functions.c

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/*-------------------------------------------------------------------------
 *
 * 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/funccache.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 references 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;
 
 
/*
 * Data associated with a SQL-language function is kept in three main
 * data structures:
 *
 * 1. SQLFunctionHashEntry is a long-lived (potentially session-lifespan)
 * struct that holds all the info we need out of the function's pg_proc row.
 * In addition it holds pointers to CachedPlanSource(s) that manage creation
 * of plans for the query(s) within the function.  A SQLFunctionHashEntry is
 * potentially shared across multiple concurrent executions of the function,
 * so it must contain no execution-specific state; but its use_count must
 * reflect the number of SQLFunctionLink structs pointing at it.
 * If the function's pg_proc row is updated, we throw away and regenerate
 * the SQLFunctionHashEntry and subsidiary data.  (Also note that if the
 * function is polymorphic or used as a trigger, there is a separate
 * SQLFunctionHashEntry for each usage, so that we need consider only one
 * set of relevant data types.)  The struct itself is in memory managed by
 * funccache.c, and its subsidiary data is kept in one of two contexts:
 *  * pcontext ("parse context") holds the raw parse trees or Query trees
 *    that we read from the pg_proc row.  These will be converted to
 *    CachedPlanSources as they are needed.  Once the last one is converted,
 *    pcontext can be freed.
 *  * hcontext ("hash context") holds everything else belonging to the
 *    SQLFunctionHashEntry.
 *
 * 2. SQLFunctionCache lasts for the duration of a single execution of
 * the SQL function.  (In "lazyEval" mode, this might span multiple calls of
 * fmgr_sql.)  It holds a reference to the CachedPlan for the current query,
 * and other data that is execution-specific.  The SQLFunctionCache itself
 * as well as its subsidiary data are kept in fcontext ("function context"),
 * which we free at completion.  In non-returnsSet mode, this is just a child
 * of the call-time context.  In returnsSet mode, it is made a child of the
 * FmgrInfo's fn_mcxt so that it will survive between fmgr_sql calls.
 *
 * 3. SQLFunctionLink is a tiny struct that just holds pointers to
 * the SQLFunctionHashEntry and the current SQLFunctionCache (if any).
 * It is pointed to by the fn_extra field of the FmgrInfo struct, and is
 * always allocated in the FmgrInfo's fn_mcxt.  Its purpose is to reduce
 * the cost of repeat lookups of the SQLFunctionHashEntry.
 */
 
typedef struct SQLFunctionHashEntry
{
    CachedFunction cfunc;       /* fields managed by funccache.c */
 
    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        readonly_func;  /* true to run in "read only" mode */
    char        prokind;        /* prokind from pg_proc row */
 
    TupleDesc   rettupdesc;     /* result tuple descriptor */
 
    List       *source_list;    /* RawStmts or Queries read from pg_proc */
    int         num_queries;    /* original length of source_list */
    bool        raw_source;     /* true if source_list contains RawStmts */
 
    List       *plansource_list;    /* CachedPlanSources for fn's queries */
 
    MemoryContext pcontext;     /* memory context holding source_list */
    MemoryContext hcontext;     /* memory context holding all else */
} SQLFunctionHashEntry;
 
typedef struct SQLFunctionCache
{
    SQLFunctionHashEntry *func; /* associated SQLFunctionHashEntry */
 
    bool        lazyEvalOK;     /* true if lazyEval is safe */
    bool        shutdown_reg;   /* true if registered shutdown callback */
    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 */
 
    /*
     * While executing a particular query within the function, cplan is the
     * CachedPlan we've obtained for that query, and eslist is a list of
     * execution_state records for the individual plans within the CachedPlan.
     * next_query_index is the 0-based index of the next CachedPlanSource to
     * get a CachedPlan from.
     */
    CachedPlan *cplan;          /* Plan for current query, if any */
    ResourceOwner cowner;       /* CachedPlan is registered with this owner */
    execution_state *eslist;    /* execution_state records */
    int         next_query_index;   /* index of next CachedPlanSource to run */
 
    /* if positive, this is the index of the query we're processing */
    int         error_query_index;
 
    MemoryContext fcontext;     /* memory context holding this struct and all
                                 * subsidiary data */
} SQLFunctionCache;
 
typedef SQLFunctionCache *SQLFunctionCachePtr;
 
/* Struct pointed to by FmgrInfo.fn_extra for a SQL function */
typedef struct SQLFunctionLink
{
    /* Permanent pointer to associated SQLFunctionHashEntry */
    SQLFunctionHashEntry *func;
 
    /* Transient pointer to SQLFunctionCache, used only if returnsSet */
    SQLFunctionCache *fcache;
 
    /* Callback to release our use-count on the SQLFunctionHashEntry */
    MemoryContextCallback mcb;
} SQLFunctionLink;
 
 
/* 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 SQLFunctionCache *init_sql_fcache(FunctionCallInfo fcinfo,
                                         bool lazyEvalOK);
static bool init_execution_state(SQLFunctionCachePtr fcache);
static void prepare_next_query(SQLFunctionHashEntry *func);
static void sql_compile_callback(FunctionCallInfo fcinfo,
                                 HeapTuple procedureTuple,
                                 const CachedFunctionHashKey *hashkey,
                                 CachedFunction *cfunc,
                                 bool forValidator);
static void sql_delete_callback(CachedFunction *cfunc);
static void sql_postrewrite_callback(List *querytree_list, void *arg);
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_compile_error_callback(void *arg);
static void sql_exec_error_callback(void *arg);
static void ShutdownSQLFunction(Datum arg);
static void RemoveSQLFunctionLink(void *arg);
static void check_sql_fn_statement(List *queryTreeList);
static bool check_sql_stmt_retval(List *queryTreeList,
                                  Oid rettype, TupleDesc rettupdesc,
                                  char prokind, bool insertDroppedCols);
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 List *get_sql_fn_result_tlist(List *queryTreeList);
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;
}
 
/*
 * Initialize the SQLFunctionCache for a SQL function
 */
static SQLFunctionCache *
init_sql_fcache(FunctionCallInfo fcinfo, bool lazyEvalOK)
{
    FmgrInfo   *finfo = fcinfo->flinfo;
    SQLFunctionHashEntry *func;
    SQLFunctionCache *fcache;
    SQLFunctionLink *flink;
    MemoryContext pcontext;
    MemoryContext fcontext;
    MemoryContext oldcontext;
 
    /*
     * If this is the first execution for this FmgrInfo, set up a link struct
     * (initially containing null pointers).  The link must live as long as
     * the FmgrInfo, so it goes in fn_mcxt.  Also set up a memory context
     * callback that will be invoked when fn_mcxt is deleted.
     */
    flink = finfo->fn_extra;
    if (flink == NULL)
    {
        flink = (SQLFunctionLink *)
            MemoryContextAllocZero(finfo->fn_mcxt, sizeof(SQLFunctionLink));
        flink->mcb.func = RemoveSQLFunctionLink;
        flink->mcb.arg = flink;
        MemoryContextRegisterResetCallback(finfo->fn_mcxt, &flink->mcb);
        finfo->fn_extra = flink;
    }
 
    /*
     * If we are resuming execution of a set-returning function, just keep
     * using the same cache.  We do not ask funccache.c to re-validate the
     * SQLFunctionHashEntry: we want to run to completion using the function's
     * initial definition.
     */
    if (flink->fcache != NULL)
    {
        Assert(flink->fcache->func == flink->func);
        return flink->fcache;
    }
 
    /*
     * Look up, or re-validate, the long-lived hash entry.  Make the hash key
     * depend on the result of get_call_result_type() when that's composite,
     * so that we can safely assume that we'll build a new hash entry if the
     * composite rowtype changes.
     */
    func = (SQLFunctionHashEntry *)
        cached_function_compile(fcinfo,
                                (CachedFunction *) flink->func,
                                sql_compile_callback,
                                sql_delete_callback,
                                sizeof(SQLFunctionHashEntry),
                                true,
                                false);
 
    /*
     * Install the hash pointer in the SQLFunctionLink, and increment its use
     * count to reflect that.  If cached_function_compile gave us back a
     * different hash entry than we were using before, we must decrement that
     * one's use count.
     */
    if (func != flink->func)
    {
        if (flink->func != NULL)
        {
            Assert(flink->func->cfunc.use_count > 0);
            flink->func->cfunc.use_count--;
        }
        flink->func = func;
        func->cfunc.use_count++;
    }
 
    /*
     * Create memory context that holds all the SQLFunctionCache data.  If we
     * return a set, we must keep this in whatever context holds the FmgrInfo
     * (anything shorter-lived risks leaving a dangling pointer in flink). But
     * in a non-SRF we'll delete it before returning, and there's no need for
     * it to outlive the caller's context.
     */
    pcontext = func->returnsSet ? finfo->fn_mcxt : CurrentMemoryContext;
    fcontext = AllocSetContextCreate(pcontext,
                                     "SQL function execution",
                                     ALLOCSET_DEFAULT_SIZES);
 
    oldcontext = MemoryContextSwitchTo(fcontext);
 
    /*
     * Create the struct proper, link it to func and fcontext.
     */
    fcache = (SQLFunctionCache *) palloc0(sizeof(SQLFunctionCache));
    fcache->func = func;
    fcache->fcontext = fcontext;
    fcache->lazyEvalOK = lazyEvalOK;
 
    /*
     * If we return a set, we must link the fcache into fn_extra so that we
     * can find it again during future calls.  But in a non-SRF there is no
     * need to link it into fn_extra at all.  Not doing so removes the risk of
     * having a dangling pointer in a long-lived FmgrInfo.
     */
    if (func->returnsSet)
        flink->fcache = fcache;
 
    /*
     * We're beginning a new execution of the function, so convert params to
     * appropriate format.
     */
    postquel_sub_params(fcache, fcinfo);
 
    MemoryContextSwitchTo(oldcontext);
 
    return fcache;
}
 
/*
 * Set up the per-query execution_state records for the next query within
 * the SQL function.
 *
 * Returns true if successful, false if there are no more queries.
 */
static bool
init_execution_state(SQLFunctionCachePtr fcache)
{
    CachedPlanSource *plansource;
    execution_state *preves = NULL;
    execution_state *lasttages = NULL;
    ListCell   *lc;
 
    /*
     * Clean up after previous query, if there was one.  Note that we just
     * leak the old execution_state records until end of function execution;
     * there aren't likely to be enough of them to matter.
     */
    if (fcache->cplan)
    {
        ReleaseCachedPlan(fcache->cplan, fcache->cowner);
        fcache->cplan = NULL;
    }
    fcache->eslist = NULL;
 
    /*
     * Get the next CachedPlanSource, or stop if there are no more.  We might
     * need to create the next CachedPlanSource; if so, advance
     * error_query_index first, so that errors detected in prepare_next_query
     * are blamed on the right statement.
     */
    if (fcache->next_query_index >= list_length(fcache->func->plansource_list))
    {
        if (fcache->next_query_index >= fcache->func->num_queries)
            return false;
        fcache->error_query_index++;
        prepare_next_query(fcache->func);
    }
    else
        fcache->error_query_index++;
 
    plansource = (CachedPlanSource *) list_nth(fcache->func->plansource_list,
                                               fcache->next_query_index);
    fcache->next_query_index++;
 
    /*
     * Generate plans for the query or queries within this CachedPlanSource.
     * Register the CachedPlan with the current resource owner.  (Saving
     * cowner here is mostly paranoia, but this way we needn't assume that
     * CurrentResourceOwner will be the same when ShutdownSQLFunction runs.)
     */
    fcache->cowner = CurrentResourceOwner;
    fcache->cplan = GetCachedPlan(plansource,
                                  fcache->paramLI,
                                  fcache->cowner,
                                  NULL);
 
    /*
     * Build execution_state list to match the number of contained plans.
     */
    foreach(lc, fcache->cplan->stmt_list)
    {
        PlannedStmt *stmt = lfirst_node(PlannedStmt, lc);
        execution_state *newes;
 
        /*
         * 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->func->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
            fcache->eslist = 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 (stmt->canSetTag)
            lasttages = newes;
 
        preves = newes;
    }
 
    /*
     * If this isn't the last CachedPlanSource, we're done here.  Otherwise,
     * we need to prepare information about how to return the results.
     */
    if (fcache->next_query_index < fcache->func->num_queries)
        return true;
 
    /*
     * 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 (fcache->func->rettype != VOIDOID)
    {
        TupleTableSlot *slot = MakeSingleTupleTableSlot(NULL,
                                                        &TTSOpsMinimalTuple);
        List       *resulttlist;
 
        /*
         * Re-fetch the (possibly modified) output tlist of the final
         * statement.  By this point, we should have thrown an error if there
         * is not one.
         */
        resulttlist = get_sql_fn_result_tlist(plansource->query_list);
 
        /*
         * We need to make a copy to ensure that it doesn't disappear
         * underneath us due to plancache invalidation.
         */
        resulttlist = copyObject(resulttlist);
 
        /*
         * 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 (fcache->func->rettupdesc && fcache->func->returnsTuple)
            fcache->junkFilter = ExecInitJunkFilterConversion(resulttlist,
                                                              fcache->func->rettupdesc,
                                                              slot);
        else
            fcache->junkFilter = ExecInitJunkFilter(resulttlist, slot);
    }
 
    if (fcache->func->returnsTuple)
    {
        /* Make sure output rowtype is properly blessed */
        BlessTupleDesc(fcache->junkFilter->jf_resultSlot->tts_tupleDescriptor);
    }
    else if (fcache->func->returnsSet && type_is_rowtype(fcache->func->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 this might need more work in future.
         */
        fcache->lazyEvalOK = true;
    }
 
    /*
     * 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 (fcache->lazyEvalOK &&
            lasttages->stmt->commandType == CMD_SELECT &&
            !lasttages->stmt->hasModifyingCTE)
            fcache->lazyEval = lasttages->lazyEval = true;
    }
 
    return true;
}
 
/*
 * Convert the SQL function's next query from source form (RawStmt or Query)
 * into a CachedPlanSource.  If it's the last query, also determine whether
 * the function returnsTuple.
 */
static void
prepare_next_query(SQLFunctionHashEntry *func)
{
    int         qindex;
    bool        islast;
    CachedPlanSource *plansource;
    List       *queryTree_list;
    MemoryContext oldcontext;
 
    /* Which query should we process? */
    qindex = list_length(func->plansource_list);
    Assert(qindex < func->num_queries); /* else caller error */
    islast = (qindex + 1 >= func->num_queries);
 
    /*
     * Parse and/or rewrite the query, creating a CachedPlanSource that holds
     * a copy of the original parsetree.  Note fine point: we make a copy of
     * each original parsetree to ensure that the source_list in pcontext
     * remains unmodified during parse analysis and rewrite.  This is normally
     * unnecessary, but we have to do it in case an error is raised during
     * parse analysis.  Otherwise, a fresh attempt to execute the function
     * will arrive back here and try to work from a corrupted source_list.
     */
    if (!func->raw_source)
    {
        /* Source queries are already parse-analyzed */
        Query      *parsetree = list_nth_node(Query, func->source_list, qindex);
 
        parsetree = copyObject(parsetree);
        plansource = CreateCachedPlanForQuery(parsetree,
                                              func->src,
                                              CreateCommandTag((Node *) parsetree));
        AcquireRewriteLocks(parsetree, true, false);
        queryTree_list = pg_rewrite_query(parsetree);
    }
    else
    {
        /* Source queries are raw parsetrees */
        RawStmt    *parsetree = list_nth_node(RawStmt, func->source_list, qindex);
 
        parsetree = copyObject(parsetree);
        plansource = CreateCachedPlan(parsetree,
                                      func->src,
                                      CreateCommandTag(parsetree->stmt));
        queryTree_list = pg_analyze_and_rewrite_withcb(parsetree,
                                                       func->src,
                                                       (ParserSetupHook) sql_fn_parser_setup,
                                                       func->pinfo,
                                                       NULL);
    }
 
    /*
     * Check that there are no statements we don't want to allow.
     */
    check_sql_fn_statement(queryTree_list);
 
    /*
     * If this is the last query, 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_stmt_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 func->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.)
     */
    if (islast)
        func->returnsTuple = check_sql_stmt_retval(queryTree_list,
                                                   func->rettype,
                                                   func->rettupdesc,
                                                   func->prokind,
                                                   false);
 
    /*
     * Now that check_sql_stmt_retval has done its thing, we can complete plan
     * cache entry creation.
     */
    CompleteCachedPlan(plansource,
                       queryTree_list,
                       NULL,
                       NULL,
                       0,
                       (ParserSetupHook) sql_fn_parser_setup,
                       func->pinfo,
                       CURSOR_OPT_PARALLEL_OK | CURSOR_OPT_NO_SCROLL,
                       false);
 
    /*
     * Install post-rewrite hook.  Its arg is the hash entry if this is the
     * last statement, else NULL.
     */
    SetPostRewriteHook(plansource,
                       sql_postrewrite_callback,
                       islast ? func : NULL);
 
    /*
     * While the CachedPlanSources can take care of themselves, our List
     * pointing to them had better be in the hcontext.
     */
    oldcontext = MemoryContextSwitchTo(func->hcontext);
    func->plansource_list = lappend(func->plansource_list, plansource);
    MemoryContextSwitchTo(oldcontext);
 
    /*
     * As soon as we've linked the CachedPlanSource into the list, mark it as
     * "saved".
     */
    SaveCachedPlan(plansource);
 
    /*
     * Finally, if this was the last statement, we can flush the pcontext with
     * the original query trees; they're all safely copied into
     * CachedPlanSources now.
     */
    if (islast)
    {
        func->source_list = NIL;    /* avoid dangling pointer */
        MemoryContextDelete(func->pcontext);
        func->pcontext = NULL;
    }
}
 
/*
 * Fill a new SQLFunctionHashEntry.
 *
 * The passed-in "cfunc" struct is expected to be zeroes, except
 * for the CachedFunction fields, which we don't touch here.
 *
 * We expect to be called in a short-lived memory context (typically a
 * query's per-tuple context).  Data that is to be part of the hash entry
 * must be copied into the hcontext or pcontext as appropriate.
 */
static void
sql_compile_callback(FunctionCallInfo fcinfo,
                     HeapTuple procedureTuple,
                     const CachedFunctionHashKey *hashkey,
                     CachedFunction *cfunc,
                     bool forValidator)
{
    SQLFunctionHashEntry *func = (SQLFunctionHashEntry *) cfunc;
    Form_pg_proc procedureStruct = (Form_pg_proc) GETSTRUCT(procedureTuple);
    ErrorContextCallback comperrcontext;
    MemoryContext hcontext;
    MemoryContext pcontext;
    MemoryContext oldcontext = CurrentMemoryContext;
    Oid         rettype;
    TupleDesc   rettupdesc;
    Datum       tmp;
    bool        isNull;
    List       *source_list;
 
    /*
     * Setup error traceback support for ereport() during compile.  (This is
     * mainly useful for reporting parse errors from pg_parse_query.)
     */
    comperrcontext.callback = sql_compile_error_callback;
    comperrcontext.arg = func;
    comperrcontext.previous = error_context_stack;
    error_context_stack = &comperrcontext;
 
    /*
     * Create the hash entry's memory context.  For now it's a child of the
     * caller's context, so that it will go away if we fail partway through.
     */
    hcontext = AllocSetContextCreate(CurrentMemoryContext,
                                     "SQL function",
                                     ALLOCSET_SMALL_SIZES);
 
    /*
     * Create the not-as-long-lived pcontext.  We make this a child of
     * hcontext so that it doesn't require separate deletion.
     */
    pcontext = AllocSetContextCreate(hcontext,
                                     "SQL function parse trees",
                                     ALLOCSET_SMALL_SIZES);
    func->pcontext = pcontext;
 
    /*
     * copy function name immediately for use by error reporting callback, and
     * for use as memory context identifier
     */
    func->fname = MemoryContextStrdup(hcontext,
                                      NameStr(procedureStruct->proname));
    MemoryContextSetIdentifier(hcontext, func->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);
 
    func->rettype = rettype;
    if (rettupdesc)
    {
        MemoryContextSwitchTo(hcontext);
        func->rettupdesc = CreateTupleDescCopy(rettupdesc);
        MemoryContextSwitchTo(oldcontext);
    }
 
    /* Fetch the typlen and byval info for the result type */
    get_typlenbyval(rettype, &func->typlen, &func->typbyval);
 
    /* Remember whether we're returning setof something */
    func->returnsSet = procedureStruct->proretset;
 
    /* Remember if function is STABLE/IMMUTABLE */
    func->readonly_func =
        (procedureStruct->provolatile != PROVOLATILE_VOLATILE);
 
    /* Remember routine kind */
    func->prokind = procedureStruct->prokind;
 
    /*
     * 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.
     */
    MemoryContextSwitchTo(hcontext);
    func->pinfo = prepare_sql_fn_parse_info(procedureTuple,
                                            fcinfo->flinfo->fn_expr,
                                            PG_GET_COLLATION());
    MemoryContextSwitchTo(oldcontext);
 
    /*
     * And of course we need the function body text.
     */
    tmp = SysCacheGetAttrNotNull(PROCOID, procedureTuple, Anum_pg_proc_prosrc);
    func->src = MemoryContextStrdup(hcontext,
                                    TextDatumGetCString(tmp));
 
    /* If we have prosqlbody, pay attention to that not prosrc. */
    tmp = SysCacheGetAttr(PROCOID,
                          procedureTuple,
                          Anum_pg_proc_prosqlbody,
                          &isNull);
    if (!isNull)
    {
        /* Source queries are already parse-analyzed */
        Node       *n;
 
        n = stringToNode(TextDatumGetCString(tmp));
        if (IsA(n, List))
            source_list = linitial_node(List, castNode(List, n));
        else
            source_list = list_make1(n);
        func->raw_source = false;
    }
    else
    {
        /* Source queries are raw parsetrees */
        source_list = pg_parse_query(func->src);
        func->raw_source = true;
    }
 
    /*
     * Note: we must save the number of queries so that we'll still remember
     * how many there are after we discard source_list.
     */
    func->num_queries = list_length(source_list);
 
    /*
     * Edge case: empty function body is OK only if it returns VOID.  Normally
     * we validate that the last statement returns the right thing in
     * check_sql_stmt_retval, but we'll never reach that if there's no last
     * statement.
     */
    if (func->num_queries == 0 && rettype != VOIDOID)
        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.")));
 
    /* Save the source trees in pcontext for now. */
    MemoryContextSwitchTo(pcontext);
    func->source_list = copyObject(source_list);
    MemoryContextSwitchTo(oldcontext);
 
    /*
     * We now have a fully valid hash entry, so reparent hcontext under
     * CacheMemoryContext to make all the subsidiary data long-lived, and only
     * then install the hcontext link so that sql_delete_callback will know to
     * delete it.
     */
    MemoryContextSetParent(hcontext, CacheMemoryContext);
    func->hcontext = hcontext;
 
    error_context_stack = comperrcontext.previous;
}
 
/*
 * Deletion callback used by funccache.c.
 *
 * Free any free-able subsidiary data of cfunc, but not the
 * struct CachedFunction itself.
 */
static void
sql_delete_callback(CachedFunction *cfunc)
{
    SQLFunctionHashEntry *func = (SQLFunctionHashEntry *) cfunc;
    ListCell   *lc;
 
    /* Release the CachedPlanSources */
    foreach(lc, func->plansource_list)
    {
        CachedPlanSource *plansource = (CachedPlanSource *) lfirst(lc);
 
        DropCachedPlan(plansource);
    }
    func->plansource_list = NIL;
 
    /*
     * If we have an hcontext, free it, thereby getting rid of all subsidiary
     * data.  (If we still have a pcontext, this gets rid of that too.)
     */
    if (func->hcontext)
        MemoryContextDelete(func->hcontext);
    func->hcontext = NULL;
}
 
/*
 * Post-rewrite callback used by plancache.c.
 *
 * This must match the processing that prepare_next_query() does between
 * rewriting and calling CompleteCachedPlan().
 */
static void
sql_postrewrite_callback(List *querytree_list, void *arg)
{
    /*
     * Check that there are no statements we don't want to allow.  (Presently,
     * there's no real point in this because the result can't change from what
     * we saw originally.  But it's cheap and maybe someday it will matter.)
     */
    check_sql_fn_statement(querytree_list);
 
    /*
     * If this is the last query, we must re-do what check_sql_stmt_retval did
     * to its targetlist.  Also check that returnsTuple didn't change (it
     * probably cannot, but be cautious).
     */
    if (arg != NULL)
    {
        SQLFunctionHashEntry *func = (SQLFunctionHashEntry *) arg;
        bool        returnsTuple;
 
        returnsTuple = check_sql_stmt_retval(querytree_list,
                                             func->rettype,
                                             func->rettupdesc,
                                             func->prokind,
                                             false);
        if (returnsTuple != func->returnsTuple)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("cached plan must not change result type")));
    }
}
 
/* 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,
                             NULL,
                             fcache->func->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 */
        if (!ExecutorStart(es->qd, eflags))
            elog(ERROR, "ExecutorStart() failed unexpectedly");
    }
 
    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->func->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->func->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]));
            /* Allow the value to be substituted into custom plans */
            prm->pflags = PARAM_FLAG_CONST;
            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->func->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->func->typbyval, fcache->func->typlen);
    }
 
    MemoryContextSwitchTo(oldcontext);
 
    return value;
}
 
/*
 * fmgr_sql: function call manager for SQL functions
 */
Datum
fmgr_sql(PG_FUNCTION_ARGS)
{
    SQLFunctionCachePtr fcache;
    SQLFunctionLink *flink;
    ErrorContextCallback sqlerrcontext;
    MemoryContext tscontext;
    MemoryContext oldcontext;
    bool        randomAccess;
    bool        lazyEvalOK;
    bool        pushed_snapshot;
    execution_state *es;
    TupleTableSlot *slot;
    Datum       result;
 
    /* 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);
        /* tuplestore must have query lifespan */
        tscontext = rsi->econtext->ecxt_per_query_memory;
    }
    else
    {
        randomAccess = false;
        lazyEvalOK = true;
        /* tuplestore needn't outlive caller context */
        tscontext = CurrentMemoryContext;
    }
 
    /*
     * Initialize fcache if starting a fresh execution.
     */
    fcache = init_sql_fcache(fcinfo, lazyEvalOK);
    /* init_sql_fcache also ensures we have a SQLFunctionLink */
    flink = fcinfo->flinfo->fn_extra;
 
    /*
     * Now we can set up error traceback support for ereport()
     */
    sqlerrcontext.callback = sql_exec_error_callback;
    sqlerrcontext.arg = fcache;
    sqlerrcontext.previous = error_context_stack;
    error_context_stack = &sqlerrcontext;
 
    /*
     * Build tuplestore to hold results, if we don't have one already.  Make
     * sure it's in a suitable context.
     */
    oldcontext = MemoryContextSwitchTo(tscontext);
 
    if (!fcache->tstore)
        fcache->tstore = tuplestore_begin_heap(randomAccess, false, work_mem);
 
    /*
     * Switch to context in which the fcache lives.  The sub-executor is
     * responsible for deleting per-tuple information.  (XXX in the case of a
     * long-lived FmgrInfo, this policy potentially causes memory leakage, but
     * it's not very clear where we could keep stuff instead.  Fortunately,
     * there are few if any cases where set-returning functions are invoked
     * via FmgrInfos that would outlive the calling query.)
     */
    MemoryContextSwitchTo(fcache->fcontext);
 
    /*
     * Find first unfinished execution_state.  If none, advance to the next
     * query in function.
     */
    do
    {
        es = fcache->eslist;
        while (es && es->status == F_EXEC_DONE)
            es = es->next;
        if (es)
            break;
    } while (init_execution_state(fcache));
 
    /*
     * 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->func->readonly_func)
            {
                CommandCounterIncrement();
                if (!pushed_snapshot)
                {
                    PushActiveSnapshot(GetTransactionSnapshot());
                    pushed_snapshot = true;
                }
                else
                    UpdateActiveSnapshotCommandId();
            }
 
            postquel_start(es, fcache);
        }
        else if (!fcache->func->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->func->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, and perhaps next query.
         */
        es = es->next;
        while (!es)
        {
            /*
             * 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;
            }
 
            if (!init_execution_state(fcache))
                break;          /* end of function */
 
            es = fcache->eslist;
        }
    }
 
    /*
     * The tuplestore now contains whatever row(s) we are supposed to return.
     */
    if (fcache->func->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(flink));
                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(flink));
                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)
            {
                /* setDesc must be allocated in suitable context */
                MemoryContextSwitchTo(tscontext);
                rsi->setDesc = CreateTupleDescCopy(fcache->junkFilter->jf_cleanTupType);
                MemoryContextSwitchTo(fcache->fcontext);
            }
 
            fcinfo->isnull = true;
            result = (Datum) 0;
 
            /* Deregister shutdown callback, if we made one */
            if (fcache->shutdown_reg)
            {
                UnregisterExprContextCallback(rsi->econtext,
                                              ShutdownSQLFunction,
                                              PointerGetDatum(flink));
                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->func->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();
 
    MemoryContextSwitchTo(oldcontext);
 
    /*
     * If we've gone through every command in the function, we are done.
     * Release the cache to start over again on next call.
     */
    if (es == NULL)
    {
        if (fcache->tstore)
            tuplestore_end(fcache->tstore);
        Assert(fcache->cplan == NULL);
        flink->fcache = NULL;
        MemoryContextDelete(fcache->fcontext);
    }
 
    error_context_stack = sqlerrcontext.previous;
 
    return result;
}
 
 
/*
 * error context callback to let us supply a traceback during compile
 */
static void
sql_compile_error_callback(void *arg)
{
    SQLFunctionHashEntry *func = (SQLFunctionHashEntry *) arg;
    int         syntaxerrposition;
 
    /*
     * We can do nothing useful if sql_compile_callback() didn't get as far as
     * copying the function name
     */
    if (func->fname == NULL)
        return;
 
    /*
     * If there is a syntax error position, convert to internal syntax error
     */
    syntaxerrposition = geterrposition();
    if (syntaxerrposition > 0 && func->src != NULL)
    {
        errposition(0);
        internalerrposition(syntaxerrposition);
        internalerrquery(func->src);
    }
 
    /*
     * sql_compile_callback() doesn't do any per-query processing, so just
     * report the context as "during startup".
     */
    errcontext("SQL function \"%s\" during startup", func->fname);
}
 
/*
 * error context callback to let us supply a call-stack traceback at runtime
 */
static void
sql_exec_error_callback(void *arg)
{
    SQLFunctionCachePtr fcache = (SQLFunctionCachePtr) arg;
    int         syntaxerrposition;
 
    /*
     * If there is a syntax error position, convert to internal syntax error
     */
    syntaxerrposition = geterrposition();
    if (syntaxerrposition > 0 && fcache->func->src != NULL)
    {
        errposition(0);
        internalerrposition(syntaxerrposition);
        internalerrquery(fcache->func->src);
    }
 
    /*
     * If we failed while executing an identifiable query within the function,
     * report that.  Otherwise say it was "during startup".
     */
    if (fcache->error_query_index > 0)
        errcontext("SQL function \"%s\" statement %d",
                   fcache->func->fname, fcache->error_query_index);
    else
        errcontext("SQL function \"%s\" during startup", fcache->func->fname);
}
 
 
/*
 * ExprContext callback function
 *
 * We register this in the active ExprContext while a set-returning SQL
 * function is running, in case the function needs to be shut down before it
 * has been run to completion.  Note that this will not be called during an
 * error abort, but we don't need it because transaction abort will take care
 * of releasing executor resources.
 */
static void
ShutdownSQLFunction(Datum arg)
{
    SQLFunctionLink *flink = (SQLFunctionLink *) DatumGetPointer(arg);
    SQLFunctionCachePtr fcache = flink->fcache;
 
    if (fcache != NULL)
    {
        execution_state *es;
 
        /* Make sure we don't somehow try to do this twice */
        flink->fcache = NULL;
 
        es = fcache->eslist;
        while (es)
        {
            /* Shut down anything still running */
            if (es->status == F_EXEC_RUN)
            {
                /* Re-establish active snapshot for any called functions */
                if (!fcache->func->readonly_func)
                    PushActiveSnapshot(es->qd->snapshot);
 
                postquel_end(es);
 
                if (!fcache->func->readonly_func)
                    PopActiveSnapshot();
            }
            es = es->next;
        }
 
        /* Release tuplestore if we have one */
        if (fcache->tstore)
            tuplestore_end(fcache->tstore);
 
        /* Release CachedPlan if we have one */
        if (fcache->cplan)
            ReleaseCachedPlan(fcache->cplan, fcache->cowner);
 
        /* Release the cache */
        MemoryContextDelete(fcache->fcontext);
    }
    /* execUtils will deregister the callback... */
}
 
/*
 * MemoryContext callback function
 *
 * We register this in the memory context that contains a SQLFunctionLink
 * struct.  When the memory context is reset or deleted, we release the
 * reference count (if any) that the link holds on the long-lived hash entry.
 * Note that this will happen even during error aborts.
 */
static void
RemoveSQLFunctionLink(void *arg)
{
    SQLFunctionLink *flink = (SQLFunctionLink *) arg;
 
    if (flink->func != NULL)
    {
        Assert(flink->func->cfunc.use_count > 0);
        flink->func->cfunc.use_count--;
        /* This should be unnecessary, but let's just be sure: */
        flink->func = NULL;
    }
}
 
/*
 * 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);
 
        check_sql_fn_statement(sublist);
    }
}
 
/*
 * As above, for a single sublist of Queries.
 */
static void
check_sql_fn_statement(List *queryTreeList)
{
    ListCell   *lc;
 
    foreach(lc, queryTreeList)
    {
        Query      *query = lfirst_node(Query, lc);
 
        /*
         * 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.
 */
bool
check_sql_fn_retval(List *queryTreeLists,
                    Oid rettype, TupleDesc rettupdesc,
                    char prokind,
                    bool insertDroppedCols)
{
    List       *queryTreeList;
 
    /*
     * We consider only the last sublist of Query nodes, so that only the last
     * original statement is a candidate to produce the result.  This is a
     * change from pre-v18 versions, which would back up to the last statement
     * that includes a canSetTag query, thus ignoring any ending statement(s)
     * that rewrite to DO INSTEAD NOTHING.  That behavior was undocumented and
     * there seems no good reason for it, except that it was an artifact of
     * the original coding.
     *
     * If the function body is completely empty, handle that the same as if
     * the last query had rewritten to nothing.
     */
    if (queryTreeLists != NIL)
        queryTreeList = llast_node(List, queryTreeLists);
    else
        queryTreeList = NIL;
 
    return check_sql_stmt_retval(queryTreeList,
                                 rettype, rettupdesc,
                                 prokind, insertDroppedCols);
}
 
/*
 * As for check_sql_fn_retval, but we are given just the last query's
 * rewritten-queries list.
 */
static bool
check_sql_stmt_retval(List *queryTreeList,
                      Oid rettype, TupleDesc rettupdesc,
                      char prokind, bool insertDroppedCols)
{
    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 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 list of Query nodes.  This isn't
     * necessarily the last parsetree, because rule rewriting can insert
     * queries after what the user wrote.
     */
    parse = NULL;
    parse_cell = NULL;
    foreach(lc, queryTreeList)
    {
        Query      *q = lfirst_node(Query, lc);
 
        if (q->canSetTag)
        {
            parse = q;
            parse_cell = lc;
        }
    }
 
    /*
     * 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
    {
        /* Last statement is a utility command, or it rewrote to nothing */
        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 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 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;
}
 
/*
 * Extract the targetlist of the last canSetTag query in the given list
 * of parsed-and-rewritten Queries.  Returns NIL if there is none.
 */
static List *
get_sql_fn_result_tlist(List *queryTreeList)
{
    Query      *parse = NULL;
    ListCell   *lc;
 
    foreach(lc, queryTreeList)
    {
        Query      *q = lfirst_node(Query, lc);
 
        if (q->canSetTag)
            parse = q;
    }
    if (parse &&
        parse->commandType == CMD_SELECT)
        return parse->targetList;
    else if (parse &&
             (parse->commandType == CMD_INSERT ||
              parse->commandType == CMD_UPDATE ||
              parse->commandType == CMD_DELETE ||
              parse->commandType == CMD_MERGE) &&
             parse->returningList)
        return parse->returningList;
    else
        return NIL;
}
 
 
/*
 * 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);
}