Ban the unification of uvars and var_args functions (#423)

* Ban the unification of uvar and var_args function

* Update CHANGELOG

* Fix the tests

* Undo indent

* Change the error message for unify_varargs

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Type definitions serialised to ACI as `typedefs` field instead of `type_defs` to increase compatibility.
 ### Removed
 ### Fixed
+- Typechecker crashes if Chain.create or Chain.clone are used without arguments.
 
 ## [7.0.1]
 ### Added

src/aeso_ast_infer_types.erl

@@ -2856,6 +2856,8 @@ unify0(Env, A, B, Variance, When) ->
 
 unify1(_Env, {uvar, _, R}, {uvar, _, R}, _Variance, _When) ->
     true;
+unify1(_Env, {uvar, _, _}, {fun_t, _, _, var_args, _}, _Variance, When) ->
+    type_error({unify_varargs, When});
 unify1(Env, {uvar, A, R}, T, _Variance, When) ->
     case occurs_check(R, T) of
         true ->
@@ -3625,7 +3627,7 @@ mk_error({multiple_main_contracts, Ann}) ->
     Msg = "Only one main contract can be defined.",
     mk_t_err(pos(Ann), Msg);
 mk_error({unify_varargs, When}) ->
-    Msg = "Cannot unify variable argument list.",
+    Msg = "Cannot infer types for variable argument list.",
     {Pos, Ctxt} = pp_when(When),
     mk_t_err(Pos, Msg, Ctxt);
 mk_error({clone_no_contract, Ann}) ->

src/aeso_pretty.erl

@@ -261,6 +261,8 @@ type(Type, Options) ->
     with_options(Options, fun() -> type(Type) end).
 
 -spec type(aeso_syntax:type()) -> doc().
+type(F = {fun_t, _, _, var_args, _}) ->
+    type(setelement(4, F, [var_args]));
 type({fun_t, _, Named, Args, Ret}) ->
     follow(hsep(args_type(Named ++ Args), text("=>")), type(Ret));
 type({type_sig, _, Named, Args, Ret}) ->
@@ -288,7 +290,9 @@ type(T = {id, _, _})   -> name(T);
 type(T = {qid, _, _})  -> name(T);
 type(T = {con, _, _})  -> name(T);
 type(T = {qcon, _, _}) -> name(T);
-type(T = {tvar, _, _}) -> name(T).
+type(T = {tvar, _, _}) -> name(T);
+
+type(var_args) -> text("var_args").
 
 -spec args_type([aeso_syntax:type()]) -> doc().
 args_type(Args) ->

test/aeso_compiler_tests.erl

@@ -1139,6 +1139,19 @@ failing_contracts() ->
                      "  `oracle(string, (int) => int)`\n"
                      "The response type must not be higher-order (contain function types)">>
                   ])
+    , ?TYPE_ERROR(var_args_unify_let,
+                  [<<?Pos(3,9)
+                     "Cannot infer types for variable argument list.\n"
+                     "when checking the type of the pattern `x : 'a` against the expected type `(gas : int, value : int, protected : bool, ref : 'b, var_args) => 'b`">>
+                  ])
+    , ?TYPE_ERROR(var_args_unify_fun_call,
+                  [<<?Pos(6,5)
+                     "Cannot infer types for variable argument list.\n"
+                     "when checking the application of\n"
+                     "  `g : (() => 'b) => 'b`\n"
+                     "to arguments\n"
+                     "  `Chain.create : (value : int, var_args) => 'c`">>
+                  ])
     ].
 
 validation_test_() ->

test/contracts/var_args_unify_fun_call.aes

@@ -0,0 +1,7 @@
+contract C =
+  stateful function g(h) =
+    h()
+
+  stateful entrypoint f() =
+    g(Chain.create)
+    123

test/contracts/var_args_unify_let.aes

@@ -0,0 +1,4 @@
+main contract C =
+  stateful entrypoint f() =
+    let x = Chain.clone
+    123