Eliminate invalid warnings for built-in modules (#231)

Fixes #230.

CHANGELOG.md

@@ -1,3 +1,8 @@
+## 1.7.1
+
+* Eliminates invalid warnings when running `--migrate-deps` on a file that
+  uses a built-in module.
+
 ## 1.7.0
 
 ### Media Logic Migrator

lib/src/migration_visitor.dart

@@ -120,6 +120,7 @@ abstract class MigrationVisitor
   @protected
   void visitDependency(Uri dependency, FileSpan context,
       {bool forImport = false}) {
+    if (dependency.scheme == 'sass') return;
     var result = importCache.import(dependency,
         baseImporter: _importer, baseUrl: _currentUrl, forImport: forImport);
     if (result != null) {

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass_migrator
-version: 1.7.0
+version: 1.7.1
 description: A tool for running migrations on Sass files
 homepage: https://github.com/sass/migrator
 

test/migrators/division/existing_sass_math.hrx

@@ -0,0 +1,12 @@
+<==> arguments
+--migrate-deps
+
+<==> input/entrypoint.scss
+@use "sass:math";
+
+$variable: 4 / 3;
+
+<==> output/entrypoint.scss
+@use "sass:math";
+
+$variable: math.div(4, 3);