target_type(NULL,
                                                                                        (Node *) var,
                                                                                        var->vartype,
                                                                                        res_type, res_typmod,
                                                                                        COERCION_ASSIGNMENT,
                                                                                        COERCE_IMPLICIT_CAST,
                                                                                        -1);
                if (cast_result == NULL)
                        return false;
                assign_expr_collations(NULL, cast_result);
                /* Did the coercion actually do anything? */
                if (cast_result != (Node *) var)
                        *upper_tlist_nontrivial = true;
                new_tle_expr = (Expr *) cast_result;
        }
        new_tle = makeTargetEntry(new_tle_expr,
                                                          list_length(*upper_tlist) + 1,
                                                          src_tle->resname, false);
        *upper_tlist = lappend(*upper_tlist, new_tle);
        return true;
}


/*
 * CreateSQLFunctionDestReceiver -- create a suitable DestReceiver object
 */
DestReceiver *
CreateSQLFunctionDestReceiver(void)
{
        DR_sqlfunction *self = (DR_sqlfunction *) palloc0(sizeof(DR_sqlfunction));

        self->pub.receiveSlot = sqlfunction_receive;
        self->pub.rStartup = sqlfunction_startup;
        self->pub.rShutdown = sqlfunction_shutdown;
        self->pub.rDestroy = sqlfunction_destroy;
        self->pub.mydest = DestSQLFunction;

        /* private fields will be set by postquel_start */

        return (DestReceiver *) self;
}

/*
 * sqlfunction_startup --- executor startup
 */
static void
sqlfunction_startup(DestReceiver *self, int operation, TupleDesc typeinfo)
{
        /* no-op */
}

/*
 * sqlfunction_receive --- receive one tuple
 */
static bool
sqlfunction_receive(TupleTableSlot *slot, DestReceiver *self)
{
        DR_sqlfunction *myState = (DR_sqlfunction *) self;

        /* Filter tuple as needed */
        slot = ExecFilterJunk(myState->filter, slot);

        /* Store the filtered tuple into the tuplestore */
        tuplestore_puttupleslot(myState->tstore, slot);

        return true;
}

/*
 * sqlfunction_shutdown --- executor end
 */
static void
sqlfunction_shutdown(DestReceiver *self)
{
        /* no-op */
}

/*
 * sqlfunction_destroy --- release DestReceiver object
 */
static void
sqlfunction_destroy(DestReceiver *self)
{
        pfree(self);
}