1 files changed, 44 insertions, 0 deletions
diff --git a/ql/ast/checkers/dependency_checker.py b/ql/ast/checkers/dependency_checker.py
new file mode 100644
index 0000000..473ef6b
--- /dev/null
+++ b/ql/ast/checkers/dependency_checker.py
@@ -0,0 +1,44 @@
+class DependencyChecker:
+    def __init__(self, combinations):
+        self.__errors = []
+        self.__check_dependencies(combinations)
+
+    @property
+    def errors(self):
+        return self.__errors
+
+    def __check_dependencies(self, combinations):
+        for (identifier, identifier_children, identifier_metadata) in combinations:
+            children = self.__find_children(identifier, combinations)
+
+            if identifier in children:
+                self.__errors.append('Cyclic dependency detected in question identifiers on line(s) {}'
+                                     .format(str(self.__find_lines(children, combinations))[1:-1]))
+
+    def __find_children(self, identifier, combinations):
+        reference, reference_children, _ = combinations[0]
+
+        if len(combinations) == 1 and identifier == reference:
+            return reference_children
+        elif len(combinations) == 1:
+            return []
+        elif identifier == reference:
+            all_children = []
+
+            for new_identifier in reference_children:
+                all_children += self.__find_children(new_identifier, combinations[1:])
+
+            return all_children + reference_children
+
+        return self.__find_children(identifier, combinations[1:])
+
+    @staticmethod
+    def __find_lines(children, combinations):
+        lines = []
+
+        for identifier, _, metadata in combinations:
+            for child in children:
+                if identifier == child:
+                    lines.append(metadata.line)
+
+        return lines