src/reader.c

   1 /* Input parser for Bison
   2
   3    Copyright (C) 1984, 1986, 1989, 1992, 1998, 2000-2003, 2005-2007,
   4    2009-2011 Free Software Foundation, Inc.
   5
   6    This file is part of Bison, the GNU Compiler Compiler.
   7
   8    This program is free software: you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation, either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  20
  21 #include <config.h>
  22 #include "system.h"
  23
  24 #include <quote.h>
  25 #include <quotearg.h>
  26
  27 #include "complain.h"
  28 #include "conflicts.h"
  29 #include "files.h"
  30 #include "getargs.h"
  31 #include "gram.h"
  32 #include "muscle-tab.h"
  33 #include "reader.h"
  34 #include "symlist.h"
  35 #include "symtab.h"
  36 #include "scan-gram.h"
  37 #include "scan-code.h"
  38
  39 static void prepare_percent_define_front_end_variables (void);
  40 static void check_and_convert_grammar (void);
  41
  42 static symbol_list *grammar = NULL;
  43 static bool start_flag = false;
  44 merger_list *merge_functions;
  45
  46 /* Was %union seen?  */
  47 bool union_seen = false;
  48
  49 /* Was a tag seen?  */
  50 bool tag_seen = false;
  51
  52 /* Should rules have a default precedence?  */
  53 bool default_prec = true;
  54 \f
  55 /*-----------------------.
  56 | Set the start symbol.  |
  57 `-----------------------*/
  58
  59 void
  60 grammar_start_symbol_set (symbol *sym, location loc)
  61 {
  62   if (start_flag)
  63     complain_at (loc, _("multiple %s declarations"), "%start");
  64   else
  65     {
  66       start_flag = true;
  67       startsymbol = sym;
  68       startsymbol_location = loc;
  69     }
  70 }
  71
  72 \f
  73
  74 /*------------------------------------------------------------------------.
  75 | Return the merger index for a merging function named NAME.  Records the |
  76 | function, if new, in MERGER_LIST.                                       |
  77 `------------------------------------------------------------------------*/
  78
  79 static int
  80 get_merge_function (uniqstr name)
  81 {
  82   merger_list *syms;
  83   merger_list head;
  84   int n;
  85
  86   if (! glr_parser)
  87     return 0;
  88
  89   head.next = merge_functions;
  90   for (syms = &head, n = 1; syms->next; syms = syms->next, n += 1)
  91     if (UNIQSTR_EQ (name, syms->next->name))
  92       break;
  93   if (syms->next == NULL)
  94     {
  95       syms->next = xmalloc (sizeof syms->next[0]);
  96       syms->next->name = uniqstr_new (name);
  97       /* After all symbol type declarations have been parsed, packgram invokes
  98          record_merge_function_type to set the type.  */
  99       syms->next->type = NULL;
 100       syms->next->next = NULL;
 101       merge_functions = head.next;
 102     }
 103   return n;
 104 }
 105
 106 /*-------------------------------------------------------------------------.
 107 | For the existing merging function with index MERGER, record the result   |
 108 | type as TYPE as required by the lhs of the rule whose %merge declaration |
 109 | is at DECLARATION_LOC.                                                   |
 110 `-------------------------------------------------------------------------*/
 111
 112 static void
 113 record_merge_function_type (int merger, uniqstr type, location declaration_loc)
 114 {
 115   int merger_find;
 116   merger_list *merge_function;
 117
 118   if (merger <= 0)
 119     return;
 120
 121   if (type == NULL)
 122     type = uniqstr_new ("");
 123
 124   merger_find = 1;
 125   for (merge_function = merge_functions;
 126        merge_function != NULL && merger_find != merger;
 127        merge_function = merge_function->next)
 128     merger_find += 1;
 129   aver (merge_function != NULL && merger_find == merger);
 130   if (merge_function->type != NULL && !UNIQSTR_EQ (merge_function->type, type))
 131     {
 132       complain_at (declaration_loc,
 133                    _("result type clash on merge function `%s': <%s> != <%s>"),
 134                    merge_function->name, type, merge_function->type);
 135       complain_at (merge_function->type_declaration_location,
 136                    _("previous declaration"));
 137     }
 138   merge_function->type = uniqstr_new (type);
 139   merge_function->type_declaration_location = declaration_loc;
 140 }
 141
 142 /*--------------------------------------.
 143 | Free all merge-function definitions.  |
 144 `--------------------------------------*/
 145
 146 void
 147 free_merger_functions (void)
 148 {
 149   merger_list *L0 = merge_functions;
 150   while (L0)
 151     {
 152       merger_list *L1 = L0->next;
 153       free (L0);
 154       L0 = L1;
 155     }
 156 }
 157
 158 \f
 159 /*-------------------------------------------------------------------.
 160 | Parse the input grammar into a one symbol_list structure.  Each    |
 161 | rule is represented by a sequence of symbols: the left hand side   |
 162 | followed by the contents of the right hand side, followed by a     |
 163 | null pointer instead of a symbol to terminate the rule.  The next  |
 164 | symbol is the lhs of the following rule.                           |
 165 |                                                                    |
 166 | All actions are copied out, labelled by the rule number they apply |
 167 | to.                                                                |
 168 `-------------------------------------------------------------------*/
 169
 170 /* The (currently) last symbol of GRAMMAR. */
 171 static symbol_list *grammar_end = NULL;
 172
 173 /* Append SYM to the grammar.  */
 174 static symbol_list *
 175 grammar_symbol_append (symbol *sym, location loc)
 176 {
 177   symbol_list *p = symbol_list_sym_new (sym, loc);
 178
 179   if (grammar_end)
 180     grammar_end->next = p;
 181   else
 182     grammar = p;
 183
 184   grammar_end = p;
 185
 186   /* A null SYM stands for an end of rule; it is not an actual
 187      part of it.  */
 188   if (sym)
 189     ++nritems;
 190
 191   return p;
 192 }
 193
 194 static void
 195 assign_named_ref (symbol_list *p, named_ref *name)
 196 {
 197   symbol *sym = p->content.sym;
 198
 199   if (name->id == sym->tag)
 200     {
 201       warn_at (name->loc,
 202                _("duplicated symbol name for %s ignored"),
 203                quote (sym->tag));
 204       named_ref_free (name);
 205     }
 206   else
 207     p->named_ref = name;
 208 }
 209
 210
 211 /* The rule currently being defined, and the previous rule.
 212    CURRENT_RULE points to the first LHS of the current rule, while
 213    PREVIOUS_RULE_END points to the *end* of the previous rule (NULL).  */
 214 static symbol_list *current_rule = NULL;
 215 static symbol_list *previous_rule_end = NULL;
 216
 217
 218 /*----------------------------------------------.
 219 | Create a new rule for LHS in to the GRAMMAR.  |
 220 `----------------------------------------------*/
 221
 222 void
 223 grammar_current_rule_begin (symbol *lhs, location loc,
 224                             named_ref *lhs_name)
 225 {
 226   symbol_list* p;
 227
 228   /* Start a new rule and record its lhs.  */
 229   ++nrules;
 230   previous_rule_end = grammar_end;
 231
 232   p = grammar_symbol_append (lhs, loc);
 233   if (lhs_name)
 234     assign_named_ref(p, lhs_name);
 235
 236   current_rule = grammar_end;
 237
 238   /* Mark the rule's lhs as a nonterminal if not already so.  */
 239   if (lhs->class == unknown_sym)
 240     {
 241       lhs->class = nterm_sym;
 242       lhs->number = nvars;
 243       ++nvars;
 244     }
 245   else if (lhs->class == token_sym)
 246     complain_at (loc, _("rule given for %s, which is a token"), lhs->tag);
 247 }
 248
 249
 250 /*----------------------------------------------------------------------.
 251 | A symbol should be used if either:                                    |
 252 |   1. It has a destructor.                                             |
 253 |   2. --warnings=midrule-values and the symbol is a mid-rule symbol    |
 254 |      (i.e., the generated LHS replacing a mid-rule action) that was   |
 255 |      assigned to or used, as in "exp: { $$ = 1; } { $$ = $1; }".      |
 256 `----------------------------------------------------------------------*/
 257
 258 static bool
 259 symbol_should_be_used (symbol_list const *s)
 260 {
 261   if (symbol_destructor_get (s->content.sym)->code)
 262     return true;
 263   if (warnings_flag & warnings_midrule_values)
 264     return ((s->midrule && s->midrule->action_props.is_value_used)
 265             || (s->midrule_parent_rule
 266                 && symbol_list_n_get (s->midrule_parent_rule,
 267                                       s->midrule_parent_rhs_index)
 268                      ->action_props.is_value_used));
 269   return false;
 270 }
 271
 272 /*----------------------------------------------------------------.
 273 | Check that the rule R is properly defined.  For instance, there |
 274 | should be no type clash on the default action.                  |
 275 `----------------------------------------------------------------*/
 276
 277 static void
 278 grammar_rule_check (const symbol_list *r)
 279 {
 280   /* Type check.
 281
 282      If there is an action, then there is nothing we can do: the user
 283      is allowed to shoot herself in the foot.
 284
 285      Don't worry about the default action if $$ is untyped, since $$'s
 286      value can't be used.  */
 287   if (!r->action_props.code && r->content.sym->type_name)
 288     {
 289       symbol *first_rhs = r->next->content.sym;
 290       /* If $$ is being set in default way, report if any type mismatch.  */
 291       if (first_rhs)
 292         {
 293           char const *lhs_type = r->content.sym->type_name;
 294           const char *rhs_type =
 295             first_rhs->type_name ? first_rhs->type_name : "";
 296           if (!UNIQSTR_EQ (lhs_type, rhs_type))
 297             warn_at (r->location,
 298                      _("type clash on default action: <%s> != <%s>"),
 299                      lhs_type, rhs_type);
 300         }
 301       /* Warn if there is no default for $$ but we need one.  */
 302       else
 303         warn_at (r->location,
 304                  _("empty rule for typed nonterminal, and no action"));
 305     }
 306
 307   /* Check that symbol values that should be used are in fact used.  */
 308   {
 309     symbol_list const *l = r;
 310     int n = 0;
 311     for (; l && l->content.sym; l = l->next, ++n)
 312       if (! (l->action_props.is_value_used
 313              || !symbol_should_be_used (l)
 314              /* The default action, $$ = $1, `uses' both.  */
 315              || (!r->action_props.code && (n == 0 || n == 1))))
 316         {
 317           if (n)
 318             warn_at (r->location, _("unused value: $%d"), n);
 319           else
 320             warn_at (r->location, _("unset value: $$"));
 321         }
 322   }
 323
 324   /* See comments in grammar_current_rule_prec_set for how POSIX
 325      mandates this complaint.  It's only for identifiers, so skip
 326      it for char literals and strings, which are always tokens.  */
 327   if (r->ruleprec
 328       && r->ruleprec->tag[0] != '\'' && r->ruleprec->tag[0] != '"'
 329       && !r->ruleprec->declared && !r->ruleprec->prec)
 330     warn_at (r->location, _("token for %%prec is not defined: %s"),
 331              r->ruleprec->tag);
 332 }
 333
 334
 335 /*-------------------------------------.
 336 | End the currently being grown rule.  |
 337 `-------------------------------------*/
 338
 339 void
 340 grammar_current_rule_end (location loc)
 341 {
 342   /* Put an empty link in the list to mark the end of this rule  */
 343   grammar_symbol_append (NULL, grammar_end->location);
 344   current_rule->location = loc;
 345 }
 346
 347
 348 /*-------------------------------------------------------------------.
 349 | The previous action turns out the be a mid-rule action.  Attach it |
 350 | to the current rule, i.e., create a dummy symbol, attach it this   |
 351 | mid-rule action, and append this dummy nonterminal to the current  |
 352 | rule.                                                              |
 353 `-------------------------------------------------------------------*/
 354
 355 void
 356 grammar_midrule_action (void)
 357 {
 358   /* Since the action was written out with this rule's number, we must
 359      give the new rule this number by inserting the new rule before
 360      it.  */
 361
 362   /* Make a DUMMY nonterminal, whose location is that of the midrule
 363      action.  Create the MIDRULE.  */
 364   location dummy_location = current_rule->action_props.location;
 365   symbol *dummy = dummy_symbol_get (dummy_location);
 366   symbol_list *midrule = symbol_list_sym_new (dummy, dummy_location);
 367
 368   /* Remember named_ref of previous action. */
 369   named_ref *action_name = current_rule->action_props.named_ref;
 370
 371   /* Make a new rule, whose body is empty, before the current one, so
 372      that the action just read can belong to it.  */
 373   ++nrules;
 374   ++nritems;
 375   /* Attach its location and actions to that of the DUMMY.  */
 376   midrule->location = dummy_location;
 377   code_props_rule_action_init (&midrule->action_props,
 378                                current_rule->action_props.code,
 379                                current_rule->action_props.location,
 380                                midrule, 0);
 381   code_props_none_init (&current_rule->action_props);
 382
 383   if (previous_rule_end)
 384     previous_rule_end->next = midrule;
 385   else
 386     grammar = midrule;
 387
 388   /* End the dummy's rule.  */
 389   midrule->next = symbol_list_sym_new (NULL, dummy_location);
 390   midrule->next->next = current_rule;
 391
 392   previous_rule_end = midrule->next;
 393
 394   /* Insert the dummy nonterminal replacing the midrule action into
 395      the current rule.  Bind it to its dedicated rule.  */
 396   grammar_current_rule_symbol_append (dummy, dummy_location,
 397                                       action_name);
 398   grammar_end->midrule = midrule;
 399   midrule->midrule_parent_rule = current_rule;
 400   midrule->midrule_parent_rhs_index = symbol_list_length (current_rule->next);
 401 }
 402
 403 /* Set the precedence symbol of the current rule to PRECSYM. */
 404
 405 void
 406 grammar_current_rule_prec_set (symbol *precsym, location loc)
 407 {
 408   /* POSIX says that any identifier is a nonterminal if it does not
 409      appear on the LHS of a grammar rule and is not defined by %token
 410      or by one of the directives that assigns precedence to a token.  We
 411      ignore this here because the only kind of identifier that POSIX
 412      allows to follow a %prec is a token and because assuming it's a
 413      token now can produce more logical error messages.  Nevertheless,
 414      grammar_rule_check does obey what we believe is the real intent of
 415      POSIX here: that an error be reported for any identifier that
 416      appears after %prec but that is not defined separately as a
 417      token.  */
 418   symbol_class_set (precsym, token_sym, loc, false);
 419   if (current_rule->ruleprec)
 420     complain_at (loc, _("only one %s allowed per rule"), "%prec");
 421   current_rule->ruleprec = precsym;
 422 }
 423
 424 /* Attach dynamic precedence DPREC to the current rule. */
 425
 426 void
 427 grammar_current_rule_dprec_set (int dprec, location loc)
 428 {
 429   if (! glr_parser)
 430     warn_at (loc, _("%s affects only GLR parsers"), "%dprec");
 431   if (dprec <= 0)
 432     complain_at (loc, _("%s must be followed by positive number"), "%dprec");
 433   else if (current_rule->dprec != 0)
 434     complain_at (loc, _("only one %s allowed per rule"), "%dprec");
 435   current_rule->dprec = dprec;
 436 }
 437
 438 /* Attach a merge function NAME with argument type TYPE to current
 439    rule. */
 440
 441 void
 442 grammar_current_rule_merge_set (uniqstr name, location loc)
 443 {
 444   if (! glr_parser)
 445     warn_at (loc, _("%s affects only GLR parsers"), "%merge");
 446   if (current_rule->merger != 0)
 447     complain_at (loc, _("only one %s allowed per rule"), "%merge");
 448   current_rule->merger = get_merge_function (name);
 449   current_rule->merger_declaration_location = loc;
 450 }
 451
 452 /* Attach SYM to the current rule.  If needed, move the previous
 453    action as a mid-rule action.  */
 454
 455 void
 456 grammar_current_rule_symbol_append (symbol *sym, location loc,
 457                                     named_ref *name)
 458 {
 459   symbol_list *p;
 460   if (current_rule->action_props.code)
 461     grammar_midrule_action ();
 462   p = grammar_symbol_append (sym, loc);
 463   if (name)
 464     assign_named_ref(p, name);
 465 }
 466
 467 /* Attach an ACTION to the current rule.  */
 468
 469 void
 470 grammar_current_rule_action_append (const char *action, location loc,
 471                                     named_ref *name)
 472 {
 473   if (current_rule->action_props.code)
 474     grammar_midrule_action ();
 475   /* After all symbol declarations have been parsed, packgram invokes
 476      code_props_translate_code.  */
 477   code_props_rule_action_init (&current_rule->action_props, action, loc,
 478                                current_rule, name);
 479 }
 480
 481 \f
 482 /*---------------------------------------------------------------.
 483 | Convert the rules into the representation using RRHS, RLHS and |
 484 | RITEM.                                                         |
 485 `---------------------------------------------------------------*/
 486
 487 static void
 488 packgram (void)
 489 {
 490   unsigned int itemno = 0;
 491   rule_number ruleno = 0;
 492   symbol_list *p = grammar;
 493
 494   ritem = xnmalloc (nritems + 1, sizeof *ritem);
 495
 496   /* This sentinel is used by build_relations in gram.c.  */
 497   *ritem++ = 0;
 498
 499   rules = xnmalloc (nrules, sizeof *rules);
 500
 501   while (p)
 502     {
 503       int rule_length = 0;
 504       symbol *ruleprec = p->ruleprec;
 505       record_merge_function_type (p->merger, p->content.sym->type_name,
 506                                   p->merger_declaration_location);
 507       rules[ruleno].user_number = ruleno;
 508       rules[ruleno].number = ruleno;
 509       rules[ruleno].lhs = p->content.sym;
 510       rules[ruleno].rhs = ritem + itemno;
 511       rules[ruleno].prec = NULL;
 512       rules[ruleno].dprec = p->dprec;
 513       rules[ruleno].merger = p->merger;
 514       rules[ruleno].precsym = NULL;
 515       rules[ruleno].location = p->location;
 516       rules[ruleno].useful = true;
 517       rules[ruleno].action = p->action_props.code;
 518       rules[ruleno].action_location = p->action_props.location;
 519
 520       /* If the midrule's $$ is set or its $n is used, remove the `$' from the
 521          symbol name so that it's a user-defined symbol so that the default
 522          %destructor and %printer apply.  */
 523       if (p->midrule_parent_rule
 524           && (p->action_props.is_value_used
 525               || symbol_list_n_get (p->midrule_parent_rule,
 526                                     p->midrule_parent_rhs_index)
 527                    ->action_props.is_value_used))
 528         p->content.sym->tag += 1;
 529
 530       /* Don't check the generated rule 0.  It has no action, so some rhs
 531          symbols may appear unused, but the parsing algorithm ensures that
 532          %destructor's are invoked appropriately.  */
 533       if (p != grammar)
 534         grammar_rule_check (p);
 535
 536       for (p = p->next; p && p->content.sym; p = p->next)
 537         {
 538           ++rule_length;
 539
 540           /* Don't allow rule_length == INT_MAX, since that might
 541              cause confusion with strtol if INT_MAX == LONG_MAX.  */
 542           if (rule_length == INT_MAX)
 543               fatal_at (rules[ruleno].location, _("rule is too long"));
 544
 545           /* item_number = symbol_number.
 546              But the former needs to contain more: negative rule numbers. */
 547           ritem[itemno++] =
 548             symbol_number_as_item_number (p->content.sym->number);
 549           /* A rule gets by default the precedence and associativity
 550              of its last token.  */
 551           if (p->content.sym->class == token_sym && default_prec)
 552             rules[ruleno].prec = p->content.sym;
 553         }
 554
 555       /* If this rule has a %prec,
 556          the specified symbol's precedence replaces the default.  */
 557       if (ruleprec)
 558         {
 559           rules[ruleno].precsym = ruleprec;
 560           rules[ruleno].prec = ruleprec;
 561         }
 562       /* An item ends by the rule number (negated).  */
 563       ritem[itemno++] = rule_number_as_item_number (ruleno);
 564       aver (itemno < ITEM_NUMBER_MAX);
 565       ++ruleno;
 566       aver (ruleno < RULE_NUMBER_MAX);
 567
 568       if (p)
 569         p = p->next;
 570     }
 571
 572   aver (itemno == nritems);
 573
 574   if (trace_flag & trace_sets)
 575     ritem_print (stderr);
 576 }
 577 \f
 578 /*------------------------------------------------------------------.
 579 | Read in the grammar specification and record it in the format     |
 580 | described in gram.h.  All actions are copied into ACTION_OBSTACK, |
 581 | in each case forming the body of a C function (YYACTION) which    |
 582 | contains a switch statement to decide which action to execute.    |
 583 `------------------------------------------------------------------*/
 584
 585 void
 586 reader (void)
 587 {
 588   /* Initialize the symbol table.  */
 589   symbols_new ();
 590
 591   /* Construct the accept symbol. */
 592   accept = symbol_get ("$accept", empty_location);
 593   accept->class = nterm_sym;
 594   accept->number = nvars++;
 595
 596   /* Construct the error token */
 597   errtoken = symbol_get ("error", empty_location);
 598   errtoken->class = token_sym;
 599   errtoken->number = ntokens++;
 600
 601   /* Construct a token that represents all undefined literal tokens.
 602      It is always token number 2.  */
 603   undeftoken = symbol_get ("$undefined", empty_location);
 604   undeftoken->class = token_sym;
 605   undeftoken->number = ntokens++;
 606
 607   gram_in = xfopen (grammar_file, "r");
 608
 609   gram__flex_debug = trace_flag & trace_scan;
 610   gram_debug = trace_flag & trace_parse;
 611   gram_scanner_initialize ();
 612   gram_parse ();
 613   prepare_percent_define_front_end_variables ();
 614
 615   if (! complaint_issued)
 616     check_and_convert_grammar ();
 617
 618   xfclose (gram_in);
 619 }
 620
 621 static void
 622 prepare_percent_define_front_end_variables (void)
 623 {
 624   /* Set %define front-end variable defaults.  */
 625   muscle_percent_define_default ("lr.keep-unreachable-states", "false");
 626   {
 627     char *lr_type;
 628     /* IELR would be a better default, but LALR is historically the
 629        default.  */
 630     muscle_percent_define_default ("lr.type", "lalr");
 631     lr_type = muscle_percent_define_get ("lr.type");
 632     if (0 != strcmp (lr_type, "canonical-lr"))
 633       muscle_percent_define_default ("lr.default-reductions", "full");
 634     else
 635       muscle_percent_define_default ("lr.default-reductions", "accepting");
 636     free (lr_type);
 637   }
 638
 639   /* Check %define front-end variables.  */
 640   {
 641     static char const * const values[] = {
 642       "lr.type", "lalr", "ielr", "canonical-lr", NULL,
 643       "lr.default-reductions", "full", "consistent", "accepting", NULL,
 644       NULL
 645     };
 646     muscle_percent_define_check_values (values);
 647   }
 648 }
 649
 650
 651 /*-------------------------------------------------------------.
 652 | Check the grammar that has just been read, and convert it to |
 653 | internal form.                                               |
 654 `-------------------------------------------------------------*/
 655
 656 static void
 657 check_and_convert_grammar (void)
 658 {
 659   /* Grammar has been read.  Do some checking.  */
 660   if (nrules == 0)
 661     fatal (_("no rules in the input grammar"));
 662
 663   /* If the user did not define her ENDTOKEN, do it now. */
 664   if (!endtoken)
 665     {
 666       endtoken = symbol_get ("$end", empty_location);
 667       endtoken->class = token_sym;
 668       endtoken->number = 0;
 669       /* Value specified by POSIX.  */
 670       endtoken->user_token_number = 0;
 671     }
 672
 673   /* Report any undefined symbols and consider them nonterminals.  */
 674   symbols_check_defined ();
 675
 676   /* Find the start symbol if no %start.  */
 677   if (!start_flag)
 678     {
 679       symbol_list *node;
 680       for (node = grammar;
 681            node != NULL && symbol_is_dummy (node->content.sym);
 682            node = node->next)
 683         {
 684           for (node = node->next;
 685                node != NULL && node->content.sym != NULL;
 686                node = node->next)
 687             ;
 688         }
 689       aver (node != NULL);
 690       grammar_start_symbol_set (node->content.sym,
 691                                 node->content.sym->location);
 692     }
 693
 694   /* Insert the initial rule, whose line is that of the first rule
 695      (not that of the start symbol):
 696
 697      accept: %start EOF.  */
 698   {
 699     symbol_list *p = symbol_list_sym_new (accept, empty_location);
 700     p->location = grammar->location;
 701     p->next = symbol_list_sym_new (startsymbol, empty_location);
 702     p->next->next = symbol_list_sym_new (endtoken, empty_location);
 703     p->next->next->next = symbol_list_sym_new (NULL, empty_location);
 704     p->next->next->next->next = grammar;
 705     nrules += 1;
 706     nritems += 3;
 707     grammar = p;
 708   }
 709
 710   aver (nsyms <= SYMBOL_NUMBER_MAXIMUM && nsyms == ntokens + nvars);
 711
 712   /* Assign the symbols their symbol numbers.  Write #defines for the
 713      token symbols into FDEFINES if requested.  */
 714   symbols_pack ();
 715
 716   /* Scan rule actions after invoking symbol_check_alias_consistency (in
 717      symbols_pack above) so that token types are set correctly before the rule
 718      action type checking.
 719
 720      Before invoking grammar_rule_check (in packgram below) on any rule, make
 721      sure all actions have already been scanned in order to set `used' flags.
 722      Otherwise, checking that a midrule's $$ should be set will not always work
 723      properly because the check must forward-reference the midrule's parent
 724      rule.  For the same reason, all the `used' flags must be set before
 725      checking whether to remove `$' from any midrule symbol name (also in
 726      packgram).  */
 727   {
 728     symbol_list *sym;
 729     for (sym = grammar; sym; sym = sym->next)
 730       code_props_translate_code (&sym->action_props);
 731   }
 732
 733   /* Convert the grammar into the format described in gram.h.  */
 734   packgram ();
 735
 736   /* The grammar as a symbol_list is no longer needed. */
 737   symbol_list_free (grammar);
 738 }