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/interfaces/ecpg/preproc/parser.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include "extern.h"
#include "preproc.h"


static bool have_lookahead;     /* is lookahead info valid? */
static int  lookahead_token;    /* one-token lookahead */
static YYSTYPE lookahead_yylval;    /* yylval for lookahead token */
static YYLTYPE lookahead_yylloc;    /* yylloc for lookahead token */


/*
 * Intermediate filter between parser and base lexer (base_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.
 */
int
filtered_base_yylex(void)
{
    int         cur_token;
    int         next_token;
    YYSTYPE     cur_yylval;
    YYLTYPE     cur_yylloc;

    /* Get next token --- we might already have it */
    if (have_lookahead)
    {
        cur_token = lookahead_token;
        base_yylval = lookahead_yylval;
        base_yylloc = lookahead_yylloc;
        have_lookahead = false;
    }
    else
        cur_token = base_yylex();

    /* 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 = base_yylval;
            cur_yylloc = base_yylloc;
            next_token = base_yylex();
            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 */
                    lookahead_token = next_token;
                    lookahead_yylval = base_yylval;
                    lookahead_yylloc = base_yylloc;
                    have_lookahead = true;
                    /* and back up the output info to cur_token */
                    base_yylval = cur_yylval;
                    base_yylloc = cur_yylloc;
                    break;
            }
            break;

        case WITH:

            /*
             * WITH TIME must be reduced to one token
             */
            cur_yylval = base_yylval;
            cur_yylloc = base_yylloc;
            next_token = base_yylex();
            switch (next_token)
            {
                case TIME:
                    cur_token = WITH_TIME;
                    break;
                default:
                    /* save the lookahead token for next time */
                    lookahead_token = next_token;
                    lookahead_yylval = base_yylval;
                    lookahead_yylloc = base_yylloc;
                    have_lookahead = true;
                    /* and back up the output info to cur_token */
                    base_yylval = cur_yylval;
                    base_yylloc = cur_yylloc;
                    break;
            }
            break;

        default:
            break;
    }

    return cur_token;
}