* NEWS: Instead of %union, you can define and use your own union type

YYSTYPE if your grammar contains at least one <type> tag.
Your YYSTYPE need not be a macro; it can be a typedef.
* doc/bison.texinfo (Value Type, Multiple Types, Location Type):
(Union Decl, Decl Summary): Document this.
* data/glr.c (YYSTYPE): Implement this.
* data/glr.cc (YYSTYPE): Likewise.
* data/lalr1.cc (YYSTYPE): Likewise.
* data/yacc.c (YYSTYPE): Likewise.
* src/output.c (prepare): Output tag_seen_flag.
* src/parse-gram.y (declaration, grammar_declaration):
Use 'union_seen' rather than 'typed' to determine whether
%union has been seen, since grammars can now be typed without
%union.
(symbol_declaration, type.opt, symbol_def):
Keep track of whether a tag has been seen.
* src/reader.c (union_seen, tag_seen): New vars.
(typed): remove.
* src/reader.h (union_seen, tag_seen, typed): Likewise.
* src/scan-code.l (untyped_var_seen): New variable.
(handle_action_dollar): Adjust to above changes.
(handle_action_dollar, handle_action_at):
Improve overflow checking for outlandish numbers.
* tests/input.at (AT_CHECK_UNUSED_VALUES): Redo test to
avoid new diagnostics generated by above changes.
* tests/regression.at (YYSTYPE typedef): Add test to check
for type tags without %union.

src/output.c

@@ -590,6 +590,7 @@ prepare (void)
   MUSCLE_INSERT_BOOL ("locations_flag", locations_flag);
   MUSCLE_INSERT_BOOL ("pure_flag", pure_parser);
   MUSCLE_INSERT_BOOL ("synclines_flag", !no_lines_flag);
+  MUSCLE_INSERT_BOOL ("tag_seen_flag", tag_seen);
   MUSCLE_INSERT_BOOL ("yacc_flag", yacc_flag);
 
   /* File names.  */

src/parse-gram.y

@@ -57,7 +57,7 @@ static char const *char_name (char);
 static void add_param (char const *, char *, location);
 
 static symbol_class current_class = unknown_sym;
-static uniqstr current_type = 0;
+static uniqstr current_type = NULL;
 static symbol *current_lhs;
 static location current_lhs_location;
 static int current_prec = 0;
@@ -209,7 +209,7 @@ declaration:
   grammar_declaration
 | PROLOGUE
     {
-      prologue_augment (translate_code ($1, @1), @1, typed);
+      prologue_augment (translate_code ($1, @1), @1, union_seen);
     }
 | "%after-header" "{...}"
     {
@@ -322,7 +322,7 @@ grammar_declaration:
     {
       char const *body = $3;
 
-      if (typed)
+      if (union_seen)
 	{
 	  /* Concatenate the union bodies, turning the first one's
 	     trailing '}' into '\n', and omitting the second one's '{'.  */
@@ -331,7 +331,7 @@ grammar_declaration:
 	  body++;
 	}
 
-      typed = true;
+      union_seen = true;
       muscle_code_grow ("stype", body, @3);
     }
 ;
@@ -352,6 +352,7 @@ symbol_declaration:
     }
 | "%type" TYPE symbols.1
     {
+      tag_seen = true;
       symbol_list *list;
       for (list = $3; list; list = list->next)
 	symbol_type_set (list->sym, $2, @2);
@@ -382,7 +383,7 @@ precedence_declarator:
 
 type.opt:
   /* Nothing. */ { current_type = NULL; }
-| TYPE           { current_type = $1; }
+| TYPE           { current_type = $1; tag_seen = true; }
 ;
 
 /* One or more nonterminals to be %typed. */
@@ -396,6 +397,7 @@ symbol_def:
   TYPE
      {
        current_type = $1;
+       tag_seen = true;
      }
 | id
      {

src/reader.c

@@ -45,7 +45,10 @@ static bool start_flag = false;
 merger_list *merge_functions;
 
 /* Was %union seen?  */
-bool typed = false;
+bool union_seen = false;
+
+/* Was a tag seen?  */
+bool tag_seen = false;
 
 /* Should rules have a default precedence?  */
 bool default_prec = true;

src/reader.h

@@ -59,7 +59,10 @@ void free_merger_functions (void);
 extern merger_list *merge_functions;
 
 /* Was %union seen?  */
-extern bool typed;
+extern bool union_seen;
+
+/* Was a tag seen?  */
+extern bool tag_seen;
 
 /* Should rules have a default precedence?  */
 extern bool default_prec;

src/scan-code.l

@@ -55,6 +55,9 @@ static void handle_action_dollar (symbol_list *rule, char *cp,
 static void handle_action_at (symbol_list *rule, char *cp, location at_loc);
 static location the_location;
 static location *loc = &the_location;
+
+/* True if an untyped $$ or $n was seen.  */
+static bool untyped_var_seen;
 %}
  /* C and C++ comments in code. */
 %x SC_COMMENT SC_LINE_COMMENT
@@ -262,48 +265,62 @@ handle_action_dollar (symbol_list *rule, char *text, location dollar_loc)
 	++cp;
       *cp = '\0';
       ++cp;
+      if (untyped_var_seen)
+	complain_at (dollar_loc, _("explicit type given in untyped grammar"));
+      tag_seen = true;
     }
 
   if (*cp == '$')
     {
       if (!type_name)
 	type_name = symbol_list_n_type_name_get (rule, dollar_loc, 0);
-      if (!type_name && typed)
-	{
-	  if (rule->midrule_parent_rule)
-	    complain_at (dollar_loc,
-			 _("$$ for the midrule at $%d of `%s' has no declared"
-			   " type"),
-			 rule->midrule_parent_rhs_index,
-			 effective_rule->sym->tag);
-	  else
-	    complain_at (dollar_loc, _("$$ of `%s' has no declared type"),
-			 rule->sym->tag);
-	}
+
       if (!type_name)
-	type_name = "";
+	{
+	  if (union_seen | tag_seen)
+	    {
+	      if (rule->midrule_parent_rule)
+		complain_at (dollar_loc,
+			     _("$$ for the midrule at $%d of `%s'"
+			       " has no declared type"),
+			     rule->midrule_parent_rhs_index,
+			     effective_rule->sym->tag);
+	      else
+		complain_at (dollar_loc, _("$$ of `%s' has no declared type"),
+			     rule->sym->tag);
+	    }
+	  else
+	    untyped_var_seen = true;
+	  type_name = "";
+	}
+
       obstack_fgrow1 (&obstack_for_string,
 		      "]b4_lhs_value([%s])[", type_name);
       rule->used = true;
     }
   else
     {
-      long int num;
-      set_errno (0);
-      num = strtol (cp, 0, 10);
-      if (INT_MIN <= num && num <= effective_rule_length && ! get_errno ())
+      long int num = strtol (cp, NULL, 10);
+
+      if (1 - INT_MAX + effective_rule_length <= num
+	  && num <= effective_rule_length)
 	{
 	  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 (effective_rule, dollar_loc, n);
-	  if (!type_name && typed)
-	    complain_at (dollar_loc, _("$%d of `%s' has no declared type"),
-			 n, effective_rule->sym->tag);
 	  if (!type_name)
-	    type_name = "";
+	    {
+	      if (union_seen | tag_seen)
+		complain_at (dollar_loc, _("$%d of `%s' has no declared type"),
+			     n, effective_rule->sym->tag);
+	      else
+		untyped_var_seen = true;
+	      type_name = "";
+	    }
+
 	  obstack_fgrow3 (&obstack_for_string,
 			  "]b4_rhs_value(%d, %d, [%s])[",
 			  effective_rule_length, n, type_name);
@@ -336,11 +353,10 @@ handle_action_at (symbol_list *rule, char *text, location at_loc)
     obstack_sgrow (&obstack_for_string, "]b4_lhs_location[");
   else
     {
-      long int num;
-      set_errno (0);
-      num = strtol (cp, 0, 10);
+      long int num = strtol (cp, NULL, 10);
 
-      if (INT_MIN <= num && num <= effective_rule_length && ! get_errno ())
+      if (1 - INT_MAX + effective_rule_length <= num
+	  && num <= effective_rule_length)
 	{
 	  int n = num;
 	  obstack_fgrow2 (&obstack_for_string, "]b4_rhs_location(%d, %d)[",
@@ -356,9 +372,9 @@ handle_action_at (symbol_list *rule, char *text, location at_loc)
 | Initialize the scanner.  |
 `-------------------------*/
 
-/* Translate the dollars and ats in \a a, whose location is l.
-   Depending on the \a sc_context (SC_RULE_ACTION, SC_SYMBOL_ACTION,
-   INITIAL), the processing is different.  */
+/* Translate the dollars and ats in \a a, whose location is \a l.  The
+   translation is for \a rule, in the context \a sc_context
+   (SC_RULE_ACTION, SC_SYMBOL_ACTION, INITIAL).  */
 
 static const char *
 translate_action (int sc_context, symbol_list *rule, const char *a, location l)