Fix: Get the type of Chain.create() from its application (#407)

* Get the type of Chain.create() from its application

* Add test contract

* Update CHANGELOG.md

* Update the tests

* Update tests again

test/aeso_compiler_tests.erl

@@ -202,6 +202,7 @@ compilable_contracts() ->
      "polymorphism_contract_interface_extensions",
      "polymorphism_contract_interface_same_decl_multi_interface",
      "polymorphism_contract_interface_same_name_same_type",
+     "polymorphism_variance_switching_chain_create",
      "missing_init_fun_state_unit",
      "complex_compare_leq",
      "complex_compare",
@@ -1025,6 +1026,20 @@ failing_contracts() ->
                      "Cannot unify `Animal` and `Cat` in a covariant context\n"
                      "when checking the type of the pattern `q15 : oracle_query(Cat, Cat)` against the expected type `oracle_query(Cat, Animal)`">>
                   ])
+    , ?TYPE_ERROR(polymorphism_variance_switching_chain_create_fail,
+                  [<<?Pos(9,22)
+                     "I is not implemented.\n"
+                     "when resolving arguments of variadic function `Chain.create`">>,
+                   <<?Pos(10,13)
+                     "Cannot unify `I` and `C` in a covariant context\n"
+                     "when checking the type of the pattern `c2 : C` against the expected type `I`">>,
+                   <<?Pos(10,22)
+                     "I is not implemented.\n"
+                     "when resolving arguments of variadic function `Chain.create`">>,
+                   <<?Pos(11,22)
+                     "I is not implemented.\n"
+                     "when resolving arguments of variadic function `Chain.create`">>
+                  ])
     , ?TYPE_ERROR(missing_definition,
                   [<<?Pos(2,14)
                      "Missing definition of function `foo`">>

test/contracts/polymorphism_variance_switching_chain_create.aes

@@ -0,0 +1,29 @@
+contract interface I =
+    entrypoint f : () => int
+
+contract C1 : I =
+    entrypoint f() = 123
+
+contract C2 : I =
+    entrypoint f() = 888
+
+namespace Make =
+    stateful function new1() : I = Chain.create() : C1
+    stateful function new2() : I = Chain.create() : C2
+
+    stateful function new(c : I) : int = c.f()
+
+main contract Main =
+    stateful entrypoint test1() =
+        let c = Make.new1()
+        Make.new(c)
+
+    stateful entrypoint test2() =
+        let c = Make.new2()
+        Make.new(c)
+
+    stateful entrypoint test3() =
+        let c1      = Chain.create() : C1  // succeeds
+        let c2 : I  = Chain.create() : C1  // succeeds
+        let c3 : C1 = Chain.create()       // succeeds
+        ()

test/contracts/polymorphism_variance_switching_chain_create_fail.aes

@@ -0,0 +1,12 @@
+contract interface I =
+    entrypoint f : () => int
+
+contract C : I =
+    entrypoint f() = 123
+
+main contract Main =
+    stateful entrypoint test() =
+        let c1 : I = Chain.create()       // fails
+        let c2 : C = Chain.create() : I   // fails
+        let c3     = Chain.create() : I   // fails
+        ()