Avoid empty-if warnings.

[bison.git] / src / reader.c

/* Input parser for Bison

   Copyright (C) 1984, 1986, 1989, 1992, 1998, 2000, 2001, 2002, 2003,
   2005, 2006, 2007 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 <http://www.gnu.org/licenses/>.  */

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

#include <quotearg.h>

#include "complain.h"
#include "conflicts.h"
#include "files.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 check_and_convert_grammar (void);

static symbol_list *grammar = NULL;
static bool start_flag = false;
merger_list *merge_functions;

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

/* Was a tag seen?  */
bool tag_seen = false;

/* Should rules have a default precedence?  */
bool default_prec = true;
\f
/*-----------------------.
| Set the start symbol.  |
`-----------------------*/

void
grammar_start_symbol_set (symbol *sym, location loc)
{
  if (start_flag)
    complain_at (loc, _("multiple %s declarations"), "%start");
  else
    {
      start_flag = true;
      startsymbol = sym;
      startsymbol_location = loc;
    }
}

\f

/*------------------------------------------------------------------------.
| 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)
{
  merger_list *syms;
  merger_list head;
  int n;

  if (! glr_parser)
    return 0;

  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->type = NULL;
      syms->next->next = NULL;
      merge_functions = head.next;
    }
  return n;
}

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

static void
record_merge_function_type (int merger, uniqstr type, location declaration_loc)
{
  int merger_find;
  merger_list *merge_function;

  if (merger <= 0)
    return;

  if (type == NULL)
    type = uniqstr_new ("");

  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->type != NULL && !UNIQSTR_EQ (merge_function->type, type))
    {
      complain_at (declaration_loc,
		   _("result type clash on merge function `%s': <%s> != <%s>"),
		   merge_function->name, type, merge_function->type);
      complain_at (merge_function->type_declaration_location,
		   _("previous declaration"));
    }
  merge_function->type = uniqstr_new (type);
  merge_function->type_declaration_location = 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;
    }
}

\f
/*-------------------------------------------------------------------.
| 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 void
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;
}

/* 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)
{
  /* Start a new rule and record its lhs.  */
  ++nrules;
  previous_rule_end = grammar_end;
  grammar_symbol_append (lhs, loc);
  current_rule = grammar_end;

  /* Mark the rule's lhs as a nonterminal if not already so.  */
  if (lhs->class == unknown_sym)
    {
      lhs->class = nterm_sym;
      lhs->number = nvars;
      ++nvars;
    }
  else if (lhs->class == token_sym)
    complain_at (loc, _("rule given for %s, which is a token"), lhs->tag);
}


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

static bool
symbol_should_be_used (symbol_list const *s)
{
  if (symbol_destructor_get (s->content.sym)->code)
    return true;
  if (warnings_flag & warnings_midrule_values)
    return ((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));
  return false;
}

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

static void
grammar_rule_check (const symbol_list *r)
{
  /* 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 && r->content.sym->type_name)
    {
      symbol *first_rhs = r->next->content.sym;
      /* If $$ is being set in default way, report if any type mismatch.  */
      if (first_rhs)
	{
	  char const *lhs_type = r->content.sym->type_name;
	  const char *rhs_type =
	    first_rhs->type_name ? first_rhs->type_name : "";
	  if (!UNIQSTR_EQ (lhs_type, rhs_type))
	    warn_at (r->location,
		     _("type clash on default action: <%s> != <%s>"),
		     lhs_type, rhs_type);
	}
      /* Warn if there is no default for $$ but we need one.  */
      else
	warn_at (r->location,
		 _("empty rule for typed nonterminal, and no action"));
    }

  /* Check that symbol values that should be used are in fact used.  */
  {
    symbol_list const *l = r;
    int n = 0;
    for (; l && l->content.sym; l = l->next, ++n)
      if (! (l->action_props.is_value_used
	     || !symbol_should_be_used (l)
	     /* The default action, $$ = $1, `uses' both.  */
	     || (!r->action_props.code && (n == 0 || n == 1))))
	{
	  if (n)
	    warn_at (r->location, _("unused value: $%d"), n);
	  else
	    warn_at (r->location, _("unset value: $$"));
	}
  }
}


/*-------------------------------------.
| 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->location);
  current_rule->location = loc;
}


/*-------------------------------------------------------------------.
| The previous action turns out the be a mid-rule action.  Attach it |
| to the current rule, i.e., create a dummy symbol, attach it this   |
| mid-rule 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_location = current_rule->action_props.location;
  symbol *dummy = dummy_symbol_get (dummy_location);
  symbol_list *midrule = symbol_list_sym_new (dummy, dummy_location);

  /* 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->location = dummy_location;
  code_props_rule_action_init (&midrule->action_props,
                               current_rule->action_props.code,
                               current_rule->action_props.location,
                               midrule);
  code_props_none_init (&current_rule->action_props);

  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_location);
  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_location);
  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)
{
  symbol_class_set (precsym, token_sym, loc, false);
  if (current_rule->ruleprec)
    complain_at (loc, _("only one %s allowed per rule"), "%prec");
  current_rule->ruleprec = precsym;
}

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

void
grammar_current_rule_dprec_set (int dprec, location loc)
{
  if (! glr_parser)
    warn_at (loc, _("%s affects only GLR parsers"), "%dprec");
  if (dprec <= 0)
    complain_at (loc, _("%s must be followed by positive number"), "%dprec");
  else if (current_rule->dprec != 0)
    complain_at (loc, _("only one %s allowed per rule"), "%dprec");
  current_rule->dprec = dprec;
}

/* 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)
    warn_at (loc, _("%s affects only GLR parsers"), "%merge");
  if (current_rule->merger != 0)
    complain_at (loc, _("only one %s allowed per rule"), "%merge");
  current_rule->merger = get_merge_function (name);
  current_rule->merger_declaration_location = loc;
}

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

void
grammar_current_rule_symbol_append (symbol *sym, location loc)
{
  if (current_rule->action_props.code)
    grammar_midrule_action ();
  grammar_symbol_append (sym, loc);
}

/* Attach an ACTION to the current rule.  */

void
grammar_current_rule_action_append (const char *action, location loc)
{
  if (current_rule->action_props.code)
    grammar_midrule_action ();
  /* 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);
}

\f
/*---------------------------------------------------------------.
| Convert the rules into the representation using RRHS, RLHS and |
| RITEM.                                                         |
`---------------------------------------------------------------*/

static void
packgram (void)
{
  unsigned int itemno = 0;
  rule_number ruleno = 0;
  symbol_list *p = grammar;

  ritem = xnmalloc (nritems + 1, sizeof *ritem);

  /* This sentinel is used by build_relations in gram.c.  */
  *ritem++ = 0;

  rules = xnmalloc (nrules, sizeof *rules);

  while (p)
    {
      int rule_length = 0;
      symbol *ruleprec = p->ruleprec;
      record_merge_function_type (p->merger, p->content.sym->type_name,
				  p->merger_declaration_location);
      rules[ruleno].user_number = ruleno;
      rules[ruleno].number = ruleno;
      rules[ruleno].lhs = p->content.sym;
      rules[ruleno].rhs = ritem + itemno;
      rules[ruleno].prec = NULL;
      rules[ruleno].dprec = p->dprec;
      rules[ruleno].merger = p->merger;
      rules[ruleno].precsym = NULL;
      rules[ruleno].location = p->location;
      rules[ruleno].useful = true;
      rules[ruleno].action = p->action_props.code;
      rules[ruleno].action_location = p->action_props.location;

      /* 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 (p->midrule_parent_rule
          && (p->action_props.is_value_used
	      || symbol_list_n_get (p->midrule_parent_rule,
				    p->midrule_parent_rhs_index)
                   ->action_props.is_value_used))
	p->content.sym->tag += 1;

      /* Don't check the generated rule 0.  It has no action, so some rhs
	 symbols may appear unused, but the parsing algorithm ensures that
	 %destructor's are invoked appropriately.  */
      if (p != grammar)
	grammar_rule_check (p);

      for (p = p->next; p && 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)
	      fatal_at (rules[ruleno].location, _("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->number);
	  /* A rule gets by default the precedence and associativity
	     of its last token.  */
	  if (p->content.sym->class == token_sym && default_prec)
	    rules[ruleno].prec = p->content.sym;
	}

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

      if (p)
	p = p->next;
    }

  aver (itemno == nritems);

  if (trace_flag & trace_sets)
    ritem_print (stderr);
}
\f
/*------------------------------------------------------------------.
| Read in the grammar specification and record it in the format     |
| described in gram.h.  All actions are copied into ACTION_OBSTACK, |
| in each case forming the body of a C function (YYACTION) which    |
| contains a switch statement to decide which action to execute.    |
`------------------------------------------------------------------*/

void
reader (void)
{
  /* Initialize the symbol table.  */
  symbols_new ();

  /* Construct the accept symbol. */
  accept = symbol_get ("$accept", empty_location);
  accept->class = nterm_sym;
  accept->number = nvars++;

  /* Construct the error token */
  errtoken = symbol_get ("error", empty_location);
  errtoken->class = token_sym;
  errtoken->number = ntokens++;

  /* Construct a token that represents all undefined literal tokens.
     It is always token number 2.  */
  undeftoken = symbol_get ("$undefined", empty_location);
  undeftoken->class = token_sym;
  undeftoken->number = ntokens++;

  gram_in = xfopen (grammar_file, "r");

  gram__flex_debug = trace_flag & trace_scan;
  gram_debug = trace_flag & trace_parse;
  gram_scanner_initialize ();
  gram_parse ();

  if (! complaint_issued)
    check_and_convert_grammar ();

  xfclose (gram_in);
}


/*-------------------------------------------------------------.
| 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)
    fatal (_("no rules in the input grammar"));

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

  /* If the user did not define her ENDTOKEN, do it now. */
  if (!endtoken)
    {
      endtoken = symbol_get ("$end", empty_location);
      endtoken->class = token_sym;
      endtoken->number = 0;
      /* Value specified by POSIX.  */
      endtoken->user_token_number = 0;
    }

  /* Find the start symbol if no %start.  */
  if (!start_flag)
    {
      symbol_list *node;
      for (node = grammar;
           node != NULL && symbol_is_dummy (node->content.sym);
           node = node->next)
        {
          for (node = node->next;
               node != NULL && node->content.sym != NULL;
               node = node->next)
            ;
        }
      aver (node != NULL);
      grammar_start_symbol_set (node->content.sym,
                                node->content.sym->location);
    }

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

     accept: %start EOF.  */
  {
    symbol_list *p = symbol_list_sym_new (accept, empty_location);
    p->location = grammar->location;
    p->next = symbol_list_sym_new (startsymbol, empty_location);
    p->next->next = symbol_list_sym_new (endtoken, empty_location);
    p->next->next->next = symbol_list_sym_new (NULL, empty_location);
    p->next->next->next->next = grammar;
    nrules += 1;
    nritems += 3;
    grammar = p;
  }

  aver (nsyms <= SYMBOL_NUMBER_MAXIMUM && nsyms == ntokens + nvars);

  /* Assign the symbols their symbol numbers.  Write #defines for the
     token symbols into FDEFINES if requested.  */
  symbols_pack ();

  /* 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 (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).  */
  {
    symbol_list *sym;
    for (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);
}