A class's name and its keyword are one dispatch value

(defmethod area point ...) and (defmethod area :point ...) were both
accepted and the second was dead code: a class stands for the keyword
its instances carry -- that is the whole of how the two dispatch styles
share a mechanism -- so the duplicate scan has to compare them as one.
It compared the written forms, which differ. Normalised in the scan and
pinned in test_flan.ml.

lib/classes.ml

@@ -124,9 +124,15 @@ let collect (decls : Ast.decl list) =
               list: one call site reaches all of them, and it can only pass \
               one number of arguments"
              m.Ast.mgen want (if want = 1 then "" else "s") n;
+         (* A class's name and its keyword are one dispatch value — a class
+            stands for the keyword its instances carry, which is the whole of
+            how the two dispatch styles share a mechanism — so [point] and
+            [:point] have to be compared as one or the second method is
+            accepted and is dead code. *)
+         let norm = function Ast.Dclass c -> Ast.Dkw c | k -> k in
          List.iter
            (fun (prev : Ast.methd) ->
-              if prev.Ast.mkey = m.Ast.mkey then
+              if norm prev.Ast.mkey = norm m.Ast.mkey then
                 Loc.failk "check/duplicate-method" d.Ast.dloc
                   "%s already has a method for %s. Two methods for one \
                    dispatch value is an ambiguity nothing resolves — there \

test/test_flan.ml

@@ -1803,6 +1803,16 @@ let () =
      (defmethod area point [p] 2)\n\
      (defn main [] i32 0)"
     ~needle:"already has a method for point";
+  (* A class's name and its keyword are one value: a class stands for the
+     keyword its instances carry, so these two methods are the same method
+     written twice and the second would be dead code. *)
+  rejects_check "a class and its keyword are one dispatch value"
+    "(defclass point [x y])\n\
+     (defgeneric area [self] dyn)\n\
+     (defmethod area point [p] 1)\n\
+     (defmethod area :point [p] 2)\n\
+     (defn main [] i32 0)"
+    ~needle:"already has a method for :point";
   rejects_check "two :else methods for one generic"
     "(defmulti d [x] dyn x)\n\
      (defmethod d :else [x] 1)\n\