postgres/src/backend/parser/parser.c

/*-------------------------------------------------------------------------
 *
 * 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;
}