tokens: define the "$undefined" token kind

* data/skeletons/bison.m4 (b4_symbol_token_kind): Give a definition to
$undefined.
(b4_token_visible_if): $undefined has an id.
* src/output.c (prepare_symbol_definitions): Stop lying: $undefined
_is_ a token.
* tests/input.at: Adjust.

data/skeletons/bison.m4

@@ -456,10 +456,6 @@ m4_define([b4_symbol_if],
          [m4_fatal([$0: field $2 of $1 is not a Boolean:] b4_symbol([$1], [$2]))])])
 
 
-# Give the error token a better name.
-m4_define([b4_symbol(1, id)],  [b4_api_PREFIX[][ERRCODE]])
-
-
 # b4_symbol_tag_comment(SYMBOL-NUM)
 # ---------------------------------
 # Issue a comment giving the tag of symbol NUM.
@@ -541,9 +537,11 @@ m4_define([b4_symbol_map],
 # Whether NUM denotes a token that has an exported definition (i.e.,
 # shows in enum yytokentype).
 m4_define([b4_token_visible_if],
-[b4_symbol_if([$1], [is_token],
-              [b4_symbol_if([$1], [has_id], [$2], [$3])],
-              [$3])])
+[m4_case(b4_symbol([$1], [tag]),
+         [$undefined], [$2],
+         [b4_symbol_if([$1], [is_token],
+                       [b4_symbol_if([$1], [has_id], [$2], [$3])],
+                       [$3])])])
 
 
 # b4_token_has_definition(NUM)

data/skeletons/c.m4

@@ -430,6 +430,12 @@ static const b4_int_type_for([$2]) yy$1[[]] =
 ## Token kinds.  ##
 ## ------------- ##
 
+# Because C enums are not scoped, because tokens are exposed in the
+# header, and because these tokens are common to all the parser, we
+# need to make sure their names don't collide: use the api.prefix.
+m4_define([b4_symbol(1, id)],  [b4_api_PREFIX[][ERRCODE]])
+m4_define([b4_symbol(2, id)],  [b4_api_PREFIX[][UNDEF]])
+
 # b4_token_define(TOKEN-NUM)
 # --------------------------
 # Output the definition of this token as #define.

src/output.c

@@ -549,8 +549,7 @@ prepare_symbol_definitions (void)
       MUSCLE_INSERT_INT (key, sym->content->user_token_number);
 
       SET_KEY ("is_token");
-      MUSCLE_INSERT_INT (key,
-                         i < ntokens && sym != undeftoken);
+      MUSCLE_INSERT_INT (key, i < ntokens);
 
       SET_KEY ("number");
       MUSCLE_INSERT_INT (key, sym->content->number);

src/parse-gram.h

@@ -79,6 +79,7 @@ extern int gram_debug;
   {
     GRAM_EOF = 0,                  /* "end of file"  */
     GRAM_ERRCODE = 1,              /* error  */
+    GRAM_UNDEF = 2,                /* $undefined  */
     STRING = 3,                    /* "string"  */
     TSTRING = 4,                   /* "translatable string"  */
     PERCENT_TOKEN = 5,             /* "%token"  */

src/symtab.c

@@ -65,6 +65,17 @@ static bool *used_assoc = NULL;
 bool tag_seen = false;
 
 
+/* Whether SYM was defined by the user.  */
+
+static bool
+symbol_is_user_defined (symbol *sym)
+{
+  return sym->tag[0] != '$'
+    && sym != errtoken && sym->alias != errtoken
+    && sym != undeftoken  && sym->alias != undeftoken;
+}
+
+
 /*--------------------------.
 | Create a new sym_content. |
 `--------------------------*/
@@ -279,6 +290,7 @@ is_identifier (uniqstr s)
 /*-----------------------------------------------.
 | Get the identifier associated to this symbol.  |
 `-----------------------------------------------*/
+
 uniqstr
 symbol_id_get (symbol const *sym)
 {
@@ -419,6 +431,7 @@ symbol_code_props_set (symbol *sym, code_props_type kind,
     sym->content->props[kind] = *code;
 }
 
+
 /*-----------------------------------------------------.
 | Set the DESTRUCTOR or PRINTER associated with TYPE.  |
 `-----------------------------------------------------*/
@@ -457,7 +470,7 @@ symbol_code_props_get (symbol *sym, code_props_type kind)
     }
 
   /* Apply default code props's only to user-defined symbols.  */
-  if (sym->tag[0] != '$' && sym != errtoken)
+  if (symbol_is_user_defined (sym))
     {
       code_props *code = &semantic_type_get (sym->content->type_name ? "*" : "",
                                              NULL)->props[kind];
@@ -831,16 +844,26 @@ symbols_new (void)
   accept->content->class = nterm_sym;
   accept->content->number = nvars++;
 
-  /* Construct the error token */
-  errtoken = symbol_get ("error", empty_loc);
+  /* Construct the YYERRCODE/"error" token */
+  errtoken = symbol_get ("YYERRCODE", empty_loc);
   errtoken->content->class = token_sym;
   errtoken->content->number = ntokens++;
+  {
+    symbol *alias = symbol_get ("error", empty_loc);
+    symbol_class_set (alias, token_sym, empty_loc, false);
+    symbol_make_alias (errtoken, alias, empty_loc);
+  }
 
-  /* Construct a token that represents all undefined literal tokens.
-     It is always token number 2.  */
-  undeftoken = symbol_get ("$undefined", empty_loc);
+  /* Construct the YYUNDEF/"$undefined" token that represents all
+     undefined literal tokens.  It is always symbol number 2.  */
+  undeftoken = symbol_get ("YYUNDEF", empty_loc);
   undeftoken->content->class = token_sym;
   undeftoken->content->number = ntokens++;
+  {
+    symbol *alias = symbol_get ("$undefined", empty_loc);
+    symbol_class_set (alias, token_sym, empty_loc, false);
+    symbol_make_alias (undeftoken, alias, empty_loc);
+  }
 
   semantic_type_table = hash_xinitialize (HT_INITIAL_CAPACITY,
                                           NULL,

tests/input.at

@@ -345,6 +345,7 @@ int main (void)
 {
   assert (YYERRCODE == 123);
   assert (YYTRANSLATE (YYERRCODE) == YYSYMBOL_YYERROR);
+  assert (YYTRANSLATE (YYUNDEF) == YYSYMBOL_YYUNDEF);
   return 0;
 }
 ]])
@@ -431,7 +432,7 @@ AT_CHECK([cat symbols.csv], [],
 [[number, class, tag, id, user_number, type,
 0, Token, $end, , 0, ,
 1, Token, error, YYERRCODE, 256, ,
-2, Nonterminal, $undefined, , 257, ,
+2, Token, $undefined, YYUNDEF, 257, ,
 3, Token, 'a', , 97, ,
 4, Token, "A1", A1, 1, ,
 5, Token, A2, A2, 258, ,