Re-established rule_specific_token, which allows giving a better syntax error...

Re-established rule_specific_token, which allows giving a better syntax error message when %% is missing.

TODO

@@ -9,8 +9,6 @@
     correlate with star size and alphabet size, etc.
     create separate graphs for 3 modes: --lalr, pager, --canonical
   In Menhir's bootstrapped parser:
-    re-establish rule_specific_token?
-      git show 64504bd5214794dc34530f93faccd9f62f049dcf
     use a canonical automaton?
 
 * When dealing with errors, should we back up to the last shift action,

bench/bad/declaration-error-b.expected

 File "declaration-error-b.mly", line 3, characters 10-11:
-Error: Ill-formed %token declaration.
-Examples of well-formed declarations:
-  %token FOO
-  %token DOT SEMICOLON
-  %token <string> LID UID
+Error: syntax error inside a declaration.
+Did you perhaps forget the %% that separates declarations and rules?

src/fancy-parser.messages

@@ -8,7 +8,7 @@ Either a declaration or %% is expected at this point.
 
 TYPE UID 
 TYPE OCAMLTYPE TYPE 
-TYPE OCAMLTYPE UID PUBLIC 
+TYPE OCAMLTYPE UID PREC 
 TYPE OCAMLTYPE UID RPAREN 
 TYPE OCAMLTYPE UID LPAREN TYPE 
 TYPE OCAMLTYPE UID COMMA TYPE 

src/fancy-parser.mly

@@ -96,6 +96,17 @@ declaration:
 | PARAMETER t = OCAMLTYPE
     { [ with_poss $startpos $endpos (DParameter t) ] }
 
+/* This production recognizes tokens that are valid in the rules section,
+   but not in the declarations section. This is a hint that a %% was
+   forgotten. */
+
+| rule_specific_token
+    {
+      Error.error (Positions.two $startpos $endpos)
+        "syntax error inside a declaration.\n\
+         Did you perhaps forget the %% that separates declarations and rules?"
+    }
+
 priority_keyword:
   LEFT
     { LeftAssoc }
@@ -104,6 +115,13 @@ priority_keyword:
 | NONASSOC
     { NonAssoc }
 
+%inline rule_specific_token:
+| PUBLIC
+| INLINE
+| COLON
+| EOF
+    { () }
+
 /* ------------------------------------------------------------------------- */
 /* Our lists of symbols are separated with optional commas. Order is
    irrelevant. */