Fixes #881.

crates/aiken-lang/src/tests/check.rs

@@ -1835,6 +1835,30 @@ fn forbid_expect_into_opaque_type_from_data() {
     ))
 }
 
+#[test]
+fn allow_expect_into_type_from_data() {
+    let source_code = r#"
+        fn bar(n: Data) {
+          expect a: Option<Int> = n
+          a
+        }
+    "#;
+
+    assert!(check(parse(source_code)).is_ok())
+}
+
+#[test]
+fn allow_expect_into_type_from_data_2() {
+    let source_code = r#"
+        fn bar(n: Data) {
+          expect Some(a): Option<Int> = n
+          a
+        }
+    "#;
+
+    assert!(check(parse(source_code)).is_ok())
+}
+
 #[test]
 fn forbid_expect_into_opaque_type_constructor_without_typecasting_in_module() {
     let source_code = r#"
@@ -1985,6 +2009,19 @@ fn allow_expect_on_var_patterns_that_are_opaque() {
     assert!(check(parse(source_code)).is_ok())
 }
 
+#[test]
+fn can_down_cast_to_data_always() {
+    let source_code = r#"
+        pub opaque type Foo { x: Int }
+        pub fn bar(a: Foo) {
+          let b: Data = a
+          b
+        }
+    "#;
+
+    assert!(check(parse(source_code)).is_ok());
+}
+
 #[test]
 fn correct_span_for_backpassing_args() {
     let source_code = r#"

crates/aiken-lang/src/tipo/environment.rs

@@ -1415,12 +1415,12 @@ impl<'a> Environment<'a> {
             && !(t1.is_function() || t2.is_function())
             && !(t1.is_generic() || t2.is_generic())
             && !(t1.is_string() || t2.is_string())
-            && !(t1.contains_opaque() || t2.contains_opaque())
+            && !t1.contains_opaque()
         {
             return Ok(());
         }
 
-        if allow_cast && (t1.contains_opaque() || t2.contains_opaque()) {
+        if allow_cast && t1.contains_opaque() {
             return Err(Error::ExpectOnOpaqueType { location });
         }