pl_scanner.c

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/*-------------------------------------------------------------------------
 *
 * pl_scanner.c
 *    lexical scanning for PL/pgSQL
 *
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/pl/plpgsql/src/pl_scanner.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "mb/pg_wchar.h"
#include "parser/scanner.h"
 
#include "plpgsql.h"
#include "pl_gram.h"            /* must be after parser/scanner.h */
 
 
/* Klugy flag to tell scanner how to look up identifiers */
IdentifierLookup plpgsql_IdentifierLookup = IDENTIFIER_LOOKUP_NORMAL;
 
/*
 * A word about keywords:
 *
 * We keep reserved and unreserved keywords in separate headers.  Be careful
 * not to put the same word in both headers.  Also be sure that pl_gram.y's
 * unreserved_keyword production agrees with the unreserved header.  The
 * reserved keywords are passed to the core scanner, so they will be
 * recognized before (and instead of) any variable name.  Unreserved words
 * are checked for separately, usually after determining that the identifier
 * isn't a known variable name.  If plpgsql_IdentifierLookup is DECLARE then
 * no variable names will be recognized, so the unreserved words always work.
 * (Note in particular that this helps us avoid reserving keywords that are
 * only needed in DECLARE sections.)
 *
 * In certain contexts it is desirable to prefer recognizing an unreserved
 * keyword over recognizing a variable name.  In particular, at the start
 * of a statement we should prefer unreserved keywords unless the statement
 * looks like an assignment (i.e., first token is followed by ':=' or '[').
 * This rule allows most statement-introducing keywords to be kept unreserved.
 * (We still have to reserve initial keywords that might follow a block
 * label, unfortunately, since the method used to determine if we are at
 * start of statement doesn't recognize such cases.  We'd also have to
 * reserve any keyword that could legitimately be followed by ':=' or '['.)
 * Some additional cases are handled in pl_gram.y using tok_is_keyword().
 *
 * We try to avoid reserving more keywords than we have to; but there's
 * little point in not reserving a word if it's reserved in the core grammar.
 * Currently, the following words are reserved here but not in the core:
 * BEGIN BY DECLARE EXECUTE FOREACH IF LOOP STRICT WHILE
 */
 
/* ScanKeywordList lookup data for PL/pgSQL keywords */
#include "pl_reserved_kwlist_d.h"
#include "pl_unreserved_kwlist_d.h"
 
/* Token codes for PL/pgSQL keywords */
#define PG_KEYWORD(kwname, value) value,
 
static const uint16 ReservedPLKeywordTokens[] = {
#include "pl_reserved_kwlist.h"
};
 
static const uint16 UnreservedPLKeywordTokens[] = {
#include "pl_unreserved_kwlist.h"
};
 
#undef PG_KEYWORD
 
/*
 * This macro must recognize all tokens that can immediately precede a
 * PL/pgSQL executable statement (that is, proc_sect or proc_stmt in the
 * grammar).  Fortunately, there are not very many, so hard-coding in this
 * fashion seems sufficient.
 */
#define AT_STMT_START(prev_token) \
    ((prev_token) == ';' || \
     (prev_token) == K_BEGIN || \
     (prev_token) == K_THEN || \
     (prev_token) == K_ELSE || \
     (prev_token) == K_LOOP)
 
 
/* Auxiliary data about a token (other than the token type) */
typedef struct
{
    YYSTYPE     lval;           /* semantic information */
    YYLTYPE     lloc;           /* offset in scanbuf */
    int         leng;           /* length in bytes */
} TokenAuxData;
 
/*
 * Scanner working state.  At some point we might wish to fold all this
 * into a YY_EXTRA struct.  For the moment, there is no need for plpgsql's
 * lexer to be re-entrant, and the notational burden of passing a yyscanner
 * pointer around is great enough to not want to do it without need.
 */
 
/* The stuff the core lexer needs */
static core_yyscan_t yyscanner = NULL;
static core_yy_extra_type core_yy;
 
/* The original input string */
static const char *scanorig;
 
/* Current token's length (corresponds to plpgsql_yylval and plpgsql_yylloc) */
static int  plpgsql_yyleng;
 
/* Current token's code (corresponds to plpgsql_yylval and plpgsql_yylloc) */
static int  plpgsql_yytoken;
 
/* Token pushback stack */
#define MAX_PUSHBACKS 4
 
static int  num_pushbacks;
static int  pushback_token[MAX_PUSHBACKS];
static TokenAuxData pushback_auxdata[MAX_PUSHBACKS];
 
/* State for plpgsql_location_to_lineno() */
static const char *cur_line_start;
static const char *cur_line_end;
static int  cur_line_num;
 
/* Internal functions */
static int  internal_yylex(TokenAuxData *auxdata);
static void push_back_token(int token, TokenAuxData *auxdata);
static void location_lineno_init(void);
 
 
/*
 * This is the yylex routine called from the PL/pgSQL grammar.
 * It is a wrapper around the core lexer, with the ability to recognize
 * PL/pgSQL variables and return them as special T_DATUM tokens.  If a
 * word or compound word does not match any variable name, or if matching
 * is turned off by plpgsql_IdentifierLookup, it is returned as
 * T_WORD or T_CWORD respectively, or as an unreserved keyword if it
 * matches one of those.
 */
int
plpgsql_yylex(void)
{
    int         tok1;
    TokenAuxData aux1;
    int         kwnum;
 
    tok1 = internal_yylex(&aux1);
    if (tok1 == IDENT || tok1 == PARAM)
    {
        int         tok2;
        TokenAuxData aux2;
 
        tok2 = internal_yylex(&aux2);
        if (tok2 == '.')
        {
            int         tok3;
            TokenAuxData aux3;
 
            tok3 = internal_yylex(&aux3);
            if (tok3 == IDENT)
            {
                int         tok4;
                TokenAuxData aux4;
 
                tok4 = internal_yylex(&aux4);
                if (tok4 == '.')
                {
                    int         tok5;
                    TokenAuxData aux5;
 
                    tok5 = internal_yylex(&aux5);
                    if (tok5 == IDENT)
                    {
                        if (plpgsql_parse_tripword(aux1.lval.str,
                                                   aux3.lval.str,
                                                   aux5.lval.str,
                                                   &aux1.lval.wdatum,
                                                   &aux1.lval.cword))
                            tok1 = T_DATUM;
                        else
                            tok1 = T_CWORD;
                    }
                    else
                    {
                        /* not A.B.C, so just process A.B */
                        push_back_token(tok5, &aux5);
                        push_back_token(tok4, &aux4);
                        if (plpgsql_parse_dblword(aux1.lval.str,
                                                  aux3.lval.str,
                                                  &aux1.lval.wdatum,
                                                  &aux1.lval.cword))
                            tok1 = T_DATUM;
                        else
                            tok1 = T_CWORD;
                    }
                }
                else
                {
                    /* not A.B.C, so just process A.B */
                    push_back_token(tok4, &aux4);
                    if (plpgsql_parse_dblword(aux1.lval.str,
                                              aux3.lval.str,
                                              &aux1.lval.wdatum,
                                              &aux1.lval.cword))
                        tok1 = T_DATUM;
                    else
                        tok1 = T_CWORD;
                }
            }
            else
            {
                /* not A.B, so just process A */
                push_back_token(tok3, &aux3);
                push_back_token(tok2, &aux2);
                if (plpgsql_parse_word(aux1.lval.str,
                                       core_yy.scanbuf + aux1.lloc,
                                       true,
                                       &aux1.lval.wdatum,
                                       &aux1.lval.word))
                    tok1 = T_DATUM;
                else if (!aux1.lval.word.quoted &&
                         (kwnum = ScanKeywordLookup(aux1.lval.word.ident,
                                                    &UnreservedPLKeywords)) >= 0)
                {
                    aux1.lval.keyword = GetScanKeyword(kwnum,
                                                       &UnreservedPLKeywords);
                    tok1 = UnreservedPLKeywordTokens[kwnum];
                }
                else
                    tok1 = T_WORD;
            }
        }
        else
        {
            /* not A.B, so just process A */
            push_back_token(tok2, &aux2);
 
            /*
             * See if it matches a variable name, except in the context where
             * we are at start of statement and the next token isn't
             * assignment or '['.  In that case, it couldn't validly be a
             * variable name, and skipping the lookup allows variable names to
             * be used that would conflict with plpgsql or core keywords that
             * introduce statements (e.g., "comment").  Without this special
             * logic, every statement-introducing keyword would effectively be
             * reserved in PL/pgSQL, which would be unpleasant.
             *
             * If it isn't a variable name, try to match against unreserved
             * plpgsql keywords.  If not one of those either, it's T_WORD.
             *
             * Note: we must call plpgsql_parse_word even if we don't want to
             * do variable lookup, because it sets up aux1.lval.word for the
             * non-variable cases.
             */
            if (plpgsql_parse_word(aux1.lval.str,
                                   core_yy.scanbuf + aux1.lloc,
                                   (!AT_STMT_START(plpgsql_yytoken) ||
                                    (tok2 == '=' || tok2 == COLON_EQUALS ||
                                     tok2 == '[')),
                                   &aux1.lval.wdatum,
                                   &aux1.lval.word))
                tok1 = T_DATUM;
            else if (!aux1.lval.word.quoted &&
                     (kwnum = ScanKeywordLookup(aux1.lval.word.ident,
                                                &UnreservedPLKeywords)) >= 0)
            {
                aux1.lval.keyword = GetScanKeyword(kwnum,
                                                   &UnreservedPLKeywords);
                tok1 = UnreservedPLKeywordTokens[kwnum];
            }
            else
                tok1 = T_WORD;
        }
    }
    else
    {
        /*
         * Not a potential plpgsql variable name, just return the data.
         *
         * Note that we also come through here if the grammar pushed back a
         * T_DATUM, T_CWORD, T_WORD, or unreserved-keyword token returned by a
         * previous lookup cycle; thus, pushbacks do not incur extra lookup
         * work, since we'll never do the above code twice for the same token.
         * This property also makes it safe to rely on the old value of
         * plpgsql_yytoken in the is-this-start-of-statement test above.
         */
    }
 
    plpgsql_yylval = aux1.lval;
    plpgsql_yylloc = aux1.lloc;
    plpgsql_yyleng = aux1.leng;
    plpgsql_yytoken = tok1;
    return tok1;
}
 
/*
 * Internal yylex function.  This wraps the core lexer and adds one feature:
 * a token pushback stack.  We also make a couple of trivial single-token
 * translations from what the core lexer does to what we want, in particular
 * interfacing from the core_YYSTYPE to YYSTYPE union.
 */
static int
internal_yylex(TokenAuxData *auxdata)
{
    int         token;
    const char *yytext;
 
    if (num_pushbacks > 0)
    {
        num_pushbacks--;
        token = pushback_token[num_pushbacks];
        *auxdata = pushback_auxdata[num_pushbacks];
    }
    else
    {
        token = core_yylex(&auxdata->lval.core_yystype,
                           &auxdata->lloc,
                           yyscanner);
 
        /* remember the length of yytext before it gets changed */
        yytext = core_yy.scanbuf + auxdata->lloc;
        auxdata->leng = strlen(yytext);
 
        /* Check for << >> and #, which the core considers operators */
        if (token == Op)
        {
            if (strcmp(auxdata->lval.str, "<<") == 0)
                token = LESS_LESS;
            else if (strcmp(auxdata->lval.str, ">>") == 0)
                token = GREATER_GREATER;
            else if (strcmp(auxdata->lval.str, "#") == 0)
                token = '#';
        }
 
        /* The core returns PARAM as ival, but we treat it like IDENT */
        else if (token == PARAM)
        {
            auxdata->lval.str = pstrdup(yytext);
        }
    }
 
    return token;
}
 
/*
 * Push back a token to be re-read by next internal_yylex() call.
 */
static void
push_back_token(int token, TokenAuxData *auxdata)
{
    if (num_pushbacks >= MAX_PUSHBACKS)
        elog(ERROR, "too many tokens pushed back");
    pushback_token[num_pushbacks] = token;
    pushback_auxdata[num_pushbacks] = *auxdata;
    num_pushbacks++;
}
 
/*
 * Push back a single token to be re-read by next plpgsql_yylex() call.
 *
 * NOTE: this does not cause yylval or yylloc to "back up".  Also, it
 * is not a good idea to push back a token code other than what you read.
 */
void
plpgsql_push_back_token(int token)
{
    TokenAuxData auxdata;
 
    auxdata.lval = plpgsql_yylval;
    auxdata.lloc = plpgsql_yylloc;
    auxdata.leng = plpgsql_yyleng;
    push_back_token(token, &auxdata);
}
 
/*
 * Tell whether a token is an unreserved keyword.
 *
 * (If it is, its lowercased form was returned as the token value, so we
 * do not need to offer that data here.)
 */
bool
plpgsql_token_is_unreserved_keyword(int token)
{
    int         i;
 
    for (i = 0; i < lengthof(UnreservedPLKeywordTokens); i++)
    {
        if (UnreservedPLKeywordTokens[i] == token)
            return true;
    }
    return false;
}
 
/*
 * Append the function text starting at startlocation and extending to
 * (not including) endlocation onto the existing contents of "buf".
 */
void
plpgsql_append_source_text(StringInfo buf,
                           int startlocation, int endlocation)
{
    Assert(startlocation <= endlocation);
    appendBinaryStringInfo(buf, scanorig + startlocation,
                           endlocation - startlocation);
}
 
/*
 * Peek one token ahead in the input stream.  Only the token code is
 * made available, not any of the auxiliary info such as location.
 *
 * NB: no variable or unreserved keyword lookup is performed here, they will
 * be returned as IDENT. Reserved keywords are resolved as usual.
 */
int
plpgsql_peek(void)
{
    int         tok1;
    TokenAuxData aux1;
 
    tok1 = internal_yylex(&aux1);
    push_back_token(tok1, &aux1);
    return tok1;
}
 
/*
 * Peek two tokens ahead in the input stream. The first token and its
 * location in the query are returned in *tok1_p and *tok1_loc, second token
 * and its location in *tok2_p and *tok2_loc.
 *
 * NB: no variable or unreserved keyword lookup is performed here, they will
 * be returned as IDENT. Reserved keywords are resolved as usual.
 */
void
plpgsql_peek2(int *tok1_p, int *tok2_p, int *tok1_loc, int *tok2_loc)
{
    int         tok1,
                tok2;
    TokenAuxData aux1,
                aux2;
 
    tok1 = internal_yylex(&aux1);
    tok2 = internal_yylex(&aux2);
 
    *tok1_p = tok1;
    if (tok1_loc)
        *tok1_loc = aux1.lloc;
    *tok2_p = tok2;
    if (tok2_loc)
        *tok2_loc = aux2.lloc;
 
    push_back_token(tok2, &aux2);
    push_back_token(tok1, &aux1);
}
 
/*
 * plpgsql_scanner_errposition
 *      Report an error cursor position, if possible.
 *
 * This is expected to be used within an ereport() call.  The return value
 * is a dummy (always 0, in fact).
 *
 * Note that this can only be used for messages emitted during initial
 * parsing of a plpgsql function, since it requires the scanorig string
 * to still be available.
 */
int
plpgsql_scanner_errposition(int location)
{
    int         pos;
 
    if (location < 0 || scanorig == NULL)
        return 0;               /* no-op if location is unknown */
 
    /* Convert byte offset to character number */
    pos = pg_mbstrlen_with_len(scanorig, location) + 1;
    /* And pass it to the ereport mechanism */
    (void) internalerrposition(pos);
    /* Also pass the function body string */
    return internalerrquery(scanorig);
}
 
/*
 * plpgsql_yyerror
 *      Report a lexer or grammar error.
 *
 * The message's cursor position refers to the current token (the one
 * last returned by plpgsql_yylex()).
 * This is OK for syntax error messages from the Bison parser, because Bison
 * parsers report error as soon as the first unparsable token is reached.
 * Beware of using yyerror for other purposes, as the cursor position might
 * be misleading!
 */
void
plpgsql_yyerror(const char *message)
{
    char       *yytext = core_yy.scanbuf + plpgsql_yylloc;
 
    if (*yytext == '\0')
    {
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
        /* translator: %s is typically the translation of "syntax error" */
                 errmsg("%s at end of input", _(message)),
                 plpgsql_scanner_errposition(plpgsql_yylloc)));
    }
    else
    {
        /*
         * If we have done any lookahead then flex will have restored the
         * character after the end-of-token.  Zap it again so that we report
         * only the single token here.  This modifies scanbuf but we no longer
         * care about that.
         */
        yytext[plpgsql_yyleng] = '\0';
 
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
        /* translator: first %s is typically the translation of "syntax error" */
                 errmsg("%s at or near \"%s\"", _(message), yytext),
                 plpgsql_scanner_errposition(plpgsql_yylloc)));
    }
}
 
/*
 * Given a location (a byte offset in the function source text),
 * return a line number.
 *
 * We expect that this is typically called for a sequence of increasing
 * location values, so optimize accordingly by tracking the endpoints
 * of the "current" line.
 */
int
plpgsql_location_to_lineno(int location)
{
    const char *loc;
 
    if (location < 0 || scanorig == NULL)
        return 0;               /* garbage in, garbage out */
    loc = scanorig + location;
 
    /* be correct, but not fast, if input location goes backwards */
    if (loc < cur_line_start)
        location_lineno_init();
 
    while (cur_line_end != NULL && loc > cur_line_end)
    {
        cur_line_start = cur_line_end + 1;
        cur_line_num++;
        cur_line_end = strchr(cur_line_start, '\n');
    }
 
    return cur_line_num;
}
 
/* initialize or reset the state for plpgsql_location_to_lineno */
static void
location_lineno_init(void)
{
    cur_line_start = scanorig;
    cur_line_num = 1;
 
    cur_line_end = strchr(cur_line_start, '\n');
}
 
/* return the most recently computed lineno */
int
plpgsql_latest_lineno(void)
{
    return cur_line_num;
}
 
 
/*
 * Called before any actual parsing is done
 *
 * Note: the passed "str" must remain valid until plpgsql_scanner_finish().
 * Although it is not fed directly to flex, we need the original string
 * to cite in error messages.
 */
void
plpgsql_scanner_init(const char *str)
{
    /* Start up the core scanner */
    yyscanner = scanner_init(str, &core_yy,
                             &ReservedPLKeywords, ReservedPLKeywordTokens);
 
    /*
     * scanorig points to the original string, which unlike the scanner's
     * scanbuf won't be modified on-the-fly by flex.  Notice that although
     * yytext points into scanbuf, we rely on being able to apply locations
     * (offsets from string start) to scanorig as well.
     */
    scanorig = str;
 
    /* Other setup */
    plpgsql_IdentifierLookup = IDENTIFIER_LOOKUP_NORMAL;
    plpgsql_yytoken = 0;
 
    num_pushbacks = 0;
 
    location_lineno_init();
}
 
/*
 * Called after parsing is done to clean up after plpgsql_scanner_init()
 */
void
plpgsql_scanner_finish(void)
{
    /* release storage */
    scanner_finish(yyscanner);
    /* avoid leaving any dangling pointers */
    yyscanner = NULL;
    scanorig = NULL;
}