Error if function reference that refers to other function over time

lib/src/migrators/module/references.dart

@@ -630,6 +630,16 @@ class _ReferenceVisitor extends ScopedAstVisitor {
     super.visitMixinRule(node);
     var member = MemberDeclaration(node);
     _declarationSources[member] = CurrentSource(_currentUrl);
+        _mixins.forEach((declaredMixins, reference) => {
+          if (declaredMixins.name == node.name &&
+              reference.sourceUrl != _currentUrl)
+            {
+              throw new MigrationException(
+                  'Mixin `${node.name}` has been previously declared' +
+                      ' in ${reference.sourceUrl.pathSegments.last} and is' +
+                      ' later on defined in ${_currentUrl.pathSegments.last}.')
+            }
+        });
     _registerLibraryUrl(member);
   }
 
@@ -660,6 +670,16 @@ class _ReferenceVisitor extends ScopedAstVisitor {
     super.visitFunctionRule(node);
     var member = MemberDeclaration(node);
     _declarationSources[member] = CurrentSource(_currentUrl);
+    _functions.forEach((declaredFunction, reference) => {
+          if (declaredFunction.name == node.name &&
+              reference.sourceUrl != _currentUrl)
+            {
+              throw new MigrationException(
+                  'Function `${node.name}` has been previously declared' +
+                      ' in ${reference.sourceUrl.pathSegments.last} and is' +
+                      ' later on defined in ${_currentUrl.pathSegments.last}.')
+            }
+        });
     _registerLibraryUrl(member);
   }
 

test/migrators/module/references/different_reference_same_function.hrx

@@ -0,0 +1,21 @@
+<==> input/entrypoint.scss
+@import "definition1";
+@import "upstream";
+@import "direct";
+
+<==> input/_direct.scss
+@import "definition2";
+@import "upstream";
+
+<==> input/definition1.scss
+@function fn() {@return 1}
+
+<==> input/definition2.scss
+@function fn() {@return 2}
+
+<==> input/upstream.scss
+a { b: fn() }
+
+<==> error.txt
+Error: Function `fn` has been previously declared in definition1.scss and is later on defined in definition2.scss.
+Migration failed!