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) 1996-2019, 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.  The immediate elements
 * of the list are always RawStmt nodes.
 */
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, ScanKeywordTokens);

    /* 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).
 *
 * This 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 replacing 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 that 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;
    int         cur_token_length;
    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->lookahead_end) = yyextra->lookahead_hold_char;
        yyextra->have_lookahead = false;
    }
    else
        cur_token = core_yylex(&(lvalp->core_yystype), llocp, yyscanner);

    /*
     * If this token isn't one that requires lookahead, just return it.  If it
     * does, determine the token length.  (We could get that via strlen(), but
     * since we have such a small set of possibilities, hardwiring seems
     * feasible and more efficient.)
     */
    switch (cur_token)
    {
        case NOT:
            cur_token_length = 3;
            break;
        case NULLS_P:
            cur_token_length = 5;
            break;
        case WITH:
            cur_token_length = 4;
            break;
        default:
            return cur_token;
    }

    /*
     * Identify end+1 of current token.  core_yylex() has temporarily stored a
     * '\0' here, and will undo that when we call it again.  We need to redo
     * it to fully revert the lookahead call for error reporting purposes.
     */
    yyextra->lookahead_end = yyextra->core_yy_extra.scanbuf +
        *llocp + cur_token_length;
    Assert(*(yyextra->lookahead_end) == '\0');

    /*
     * Save and restore *llocp around the call.  It might look like we could
     * avoid this by just passing &lookahead_yylloc to core_yylex(), but that
     * does not work because flex actually holds onto the last-passed pointer
     * internally, and will use that for error reporting.  We need any error
     * reports to point to the current token, not the next one.
     */
    cur_yylloc = *llocp;

    /* Get next token, saving outputs into lookahead variables */
    next_token = core_yylex(&(yyextra->lookahead_yylval), llocp, yyscanner);
    yyextra->lookahead_token = next_token;
    yyextra->lookahead_yylloc = *llocp;

    *llocp = cur_yylloc;

    /* Now revert the un-truncation of the current token */
    yyextra->lookahead_hold_char = *(yyextra->lookahead_end);
    *(yyextra->lookahead_end) = '\0';

    yyextra->have_lookahead = true;

    /* Replace cur_token if needed, based on lookahead */
    switch (cur_token)
    {
        case NOT:
            /* Replace NOT by NOT_LA if it's followed by BETWEEN, IN, etc */
            switch (next_token)
            {
                case BETWEEN:
                case IN_P:
                case LIKE:
                case ILIKE:
                case SIMILAR:
                    cur_token = NOT_LA;
                    break;
            }
            break;

        case NULLS_P:
            /* Replace NULLS_P by NULLS_LA if it's followed by FIRST or LAST */
            switch (next_token)
            {
                case FIRST_P:
                case LAST_P:
                    cur_token = NULLS_LA;
                    break;
            }
            break;

        case WITH:
            /* Replace WITH by WITH_LA if it's followed by TIME or ORDINALITY */
            switch (next_token)
            {
                case TIME:
                case ORDINALITY:
                    cur_token = WITH_LA;
                    break;
            }
            break;
    }

    return cur_token;
}