/*--------------------------------------------------------------------

 * Symbols referenced in this file:

 * - raw_parser

 * - base_yylex

 * - check_uescapechar

 * - str_udeescape

 * - hexval

 * - check_unicode_value

 * - raw_parser

 *--------------------------------------------------------------------

 */

/*-------------------------------------------------------------------------

 *

 * 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) 1996-2022, PostgreSQL Global Development Group

 * Portions Copyright (c) 1994, Regents of the University of California

 *

 * IDENTIFICATION

 *    src/backend/parser/parser.c

 *

 *-------------------------------------------------------------------------

 */

#include "postgres.h"

#include "mb/pg_wchar.h"

#include "parser/gramparse.h"

#include "parser/parser.h"

#include "parser/scansup.h"

static bool check_uescapechar(unsigned char escape);

static char *str_udeescape(const char *str, char escape,

               int position, core_yyscan_t yyscanner);

/*

 * raw_parser

 *    Given a query in string form, do lexical and grammatical analysis.

 *

 * Returns a list of raw (un-analyzed) parse trees.  The contents of the

 * list have the form required by the specified RawParseMode.

 */

List *

raw_parser(const char *str, RawParseMode mode)

{

  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 us to initialize the lookahead token, if any */

  if (mode == RAW_PARSE_DEFAULT)

    yyextra.have_lookahead = false;

  else

  {

    /* this array is indexed by RawParseMode enum */

    static const int mode_token[] = {

      0,          /* RAW_PARSE_DEFAULT */

      MODE_TYPE_NAME,   /* RAW_PARSE_TYPE_NAME */

      MODE_PLPGSQL_EXPR, /* RAW_PARSE_PLPGSQL_EXPR */

      MODE_PLPGSQL_ASSIGN1, /* RAW_PARSE_PLPGSQL_ASSIGN1 */

      MODE_PLPGSQL_ASSIGN2, /* RAW_PARSE_PLPGSQL_ASSIGN2 */

      MODE_PLPGSQL_ASSIGN3  /* RAW_PARSE_PLPGSQL_ASSIGN3 */

    };

    yyextra.have_lookahead = true;

    yyextra.lookahead_token = mode_token[mode];

    yyextra.lookahead_yylloc = 0;

    yyextra.lookahead_end = NULL;

  }

  /* 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.

 *

 * 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.

 *

 * 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;

    if (yyextra->lookahead_end)

      *(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 --- at least for the fixed-length cases.)

   */

  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;

    case UIDENT:

    case USCONST:

      cur_token_length = strlen(yyextra->core_yy_extra.scanbuf + *llocp);

      break;

    case SQL_COMMENT:

    case C_COMMENT:

      return base_yylex(lvalp, llocp, yyscanner);

    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;

    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 *llocp */

        cur_yylloc = *llocp;

        /* Un-truncate current token so errors point to third token */

        *(yyextra->lookahead_end) = yyextra->lookahead_hold_char;

        /* Get third token */

        next_token = core_yylex(&(yyextra->lookahead_yylval),

                    llocp, yyscanner);

        /* If we throw error here, it will point to third token */

        if (next_token != SCONST)

          scanner_yyerror("UESCAPE must be followed by a simple string literal",

                  yyscanner);

        escstr = yyextra->lookahead_yylval.str;

        if (strlen(escstr) != 1 || !check_uescapechar(escstr[0]))

          scanner_yyerror("invalid Unicode escape character",

                  yyscanner);

        /* Now restore *llocp; errors will point to first token */

        *llocp = cur_yylloc;

        /* Apply Unicode conversion */

        lvalp->core_yystype.str =

          str_udeescape(lvalp->core_yystype.str,

                  escstr[0],

                  *llocp,

                  yyscanner);

        /*

         * We don't need to revert the un-truncation of UESCAPE.  What

         * we do want to do is clear have_lookahead, thereby consuming

         * all three tokens.

         */

        yyextra->have_lookahead = false;

      }

      else

      {

        /* No UESCAPE, so convert using default escape character */

        lvalp->core_yystype.str =

          str_udeescape(lvalp->core_yystype.str,

                  '\\',

                  *llocp,

                  yyscanner);

      }

      if (cur_token == UIDENT)

      {

        /* It's an identifier, so truncate as appropriate */

        truncate_identifier(lvalp->core_yystype.str,

                  strlen(lvalp->core_yystype.str),

                  true);

        cur_token = IDENT;

      }

      else if (cur_token == USCONST)

      {

        cur_token = SCONST;

      }

      break;

  }

  return cur_token;

}

/* convert hex digit (caller should have verified that) to value */

static unsigned int

hexval(unsigned char c)

{

  if (c >= '0' && c <= '9')

    return c - '0';

  if (c >= 'a' && c <= 'f')

    return c - 'a' + 0xA;

  if (c >= 'A' && c <= 'F')

    return c - 'A' + 0xA;

  elog(ERROR, "invalid hexadecimal digit");

  return 0;         /* not reached */

}

/* is Unicode code point acceptable? */

static void

check_unicode_value(pg_wchar c)

{

  if (!is_valid_unicode_codepoint(c))

    ereport(ERROR,

        (errcode(ERRCODE_SYNTAX_ERROR),

         errmsg("invalid Unicode escape value")));

}

/* is 'escape' acceptable as Unicode escape character (UESCAPE syntax) ? */

static bool

check_uescapechar(unsigned char escape)

{

  if (isxdigit(escape)

    || escape == '+'

    || escape == '\''

    || escape == '"'

    || scanner_isspace(escape))

    return false;

  else

    return true;

}

/*

 * Process Unicode escapes in "str", producing a palloc'd plain string

 *

 * escape: the escape character to use

 * position: start position of U&'' or U&"" string token

 * yyscanner: context information needed for error reports

 */

static char *

str_udeescape(const char *str, char escape,

        int position, core_yyscan_t yyscanner)

{

  const char *in;

  char     *new,

         *out;

  size_t    new_len;

  pg_wchar  pair_first = 0;

  ScannerCallbackState scbstate;

  /*

   * Guesstimate that result will be no longer than input, but allow enough

   * padding for Unicode conversion.

   */

  new_len = strlen(str) + MAX_UNICODE_EQUIVALENT_STRING + 1;

  new = palloc(new_len);

  in = str;

  out = new;

  while (*in)

  {

    /* Enlarge string if needed */

    size_t    out_dist = out - new;

    if (out_dist > new_len - (MAX_UNICODE_EQUIVALENT_STRING + 1))

    {

      new_len *= 2;

      new = repalloc(new, new_len);

      out = new + out_dist;

    }

    if (in[0] == escape)

    {

      /*

       * Any errors reported while processing this escape sequence will

       * have an error cursor pointing at the escape.

       */

      setup_scanner_errposition_callback(&scbstate, yyscanner,

                         in - str + position + 3);  /* 3 for U&" */

      if (in[1] == escape)

      {

        if (pair_first)

          goto invalid_pair;

        *out++ = escape;

        in += 2;

      }

      else if (isxdigit((unsigned char) in[1]) &&

           isxdigit((unsigned char) in[2]) &&

           isxdigit((unsigned char) in[3]) &&

           isxdigit((unsigned char) in[4]))

      {

        pg_wchar  unicode;

        unicode = (hexval(in[1]) << 12) +

          (hexval(in[2]) << 8) +

          (hexval(in[3]) << 4) +

          hexval(in[4]);

        check_unicode_value(unicode);

        if (pair_first)

        {

          if (is_utf16_surrogate_second(unicode))

          {

            unicode = surrogate_pair_to_codepoint(pair_first, unicode);

            pair_first = 0;

          }

          else

            goto invalid_pair;

        }

        else if (is_utf16_surrogate_second(unicode))

          goto invalid_pair;

        if (is_utf16_surrogate_first(unicode))

          pair_first = unicode;

        else

        {

          pg_unicode_to_server(unicode, (unsigned char *) out);

          out += strlen(out);

        }

        in += 5;

      }

      else if (in[1] == '+' &&

           isxdigit((unsigned char) in[2]) &&

           isxdigit((unsigned char) in[3]) &&

           isxdigit((unsigned char) in[4]) &&

           isxdigit((unsigned char) in[5]) &&

           isxdigit((unsigned char) in[6]) &&

           isxdigit((unsigned char) in[7]))

      {

        pg_wchar  unicode;

        unicode = (hexval(in[2]) << 20) +

          (hexval(in[3]) << 16) +

          (hexval(in[4]) << 12) +

          (hexval(in[5]) << 8) +

          (hexval(in[6]) << 4) +

          hexval(in[7]);

        check_unicode_value(unicode);

        if (pair_first)

        {

          if (is_utf16_surrogate_second(unicode))

          {

            unicode = surrogate_pair_to_codepoint(pair_first, unicode);

            pair_first = 0;

          }

          else

            goto invalid_pair;

        }

        else if (is_utf16_surrogate_second(unicode))

          goto invalid_pair;

        if (is_utf16_surrogate_first(unicode))

          pair_first = unicode;

        else

        {

          pg_unicode_to_server(unicode, (unsigned char *) out);

          out += strlen(out);

        }

        in += 8;

      }

      else

        ereport(ERROR,

            (errcode(ERRCODE_SYNTAX_ERROR),

             errmsg("invalid Unicode escape"),

             errhint("Unicode escapes must be \\XXXX or \\+XXXXXX.")));

      cancel_scanner_errposition_callback(&scbstate);

    }

    else

    {

      if (pair_first)

        goto invalid_pair;

      *out++ = *in++;

    }

  }

  /* unfinished surrogate pair? */

  if (pair_first)

    goto invalid_pair;

  *out = '\0';

  return new;

  /*

   * We might get here with the error callback active, or not.  Call

   * scanner_errposition to make sure an error cursor appears; if the

   * callback is active, this is duplicative but harmless.

   */

invalid_pair:

  ereport(ERROR,

      (errcode(ERRCODE_SYNTAX_ERROR),

       errmsg("invalid Unicode surrogate pair"),

       scanner_errposition(in - str + position + 3, /* 3 for U&" */

                 yyscanner)));

  return NULL;       /* keep compiler quiet */

}