Warn about unused values.

* src/symlist.h, src/symlist.c (symbol_list, symbol_list_new): Add
a `used' member.
(symbol_list_n_get, symbol_list_n_used_set): New.
(symbol_list_n_type_name_get): Use symbol_list_n_get.
* src/scan-gram.l (handle_action_dollar): Flag used symbols.
* src/reader.c (grammar_current_rule_check): Check that values are
used.
* src/symtab.c (symbol_print): Accept 0.
* tests/existing.at: Remove the type information.
Empty the actions.
Remove useless actions (beware of mid-rule actions: perl -000
-pi -e 's/s*{}(?=[ns]*[|;])//g').
* tests/actions.at (Exotic Dollars): Use unused values.
* tests/calc.at: Likewise.
* tests/glr-regression.at (No users destructors if stack 0 deleted):
Likewise.
* src/gram.c (rule_useful_p, rule_never_reduced_p): Use
rule_useful_p.

ChangeLog

@@ -1,3 +1,26 @@
+2005-12-22  Akim Demaille  <akim@epita.fr>
+
+	Warn about unused values.
+	* src/symlist.h, src/symlist.c (symbol_list, symbol_list_new): Add
+	a `used' member.
+	(symbol_list_n_get, symbol_list_n_used_set): New.
+	(symbol_list_n_type_name_get): Use symbol_list_n_get.
+	* src/scan-gram.l (handle_action_dollar): Flag used symbols.
+	* src/reader.c (grammar_current_rule_check): Check that values are
+	used.
+	* src/symtab.c (symbol_print): Accept 0.
+	* tests/existing.at: Remove the type information.
+	Empty the actions.
+	Remove useless actions (beware of mid-rule actions: perl -000
+	-pi -e 's/\s*\{\}(?=[\n\s]*[|;])//g').
+	* tests/actions.at (Exotic Dollars): Use unused values.
+	* tests/calc.at: Likewise.
+	* tests/glr-regression.at (No users destructors if stack 0 deleted):
+	Likewise.
+
+	* src/gram.c (rule_useful_p, rule_never_reduced_p): Use
+	rule_useful_p.
+
 2005-12-21  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Undo 2005-12-01 tentative license wording change.  The wording is

NEWS

@@ -3,6 +3,24 @@ Bison News
 
 Changes in version 2.1a:
 
+* New warning: unused values
+  Typed right-hand side symbols whose value are not used are reported.
+  For instance
+
+       exp: exp "?" exp ":" exp { $$ = $1 + $3; }
+          | exp "+" exp
+	  ;
+
+  will trigger a warning about $5 of the first rule, and $3 in the
+  second ($1 is copied to $$ by the default rule).  To avoid this
+  warning, let Bison believe the value is used, e.g.
+
+       exp: exp "?" exp ":" exp { $$ = $1 + $3; $5; }
+          | exp "+" exp         { $$ = $1; $3; }
+
+  This helps catching lost values and memory leaks: if a value is
+  ignored, its associated memory will never be reclaimed.
+
 * %destructor vs. YYABORT, YYACCEPT, and YYERROR.
   Destructors are now called when user code invokes YYABORT, YYACCEPT,
   and YYERROR, for all objects on the stack, other than objects

src/gram.c

@@ -65,7 +65,7 @@ rule_useful_p (rule *r)
 bool
 rule_useless_p (rule *r)
 {
-  return r->number >= nrules;
+  return !rule_useful_p (r);
 }
 
 
@@ -77,7 +77,7 @@ rule_useless_p (rule *r)
 bool
 rule_never_reduced_p (rule *r)
 {
-  return !r->useful && r->number < nrules;
+  return !r->useful && rule_useful_p (r);
 }
 
 
@@ -317,8 +317,7 @@ grammar_rules_never_reduced_report (const char *message)
     if (!rules[r].useful)
       {
 	location_print (stderr, rules[r].location);
-	fprintf (stderr, ": %s: %s: ",
-		 _("warning"), message);
+	fprintf (stderr, ": %s: %s: ", _("warning"), message);
 	rule_print (&rules[r], stderr);
       }
 }

src/reader.c

@@ -40,7 +40,7 @@ static symbol_list *grammar = NULL;
 static bool start_flag = false;
 merger_list *merge_functions;
 
-/* Has %union been seen?  */
+/* Was %union seen?  */
 bool typed = false;
 
 /* Should rules have a default precedence?  */
@@ -104,7 +104,7 @@ get_merge_function (uniqstr name, uniqstr type, location loc)
     type = uniqstr_new ("");
 
   head.next = merge_functions;
-  for (syms = &head, n = 1; syms->next != NULL; syms = syms->next, n += 1)
+  for (syms = &head, n = 1; syms->next; syms = syms->next, n += 1)
     if (UNIQSTR_EQ (name, syms->next->name))
       break;
   if (syms->next == NULL)
@@ -128,11 +128,8 @@ get_merge_function (uniqstr name, uniqstr type, location loc)
 void
 free_merger_functions (void)
 {
-  merger_list *L0;
-  if (! glr_parser)
-    return;
-  L0 = merge_functions;
-  while (L0 != NULL)
+  merger_list *L0 = merge_functions;
+  while (L0)
     {
       merger_list *L1 = L0->next;
       free (L0);
@@ -150,13 +147,6 @@ free_merger_functions (void)
 |                                                                    |
 | All actions are copied out, labelled by the rule number they apply |
 | to.                                                                |
-|                                                                    |
-| Bison used to allow some %directives in the rules sections, but    |
-| this is no longer consider appropriate: (i) the documented grammar |
-| doesn't claim it, (ii), it would promote bad style, (iii), error   |
-| recovery for %directives consists in skipping the junk until a `%' |
-| is seen and helrp synchronizing.  This scheme is definitely wrong  |
-| in the rules section.                                              |
 `-------------------------------------------------------------------*/
 
 /* The (currently) last symbol of GRAMMAR. */
@@ -206,7 +196,6 @@ grammar_rule_begin (symbol *lhs, location 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;
@@ -217,39 +206,55 @@ grammar_rule_begin (symbol *lhs, location loc)
     complain_at (loc, _("rule given for %s, which is a token"), lhs->tag);
 }
 
-/* Check that the last rule (CURRENT_RULE) is properly defined.  For
-   instance, there should be no type clash on the default action.  */
+
+/*------------------------------------------------------------------.
+| Check that the last rule (CURRENT_RULE) is properly defined.  For |
+| instance, there should be no type clash on the default action.    |
+`------------------------------------------------------------------*/
 
 static void
 grammar_current_rule_check (void)
 {
   symbol *lhs = current_rule->sym;
   char const *lhs_type = lhs->type_name;
-  symbol *first_rhs = current_rule->next->sym;
 
-  /* If there is an action, then there is nothing we can do: the user
-     is allowed to shoot herself in the foot.  */
-  if (current_rule->action)
-    return;
+  /* Type check.
 
-  /* Don't worry about the default action if $$ is untyped, since $$'s
+     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 (! lhs_type)
-    return;
-
-  /* If $$ is being set in default way, report if any type mismatch.  */
-  if (first_rhs)
+  if (!current_rule->action && lhs_type)
     {
-      const char *rhs_type = first_rhs->type_name ? first_rhs->type_name : "";
-      if (!UNIQSTR_EQ (lhs_type, rhs_type))
+      symbol *first_rhs = current_rule->next->sym;
+      /* If $$ is being set in default way, report if any type mismatch.  */
+      if (first_rhs)
+	{
+	  const char *rhs_type =
+	    first_rhs->type_name ? first_rhs->type_name : "";
+	  if (!UNIQSTR_EQ (lhs_type, rhs_type))
+	    warn_at (current_rule->location,
+		     _("type clash on default action: <%s> != <%s>"),
+		     lhs_type, rhs_type);
+	}
+      /* Warn if there is no default for $$ but we need one.  */
+      else
 	warn_at (current_rule->location,
-		 _("type clash on default action: <%s> != <%s>"),
-		 lhs_type, rhs_type);
+		 _("empty rule for typed nonterminal, and no action"));
+    }
+
+  /* Check that all the symbol values are used. */
+  if (typed)
+    {
+      symbol_list *l = current_rule;
+      int n = 1;
+      for (l = current_rule->next; l && l->sym; l = l->next, ++n)
+	/* The default action `uses' $1. */
+	if (! (!current_rule->action && n == 1)
+	    && l->sym->type_name && !l->used)
+	  warn_at (current_rule->location, _("unused value: $%d"), n);
     }
-  /* Warn if there is no default for $$ but we need one.  */
-  else
-    warn_at (current_rule->location,
-	     _("empty rule for typed nonterminal, and no action"));
 }
 
 

src/reader.h

@@ -77,7 +77,10 @@ void free_merger_functions (void);
 
 extern merger_list *merge_functions;
 
+/* Was %union seen?  */
 extern bool typed;
+
+/* Should rules have a default precedence?  */
 extern bool default_prec;
 
 #endif /* !READER_H_ */

src/scan-gram.l

@@ -825,9 +825,9 @@ handle_action_dollar (char *text, location loc)
       if (INT_MIN <= num && num <= rule_length && ! get_errno ())
 	{
 	  int n = num;
-	  if (1-n > max_left_semantic_context)
-	    max_left_semantic_context = 1-n;
-	  if (!type_name && n > 0)
+	  if (max_left_semantic_context < 1 - n)
+	    max_left_semantic_context = 1 - n;
+	  if (!type_name && 0 < n)
 	    type_name = symbol_list_n_type_name_get (current_rule, loc, n);
 	  if (!type_name && typed)
 	    complain_at (loc, _("$%d of `%s' has no declared type"),
@@ -837,6 +837,8 @@ handle_action_dollar (char *text, location loc)
 	  obstack_fgrow3 (&obstack_for_string,
 			  "]b4_rhs_value(%d, %d, [%s])[",
 			  rule_length, n, type_name);
+	  if (typed)
+	    symbol_list_n_used_set (current_rule, n, true);
 	}
       else
 	complain_at (loc, _("integer out of range: %s"), quote (text));

src/symlist.c

@@ -34,13 +34,19 @@ symbol_list *
 symbol_list_new (symbol *sym, location loc)
 {
   symbol_list *res = xmalloc (sizeof *res);
-  res->next = NULL;
+
   res->sym = sym;
   res->location = loc;
+
   res->action = NULL;
+  res->used = false;
+
   res->ruleprec = NULL;
   res->dprec = 0;
   res->merger = 0;
+
+  res->next = NULL;
+
   return res;
 }
 
@@ -56,7 +62,7 @@ symbol_list_print (symbol_list *l, FILE *f)
     {
       symbol_print (l->sym, f);
       if (l && l->sym)
-	fputc (' ', f);
+	fprintf (f, ", ");
     }
 }
 
@@ -90,43 +96,64 @@ symbol_list_free (symbol_list *list)
 `--------------------*/
 
 unsigned int
-symbol_list_length (symbol_list *list)
+symbol_list_length (symbol_list *l)
 {
   int res = 0;
-  for (/* Nothing. */; list; list = list->next)
+  for (/* Nothing. */; l; l = l->next)
     ++res;
   return res;
 }
 
 
-/*--------------------------------------------------------------.
-| Get the data type (alternative in the union) of the value for |
-| symbol N in symbol list RP.                                   |
-`--------------------------------------------------------------*/
+/*--------------------------------.
+| Get symbol N in symbol list L.  |
+`--------------------------------*/
 
-uniqstr
-symbol_list_n_type_name_get (symbol_list *rp, location loc, int n)
+symbol_list *
+symbol_list_n_get (symbol_list *l, int n)
 {
   int i;
 
   if (n < 0)
+    return NULL;
+
+  for (i = 0; i < n; ++i)
+    {
+      l = l->next;
+      if (l == NULL || l->sym == NULL)
+	return NULL;
+    }
+
+  return l;
+}
+
+
+/*--------------------------------------------------------------.
+| Get the data type (alternative in the union) of the value for |
+| symbol N in symbol list L.                                    |
+`--------------------------------------------------------------*/
+
+uniqstr
+symbol_list_n_type_name_get (symbol_list *l, location loc, int n)
+{
+  l = symbol_list_n_get (l, n);
+  if (!l)
     {
       complain_at (loc, _("invalid $ value: $%d"), n);
       return NULL;
     }
-
-  i = 0;
-
-  while (i < n)
-    {
-      rp = rp->next;
-      if (rp == NULL || rp->sym == NULL)
-	{
-	  complain_at (loc, _("invalid $ value: $%d"), n);
-	  return NULL;
-	}
-      ++i;
-    }
-
-  return rp->sym->type_name;
+  return l->sym->type_name;
+}
+
+
+/*----------------------------------------.
+| The symbol N in symbol list L is USED.  |
+`----------------------------------------*/
+
+void
+symbol_list_n_used_set (symbol_list *l, int n, bool used)
+{
+  l = symbol_list_n_get (l, n);
+  if (l)
+    l->used = used;
 }

src/symlist.h

@@ -25,9 +25,10 @@
 # include "location.h"
 # include "symtab.h"
 
+/* A list of symbols, used during the parsing to store the rules.  */
 typedef struct symbol_list
 {
-  struct symbol_list *next;
+  /* The symbol.  */
   symbol *sym;
   location location;
 
@@ -35,9 +36,16 @@ typedef struct symbol_list
   const char *action;
   location action_location;
 
+  /* Whether this symbol's value is used in the current action. */
+  bool used;
+
+  /* Precedence/associativity.  */
   symbol *ruleprec;
   int dprec;
   int merger;
+
+  /* The list.  */
+  struct symbol_list *next;
 } symbol_list;
 
 
@@ -48,18 +56,24 @@ symbol_list *symbol_list_new (symbol *sym, location loc);
 void symbol_list_print (symbol_list *l, FILE *f);
 
 /* Prepend SYM at LOC to the LIST.  */
-symbol_list *symbol_list_prepend (symbol_list *list,
+symbol_list *symbol_list_prepend (symbol_list *l,
 				  symbol *sym,
 				  location loc);
 
 /* Free the LIST, but not the symbols it contains.  */
-void symbol_list_free (symbol_list *list);
+void symbol_list_free (symbol_list *l);
 
 /* Return its length. */
-unsigned int symbol_list_length (symbol_list *list);
+unsigned int symbol_list_length (symbol_list *l);
+
+/* Get symbol N in symbol list L.  */
+symbol_list *symbol_list_n_get (symbol_list *l, int n);
 
 /* Get the data type (alternative in the union) of the value for
    symbol N in rule RULE.  */
-uniqstr symbol_list_n_type_name_get (symbol_list *rp, location loc, int n);
+uniqstr symbol_list_n_type_name_get (symbol_list *l, location loc, int n);
+
+/* The symbol N in symbol list L is USED.  */
+void symbol_list_n_used_set (symbol_list *l, int n, bool used);
 
 #endif /* !SYMLIST_H_ */

src/symtab.c

@@ -85,10 +85,15 @@ symbol_new (uniqstr tag, location loc)
 void
 symbol_print (symbol *s, FILE *f)
 {
-  fprintf (f, "\"%s\"", s->tag);
-  SYMBOL_ATTR_PRINT (type_name);
-  SYMBOL_ATTR_PRINT (destructor);
-  SYMBOL_ATTR_PRINT (printer);
+  if (s)
+    {
+      fprintf (f, "\"%s\"", s->tag);
+      SYMBOL_ATTR_PRINT (type_name);
+      SYMBOL_ATTR_PRINT (destructor);
+      SYMBOL_ATTR_PRINT (printer);
+    }
+  else
+    fprintf (f, "<NULL>");
 }
 
 #undef SYMBOL_ATTR_PRINT

tests/actions.at

@@ -98,6 +98,7 @@ AT_DATA_GRAMMAR([[input.y]],
   static int yylex (void);
 # define YYDEBUG         1
 # define YYERROR_VERBOSE 1
+# define USE(Var)
 %}
 
 %union
@@ -112,6 +113,7 @@ AT_DATA_GRAMMAR([[input.y]],
 exp: a_1 a_2 { $<val>$ = 3; } { $<val>$ = $<val>3 + 1; } a_5
      sum_of_the_five_previous_values
     {
+       USE (($1, $2, $5));
        printf ("%d\n", $6);
     }
 ;

tests/calc.at

@@ -54,6 +54,7 @@ AT_LALR1_CC_IF(
 # define alarm(seconds) /* empty */
 #endif
 #include <ctype.h>
+#define USE(Var)
 
 /* Exercise pre-prologue dependency to %union.  */
 typedef int semantic_value;
@@ -109,7 +110,7 @@ input:
 
 line:
   '\n'
-| exp '\n'           { ]AT_PARAM_IF([*result = global_result = $1;])[ }
+| exp '\n'           { ]AT_PARAM_IF([*result = global_result = $1], [USE ($1)])[; }
 ;
 
 exp:

tests/glr-regression.at

@@ -746,13 +746,14 @@ AT_SETUP([No users destructors if stack 0 deleted])
 AT_DATA_GRAMMAR([glr-regr9.y],
 [[
 %{
-  #include <stdio.h>
-  #include <stdlib.h>
+# include <stdio.h>
+# include <stdlib.h>
   static void yyerror (char const *);
   static int yylex (void);
-  #define YYSTACKEXPANDABLE 0
+# define YYSTACKEXPANDABLE 0
   static int tokens = 0;
   static int destructors = 0;
+# define USE(Var)
 %}
 
 %glr-parser
@@ -766,7 +767,7 @@ AT_DATA_GRAMMAR([glr-regr9.y],
 %%
 
 start:
-  ambig0 'a' { destructors += 2; }
+    ambig0 'a'   { destructors += 2; USE ($2); }
   | ambig1 start { destructors += 1; }
   | ambig2 start { destructors += 1; }
   ;