parser.c

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/*-------------------------------------------------------------------------
 *
 * parser.c
 *      Main entry point/driver for PostgreSQL grammar
 *
 * This should match src/backend/parser/parser.c, except that we do not
 * need to bother with re-entrant interfaces.
 *
 * Note: ECPG doesn't report error location like the backend does.
 * This file will need work if we ever want it to.
 *
 *
 * Portions Copyright (c) 1996-2025, 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 "preproc_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 */
static char *lookahead_yytext;  /* start current token */
 
static int  base_yylex_location(void);
static bool check_uescapechar(unsigned char escape);
static bool ecpg_isspace(char ch);
 
 
/*
 * Intermediate filter between parser and base lexer (base_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.
 *
 * We also use this filter to convert UIDENT and USCONST sequences into
 * plain IDENT and SCONST tokens.  While that could be handled by additional
 * productions in the main grammar, it's more efficient to do it like this.
 */
int
filtered_base_yylex(void)
{
    int         cur_token;
    int         next_token;
    YYSTYPE     cur_yylval;
    YYLTYPE     cur_yylloc;
    char       *cur_yytext;
 
    /* Get next token --- we might already have it */
    if (have_lookahead)
    {
        cur_token = lookahead_token;
        base_yylval = lookahead_yylval;
        base_yylloc = lookahead_yylloc;
        base_yytext = lookahead_yytext;
        have_lookahead = false;
    }
    else
        cur_token = base_yylex_location();
 
    /*
     * If this token isn't one that requires lookahead, just return it.
     */
    switch (cur_token)
    {
        case FORMAT:
        case NOT:
        case NULLS_P:
        case WITH:
        case WITHOUT:
        case UIDENT:
        case USCONST:
            break;
        default:
            return cur_token;
    }
 
    /* Save and restore lexer output variables around the call */
    cur_yylval = base_yylval;
    cur_yylloc = base_yylloc;
    cur_yytext = base_yytext;
 
    /* Get next token, saving outputs into lookahead variables */
    next_token = base_yylex_location();
 
    lookahead_token = next_token;
    lookahead_yylval = base_yylval;
    lookahead_yylloc = base_yylloc;
    lookahead_yytext = base_yytext;
 
    base_yylval = cur_yylval;
    base_yylloc = cur_yylloc;
    base_yytext = cur_yytext;
 
    have_lookahead = true;
 
    /* Replace cur_token if needed, based on lookahead */
    switch (cur_token)
    {
        case FORMAT:
            /* Replace FORMAT by FORMAT_LA if it's followed by JSON */
            switch (next_token)
            {
                case JSON:
                    cur_token = FORMAT_LA;
                    break;
            }
            break;
 
        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;
 
        case WITHOUT:
            /* Replace WITHOUT by WITHOUT_LA if it's followed by TIME */
            switch (next_token)
            {
                case TIME:
                    cur_token = WITHOUT_LA;
                    break;
            }
            break;
        case UIDENT:
        case USCONST:
            /* Look ahead for UESCAPE */
            if (next_token == UESCAPE)
            {
                /* Yup, so get third token, which had better be SCONST */
                const char *escstr;
 
                /*
                 * Again save and restore lexer output variables around the
                 * call
                 */
                cur_yylval = base_yylval;
                cur_yylloc = base_yylloc;
                cur_yytext = base_yytext;
 
                /* Get third token */
                next_token = base_yylex_location();
 
                if (next_token != SCONST)
                    mmerror(PARSE_ERROR, ET_ERROR, "UESCAPE must be followed by a simple string literal");
 
                /*
                 * Save and check escape string, which the scanner returns
                 * with quotes
                 */
                escstr = base_yylval.str;
                if (strlen(escstr) != 3 || !check_uescapechar(escstr[1]))
                    mmerror(PARSE_ERROR, ET_ERROR, "invalid Unicode escape character");
 
                base_yylval = cur_yylval;
                base_yylloc = cur_yylloc;
                base_yytext = cur_yytext;
 
                /* Combine 3 tokens into 1 */
                base_yylval.str = make3_str(base_yylval.str,
                                            " UESCAPE ",
                                            escstr);
                base_yylloc = loc_strdup(base_yylval.str);
 
                /* Clear have_lookahead, thereby consuming all three tokens */
                have_lookahead = false;
            }
 
            if (cur_token == UIDENT)
                cur_token = IDENT;
            else if (cur_token == USCONST)
                cur_token = SCONST;
            break;
    }
 
    return cur_token;
}
 
/*
 * Call base_yylex() and fill in base_yylloc.
 *
 * pgc.l does not worry about setting yylloc, and given what we want for
 * that, trying to set it there would be pretty inconvenient.  What we
 * want is: if the returned token has type <str>, then duplicate its
 * string value as yylloc; otherwise, make a downcased copy of yytext.
 * The downcasing is ASCII-only because all that we care about there
 * is producing uniformly-cased output of keywords.  (That's mostly
 * cosmetic, but there are places in ecpglib that expect to receive
 * downcased keywords, plus it keeps us regression-test-compatible
 * with the pre-v18 implementation of ecpg.)
 */
static int
base_yylex_location(void)
{
    int         token = base_yylex();
 
    switch (token)
    {
            /* List a token here if pgc.l assigns to base_yylval.str for it */
        case Op:
        case CSTRING:
        case CPP_LINE:
        case CVARIABLE:
        case BCONST:
        case SCONST:
        case USCONST:
        case XCONST:
        case FCONST:
        case IDENT:
        case UIDENT:
        case IP:
            /* Duplicate the <str> value */
            base_yylloc = loc_strdup(base_yylval.str);
            break;
        default:
            /* Else just use the input, i.e., yytext */
            base_yylloc = loc_strdup(base_yytext);
            /* Apply an ASCII-only downcasing */
            for (unsigned char *ptr = (unsigned char *) base_yylloc; *ptr; ptr++)
            {
                if (*ptr >= 'A' && *ptr <= 'Z')
                    *ptr += 'a' - 'A';
            }
            break;
    }
    return token;
}
 
/*
 * check_uescapechar() and ecpg_isspace() should match their equivalents
 * in pgc.l.
 */
 
/* is 'escape' acceptable as Unicode escape character (UESCAPE syntax) ? */
static bool
check_uescapechar(unsigned char escape)
{
    if (isxdigit(escape)
        || escape == '+'
        || escape == '\''
        || escape == '"'
        || ecpg_isspace(escape))
        return false;
    else
        return true;
}
 
/*
 * ecpg_isspace() --- return true if flex scanner considers char whitespace
 */
static bool
ecpg_isspace(char ch)
{
    if (ch == ' ' ||
        ch == '\t' ||
        ch == '\n' ||
        ch == '\r' ||
        ch == '\f')
        return true;
    return false;
}