Try defining subtype(union(), union()) with type_diff()

This solves the problem captured in
test/known_problems/should_pass/different_normalization_levels.erl
but leads to a lot of other test failures.

Author: erszcz

src/typechecker.erl

@@ -361,15 +361,21 @@ compat_ty({type, _, 'fun', [{type, _, product, Args1}, Res1]},
     {Aps, constraints:combine(Cs, Css, Env)};
 
 %% Unions
-compat_ty({type, _, union, Tys1}, {type, _, union, Tys2}, Seen, Env) ->
-    lists:foldl(fun (Ty1, {Seen1, C1}) ->
-                    {Seen2, C2} = any_type(Ty1, Tys2, Seen1, Env),
-                    {Seen2, constraints:combine(C1, C2, Env)}
-                end, {Seen, constraints:empty()}, Tys1);
-compat_ty(Ty1, {type, _, union, Tys2}, Seen, Env) ->
-    any_type(Ty1, Tys2, Seen, Env);
-compat_ty({type, _, union, Tys1}, Ty2, Seen, Env) ->
-    all_type(Tys1, Ty2, Seen, Env);
+compat_ty({type, _, union, _} = U1, {type, _, union, _} = U2, Seen, Env) ->
+    case type_diff(U1, U2, Env) of
+        ?type(none) -> ret(Seen);
+        false -> throw(nomatch)
+    end;
+
+%compat_ty({type, _, union, Tys1}, {type, _, union, Tys2}, Seen, Env) ->
+%    lists:foldl(fun (Ty1, {Seen1, C1}) ->
+%                    {Seen2, C2} = any_type(Ty1, Tys2, Seen1, Env),
+%                    {Seen2, constraints:combine(C1, C2, Env)}
+%                end, {Seen, constraints:empty()}, Tys1);
+%compat_ty(Ty1, {type, _, union, Tys2}, Seen, Env) ->
+%    any_type(Ty1, Tys2, Seen, Env);
+%compat_ty({type, _, union, Tys1}, Ty2, Seen, Env) ->
+%    all_type(Tys1, Ty2, Seen, Env);
 
 % Integer types
 compat_ty(Ty1, Ty2, Seen, _Env) when ?is_int_type(Ty1), ?is_int_type(Ty2) ->
@@ -608,16 +614,16 @@ any_type(Ty1, Tys, Seen0, Env) ->
 %% @doc All types in `Tys' must be compatible with `Ty'.
 %% Returns all the gather memoizations and constraints.
 %% Does not return (throws `nomatch') if any of the types is not compatible.
--spec all_type([type()], type(), map(), env()) -> compat_acc().
-all_type(Tys, Ty, Seen, Env) ->
-    all_type(Tys, Ty, Seen, [], Env).
-
--spec all_type([type()], type(), map(), [constraints:t()], env()) -> compat_acc().
-all_type([], _Ty, Seen, Css, Env) ->
-    {Seen, constraints:combine(Css, Env)};
-all_type([Ty1|Tys], Ty, AIn, Css, Env) ->
-    {AOut, Cs} = compat(Ty1, Ty, AIn, Env),
-    all_type(Tys, Ty, AOut, [Cs|Css], Env).
+%-spec all_type([type()], type(), map(), env()) -> compat_acc().
+%all_type(Tys, Ty, Seen, Env) ->
+%    all_type(Tys, Ty, Seen, [], Env).
+
+%-spec all_type([type()], type(), map(), [constraints:t()], env()) -> compat_acc().
+%all_type([], _Ty, Seen, Css, Env) ->
+%    {Seen, constraints:combine(Css, Env)};
+%all_type([Ty1|Tys], Ty, AIn, Css, Env) ->
+%    {AOut, Cs} = compat(Ty1, Ty, AIn, Env),
+%    all_type(Tys, Ty, AOut, [Cs|Css], Env).
 
 %% Looks up the fields of a record by name and, if present, by the module where
 %% it belongs if a filename is included in the Anno.