Analyzer lets unions of the same type be assigned to eachother

analyzer/assignment.go

@@ -91,7 +91,7 @@ func (this *Tree) canAssign (
 	}
 
 	// then, check for union assignment
-	if destination, ok := this.isUnion(destination); ok {
+	if _, ok := this.isUnion(destination); ok {
 		return this.canAssignUnion(pos, destination, source)
 	}
 
@@ -295,12 +295,19 @@ func (this *Tree) canAssignInterface (
 // analyzed source type, and determines whether source can be assigned to
 // destination.
 func (this *Tree) canAssignUnion (
-	pos         errors.Position,
-	destination *entity.TypeUnion,
-	source      entity.Type,
+	pos            errors.Position,
+	destination    entity.Type,
+	source         entity.Type,
 ) error {
-	hash := source.Hash()
-	if _, ok := destination.AllowedMap[hash]; ok { return nil }
+	sourceHash      := source.Hash()
+	destinationHash := destination.Hash()
+	union, _        := this.isUnion(destination)
+
+	// check if types are identical
+	if sourceHash == destinationHash { return nil }
+	// check if type is included within the union
+	if _, ok := union.AllowedMap[sourceHash]; ok { return nil }
+	
 	return errors.Errorf (
 		pos, "%v is not included within union %v",
 		source, destination)

analyzer/assignment_test.go

@@ -273,7 +273,7 @@ U: (| Int F64)
 
 func TestAssignmentUnionErrNotListed (test *testing.T) {
 testStringErr (test,
-"I64 is not included within union (| Int F64)", 5, 8,
+"I64 is not included within union U", 5, 8,
 `
 U: (| Int F64)
 [main] = {