Merge pull request #505 from xxdavid/fix_add_type_pat_union

Fix exhaustiveness checking for union types

src/typechecker.erl

@@ -2176,10 +2176,7 @@ type_check_list_op(Env, Arg1, Arg2) ->
         {false, _} ->
             throw(type_error(Arg1, Ty1, type(list)));
         {_, false} ->
-            throw(type_error(Arg2, Ty2, type(list)));
-        _ ->
-            %% Prevent "Nonexhaustive patterns" when self-gradualizing.
-            erlang:error(unreachable)
+            throw(type_error(Arg2, Ty2, type(list)))
     end.
 
 -spec type_check_call_ty(env(), _, _, _) -> {type(), env(), constraints:t()}.
@@ -4833,11 +4830,10 @@ add_type_pat_union(Pat, ?type(union, UnionTys) = UnionTy, Env) ->
         _SomeTysMatched ->
             %% TODO: The constraints should be merged with *or* semantics
             %%       and var binds with intersection
-            {Ty, Cs} = glb(PatTys, Env),
-            {Ty,
+            {lub(PatTys, Env),
              normalize(type(union, UBounds), Env),
              union_var_binds(Envs, Env),
-             constraints:combine([Cs|Css])}
+             constraints:combine(Css)}
     end.
 
 %% TODO: This is incomplete!

test/known_problems/should_pass/intersection_should_pass.erl

@@ -0,0 +1,16 @@
+-module(intersection_should_pass).
+
+-export([f/1,
+         g/1]).
+
+-spec f(a|b) -> a|b.
+f(V) -> h(V).
+
+-spec g(a|b) -> a|b.
+g(V) ->
+    A = h(V),
+    A.
+
+-spec h(a) -> a;
+       (b) -> b.
+h(V) -> V.

test/should_fail/intersection_fail.erl

@@ -0,0 +1,10 @@
+-module(intersection_fail).
+
+-export([k/1]).
+
+-spec i(a, b) -> {a, b};
+       (d, e) -> {d, e}.
+i(V, U) -> {V, U}.
+
+-spec k({a, e} | {d, b}) -> {a, e} | {d, b}.
+k({V, U}) -> i(V, U).

test/should_pass/exhaustiveness_union_types.erl

@@ -0,0 +1,13 @@
+-module(exhaustiveness_union_types).
+
+-export([g/0]).
+
+-spec f() -> ok | {error, foo} | {error, bar}.
+f() -> ok.
+
+-spec g() -> integer().
+g() ->
+    case f() of
+        ok -> 42;
+        {error, _Sth} -> 43
+    end.

test/known_problems/should_pass/intersection.erl → test/should_pass/intersection.erl

@@ -1,17 +1,7 @@
 -module(intersection).
--export([f/1, g/1, j/1]).
 
--spec f(a|b) -> a|b.
-f(V) -> h(V).
-
--spec g(a|b) -> a|b.
-g(V) ->
-    A = h(V),
-    A.
-
--spec h(a) -> a;
-       (b) -> b.
-h(V) -> V.
+-export([i/2,
+         j/1]).
 
 -spec i(a, b) -> {a, b};
        (d, e) -> {d, e}.