parser.c

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/*-------------------------------------------------------------------------
 *
 * parser.c
 *      Main entry point/driver for PostgreSQL grammar
 *
 * Note that the grammar is not allowed to perform any table access
 * (since we need to be able to do basic parsing even while inside an
 * aborted transaction).  Therefore, the data structures returned by
 * the grammar are "raw" parsetrees that still need to be analyzed by
 * analyze.c and related files.
 *
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/parser/parser.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "parser/gramparse.h"
#include "parser/parser.h"


/*
 * raw_parser
 *      Given a query in string form, do lexical and grammatical analysis.
 *
 * Returns a list of raw (un-analyzed) parse trees.
 */
List *
raw_parser(const char *str)
{
    core_yyscan_t yyscanner;
    base_yy_extra_type yyextra;
    int         yyresult;

    /* initialize the flex scanner */
    yyscanner = scanner_init(str, &yyextra.core_yy_extra,
                             ScanKeywords, NumScanKeywords);

    /* base_yylex() only needs this much initialization */
    yyextra.have_lookahead = false;

    /* initialize the bison parser */
    parser_init(&yyextra);

    /* Parse! */
    yyresult = base_yyparse(yyscanner);

    /* Clean up (release memory) */
    scanner_finish(yyscanner);

    if (yyresult)               /* error */
        return NIL;

    return yyextra.parsetree;
}


/*
 * Intermediate filter between parser and core lexer (core_yylex in scan.l).
 *
 * The filter is needed because in some cases the standard SQL grammar
 * requires more than one token lookahead.  We reduce these cases to one-token
 * lookahead by combining tokens here, in order to keep the grammar LALR(1).
 *
 * Using a filter is simpler than trying to recognize multiword tokens
 * directly in scan.l, because we'd have to allow for comments between the
 * words.  Furthermore it's not clear how to do it without re-introducing
 * scanner backtrack, which would cost more performance than this filter
 * layer does.
 *
 * The filter also provides a convenient place to translate between
 * the core_YYSTYPE and YYSTYPE representations (which are really the
 * same thing anyway, but notationally they're different).
 */
int
base_yylex(YYSTYPE *lvalp, YYLTYPE *llocp, core_yyscan_t yyscanner)
{
    base_yy_extra_type *yyextra = pg_yyget_extra(yyscanner);
    int         cur_token;
    int         next_token;
    core_YYSTYPE cur_yylval;
    YYLTYPE     cur_yylloc;

    /* Get next token --- we might already have it */
    if (yyextra->have_lookahead)
    {
        cur_token = yyextra->lookahead_token;
        lvalp->core_yystype = yyextra->lookahead_yylval;
        *llocp = yyextra->lookahead_yylloc;
        yyextra->have_lookahead = false;
    }
    else
        cur_token = core_yylex(&(lvalp->core_yystype), llocp, yyscanner);

    /* Do we need to look ahead for a possible multiword token? */
    switch (cur_token)
    {
        case NULLS_P:

            /*
             * NULLS FIRST and NULLS LAST must be reduced to one token
             */
            cur_yylval = lvalp->core_yystype;
            cur_yylloc = *llocp;
            next_token = core_yylex(&(lvalp->core_yystype), llocp, yyscanner);
            switch (next_token)
            {
                case FIRST_P:
                    cur_token = NULLS_FIRST;
                    break;
                case LAST_P:
                    cur_token = NULLS_LAST;
                    break;
                default:
                    /* save the lookahead token for next time */
                    yyextra->lookahead_token = next_token;
                    yyextra->lookahead_yylval = lvalp->core_yystype;
                    yyextra->lookahead_yylloc = *llocp;
                    yyextra->have_lookahead = true;
                    /* and back up the output info to cur_token */
                    lvalp->core_yystype = cur_yylval;
                    *llocp = cur_yylloc;
                    break;
            }
            break;

        case WITH:

            /*
             * WITH TIME must be reduced to one token
             */
            cur_yylval = lvalp->core_yystype;
            cur_yylloc = *llocp;
            next_token = core_yylex(&(lvalp->core_yystype), llocp, yyscanner);
            switch (next_token)
            {
                case TIME:
                    cur_token = WITH_TIME;
                    break;
                default:
                    /* save the lookahead token for next time */
                    yyextra->lookahead_token = next_token;
                    yyextra->lookahead_yylval = lvalp->core_yystype;
                    yyextra->lookahead_yylloc = *llocp;
                    yyextra->have_lookahead = true;
                    /* and back up the output info to cur_token */
                    lvalp->core_yystype = cur_yylval;
                    *llocp = cur_yylloc;
                    break;
            }
            break;

        default:
            break;
    }

    return cur_token;
}