Use lists:usort/1 instead of lists:uniq/1 on OTP < 25

lists:uniq/1 was introduced in OTP 25.

Author: xxdavid

src/constraints.erl

@@ -65,7 +65,7 @@ do_combine(Cs1, Cs2, Env) ->
 
 -spec variables(t()) -> [var()].
 variables(#constraints{ upper_bounds = UBounds, lower_bounds = LBounds }) ->
-    lists:uniq(maps:keys(UBounds) ++ maps:keys(LBounds)).
+    gradualizer_lib:uniq(maps:keys(UBounds) ++ maps:keys(LBounds)).
 
 
 %% Checks that all lower bounds are subtypes of respective upper bounds.

src/gradualizer_lib.erl

@@ -1,7 +1,7 @@
 %% @private
 -module(gradualizer_lib).
 
--export([merge_with/3, top_sort/1, get_type_definition/3,
+-export([merge_with/3, uniq/1, top_sort/1, get_type_definition/3,
          pick_values/2, fold_ast/3, get_ast_children/1,
          empty_tenv/0, create_tenv/3,
          remove_pos_typed_record_field/1,
@@ -45,6 +45,13 @@ merge_with(F, M1, M2) ->
     end.
 -endif.
 
+-spec uniq([A]) -> [A].
+-if(?OTP_RELEASE >= 25).
+uniq(List) -> lists:uniq(List).
+-else.
+uniq(List) -> lists:usort(List).
+-endif.
+
 %% -- Topological sort
 
 -type graph(Node) :: #{Node => [Node]}. %% List of incoming edges (dependencies).