src/reader.c

/* Input parser for Bison

   Copyright (C) 1984, 1986, 1989, 1992, 1998, 2000-2003, 2005-2007,
   2009-2015, 2018-2022 Free Software Foundation, Inc.

   This file is part of Bison, the GNU Compiler Compiler.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>
#include "system.h"

#include <quote.h>
#include <vasnprintf.h>

#include "complain.h"
#include "conflicts.h"
#include "files.h"
#include "fixits.h"
#include "getargs.h"
#include "gram.h"
#include "muscle-tab.h"
#include "reader.h"
#include "symlist.h"
#include "symtab.h"
#include "scan-gram.h"
#include "scan-code.h"

static void prepare_percent_define_front_end_variables (void);
static void check_and_convert_grammar (void);

static symbol_list *grammar = NULL;
symbol_list *start_symbols = NULL;
merger_list *merge_functions = NULL;

/* Was %union seen?  */
bool union_seen = false;

/* Should rules have a default precedence?  */
bool default_prec = true;


void
grammar_start_symbols_add (symbol_list *syms)
{
  /* Report and ignore duplicates.  Append the others to START_SYMBOLS.  */
  symbol_list *last = symbol_list_last (start_symbols);
  for (symbol_list *l = syms; l && l->content.sym; /* nothing */)
    {
      /* Is there a previous definition?  */
      symbol_list *first = symbol_list_find_symbol (start_symbols, l->content.sym);
      if (first)
        {
          duplicate_directive ("%start", first->sym_loc, l->sym_loc);
          symbol_list *dupl = l;
          l = l->next;
          dupl->next = NULL;
          symbol_list_free (dupl);
        }
      else
        {
          if (last)
            {
              last->next = l;
              last = l;
            }
          else
            {
              last = l;
              start_symbols = last;
            }
          symbol_list *next = l->next;
          l->next = NULL;
          l = next;
        }
    }
}



/*------------------------------------------------------------------------.
| Return the merger index for a merging function named NAME.  Records the |
| function, if new, in MERGER_LIST.                                       |
`------------------------------------------------------------------------*/

static int
get_merge_function (uniqstr name)
{
  if (! glr_parser)
    return 0;

  merger_list *syms;
  merger_list head;
  int n;

  head.next = merge_functions;
  for (syms = &head, n = 1; syms->next; syms = syms->next, n += 1)
    if (UNIQSTR_EQ (name, syms->next->name))
      break;
  if (syms->next == NULL)
    {
      syms->next = xmalloc (sizeof syms->next[0]);
      syms->next->name = uniqstr_new (name);
      /* After all symbol type declarations have been parsed, packgram invokes
         record_merge_function_type to set the type.  */
      syms->next->sym = NULL;
      syms->next->next = NULL;
      merge_functions = head.next;
    }
  return n;
}

/*-------------------------------------------------------------------.
| For the existing merging function with index MERGER, record that   |
| the result type is that of SYM, as required by the lhs (i.e., SYM) |
| of the rule whose %merge declaration is at DECLARATION_LOC.        |
`-------------------------------------------------------------------*/

static void
record_merge_function_type (int merger, symbol *sym, location declaration_loc)
{
  if (merger <= 0)
    return;

  uniqstr type
    = sym->content->type_name ? sym->content->type_name : uniqstr_new ("");

  merger_list *merge_function;
  int merger_find = 1;
  for (merge_function = merge_functions;
       merge_function != NULL && merger_find != merger;
       merge_function = merge_function->next)
    merger_find += 1;
  aver (merge_function != NULL && merger_find == merger);
  if (merge_function->sym && merge_function->sym->content->type_name)
    {
      if (!UNIQSTR_EQ (merge_function->sym->content->type_name, type))
        {
          complain (&declaration_loc, complaint,
                    _("result type clash on merge function %s: "
                      "<%s> != <%s>"),
                    quote (merge_function->name), type,
                    merge_function->sym->content->type_name);
          subcomplain (&merge_function->type_declaration_loc, complaint,
                       _("previous declaration"));
        }
    }
  else
    {
      merge_function->sym = sym;
      merge_function->type_declaration_loc = declaration_loc;
    }
}

/*--------------------------------------.
| Free all merge-function definitions.  |
`--------------------------------------*/

void
free_merger_functions (void)
{
  merger_list *L0 = merge_functions;
  while (L0)
    {
      merger_list *L1 = L0->next;
      free (L0);
      L0 = L1;
    }
}


/*-------------------------------------------------------------------.
| Parse the input grammar into a one symbol_list structure.  Each    |
| rule is represented by a sequence of symbols: the left hand side   |
| followed by the contents of the right hand side, followed by a     |
| null pointer instead of a symbol to terminate the rule.  The next  |
| symbol is the lhs of the following rule.                           |
|                                                                    |
| All actions are copied out, labelled by the rule number they apply |
| to.                                                                |
`-------------------------------------------------------------------*/

/* The (currently) last symbol of GRAMMAR. */
static symbol_list *grammar_end = NULL;

/* Append SYM to the grammar.  */
static symbol_list *
grammar_symbol_append (symbol *sym, location loc)
{
  symbol_list *p = symbol_list_sym_new (sym, loc);

  if (grammar_end)
    grammar_end->next = p;
  else
    grammar = p;

  grammar_end = p;

  /* A null SYM stands for an end of rule; it is not an actual
     part of it.  */
  if (sym)
    ++nritems;

  return p;
}

static void
assign_named_ref (symbol_list *p, named_ref *name)
{
  symbol *sym = p->content.sym;

  if (name->id == sym->tag)
    {
      complain (&name->loc, Wother,
                _("duplicated symbol name for %s ignored"),
                quote (sym->tag));
      named_ref_free (name);
    }
  else
    p->named_ref = name;
}


/* The rule currently being defined, and the previous rule.
   CURRENT_RULE points to the first LHS of the current rule, while
   PREVIOUS_RULE_END points to the *end* of the previous rule (NULL).  */
static symbol_list *current_rule = NULL;
static symbol_list *previous_rule_end = NULL;


/*----------------------------------------------.
| Create a new rule for LHS in to the GRAMMAR.  |
`----------------------------------------------*/

void
grammar_current_rule_begin (symbol *lhs, location loc,
                            named_ref *lhs_name)
{
  /* Start a new rule and record its lhs.  */
  ++nrules;
  previous_rule_end = grammar_end;

  current_rule = grammar_symbol_append (lhs, loc);
  if (lhs_name)
    assign_named_ref (current_rule, named_ref_copy (lhs_name));

  /* Mark the rule's lhs as a nonterminal if not already so.  */
  if (lhs->content->class == unknown_sym || lhs->content->class == pct_type_sym)
    symbol_class_set (lhs, nterm_sym, empty_loc, false);
  else if (lhs->content->class == token_sym)
    complain (&loc, complaint, _("rule given for %s, which is a token"),
              lhs->tag);
}


/*----------------------------------------------------------------------.
| A symbol should be used if either:                                    |
|   1. It has a destructor.                                             |
|   2. The symbol is a midrule symbol (i.e., the generated LHS          |
|      replacing a midrule action) that was assigned to or used, as in  |
|      "exp: { $$ = 1; } { $$ = $1; }".                                 |
`----------------------------------------------------------------------*/

static bool
symbol_should_be_used (symbol_list const *s, bool *midrule_warning)
{
  if (symbol_code_props_get (s->content.sym, destructor)->code)
    return true;
  if ((s->midrule && s->midrule->action_props.is_value_used)
      || (s->midrule_parent_rule
          && (symbol_list_n_get (s->midrule_parent_rule,
                                 s->midrule_parent_rhs_index)
              ->action_props.is_value_used)))
    {
      *midrule_warning = true;
      return true;
    }
  return false;
}

/*-----------------------------------------------------------------.
| Check that the rule R is properly defined.  For instance, there  |
| should be no type clash on the default action.  Possibly install |
| the default action.                                              |
`-----------------------------------------------------------------*/

static void
grammar_rule_check_and_complete (symbol_list *r)
{
  const symbol *lhs = r->content.sym;
  const symbol *first_rhs = r->next->content.sym;

  /* Type check.

     If there is an action, then there is nothing we can do: the user
     is allowed to shoot herself in the foot.

     Don't worry about the default action if $$ is untyped, since $$'s
     value can't be used.  */
  if (!r->action_props.code && lhs->content->type_name)
    {
      /* If $$ is being set in default way, report if any type mismatch.  */
      if (first_rhs)
        {
          char const *lhs_type = lhs->content->type_name;
          char const *rhs_type =
            first_rhs->content->type_name ? first_rhs->content->type_name : "";
          if (!UNIQSTR_EQ (lhs_type, rhs_type))
            complain (&r->rhs_loc, Wother,
                      _("type clash on default action: <%s> != <%s>"),
                      lhs_type, rhs_type);
          else
            {
              /* Install the default action only for C++.  */
              const bool is_cxx =
                STREQ (language->language, "c++")
                || (skeleton && (STREQ (skeleton, "glr.cc")
                                 || STREQ (skeleton, "glr2.cc")
                                 || STREQ (skeleton, "lalr1.cc")));
              if (is_cxx)
                {
                  code_props_rule_action_init (&r->action_props, "{ $$ = $1; }",
                                               r->rhs_loc, r,
                                               /* name */ NULL,
                                               /* type */ NULL,
                                               /* is_predicate */ false);
                  code_props_translate_code (&r->action_props);
                }
            }
        }
      /* Warn if there is no default for $$ but we need one.  */
      else
        complain (&r->rhs_loc, Wother,
                  _("empty rule for typed nonterminal, and no action"));
    }

  /* For each start symbol, build the action of its start rule.  Use
     the same obstack as the one used by scan-code, which is in charge
     of actions. */
  const bool multistart = start_symbols && start_symbols->next;
  if (multistart && lhs == acceptsymbol)
    {
      const symbol *start = r->next->next->content.sym;
      if (start->content->type_name)
        obstack_printf (obstack_for_actions,
                        "{ ]b4_accept""([%s%d])[; }",
                        start->content->class == nterm_sym ? "orig " : "",
                        start->content->number);
      else
        obstack_printf (obstack_for_actions,
                        "{ ]b4_accept[; }");
      code_props_rule_action_init (&r->action_props,
                                   obstack_finish0 (obstack_for_actions),
                                   r->rhs_loc, r,
                                   /* name */ NULL,
                                   /* type */ NULL,
                                   /* is_predicate */ false);
    }


  /* Check that symbol values that should be used are in fact used.
     Don't check the generated start rules.  It has no action, so some
     rhs symbols may appear unused, but the parsing algorithm ensures
     that %destructor's are invoked appropriately.  */
  if (lhs != acceptsymbol)
    {
      int n = 0;
      for (symbol_list const *l = r; l && l->content.sym; l = l->next, ++n)
        {
          bool midrule_warning = false;
          if (!l->action_props.is_value_used
              && symbol_should_be_used (l, &midrule_warning)
              /* The default action, $$ = $1, 'uses' both.  */
              && (r->action_props.code || (n != 0 && n != 1)))
            {
              warnings warn_flag = midrule_warning ? Wmidrule_values : Wother;
              if (n)
                complain (&l->sym_loc, warn_flag, _("unused value: $%d"), n);
              else
                complain (&l->rhs_loc, warn_flag, _("unset value: $$"));
            }
        }
    }

  /* Check that %empty => empty rule.  */
  if (r->percent_empty_loc.start.file
      && r->next && r->next->content.sym)
    {
      complain (&r->percent_empty_loc, complaint,
                _("%%empty on non-empty rule"));
      fixits_register (&r->percent_empty_loc, "");
    }

  /* Check that empty rule => %empty.  */
  if (!(r->next && r->next->content.sym)
      && !r->midrule_parent_rule
      && !r->percent_empty_loc.start.file
      && warning_is_enabled (Wempty_rule))
    {
      complain (&r->rhs_loc, Wempty_rule, _("empty rule without %%empty"));
      if (feature_flag & feature_caret)
        location_caret_suggestion (r->rhs_loc, "%empty", stderr);
      location loc = r->rhs_loc;
      loc.end = loc.start;
      fixits_register (&loc, " %empty ");
    }

  /* See comments in grammar_current_rule_prec_set for how POSIX
     mandates this complaint.  It's only for identifiers, so skip
     it for char literals and strings, which are always tokens.  */
  if (r->ruleprec
      && r->ruleprec->tag[0] != '\'' && r->ruleprec->tag[0] != '"'
      && r->ruleprec->content->status != declared
      && !r->ruleprec->content->prec)
    complain (&r->rhs_loc, Wother,
              _("token for %%prec is not defined: %s"), r->ruleprec->tag);

  /* Check that the (main) action was not typed.  */
  if (r->action_props.type)
    complain (&r->rhs_loc, Wother,
              _("only midrule actions can be typed: %s"), r->action_props.type);
}


/*-------------------------------------.
| End the currently being grown rule.  |
`-------------------------------------*/

void
grammar_current_rule_end (location loc)
{
  /* Put an empty link in the list to mark the end of this rule  */
  grammar_symbol_append (NULL, grammar_end->rhs_loc);
  current_rule->rhs_loc = loc;
}


/*-------------------------------------------------------------------.
| The previous action turns out to be a midrule action.  Attach it   |
| to the current rule, i.e., create a dummy symbol, attach it this   |
| midrule action, and append this dummy nonterminal to the current   |
| rule.                                                              |
`-------------------------------------------------------------------*/

void
grammar_midrule_action (void)
{
  /* Since the action was written out with this rule's number, we must
     give the new rule this number by inserting the new rule before
     it.  */

  /* Make a DUMMY nonterminal, whose location is that of the midrule
     action.  Create the MIDRULE.  */
  location dummy_loc = current_rule->action_props.location;
  symbol *dummy = dummy_symbol_get (dummy_loc);
  symbol_type_set (dummy,
                   current_rule->action_props.type, current_rule->action_props.location);
  symbol_list *midrule = symbol_list_sym_new (dummy, dummy_loc);

  /* Remember named_ref of previous action. */
  named_ref *action_name = current_rule->action_props.named_ref;

  /* Make a new rule, whose body is empty, before the current one, so
     that the action just read can belong to it.  */
  ++nrules;
  ++nritems;
  /* Attach its location and actions to that of the DUMMY.  */
  midrule->rhs_loc = dummy_loc;
  code_props_rule_action_init (&midrule->action_props,
                               current_rule->action_props.code,
                               current_rule->action_props.location,
                               midrule,
                               /* name_ref */ NULL,
                               /* type */ NULL,
                               current_rule->action_props.is_predicate);
  code_props_none_init (&current_rule->action_props);

  midrule->expected_sr_conflicts = current_rule->expected_sr_conflicts;
  midrule->expected_rr_conflicts = current_rule->expected_rr_conflicts;
  current_rule->expected_sr_conflicts = -1;
  current_rule->expected_rr_conflicts = -1;

  if (previous_rule_end)
    previous_rule_end->next = midrule;
  else
    grammar = midrule;

  /* End the dummy's rule.  */
  midrule->next = symbol_list_sym_new (NULL, dummy_loc);
  midrule->next->next = current_rule;

  previous_rule_end = midrule->next;

  /* Insert the dummy nonterminal replacing the midrule action into
     the current rule.  Bind it to its dedicated rule.  */
  grammar_current_rule_symbol_append (dummy, dummy_loc,
                                      action_name);
  grammar_end->midrule = midrule;
  midrule->midrule_parent_rule = current_rule;
  midrule->midrule_parent_rhs_index = symbol_list_length (current_rule->next);
}

/* Set the precedence symbol of the current rule to PRECSYM. */

void
grammar_current_rule_prec_set (symbol *precsym, location loc)
{
  /* POSIX says that any identifier is a nonterminal if it does not
     appear on the LHS of a grammar rule and is not defined by %token
     or by one of the directives that assigns precedence to a token.
     We ignore this here because the only kind of identifier that
     POSIX allows to follow a %prec is a token and because assuming
     it's a token now can produce more logical error messages.
     Nevertheless, grammar_rule_check_and_complete does obey what we
     believe is the real intent of POSIX here: that an error be
     reported for any identifier that appears after %prec but that is
     not defined separately as a token.  */
  symbol_class_set (precsym, token_sym, loc, false);
  if (current_rule->ruleprec)
    duplicate_rule_directive ("%prec",
                              current_rule->ruleprec->location, loc);
  else
    current_rule->ruleprec = precsym;
}

/* Set %empty for the current rule. */

void
grammar_current_rule_empty_set (location loc)
{
  /* If %empty is used and -Wno-empty-rule is not, then enable
     -Wempty-rule.  */
  if (warning_is_unset (Wempty_rule))
    warning_argmatch ("empty-rule", 0, 0);
  if (current_rule->percent_empty_loc.start.file)
    duplicate_rule_directive ("%empty",
                              current_rule->percent_empty_loc, loc);
  else
    current_rule->percent_empty_loc = loc;
}

/* Attach dynamic precedence DPREC to the current rule. */

void
grammar_current_rule_dprec_set (int dprec, location loc)
{
  if (! glr_parser)
    complain (&loc, Wother, _("%s affects only GLR parsers"),
              "%dprec");
  if (dprec <= 0)
    complain (&loc, complaint, _("%s must be followed by positive number"),
              "%dprec");
  else if (current_rule->dprec != 0)
    duplicate_rule_directive ("%dprec",
                              current_rule->dprec_loc, loc);
  else
    {
      current_rule->dprec = dprec;
      current_rule->dprec_loc = loc;
    }
}

/* Attach a merge function NAME with argument type TYPE to current
   rule. */

void
grammar_current_rule_merge_set (uniqstr name, location loc)
{
  if (! glr_parser)
    complain (&loc, Wother, _("%s affects only GLR parsers"),
              "%merge");
  if (current_rule->merger != 0)
    duplicate_rule_directive ("%merge",
                              current_rule->merger_declaration_loc, loc);
  else
    {
      current_rule->merger = get_merge_function (name);
      current_rule->merger_declaration_loc = loc;
    }
}

/* Attach SYM to the current rule.  If needed, move the previous
   action as a midrule action.  */

void
grammar_current_rule_symbol_append (symbol *sym, location loc,
                                    named_ref *name)
{
  if (current_rule->action_props.code)
    grammar_midrule_action ();
  symbol_list *p = grammar_symbol_append (sym, loc);
  if (name)
    assign_named_ref (p, name);
  if (sym->content->status == undeclared || sym->content->status == used)
    sym->content->status = needed;
}

void
grammar_current_rule_action_append (const char *action, location loc,
                                    named_ref *name, uniqstr type)
{
  if (current_rule->action_props.code)
    grammar_midrule_action ();
  if (type)
    complain (&loc, Wyacc,
              _("POSIX Yacc does not support typed midrule actions"));
  /* After all symbol declarations have been parsed, packgram invokes
     code_props_translate_code.  */
  code_props_rule_action_init (&current_rule->action_props, action, loc,
                               current_rule,
                               name, type,
                               /* is_predicate */ false);
}

void
grammar_current_rule_predicate_append (const char *pred, location loc)
{
  if (current_rule->action_props.code)
    grammar_midrule_action ();
  code_props_rule_action_init (&current_rule->action_props, pred, loc,
                               current_rule,
                               NULL, NULL,
                               /* is_predicate */ true);
}

/* Set the expected number of shift/reduce (reduce/reduce) conflicts
 * for the current rule.  If a midrule is encountered later, the count
 * is transferred to it and reset in the current rule to -1. */

void
grammar_current_rule_expect_sr (int count, location loc)
{
  (void) loc;
  current_rule->expected_sr_conflicts = count;
}

void
grammar_current_rule_expect_rr (int count, location loc)
{
  if (! glr_parser)
    complain (&loc, Wother, _("%s affects only GLR parsers"),
              "%expect-rr");
  else
    current_rule->expected_rr_conflicts = count;
}


/*---------------------------------------------.
| Build RULES and RITEM from what was parsed.  |
`---------------------------------------------*/

static void
packgram (void)
{
  int itemno = 0;
  ritem = xnmalloc (nritems + 1, sizeof *ritem);
  /* This sentinel is used by build_relations() in lalr.c.  */
  *ritem++ = 0;

  rule_number ruleno = 0;
  rules = xnmalloc (nrules, sizeof *rules);

  for (symbol_list *p = grammar; p; p = p->next)
    {
      symbol_list *lhs = p;
      record_merge_function_type (lhs->merger, lhs->content.sym,
                                  lhs->merger_declaration_loc);
      /* If the midrule's $$ is set or its $n is used, remove the '$' from the
         symbol name so that it's a user-defined symbol so that the default
         %destructor and %printer apply.  */
      if (lhs->midrule_parent_rule /* i.e., symbol_is_dummy (lhs->content.sym).  */
          && (lhs->action_props.is_value_used
              || (symbol_list_n_get (lhs->midrule_parent_rule,
                                     lhs->midrule_parent_rhs_index)
                  ->action_props.is_value_used)))
        lhs->content.sym->tag += 1;

      grammar_rule_check_and_complete (lhs);

      rules[ruleno].code = ruleno;
      rules[ruleno].number = ruleno;
      rules[ruleno].lhs = lhs->content.sym->content;
      rules[ruleno].rhs = ritem + itemno;
      rules[ruleno].prec = NULL;
      rules[ruleno].dprec = lhs->dprec;
      rules[ruleno].merger = lhs->merger;
      rules[ruleno].precsym = NULL;
      rules[ruleno].location = lhs->rhs_loc;
      rules[ruleno].useful = true;
      rules[ruleno].action = lhs->action_props.code;
      rules[ruleno].action_loc = lhs->action_props.location;
      rules[ruleno].is_predicate = lhs->action_props.is_predicate;
      rules[ruleno].expected_sr_conflicts = lhs->expected_sr_conflicts;
      rules[ruleno].expected_rr_conflicts = lhs->expected_rr_conflicts;

      /* Traverse the rhs.  */
      {
        size_t rule_length = 0;
        for (p = lhs->next; p->content.sym; p = p->next)
          {
            ++rule_length;

            /* Don't allow rule_length == INT_MAX, since that might
               cause confusion with strtol if INT_MAX == LONG_MAX.  */
            if (rule_length == INT_MAX)
              complain (&rules[ruleno].location, fatal, _("rule is too long"));

            /* item_number = symbol_number.
               But the former needs to contain more: negative rule numbers. */
            ritem[itemno++] =
              symbol_number_as_item_number (p->content.sym->content->number);
            /* A rule gets by default the precedence and associativity
               of its last token.  */
            if (p->content.sym->content->class == token_sym && default_prec)
              rules[ruleno].prec = p->content.sym->content;
          }
      }

      /* If this rule has a %prec,
         the specified symbol's precedence replaces the default.  */
      if (lhs->ruleprec)
        {
          rules[ruleno].precsym = lhs->ruleprec->content;
          rules[ruleno].prec = lhs->ruleprec->content;
        }

      /* An item ends by the rule number (negated).  */
      ritem[itemno++] = rule_number_as_item_number (ruleno);
      aver (itemno < ITEM_NUMBER_MAX);
      ++ruleno;
      aver (ruleno < RULE_NUMBER_MAX);
    }

  aver (itemno == nritems);

  if (trace_flag & trace_sets)
    ritem_print (stderr);
}


/*--------------------------------------------------------------.
| Read in the grammar specification and record it in the format |
| described in gram.h.                                          |
`--------------------------------------------------------------*/

void
reader (const char *gram)
{
  /* Set up symbol_table, semantic_type_table, and the built-in
     symbols.  */
  symbols_new ();

  gram_scanner_open (gram);
  parser_init ();
  gram_parse ();
  gram_scanner_close ();

  prepare_percent_define_front_end_variables ();

  if (complaint_status  < status_complaint)
    check_and_convert_grammar ();
}

static void
prepare_percent_define_front_end_variables (void)
{
  /* Set %define front-end variable defaults.  */
  muscle_percent_define_default ("lr.keep-unreachable-state", "false");
  {
    /* IELR would be a better default, but LALR is historically the
       default.  */
    muscle_percent_define_default ("lr.type", "lalr");
    char *lr_type = muscle_percent_define_get ("lr.type");
    if (STRNEQ (lr_type, "canonical-lr"))
      muscle_percent_define_default ("lr.default-reduction", "most");
    else
      muscle_percent_define_default ("lr.default-reduction", "accepting");
    free (lr_type);
  }
  muscle_percent_define_default ("tool.xsltproc", "xsltproc");

  /* Check %define front-end variables.  */
  {
    static char const * const values[] =
      {
       "lr.type", "lr""(0)", "lalr", "ielr", "canonical-lr", NULL,
       "lr.default-reduction", "most", "consistent", "accepting", NULL,
       NULL
      };
    muscle_percent_define_check_values (values);
  }
}

/* Find the first LHS which is not a dummy.  */

static symbol *
find_start_symbol (void)
{
  symbol_list *res = grammar;
  /* Skip all the possible dummy rules of the first rule.  */
  for (; symbol_is_dummy (res->content.sym); res = res->next)
    /* Skip the LHS, and then all the RHS of the dummy rule.  */
    for (res = res->next; res->content.sym; res = res->next)
      continue;
  return res->content.sym;
}


/* Insert an initial rule, whose location is that of the first rule
   (not that of the start symbol):

   $accept: SWITCHING_TOKEN START $end.  */
static void
create_start_rule (symbol *swtok, symbol *start)
{
  symbol_list *initial_rule = symbol_list_sym_new (acceptsymbol, empty_loc);
  initial_rule->rhs_loc = grammar->rhs_loc;
  symbol_list *p = initial_rule;
  if (swtok)
    {
      // Cannot create the action now, as the symbols have not yet
      // been assigned their number (by symbol_pack), which we need to
      // know the type name.  So the action is created in
      // grammar_rule_check_and_complete, which is run after
      // symbol_pack.
      p->next = symbol_list_sym_new (swtok, empty_loc);
      p = p->next;
    }
  p->next = symbol_list_sym_new (start, empty_loc);
  p = p->next;
  p->next = symbol_list_sym_new (eoftoken, empty_loc);
  p = p->next;
  p->next = symbol_list_sym_new (NULL, empty_loc);
  p = p->next;
  p->next = grammar;
  nrules += 1;
  nritems += 3 + !!swtok;
  grammar = initial_rule;
}

/* Fetch (or create) a token "YY_PARSE_foo" for start symbol "foo".

   We don't use the simple "YY_FOO" because (i) we might get clashes
   with some of our symbols (e.g., cast => YY_CAST), and (ii) upcasing
   introduces possible clashes between terminal FOO and nonterminal
   foo.  */
symbol *
switching_token (const symbol *start)
{
  char buf[100];
  size_t len = sizeof buf;
  char *name = asnprintf (buf, &len, "YY_PARSE_%s", symbol_id_get (start));
  if (!name)
    xalloc_die ();
  // Setting the location ensures deterministic symbol numbers.
  symbol *res = symbol_get (name, start->location);
  if (name != buf)
    free (name);
  symbol_class_set (res, token_sym, start->location, false);
  return res;
}

/* Create the start rules in reverse order, since they are inserted at
   the top of the grammar.  That way the rules follow the order of
   declaration to %start.  */

static void
create_multiple_start_rules (symbol_list *start_syms)
{
  if (start_syms)
    {
      create_multiple_start_rules (start_syms->next);
      assert (start_syms->content_type == SYMLIST_SYMBOL);
      symbol *start = start_syms->content.sym;
      symbol *swtok = switching_token (start);
      create_start_rule (swtok, start);
    }
}

/* For each start symbol "foo", create the rule "$accept: YY_FOO
   foo $end". */
static void
create_start_rules (void)
{
  if (!start_symbols)
    {
      symbol *start = find_start_symbol ();
      start_symbols = symbol_list_sym_new (start, start->location);
    }

  const bool several = start_symbols->next;
  if (several)
    create_multiple_start_rules (start_symbols);
  else
    {
      symbol *start = start_symbols->content.sym;
      create_start_rule (NULL, start);
    }
}

static void
check_start_symbols (void)
{
  const bool multistart = start_symbols && start_symbols->next;
  // Sanity checks on the start symbols.
  for (symbol_list *list = start_symbols; list; list = list->next)
    {
      const symbol *start = list->content.sym;
      if (start->content->class == unknown_sym)
        {
          complain (&start->location, complaint,
                    _("the start symbol %s is undefined"),
                    start->tag);
          // I claim this situation is unreachable.  This is caught
          // before, and we get "symbol 'foo' is used, but is not
          // defined as a token and has no rules".
          abort ();
        }
      // If your only start symbol is a token, you're weird.
      if (!multistart && start->content->class == token_sym)
        complain (&start->location, complaint,
                  _("the start symbol %s is a token"),
                  start->tag);
    }
  if (complaint_status == status_complaint)
    exit (EXIT_FAILURE);
}


/*-------------------------------------------------------------.
| Check the grammar that has just been read, and convert it to |
| internal form.                                               |
`-------------------------------------------------------------*/

static void
check_and_convert_grammar (void)
{
  /* Grammar has been read.  Do some checking.  */
  if (nrules == 0)
    complain (NULL, fatal, _("no rules in the input grammar"));

  /* If the user did not define her EOFTOKEN, do it now. */
  if (!eoftoken)
    {
      eoftoken = symbol_get ("YYEOF", empty_loc);
      eoftoken->content->class = token_sym;
      eoftoken->content->number = 0;
      /* Value specified by POSIX.  */
      eoftoken->content->code = 0;
      {
        symbol *alias = symbol_get ("$end", empty_loc);
        symbol_class_set (alias, token_sym, empty_loc, false);
        symbol_make_alias (eoftoken, alias, empty_loc);
      }
    }

  /* Insert the initial rule(s).  */
  create_start_rules ();

  /* Report any undefined symbols and consider them nonterminals.  */
  symbols_check_defined ();

  if (SYMBOL_NUMBER_MAXIMUM - nnterms < ntokens)
    complain (NULL, fatal, "too many symbols in input grammar (limit is %d)",
              SYMBOL_NUMBER_MAXIMUM);

  nsyms = ntokens + nnterms;

  /* Assign the symbols their symbol numbers.  */
  symbols_pack ();

  check_start_symbols ();

  /* Scan rule actions after invoking symbol_check_alias_consistency
     (in symbols_pack above) so that token types are set correctly
     before the rule action type checking.

     Before invoking grammar_rule_check_and_complete (in packgram
     below) on any rule, make sure all actions have already been
     scanned in order to set 'used' flags.  Otherwise, checking that a
     midrule's $$ should be set will not always work properly because
     the check must forward-reference the midrule's parent rule.  For
     the same reason, all the 'used' flags must be set before checking
     whether to remove '$' from any midrule symbol name (also in
     packgram).  */
  for (symbol_list *sym = grammar; sym; sym = sym->next)
    code_props_translate_code (&sym->action_props);

  /* Convert the grammar into the format described in gram.h.  */
  packgram ();

  /* The grammar as a symbol_list is no longer needed. */
  symbol_list_free (grammar);
}