Error if function reference that refers to other function over time

lib/src/migrators/module/references.dart

@@ -630,6 +630,15 @@ 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 +669,15 @@ 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/calc_interpolation/calc_remove_interpolation.hrx

@@ -9,8 +9,7 @@ $d: 5;
 
 // More than one interpolations
 .a { 
-    .b: calc($b - #{$c + 1} + #{$d}); 
-    .c: calc(100% - #{$TABLE_TITLE + 2px});
+    .b: calc($b - #{$c + 1} + #{$d});
 }
 
 // Nested
@@ -36,8 +35,7 @@ $d: 5;
 
 // More than one interpolations
 .a { 
-    .b: calc($b - ($c + 1) + $d); 
-    .c: calc(100% - ($TABLE-TITLE + 2px));
+    .b: calc($b - ($c + 1) + $d);
 }
 
 // Nested

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!

test/migrators/module/references/different_reference_same_mixin.hrx

@@ -0,0 +1,27 @@
+<==> input/entrypoint.scss
+@import "definition1";
+@import "upstream";
+@import "direct";
+
+<==> input/_direct.scss
+@import "definition2";
+@import "upstream";
+
+<==> input/definition1.scss
+@mixin fn {
+  margin: 0;
+  padding: 0;
+  list-style: none;
+}
+
+<==> input/definition2.scss
+@mixin fn {
+  color: blue;
+}
+
+<==> input/upstream.scss
+@include fn;
+
+<==> error.txt
+Error: Mixin `fn` has been previously declared in definition1.scss and is later on defined in definition2.scss.
+Migration failed!