functions.c

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/*-------------------------------------------------------------------------
 *
 * functions.c
 *    Execution of SQL-language functions
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/functions.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "executor/functions.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
#include "parser/parse_func.h"
#include "rewrite/rewriteHandler.h"
#include "storage/proc.h"
#include "tcop/utility.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
 
 
/*
 * Specialized DestReceiver for collecting query output in a SQL function
 */
typedef struct
{
    DestReceiver pub;           /* publicly-known function pointers */
    Tuplestorestate *tstore;    /* where to put result tuples */
    MemoryContext cxt;          /* context containing tstore */
    JunkFilter *filter;         /* filter to convert tuple type */
} DR_sqlfunction;
 
/*
 * We have an execution_state record for each query in a function.  Each
 * record contains a plantree for its query.  If the query is currently in
 * F_EXEC_RUN state then there's a QueryDesc too.
 *
 * The "next" fields chain together all the execution_state records generated
 * from a single original parsetree.  (There will only be more than one in
 * case of rule expansion of the original parsetree.)
 */
typedef enum
{
    F_EXEC_START, F_EXEC_RUN, F_EXEC_DONE
} ExecStatus;
 
typedef struct execution_state
{
    struct execution_state *next;
    ExecStatus  status;
    bool        setsResult;     /* true if this query produces func's result */
    bool        lazyEval;       /* true if should fetch one row at a time */
    PlannedStmt *stmt;          /* plan for this query */
    QueryDesc  *qd;             /* null unless status == RUN */
} execution_state;
 
 
/*
 * An SQLFunctionCache record is built during the first call,
 * and linked to from the fn_extra field of the FmgrInfo struct.
 *
 * Note that currently this has only the lifespan of the calling query.
 * Someday we should rewrite this code to use plancache.c to save parse/plan
 * results for longer than that.
 *
 * Physically, though, the data has the lifespan of the FmgrInfo that's used
 * to call the function, and there are cases (particularly with indexes)
 * where the FmgrInfo might survive across transactions.  We cannot assume
 * that the parse/plan trees are good for longer than the (sub)transaction in
 * which parsing was done, so we must mark the record with the LXID/subxid of
 * its creation time, and regenerate everything if that's obsolete.  To avoid
 * memory leakage when we do have to regenerate things, all the data is kept
 * in a sub-context of the FmgrInfo's fn_mcxt.
 */
typedef struct
{
    char       *fname;          /* function name (for error msgs) */
    char       *src;            /* function body text (for error msgs) */
 
    SQLFunctionParseInfoPtr pinfo;  /* data for parser callback hooks */
 
    Oid         rettype;        /* actual return type */
    int16       typlen;         /* length of the return type */
    bool        typbyval;       /* true if return type is pass by value */
    bool        returnsSet;     /* true if returning multiple rows */
    bool        returnsTuple;   /* true if returning whole tuple result */
    bool        shutdown_reg;   /* true if registered shutdown callback */
    bool        readonly_func;  /* true to run in "read only" mode */
    bool        lazyEval;       /* true if using lazyEval for result query */
 
    ParamListInfo paramLI;      /* Param list representing current args */
 
    Tuplestorestate *tstore;    /* where we accumulate result tuples */
 
    JunkFilter *junkFilter;     /* will be NULL if function returns VOID */
 
    /*
     * func_state is a List of execution_state records, each of which is the
     * first for its original parsetree, with any additional records chained
     * to it via the "next" fields.  This sublist structure is needed to keep
     * track of where the original query boundaries are.
     */
    List       *func_state;
 
    MemoryContext fcontext;     /* memory context holding this struct and all
                                 * subsidiary data */
 
    LocalTransactionId lxid;    /* lxid in which cache was made */
    SubTransactionId subxid;    /* subxid in which cache was made */
} SQLFunctionCache;
 
typedef SQLFunctionCache *SQLFunctionCachePtr;
 
 
/* non-export function prototypes */
static Node *sql_fn_param_ref(ParseState *pstate, ParamRef *pref);
static Node *sql_fn_post_column_ref(ParseState *pstate,
                                    ColumnRef *cref, Node *var);
static Node *sql_fn_make_param(SQLFunctionParseInfoPtr pinfo,
                               int paramno, int location);
static Node *sql_fn_resolve_param_name(SQLFunctionParseInfoPtr pinfo,
                                       const char *paramname, int location);
static List *init_execution_state(List *queryTree_list,
                                  SQLFunctionCachePtr fcache,
                                  bool lazyEvalOK);
static void init_sql_fcache(FunctionCallInfo fcinfo, Oid collation, bool lazyEvalOK);
static void postquel_start(execution_state *es, SQLFunctionCachePtr fcache);
static bool postquel_getnext(execution_state *es, SQLFunctionCachePtr fcache);
static void postquel_end(execution_state *es);
static void postquel_sub_params(SQLFunctionCachePtr fcache,
                                FunctionCallInfo fcinfo);
static Datum postquel_get_single_result(TupleTableSlot *slot,
                                        FunctionCallInfo fcinfo,
                                        SQLFunctionCachePtr fcache,
                                        MemoryContext resultcontext);
static void sql_exec_error_callback(void *arg);
static void ShutdownSQLFunction(Datum arg);
static bool coerce_fn_result_column(TargetEntry *src_tle,
                                    Oid res_type, int32 res_typmod,
                                    bool tlist_is_modifiable,
                                    List **upper_tlist,
                                    bool *upper_tlist_nontrivial);
static void sqlfunction_startup(DestReceiver *self, int operation, TupleDesc typeinfo);
static bool sqlfunction_receive(TupleTableSlot *slot, DestReceiver *self);
static void sqlfunction_shutdown(DestReceiver *self);
static void sqlfunction_destroy(DestReceiver *self);
 
 
/*
 * Prepare the SQLFunctionParseInfo struct for parsing a SQL function body
 *
 * This includes resolving actual types of polymorphic arguments.
 *
 * call_expr can be passed as NULL, but then we will fail if there are any
 * polymorphic arguments.
 */
SQLFunctionParseInfoPtr
prepare_sql_fn_parse_info(HeapTuple procedureTuple,
                          Node *call_expr,
                          Oid inputCollation)
{
    SQLFunctionParseInfoPtr pinfo;
    Form_pg_proc procedureStruct = (Form_pg_proc) GETSTRUCT(procedureTuple);
    int         nargs;
 
    pinfo = (SQLFunctionParseInfoPtr) palloc0(sizeof(SQLFunctionParseInfo));
 
    /* Function's name (only) can be used to qualify argument names */
    pinfo->fname = pstrdup(NameStr(procedureStruct->proname));
 
    /* Save the function's input collation */
    pinfo->collation = inputCollation;
 
    /*
     * Copy input argument types from the pg_proc entry, then resolve any
     * polymorphic types.
     */
    pinfo->nargs = nargs = procedureStruct->pronargs;
    if (nargs > 0)
    {
        Oid        *argOidVect;
        int         argnum;
 
        argOidVect = (Oid *) palloc(nargs * sizeof(Oid));
        memcpy(argOidVect,
               procedureStruct->proargtypes.values,
               nargs * sizeof(Oid));
 
        for (argnum = 0; argnum < nargs; argnum++)
        {
            Oid         argtype = argOidVect[argnum];
 
            if (IsPolymorphicType(argtype))
            {
                argtype = get_call_expr_argtype(call_expr, argnum);
                if (argtype == InvalidOid)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                             errmsg("could not determine actual type of argument declared %s",
                                    format_type_be(argOidVect[argnum]))));
                argOidVect[argnum] = argtype;
            }
        }
 
        pinfo->argtypes = argOidVect;
    }
 
    /*
     * Collect names of arguments, too, if any
     */
    if (nargs > 0)
    {
        Datum       proargnames;
        Datum       proargmodes;
        int         n_arg_names;
        bool        isNull;
 
        proargnames = SysCacheGetAttr(PROCNAMEARGSNSP, procedureTuple,
                                      Anum_pg_proc_proargnames,
                                      &isNull);
        if (isNull)
            proargnames = PointerGetDatum(NULL);    /* just to be sure */
 
        proargmodes = SysCacheGetAttr(PROCNAMEARGSNSP, procedureTuple,
                                      Anum_pg_proc_proargmodes,
                                      &isNull);
        if (isNull)
            proargmodes = PointerGetDatum(NULL);    /* just to be sure */
 
        n_arg_names = get_func_input_arg_names(proargnames, proargmodes,
                                               &pinfo->argnames);
 
        /* Paranoia: ignore the result if too few array entries */
        if (n_arg_names < nargs)
            pinfo->argnames = NULL;
    }
    else
        pinfo->argnames = NULL;
 
    return pinfo;
}
 
/*
 * Parser setup hook for parsing a SQL function body.
 */
void
sql_fn_parser_setup(struct ParseState *pstate, SQLFunctionParseInfoPtr pinfo)
{
    pstate->p_pre_columnref_hook = NULL;
    pstate->p_post_columnref_hook = sql_fn_post_column_ref;
    pstate->p_paramref_hook = sql_fn_param_ref;
    /* no need to use p_coerce_param_hook */
    pstate->p_ref_hook_state = (void *) pinfo;
}
 
/*
 * sql_fn_post_column_ref       parser callback for ColumnRefs
 */
static Node *
sql_fn_post_column_ref(ParseState *pstate, ColumnRef *cref, Node *var)
{
    SQLFunctionParseInfoPtr pinfo = (SQLFunctionParseInfoPtr) pstate->p_ref_hook_state;
    int         nnames;
    Node       *field1;
    Node       *subfield = NULL;
    const char *name1;
    const char *name2 = NULL;
    Node       *param;
 
    /*
     * Never override a table-column reference.  This corresponds to
     * considering the parameter names to appear in a scope outside the
     * individual SQL commands, which is what we want.
     */
    if (var != NULL)
        return NULL;
 
    /*----------
     * The allowed syntaxes are:
     *
     * A        A = parameter name
     * A.B      A = function name, B = parameter name
     *          OR: A = record-typed parameter name, B = field name
     *          (the first possibility takes precedence)
     * A.B.C    A = function name, B = record-typed parameter name,
     *          C = field name
     * A.*      Whole-row reference to composite parameter A.
     * A.B.*    Same, with A = function name, B = parameter name
     *
     * Here, it's sufficient to ignore the "*" in the last two cases --- the
     * main parser will take care of expanding the whole-row reference.
     *----------
     */
    nnames = list_length(cref->fields);
 
    if (nnames > 3)
        return NULL;
 
    if (IsA(llast(cref->fields), A_Star))
        nnames--;
 
    field1 = (Node *) linitial(cref->fields);
    name1 = strVal(field1);
    if (nnames > 1)
    {
        subfield = (Node *) lsecond(cref->fields);
        name2 = strVal(subfield);
    }
 
    if (nnames == 3)
    {
        /*
         * Three-part name: if the first part doesn't match the function name,
         * we can fail immediately. Otherwise, look up the second part, and
         * take the third part to be a field reference.
         */
        if (strcmp(name1, pinfo->fname) != 0)
            return NULL;
 
        param = sql_fn_resolve_param_name(pinfo, name2, cref->location);
 
        subfield = (Node *) lthird(cref->fields);
        Assert(IsA(subfield, String));
    }
    else if (nnames == 2 && strcmp(name1, pinfo->fname) == 0)
    {
        /*
         * Two-part name with first part matching function name: first see if
         * second part matches any parameter name.
         */
        param = sql_fn_resolve_param_name(pinfo, name2, cref->location);
 
        if (param)
        {
            /* Yes, so this is a parameter reference, no subfield */
            subfield = NULL;
        }
        else
        {
            /* No, so try to match as parameter name and subfield */
            param = sql_fn_resolve_param_name(pinfo, name1, cref->location);
        }
    }
    else
    {
        /* Single name, or parameter name followed by subfield */
        param = sql_fn_resolve_param_name(pinfo, name1, cref->location);
    }
 
    if (!param)
        return NULL;            /* No match */
 
    if (subfield)
    {
        /*
         * Must be a reference to a field of a composite parameter; otherwise
         * ParseFuncOrColumn will return NULL, and we'll fail back at the
         * caller.
         */
        param = ParseFuncOrColumn(pstate,
                                  list_make1(subfield),
                                  list_make1(param),
                                  pstate->p_last_srf,
                                  NULL,
                                  false,
                                  cref->location);
    }
 
    return param;
}
 
/*
 * sql_fn_param_ref     parser callback for ParamRefs ($n symbols)
 */
static Node *
sql_fn_param_ref(ParseState *pstate, ParamRef *pref)
{
    SQLFunctionParseInfoPtr pinfo = (SQLFunctionParseInfoPtr) pstate->p_ref_hook_state;
    int         paramno = pref->number;
 
    /* Check parameter number is valid */
    if (paramno <= 0 || paramno > pinfo->nargs)
        return NULL;            /* unknown parameter number */
 
    return sql_fn_make_param(pinfo, paramno, pref->location);
}
 
/*
 * sql_fn_make_param        construct a Param node for the given paramno
 */
static Node *
sql_fn_make_param(SQLFunctionParseInfoPtr pinfo,
                  int paramno, int location)
{
    Param      *param;
 
    param = makeNode(Param);
    param->paramkind = PARAM_EXTERN;
    param->paramid = paramno;
    param->paramtype = pinfo->argtypes[paramno - 1];
    param->paramtypmod = -1;
    param->paramcollid = get_typcollation(param->paramtype);
    param->location = location;
 
    /*
     * If we have a function input collation, allow it to override the
     * type-derived collation for parameter symbols.  (XXX perhaps this should
     * not happen if the type collation is not default?)
     */
    if (OidIsValid(pinfo->collation) && OidIsValid(param->paramcollid))
        param->paramcollid = pinfo->collation;
 
    return (Node *) param;
}
 
/*
 * Search for a function parameter of the given name; if there is one,
 * construct and return a Param node for it.  If not, return NULL.
 * Helper function for sql_fn_post_column_ref.
 */
static Node *
sql_fn_resolve_param_name(SQLFunctionParseInfoPtr pinfo,
                          const char *paramname, int location)
{
    int         i;
 
    if (pinfo->argnames == NULL)
        return NULL;
 
    for (i = 0; i < pinfo->nargs; i++)
    {
        if (pinfo->argnames[i] && strcmp(pinfo->argnames[i], paramname) == 0)
            return sql_fn_make_param(pinfo, i + 1, location);
    }
 
    return NULL;
}
 
/*
 * Set up the per-query execution_state records for a SQL function.
 *
 * The input is a List of Lists of parsed and rewritten, but not planned,
 * querytrees.  The sublist structure denotes the original query boundaries.
 */
static List *
init_execution_state(List *queryTree_list,
                     SQLFunctionCachePtr fcache,
                     bool lazyEvalOK)
{
    List       *eslist = NIL;
    execution_state *lasttages = NULL;
    ListCell   *lc1;
 
    foreach(lc1, queryTree_list)
    {
        List       *qtlist = lfirst_node(List, lc1);
        execution_state *firstes = NULL;
        execution_state *preves = NULL;
        ListCell   *lc2;
 
        foreach(lc2, qtlist)
        {
            Query      *queryTree = lfirst_node(Query, lc2);
            PlannedStmt *stmt;
            execution_state *newes;
 
            /* Plan the query if needed */
            if (queryTree->commandType == CMD_UTILITY)
            {
                /* Utility commands require no planning. */
                stmt = makeNode(PlannedStmt);
                stmt->commandType = CMD_UTILITY;
                stmt->canSetTag = queryTree->canSetTag;
                stmt->utilityStmt = queryTree->utilityStmt;
                stmt->stmt_location = queryTree->stmt_location;
                stmt->stmt_len = queryTree->stmt_len;
            }
            else
                stmt = pg_plan_query(queryTree,
                                     fcache->src,
                                     CURSOR_OPT_PARALLEL_OK,
                                     NULL);
 
            /*
             * Precheck all commands for validity in a function.  This should
             * generally match the restrictions spi.c applies.
             */
            if (stmt->commandType == CMD_UTILITY)
            {
                if (IsA(stmt->utilityStmt, CopyStmt) &&
                    ((CopyStmt *) stmt->utilityStmt)->filename == NULL)
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("cannot COPY to/from client in an SQL function")));
 
                if (IsA(stmt->utilityStmt, TransactionStmt))
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                    /* translator: %s is a SQL statement name */
                             errmsg("%s is not allowed in an SQL function",
                                    CreateCommandName(stmt->utilityStmt))));
            }
 
            if (fcache->readonly_func && !CommandIsReadOnly(stmt))
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                /* translator: %s is a SQL statement name */
                         errmsg("%s is not allowed in a non-volatile function",
                                CreateCommandName((Node *) stmt))));
 
            /* OK, build the execution_state for this query */
            newes = (execution_state *) palloc(sizeof(execution_state));
            if (preves)
                preves->next = newes;
            else
                firstes = newes;
 
            newes->next = NULL;
            newes->status = F_EXEC_START;
            newes->setsResult = false;  /* might change below */
            newes->lazyEval = false;    /* might change below */
            newes->stmt = stmt;
            newes->qd = NULL;
 
            if (queryTree->canSetTag)
                lasttages = newes;
 
            preves = newes;
        }
 
        eslist = lappend(eslist, firstes);
    }
 
    /*
     * Mark the last canSetTag query as delivering the function result; then,
     * if it is a plain SELECT, mark it for lazy evaluation. If it's not a
     * SELECT we must always run it to completion.
     *
     * Note: at some point we might add additional criteria for whether to use
     * lazy eval.  However, we should prefer to use it whenever the function
     * doesn't return set, since fetching more than one row is useless in that
     * case.
     *
     * Note: don't set setsResult if the function returns VOID, as evidenced
     * by not having made a junkfilter.  This ensures we'll throw away any
     * output from the last statement in such a function.
     */
    if (lasttages && fcache->junkFilter)
    {
        lasttages->setsResult = true;
        if (lazyEvalOK &&
            lasttages->stmt->commandType == CMD_SELECT &&
            !lasttages->stmt->hasModifyingCTE)
            fcache->lazyEval = lasttages->lazyEval = true;
    }
 
    return eslist;
}
 
/*
 * Initialize the SQLFunctionCache for a SQL function
 */
static void
init_sql_fcache(FunctionCallInfo fcinfo, Oid collation, bool lazyEvalOK)
{
    FmgrInfo   *finfo = fcinfo->flinfo;
    Oid         foid = finfo->fn_oid;
    MemoryContext fcontext;
    MemoryContext oldcontext;
    Oid         rettype;
    TupleDesc   rettupdesc;
    HeapTuple   procedureTuple;
    Form_pg_proc procedureStruct;
    SQLFunctionCachePtr fcache;
    List       *queryTree_list;
    List       *resulttlist;
    ListCell   *lc;
    Datum       tmp;
    bool        isNull;
 
    /*
     * Create memory context that holds all the SQLFunctionCache data.  It
     * must be a child of whatever context holds the FmgrInfo.
     */
    fcontext = AllocSetContextCreate(finfo->fn_mcxt,
                                     "SQL function",
                                     ALLOCSET_DEFAULT_SIZES);
 
    oldcontext = MemoryContextSwitchTo(fcontext);
 
    /*
     * Create the struct proper, link it to fcontext and fn_extra.  Once this
     * is done, we'll be able to recover the memory after failure, even if the
     * FmgrInfo is long-lived.
     */
    fcache = (SQLFunctionCachePtr) palloc0(sizeof(SQLFunctionCache));
    fcache->fcontext = fcontext;
    finfo->fn_extra = (void *) fcache;
 
    /*
     * get the procedure tuple corresponding to the given function Oid
     */
    procedureTuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(foid));
    if (!HeapTupleIsValid(procedureTuple))
        elog(ERROR, "cache lookup failed for function %u", foid);
    procedureStruct = (Form_pg_proc) GETSTRUCT(procedureTuple);
 
    /*
     * copy function name immediately for use by error reporting callback, and
     * for use as memory context identifier
     */
    fcache->fname = pstrdup(NameStr(procedureStruct->proname));
    MemoryContextSetIdentifier(fcontext, fcache->fname);
 
    /*
     * Resolve any polymorphism, obtaining the actual result type, and the
     * corresponding tupdesc if it's a rowtype.
     */
    (void) get_call_result_type(fcinfo, &rettype, &rettupdesc);
 
    fcache->rettype = rettype;
 
    /* Fetch the typlen and byval info for the result type */
    get_typlenbyval(rettype, &fcache->typlen, &fcache->typbyval);
 
    /* Remember whether we're returning setof something */
    fcache->returnsSet = procedureStruct->proretset;
 
    /* Remember if function is STABLE/IMMUTABLE */
    fcache->readonly_func =
        (procedureStruct->provolatile != PROVOLATILE_VOLATILE);
 
    /*
     * We need the actual argument types to pass to the parser.  Also make
     * sure that parameter symbols are considered to have the function's
     * resolved input collation.
     */
    fcache->pinfo = prepare_sql_fn_parse_info(procedureTuple,
                                              finfo->fn_expr,
                                              collation);
 
    /*
     * And of course we need the function body text.
     */
    tmp = SysCacheGetAttrNotNull(PROCOID, procedureTuple, Anum_pg_proc_prosrc);
    fcache->src = TextDatumGetCString(tmp);
 
    /* If we have prosqlbody, pay attention to that not prosrc. */
    tmp = SysCacheGetAttr(PROCOID,
                          procedureTuple,
                          Anum_pg_proc_prosqlbody,
                          &isNull);
 
    /*
     * Parse and rewrite the queries in the function text.  Use sublists to
     * keep track of the original query boundaries.
     *
     * Note: since parsing and planning is done in fcontext, we will generate
     * a lot of cruft that lives as long as the fcache does.  This is annoying
     * but we'll not worry about it until the module is rewritten to use
     * plancache.c.
     */
    queryTree_list = NIL;
    if (!isNull)
    {
        Node       *n;
        List       *stored_query_list;
 
        n = stringToNode(TextDatumGetCString(tmp));
        if (IsA(n, List))
            stored_query_list = linitial_node(List, castNode(List, n));
        else
            stored_query_list = list_make1(n);
 
        foreach(lc, stored_query_list)
        {
            Query      *parsetree = lfirst_node(Query, lc);
            List       *queryTree_sublist;
 
            AcquireRewriteLocks(parsetree, true, false);
            queryTree_sublist = pg_rewrite_query(parsetree);
            queryTree_list = lappend(queryTree_list, queryTree_sublist);
        }
    }
    else
    {
        List       *raw_parsetree_list;
 
        raw_parsetree_list = pg_parse_query(fcache->src);
 
        foreach(lc, raw_parsetree_list)
        {
            RawStmt    *parsetree = lfirst_node(RawStmt, lc);
            List       *queryTree_sublist;
 
            queryTree_sublist = pg_analyze_and_rewrite_withcb(parsetree,
                                                              fcache->src,
                                                              (ParserSetupHook) sql_fn_parser_setup,
                                                              fcache->pinfo,
                                                              NULL);
            queryTree_list = lappend(queryTree_list, queryTree_sublist);
        }
    }
 
    /*
     * Check that there are no statements we don't want to allow.
     */
    check_sql_fn_statements(queryTree_list);
 
    /*
     * Check that the function returns the type it claims to.  Although in
     * simple cases this was already done when the function was defined, we
     * have to recheck because database objects used in the function's queries
     * might have changed type.  We'd have to recheck anyway if the function
     * had any polymorphic arguments.  Moreover, check_sql_fn_retval takes
     * care of injecting any required column type coercions.  (But we don't
     * ask it to insert nulls for dropped columns; the junkfilter handles
     * that.)
     *
     * Note: we set fcache->returnsTuple according to whether we are returning
     * the whole tuple result or just a single column.  In the latter case we
     * clear returnsTuple because we need not act different from the scalar
     * result case, even if it's a rowtype column.  (However, we have to force
     * lazy eval mode in that case; otherwise we'd need extra code to expand
     * the rowtype column into multiple columns, since we have no way to
     * notify the caller that it should do that.)
     */
    fcache->returnsTuple = check_sql_fn_retval(queryTree_list,
                                               rettype,
                                               rettupdesc,
                                               false,
                                               &resulttlist);
 
    /*
     * Construct a JunkFilter we can use to coerce the returned rowtype to the
     * desired form, unless the result type is VOID, in which case there's
     * nothing to coerce to.  (XXX Frequently, the JunkFilter isn't doing
     * anything very interesting, but much of this module expects it to be
     * there anyway.)
     */
    if (rettype != VOIDOID)
    {
        TupleTableSlot *slot = MakeSingleTupleTableSlot(NULL,
                                                        &TTSOpsMinimalTuple);
 
        /*
         * If the result is composite, *and* we are returning the whole tuple
         * result, we need to insert nulls for any dropped columns.  In the
         * single-column-result case, there might be dropped columns within
         * the composite column value, but it's not our problem here.  There
         * should be no resjunk entries in resulttlist, so in the second case
         * the JunkFilter is certainly a no-op.
         */
        if (rettupdesc && fcache->returnsTuple)
            fcache->junkFilter = ExecInitJunkFilterConversion(resulttlist,
                                                              rettupdesc,
                                                              slot);
        else
            fcache->junkFilter = ExecInitJunkFilter(resulttlist, slot);
    }
 
    if (fcache->returnsTuple)
    {
        /* Make sure output rowtype is properly blessed */
        BlessTupleDesc(fcache->junkFilter->jf_resultSlot->tts_tupleDescriptor);
    }
    else if (fcache->returnsSet && type_is_rowtype(fcache->rettype))
    {
        /*
         * Returning rowtype as if it were scalar --- materialize won't work.
         * Right now it's sufficient to override any caller preference for
         * materialize mode, but to add more smarts in init_execution_state
         * about this, we'd probably need a three-way flag instead of bool.
         */
        lazyEvalOK = true;
    }
 
    /* Finally, plan the queries */
    fcache->func_state = init_execution_state(queryTree_list,
                                              fcache,
                                              lazyEvalOK);
 
    /* Mark fcache with time of creation to show it's valid */
    fcache->lxid = MyProc->lxid;
    fcache->subxid = GetCurrentSubTransactionId();
 
    ReleaseSysCache(procedureTuple);
 
    MemoryContextSwitchTo(oldcontext);
}
 
/* Start up execution of one execution_state node */
static void
postquel_start(execution_state *es, SQLFunctionCachePtr fcache)
{
    DestReceiver *dest;
 
    Assert(es->qd == NULL);
 
    /* Caller should have ensured a suitable snapshot is active */
    Assert(ActiveSnapshotSet());
 
    /*
     * If this query produces the function result, send its output to the
     * tuplestore; else discard any output.
     */
    if (es->setsResult)
    {
        DR_sqlfunction *myState;
 
        dest = CreateDestReceiver(DestSQLFunction);
        /* pass down the needed info to the dest receiver routines */
        myState = (DR_sqlfunction *) dest;
        Assert(myState->pub.mydest == DestSQLFunction);
        myState->tstore = fcache->tstore;
        myState->cxt = CurrentMemoryContext;
        myState->filter = fcache->junkFilter;
    }
    else
        dest = None_Receiver;
 
    es->qd = CreateQueryDesc(es->stmt,
                             fcache->src,
                             GetActiveSnapshot(),
                             InvalidSnapshot,
                             dest,
                             fcache->paramLI,
                             es->qd ? es->qd->queryEnv : NULL,
                             0);
 
    /* Utility commands don't need Executor. */
    if (es->qd->operation != CMD_UTILITY)
    {
        /*
         * In lazyEval mode, do not let the executor set up an AfterTrigger
         * context.  This is necessary not just an optimization, because we
         * mustn't exit from the function execution with a stacked
         * AfterTrigger level still active.  We are careful not to select
         * lazyEval mode for any statement that could possibly queue triggers.
         */
        int         eflags;
 
        if (es->lazyEval)
            eflags = EXEC_FLAG_SKIP_TRIGGERS;
        else
            eflags = 0;         /* default run-to-completion flags */
        ExecutorStart(es->qd, eflags);
    }
 
    es->status = F_EXEC_RUN;
}
 
/* Run one execution_state; either to completion or to first result row */
/* Returns true if we ran to completion */
static bool
postquel_getnext(execution_state *es, SQLFunctionCachePtr fcache)
{
    bool        result;
 
    if (es->qd->operation == CMD_UTILITY)
    {
        ProcessUtility(es->qd->plannedstmt,
                       fcache->src,
                       true,    /* protect function cache's parsetree */
                       PROCESS_UTILITY_QUERY,
                       es->qd->params,
                       es->qd->queryEnv,
                       es->qd->dest,
                       NULL);
        result = true;          /* never stops early */
    }
    else
    {
        /* Run regular commands to completion unless lazyEval */
        uint64      count = (es->lazyEval) ? 1 : 0;
 
        ExecutorRun(es->qd, ForwardScanDirection, count, !fcache->returnsSet || !es->lazyEval);
 
        /*
         * If we requested run to completion OR there was no tuple returned,
         * command must be complete.
         */
        result = (count == 0 || es->qd->estate->es_processed == 0);
    }
 
    return result;
}
 
/* Shut down execution of one execution_state node */
static void
postquel_end(execution_state *es)
{
    /* mark status done to ensure we don't do ExecutorEnd twice */
    es->status = F_EXEC_DONE;
 
    /* Utility commands don't need Executor. */
    if (es->qd->operation != CMD_UTILITY)
    {
        ExecutorFinish(es->qd);
        ExecutorEnd(es->qd);
    }
 
    es->qd->dest->rDestroy(es->qd->dest);
 
    FreeQueryDesc(es->qd);
    es->qd = NULL;
}
 
/* Build ParamListInfo array representing current arguments */
static void
postquel_sub_params(SQLFunctionCachePtr fcache,
                    FunctionCallInfo fcinfo)
{
    int         nargs = fcinfo->nargs;
 
    if (nargs > 0)
    {
        ParamListInfo paramLI;
        Oid        *argtypes = fcache->pinfo->argtypes;
 
        if (fcache->paramLI == NULL)
        {
            paramLI = makeParamList(nargs);
            fcache->paramLI = paramLI;
        }
        else
        {
            paramLI = fcache->paramLI;
            Assert(paramLI->numParams == nargs);
        }
 
        for (int i = 0; i < nargs; i++)
        {
            ParamExternData *prm = &paramLI->params[i];
 
            /*
             * If an incoming parameter value is a R/W expanded datum, we
             * force it to R/O.  We'd be perfectly entitled to scribble on it,
             * but the problem is that if the parameter is referenced more
             * than once in the function, earlier references might mutate the
             * value seen by later references, which won't do at all.  We
             * could do better if we could be sure of the number of Param
             * nodes in the function's plans; but we might not have planned
             * all the statements yet, nor do we have plan tree walker
             * infrastructure.  (Examining the parse trees is not good enough,
             * because of possible function inlining during planning.)
             */
            prm->isnull = fcinfo->args[i].isnull;
            prm->value = MakeExpandedObjectReadOnly(fcinfo->args[i].value,
                                                    prm->isnull,
                                                    get_typlen(argtypes[i]));
            prm->pflags = 0;
            prm->ptype = argtypes[i];
        }
    }
    else
        fcache->paramLI = NULL;
}
 
/*
 * Extract the SQL function's value from a single result row.  This is used
 * both for scalar (non-set) functions and for each row of a lazy-eval set
 * result.
 */
static Datum
postquel_get_single_result(TupleTableSlot *slot,
                           FunctionCallInfo fcinfo,
                           SQLFunctionCachePtr fcache,
                           MemoryContext resultcontext)
{
    Datum       value;
    MemoryContext oldcontext;
 
    /*
     * Set up to return the function value.  For pass-by-reference datatypes,
     * be sure to allocate the result in resultcontext, not the current memory
     * context (which has query lifespan).  We can't leave the data in the
     * TupleTableSlot because we intend to clear the slot before returning.
     */
    oldcontext = MemoryContextSwitchTo(resultcontext);
 
    if (fcache->returnsTuple)
    {
        /* We must return the whole tuple as a Datum. */
        fcinfo->isnull = false;
        value = ExecFetchSlotHeapTupleDatum(slot);
    }
    else
    {
        /*
         * Returning a scalar, which we have to extract from the first column
         * of the SELECT result, and then copy into result context if needed.
         */
        value = slot_getattr(slot, 1, &(fcinfo->isnull));
 
        if (!fcinfo->isnull)
            value = datumCopy(value, fcache->typbyval, fcache->typlen);
    }
 
    MemoryContextSwitchTo(oldcontext);
 
    return value;
}
 
/*
 * fmgr_sql: function call manager for SQL functions
 */
Datum
fmgr_sql(PG_FUNCTION_ARGS)
{
    SQLFunctionCachePtr fcache;
    ErrorContextCallback sqlerrcontext;
    MemoryContext oldcontext;
    bool        randomAccess;
    bool        lazyEvalOK;
    bool        is_first;
    bool        pushed_snapshot;
    execution_state *es;
    TupleTableSlot *slot;
    Datum       result;
    List       *eslist;
    ListCell   *eslc;
 
    /*
     * Setup error traceback support for ereport()
     */
    sqlerrcontext.callback = sql_exec_error_callback;
    sqlerrcontext.arg = fcinfo->flinfo;
    sqlerrcontext.previous = error_context_stack;
    error_context_stack = &sqlerrcontext;
 
    /* Check call context */
    if (fcinfo->flinfo->fn_retset)
    {
        ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;
 
        /*
         * For simplicity, we require callers to support both set eval modes.
         * There are cases where we must use one or must use the other, and
         * it's not really worthwhile to postpone the check till we know. But
         * note we do not require caller to provide an expectedDesc.
         */
        if (!rsi || !IsA(rsi, ReturnSetInfo) ||
            (rsi->allowedModes & SFRM_ValuePerCall) == 0 ||
            (rsi->allowedModes & SFRM_Materialize) == 0)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("set-valued function called in context that cannot accept a set")));
        randomAccess = rsi->allowedModes & SFRM_Materialize_Random;
        lazyEvalOK = !(rsi->allowedModes & SFRM_Materialize_Preferred);
    }
    else
    {
        randomAccess = false;
        lazyEvalOK = true;
    }
 
    /*
     * Initialize fcache (build plans) if first time through; or re-initialize
     * if the cache is stale.
     */
    fcache = (SQLFunctionCachePtr) fcinfo->flinfo->fn_extra;
 
    if (fcache != NULL)
    {
        if (fcache->lxid != MyProc->lxid ||
            !SubTransactionIsActive(fcache->subxid))
        {
            /* It's stale; unlink and delete */
            fcinfo->flinfo->fn_extra = NULL;
            MemoryContextDelete(fcache->fcontext);
            fcache = NULL;
        }
    }
 
    if (fcache == NULL)
    {
        init_sql_fcache(fcinfo, PG_GET_COLLATION(), lazyEvalOK);
        fcache = (SQLFunctionCachePtr) fcinfo->flinfo->fn_extra;
    }
 
    /*
     * Switch to context in which the fcache lives.  This ensures that our
     * tuplestore etc will have sufficient lifetime.  The sub-executor is
     * responsible for deleting per-tuple information.  (XXX in the case of a
     * long-lived FmgrInfo, this policy represents more memory leakage, but
     * it's not entirely clear where to keep stuff instead.)
     */
    oldcontext = MemoryContextSwitchTo(fcache->fcontext);
 
    /*
     * Find first unfinished query in function, and note whether it's the
     * first query.
     */
    eslist = fcache->func_state;
    es = NULL;
    is_first = true;
    foreach(eslc, eslist)
    {
        es = (execution_state *) lfirst(eslc);
 
        while (es && es->status == F_EXEC_DONE)
        {
            is_first = false;
            es = es->next;
        }
 
        if (es)
            break;
    }
 
    /*
     * Convert params to appropriate format if starting a fresh execution. (If
     * continuing execution, we can re-use prior params.)
     */
    if (is_first && es && es->status == F_EXEC_START)
        postquel_sub_params(fcache, fcinfo);
 
    /*
     * Build tuplestore to hold results, if we don't have one already. Note
     * it's in the query-lifespan context.
     */
    if (!fcache->tstore)
        fcache->tstore = tuplestore_begin_heap(randomAccess, false, work_mem);
 
    /*
     * Execute each command in the function one after another until we either
     * run out of commands or get a result row from a lazily-evaluated SELECT.
     *
     * Notes about snapshot management:
     *
     * In a read-only function, we just use the surrounding query's snapshot.
     *
     * In a non-read-only function, we rely on the fact that we'll never
     * suspend execution between queries of the function: the only reason to
     * suspend execution before completion is if we are returning a row from a
     * lazily-evaluated SELECT.  So, when first entering this loop, we'll
     * either start a new query (and push a fresh snapshot) or re-establish
     * the active snapshot from the existing query descriptor.  If we need to
     * start a new query in a subsequent execution of the loop, either we need
     * a fresh snapshot (and pushed_snapshot is false) or the existing
     * snapshot is on the active stack and we can just bump its command ID.
     */
    pushed_snapshot = false;
    while (es)
    {
        bool        completed;
 
        if (es->status == F_EXEC_START)
        {
            /*
             * If not read-only, be sure to advance the command counter for
             * each command, so that all work to date in this transaction is
             * visible.  Take a new snapshot if we don't have one yet,
             * otherwise just bump the command ID in the existing snapshot.
             */
            if (!fcache->readonly_func)
            {
                CommandCounterIncrement();
                if (!pushed_snapshot)
                {
                    PushActiveSnapshot(GetTransactionSnapshot());
                    pushed_snapshot = true;
                }
                else
                    UpdateActiveSnapshotCommandId();
            }
 
            postquel_start(es, fcache);
        }
        else if (!fcache->readonly_func && !pushed_snapshot)
        {
            /* Re-establish active snapshot when re-entering function */
            PushActiveSnapshot(es->qd->snapshot);
            pushed_snapshot = true;
        }
 
        completed = postquel_getnext(es, fcache);
 
        /*
         * If we ran the command to completion, we can shut it down now. Any
         * row(s) we need to return are safely stashed in the tuplestore, and
         * we want to be sure that, for example, AFTER triggers get fired
         * before we return anything.  Also, if the function doesn't return
         * set, we can shut it down anyway because it must be a SELECT and we
         * don't care about fetching any more result rows.
         */
        if (completed || !fcache->returnsSet)
            postquel_end(es);
 
        /*
         * Break from loop if we didn't shut down (implying we got a
         * lazily-evaluated row).  Otherwise we'll press on till the whole
         * function is done, relying on the tuplestore to keep hold of the
         * data to eventually be returned.  This is necessary since an
         * INSERT/UPDATE/DELETE RETURNING that sets the result might be
         * followed by additional rule-inserted commands, and we want to
         * finish doing all those commands before we return anything.
         */
        if (es->status != F_EXEC_DONE)
            break;
 
        /*
         * Advance to next execution_state, which might be in the next list.
         */
        es = es->next;
        while (!es)
        {
            eslc = lnext(eslist, eslc);
            if (!eslc)
                break;          /* end of function */
 
            es = (execution_state *) lfirst(eslc);
 
            /*
             * Flush the current snapshot so that we will take a new one for
             * the new query list.  This ensures that new snaps are taken at
             * original-query boundaries, matching the behavior of interactive
             * execution.
             */
            if (pushed_snapshot)
            {
                PopActiveSnapshot();
                pushed_snapshot = false;
            }
        }
    }
 
    /*
     * The tuplestore now contains whatever row(s) we are supposed to return.
     */
    if (fcache->returnsSet)
    {
        ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;
 
        if (es)
        {
            /*
             * If we stopped short of being done, we must have a lazy-eval
             * row.
             */
            Assert(es->lazyEval);
            /* Re-use the junkfilter's output slot to fetch back the tuple */
            Assert(fcache->junkFilter);
            slot = fcache->junkFilter->jf_resultSlot;
            if (!tuplestore_gettupleslot(fcache->tstore, true, false, slot))
                elog(ERROR, "failed to fetch lazy-eval tuple");
            /* Extract the result as a datum, and copy out from the slot */
            result = postquel_get_single_result(slot, fcinfo,
                                                fcache, oldcontext);
            /* Clear the tuplestore, but keep it for next time */
            /* NB: this might delete the slot's content, but we don't care */
            tuplestore_clear(fcache->tstore);
 
            /*
             * Let caller know we're not finished.
             */
            rsi->isDone = ExprMultipleResult;
 
            /*
             * Ensure we will get shut down cleanly if the exprcontext is not
             * run to completion.
             */
            if (!fcache->shutdown_reg)
            {
                RegisterExprContextCallback(rsi->econtext,
                                            ShutdownSQLFunction,
                                            PointerGetDatum(fcache));
                fcache->shutdown_reg = true;
            }
        }
        else if (fcache->lazyEval)
        {
            /*
             * We are done with a lazy evaluation.  Clean up.
             */
            tuplestore_clear(fcache->tstore);
 
            /*
             * Let caller know we're finished.
             */
            rsi->isDone = ExprEndResult;
 
            fcinfo->isnull = true;
            result = (Datum) 0;
 
            /* Deregister shutdown callback, if we made one */
            if (fcache->shutdown_reg)
            {
                UnregisterExprContextCallback(rsi->econtext,
                                              ShutdownSQLFunction,
                                              PointerGetDatum(fcache));
                fcache->shutdown_reg = false;
            }
        }
        else
        {
            /*
             * We are done with a non-lazy evaluation.  Return whatever is in
             * the tuplestore.  (It is now caller's responsibility to free the
             * tuplestore when done.)
             */
            rsi->returnMode = SFRM_Materialize;
            rsi->setResult = fcache->tstore;
            fcache->tstore = NULL;
            /* must copy desc because execSRF.c will free it */
            if (fcache->junkFilter)
                rsi->setDesc = CreateTupleDescCopy(fcache->junkFilter->jf_cleanTupType);
 
            fcinfo->isnull = true;
            result = (Datum) 0;
 
            /* Deregister shutdown callback, if we made one */
            if (fcache->shutdown_reg)
            {
                UnregisterExprContextCallback(rsi->econtext,
                                              ShutdownSQLFunction,
                                              PointerGetDatum(fcache));
                fcache->shutdown_reg = false;
            }
        }
    }
    else
    {
        /*
         * Non-set function.  If we got a row, return it; else return NULL.
         */
        if (fcache->junkFilter)
        {
            /* Re-use the junkfilter's output slot to fetch back the tuple */
            slot = fcache->junkFilter->jf_resultSlot;
            if (tuplestore_gettupleslot(fcache->tstore, true, false, slot))
                result = postquel_get_single_result(slot, fcinfo,
                                                    fcache, oldcontext);
            else
            {
                fcinfo->isnull = true;
                result = (Datum) 0;
            }
        }
        else
        {
            /* Should only get here for VOID functions and procedures */
            Assert(fcache->rettype == VOIDOID);
            fcinfo->isnull = true;
            result = (Datum) 0;
        }
 
        /* Clear the tuplestore, but keep it for next time */
        tuplestore_clear(fcache->tstore);
    }
 
    /* Pop snapshot if we have pushed one */
    if (pushed_snapshot)
        PopActiveSnapshot();
 
    /*
     * If we've gone through every command in the function, we are done. Reset
     * the execution states to start over again on next call.
     */
    if (es == NULL)
    {
        foreach(eslc, fcache->func_state)
        {
            es = (execution_state *) lfirst(eslc);
            while (es)
            {
                es->status = F_EXEC_START;
                es = es->next;
            }
        }
    }
 
    error_context_stack = sqlerrcontext.previous;
 
    MemoryContextSwitchTo(oldcontext);
 
    return result;
}
 
 
/*
 * error context callback to let us supply a call-stack traceback
 */
static void
sql_exec_error_callback(void *arg)
{
    FmgrInfo   *flinfo = (FmgrInfo *) arg;
    SQLFunctionCachePtr fcache = (SQLFunctionCachePtr) flinfo->fn_extra;
    int         syntaxerrposition;
 
    /*
     * We can do nothing useful if init_sql_fcache() didn't get as far as
     * saving the function name
     */
    if (fcache == NULL || fcache->fname == NULL)
        return;
 
    /*
     * If there is a syntax error position, convert to internal syntax error
     */
    syntaxerrposition = geterrposition();
    if (syntaxerrposition > 0 && fcache->src != NULL)
    {
        errposition(0);
        internalerrposition(syntaxerrposition);
        internalerrquery(fcache->src);
    }
 
    /*
     * Try to determine where in the function we failed.  If there is a query
     * with non-null QueryDesc, finger it.  (We check this rather than looking
     * for F_EXEC_RUN state, so that errors during ExecutorStart or
     * ExecutorEnd are blamed on the appropriate query; see postquel_start and
     * postquel_end.)
     */
    if (fcache->func_state)
    {
        execution_state *es;
        int         query_num;
        ListCell   *lc;
 
        es = NULL;
        query_num = 1;
        foreach(lc, fcache->func_state)
        {
            es = (execution_state *) lfirst(lc);
            while (es)
            {
                if (es->qd)
                {
                    errcontext("SQL function \"%s\" statement %d",
                               fcache->fname, query_num);
                    break;
                }
                es = es->next;
            }
            if (es)
                break;
            query_num++;
        }
        if (es == NULL)
        {
            /*
             * couldn't identify a running query; might be function entry,
             * function exit, or between queries.
             */
            errcontext("SQL function \"%s\"", fcache->fname);
        }
    }
    else
    {
        /*
         * Assume we failed during init_sql_fcache().  (It's possible that the
         * function actually has an empty body, but in that case we may as
         * well report all errors as being "during startup".)
         */
        errcontext("SQL function \"%s\" during startup", fcache->fname);
    }
}
 
 
/*
 * callback function in case a function-returning-set needs to be shut down
 * before it has been run to completion
 */
static void
ShutdownSQLFunction(Datum arg)
{
    SQLFunctionCachePtr fcache = (SQLFunctionCachePtr) DatumGetPointer(arg);
    execution_state *es;
    ListCell   *lc;
 
    foreach(lc, fcache->func_state)
    {
        es = (execution_state *) lfirst(lc);
        while (es)
        {
            /* Shut down anything still running */
            if (es->status == F_EXEC_RUN)
            {
                /* Re-establish active snapshot for any called functions */
                if (!fcache->readonly_func)
                    PushActiveSnapshot(es->qd->snapshot);
 
                postquel_end(es);
 
                if (!fcache->readonly_func)
                    PopActiveSnapshot();
            }
 
            /* Reset states to START in case we're called again */
            es->status = F_EXEC_START;
            es = es->next;
        }
    }
 
    /* Release tuplestore if we have one */
    if (fcache->tstore)
        tuplestore_end(fcache->tstore);
    fcache->tstore = NULL;
 
    /* execUtils will deregister the callback... */
    fcache->shutdown_reg = false;
}
 
/*
 * check_sql_fn_statements
 *
 * Check statements in an SQL function.  Error out if there is anything that
 * is not acceptable.
 */
void
check_sql_fn_statements(List *queryTreeLists)
{
    ListCell   *lc;
 
    /* We are given a list of sublists of Queries */
    foreach(lc, queryTreeLists)
    {
        List       *sublist = lfirst_node(List, lc);
        ListCell   *lc2;
 
        foreach(lc2, sublist)
        {
            Query      *query = lfirst_node(Query, lc2);
 
            /*
             * Disallow calling procedures with output arguments.  The current
             * implementation would just throw the output values away, unless
             * the statement is the last one.  Per SQL standard, we should
             * assign the output values by name.  By disallowing this here, we
             * preserve an opportunity for future improvement.
             */
            if (query->commandType == CMD_UTILITY &&
                IsA(query->utilityStmt, CallStmt))
            {
                CallStmt   *stmt = (CallStmt *) query->utilityStmt;
 
                if (stmt->outargs != NIL)
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("calling procedures with output arguments is not supported in SQL functions")));
            }
        }
    }
}
 
/*
 * check_sql_fn_retval()
 *      Check return value of a list of lists of sql parse trees.
 *
 * The return value of a sql function is the value returned by the last
 * canSetTag query in the function.  We do some ad-hoc type checking and
 * coercion here to ensure that the function returns what it's supposed to.
 * Note that we may actually modify the last query to make it match!
 *
 * This function returns true if the sql function returns the entire tuple
 * result of its final statement, or false if it returns just the first column
 * result of that statement.  It throws an error if the final statement doesn't
 * return the right type at all.
 *
 * Note that because we allow "SELECT rowtype_expression", the result can be
 * false even when the declared function return type is a rowtype.
 *
 * For a polymorphic function the passed rettype must be the actual resolved
 * output type of the function.  (This means we can't check the type during
 * function definition of a polymorphic function.)  If we do see a polymorphic
 * rettype we'll throw an error, saying it is not a supported rettype.
 *
 * If the function returns composite, the passed rettupdesc should describe
 * the expected output.  If rettupdesc is NULL, we can't verify that the
 * output matches; that should only happen in fmgr_sql_validator(), or when
 * the function returns RECORD and the caller doesn't actually care which
 * composite type it is.
 *
 * (Typically, rettype and rettupdesc are computed by get_call_result_type
 * or a sibling function.)
 *
 * In addition to coercing individual output columns, we can modify the
 * output to include dummy NULL columns for any dropped columns appearing
 * in rettupdesc.  This is done only if the caller asks for it.
 *
 * If resultTargetList isn't NULL, then *resultTargetList is set to the
 * targetlist that defines the final statement's result.  Exception: if the
 * function is defined to return VOID then *resultTargetList is set to NIL.
 */
bool
check_sql_fn_retval(List *queryTreeLists,
                    Oid rettype, TupleDesc rettupdesc,
                    bool insertDroppedCols,
                    List **resultTargetList)
{
    bool        is_tuple_result = false;
    Query      *parse;
    ListCell   *parse_cell;
    List       *tlist;
    int         tlistlen;
    bool        tlist_is_modifiable;
    char        fn_typtype;
    List       *upper_tlist = NIL;
    bool        upper_tlist_nontrivial = false;
    ListCell   *lc;
 
    if (resultTargetList)
        *resultTargetList = NIL;    /* initialize in case of VOID result */
 
    /*
     * If it's declared to return VOID, we don't care what's in the function.
     * (This takes care of the procedure case, as well.)
     */
    if (rettype == VOIDOID)
        return false;
 
    /*
     * Find the last canSetTag query in the function body (which is presented
     * to us as a list of sublists of Query nodes).  This isn't necessarily
     * the last parsetree, because rule rewriting can insert queries after
     * what the user wrote.  Note that it might not even be in the last
     * sublist, for example if the last query rewrites to DO INSTEAD NOTHING.
     * (It might not be unreasonable to throw an error in such a case, but
     * this is the historical behavior and it doesn't seem worth changing.)
     */
    parse = NULL;
    parse_cell = NULL;
    foreach(lc, queryTreeLists)
    {
        List       *sublist = lfirst_node(List, lc);
        ListCell   *lc2;
 
        foreach(lc2, sublist)
        {
            Query      *q = lfirst_node(Query, lc2);
 
            if (q->canSetTag)
            {
                parse = q;
                parse_cell = lc2;
            }
        }
    }
 
    /*
     * If it's a plain SELECT, it returns whatever the targetlist says.
     * Otherwise, if it's INSERT/UPDATE/DELETE 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->returningList)
    {
        tlist = parse->returningList;
        /* returningList can always be modified */
        tlist_is_modifiable = true;
    }
    else
    {
        /* Empty function body, or last statement is a utility command */
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                 errmsg("return type mismatch in function declared to return %s",
                        format_type_be(rettype)),
                 errdetail("Function's final statement must be SELECT or INSERT/UPDATE/DELETE 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.
         */
        if (tlistlen == 1)
        {
            TargetEntry *tle = (TargetEntry *) linitial(tlist);
 
            Assert(!tle->resjunk);
            if (coerce_fn_result_column(tle, rettype, -1,
                                        tlist_is_modifiable,
                                        &upper_tlist,
                                        &upper_tlist_nontrivial))
            {
                /* Note that we're NOT setting is_tuple_result */
                goto tlist_coercion_finished;
            }
        }
 
        /*
         * If the caller didn't provide an expected tupdesc, we can't do any
         * further checking.  Assume we're returning the whole tuple.
         */
        if (rettupdesc == NULL)
        {
            /* Return tlist if requested */
            if (resultTargetList)
                *resultTargetList = tlist;
            return true;
        }
 
        /*
         * Verify that the targetlist matches the return tuple type.  We scan
         * the non-resjunk columns, and coerce them if necessary to match the
         * datatypes of the non-deleted attributes.  For deleted attributes,
         * insert NULL result columns if the caller asked for that.
         */
        tupnatts = rettupdesc->natts;
        tuplogcols = 0;         /* we'll count nondeleted cols as we go */
        colindex = 0;
 
        foreach(lc, tlist)
        {
            TargetEntry *tle = (TargetEntry *) lfirst(lc);
            Form_pg_attribute attr;
 
            /* resjunk columns can simply be ignored */
            if (tle->resjunk)
                continue;
 
            do
            {
                colindex++;
                if (colindex > tupnatts)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                             errmsg("return type mismatch in function declared to return %s",
                                    format_type_be(rettype)),
                             errdetail("Final statement returns too many columns.")));
                attr = TupleDescAttr(rettupdesc, colindex - 1);
                if (attr->attisdropped && insertDroppedCols)
                {
                    Expr       *null_expr;
 
                    /* The type of the null we insert isn't important */
                    null_expr = (Expr *) makeConst(INT4OID,
                                                   -1,
                                                   InvalidOid,
                                                   sizeof(int32),
                                                   (Datum) 0,
                                                   true,    /* isnull */
                                                   true /* byval */ );
                    upper_tlist = lappend(upper_tlist,
                                          makeTargetEntry(null_expr,
                                                          list_length(upper_tlist) + 1,
                                                          NULL,
                                                          false));
                    upper_tlist_nontrivial = true;
                }
            } while (attr->attisdropped);
            tuplogcols++;
 
            if (!coerce_fn_result_column(tle,
                                         attr->atttypid, attr->atttypmod,
                                         tlist_is_modifiable,
                                         &upper_tlist,
                                         &upper_tlist_nontrivial))
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                         errmsg("return type mismatch in function declared to return %s",
                                format_type_be(rettype)),
                         errdetail("Final statement returns %s instead of %s at column %d.",
                                   format_type_be(exprType((Node *) tle->expr)),
                                   format_type_be(attr->atttypid),
                                   tuplogcols)));
        }
 
        /* remaining columns in rettupdesc had better all be dropped */
        for (colindex++; colindex <= tupnatts; colindex++)
        {
            if (!TupleDescAttr(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);
 
        /* Replace original query in the correct element of the query list */
        lfirst(parse_cell) = newquery;
    }
 
    /* Return tlist (possibly modified) if requested */
    if (resultTargetList)
        *resultTargetList = upper_tlist;
 
    return is_tuple_result;
}
 
/*
 * Process one function result column for check_sql_fn_retval
 *
 * Coerce the output value to the required type/typmod, and add a column
 * to *upper_tlist for it.  Set *upper_tlist_nontrivial to true if we
 * add an upper tlist item that's not just a Var.
 *
 * Returns true if OK, false if could not coerce to required type
 * (in which case, no changes have been made)
 */
static bool
coerce_fn_result_column(TargetEntry *src_tle,
                        Oid res_type,
                        int32 res_typmod,
                        bool tlist_is_modifiable,
                        List **upper_tlist,
                        bool *upper_tlist_nontrivial)
{
    TargetEntry *new_tle;
    Expr       *new_tle_expr;
    Node       *cast_result;
 
    /*
     * If the TLE has a sortgroupref marking, don't change it, as it probably
     * is referenced by ORDER BY, DISTINCT, etc, and changing its type would
     * break query semantics.  Otherwise, it's safe to modify in-place unless
     * the query as a whole has issues with that.
     */
    if (tlist_is_modifiable && src_tle->ressortgroupref == 0)
    {
        /* OK to modify src_tle in place, if necessary */
        cast_result = coerce_to_target_type(NULL,
                                            (Node *) src_tle->expr,
                                            exprType((Node *) src_tle->expr),
                                            res_type, res_typmod,
                                            COERCION_ASSIGNMENT,
                                            COERCE_IMPLICIT_CAST,
                                            -1);
        if (cast_result == NULL)
            return false;
        assign_expr_collations(NULL, cast_result);
        src_tle->expr = (Expr *) cast_result;
        /* Make a Var referencing the possibly-modified TLE */
        new_tle_expr = (Expr *) makeVarFromTargetEntry(1, src_tle);
    }
    else
    {
        /* Any casting must happen in the upper tlist */
        Var        *var = makeVarFromTargetEntry(1, src_tle);
 
        cast_result = coerce_to_target_type(NULL,
                                            (Node *) var,
                                            var->vartype,
                                            res_type, res_typmod,
                                            COERCION_ASSIGNMENT,
                                            COERCE_IMPLICIT_CAST,
                                            -1);
        if (cast_result == NULL)
            return false;
        assign_expr_collations(NULL, cast_result);
        /* Did the coercion actually do anything? */
        if (cast_result != (Node *) var)
            *upper_tlist_nontrivial = true;
        new_tle_expr = (Expr *) cast_result;
    }
    new_tle = makeTargetEntry(new_tle_expr,
                              list_length(*upper_tlist) + 1,
                              src_tle->resname, false);
    *upper_tlist = lappend(*upper_tlist, new_tle);
    return true;
}
 
 
/*
 * CreateSQLFunctionDestReceiver -- create a suitable DestReceiver object
 */
DestReceiver *
CreateSQLFunctionDestReceiver(void)
{
    DR_sqlfunction *self = (DR_sqlfunction *) palloc0(sizeof(DR_sqlfunction));
 
    self->pub.receiveSlot = sqlfunction_receive;
    self->pub.rStartup = sqlfunction_startup;
    self->pub.rShutdown = sqlfunction_shutdown;
    self->pub.rDestroy = sqlfunction_destroy;
    self->pub.mydest = DestSQLFunction;
 
    /* private fields will be set by postquel_start */
 
    return (DestReceiver *) self;
}
 
/*
 * sqlfunction_startup --- executor startup
 */
static void
sqlfunction_startup(DestReceiver *self, int operation, TupleDesc typeinfo)
{
    /* no-op */
}
 
/*
 * sqlfunction_receive --- receive one tuple
 */
static bool
sqlfunction_receive(TupleTableSlot *slot, DestReceiver *self)
{
    DR_sqlfunction *myState = (DR_sqlfunction *) self;
 
    /* Filter tuple as needed */
    slot = ExecFilterJunk(myState->filter, slot);
 
    /* Store the filtered tuple into the tuplestore */
    tuplestore_puttupleslot(myState->tstore, slot);
 
    return true;
}
 
/*
 * sqlfunction_shutdown --- executor end
 */
static void
sqlfunction_shutdown(DestReceiver *self)
{
    /* no-op */
}
 
/*
 * sqlfunction_destroy --- release DestReceiver object
 */
static void
sqlfunction_destroy(DestReceiver *self)
{
    pfree(self);
}