Enable hot reloading of the functional mixins (#146)

* Enable hot reloading of the functional mixins

* Update tests: add dependency case

index.js

@@ -33,6 +33,19 @@ function addMixin(helpers, mixins, rule, file) {
   rule.remove()
 }
 
+function processModulesForHotReloadRecursively(module, helpers) {
+  let moduleId = module.id
+  module.children.forEach(childModule => {
+    helpers.result.messages.push({
+      type: 'dependency',
+      file: childModule.id,
+      parent: moduleId
+    })
+    processModulesForHotReloadRecursively(childModule, helpers)
+  })
+  delete require.cache[moduleId]
+}
+
 function loadGlobalMixin(helpers, globs) {
   let cwd = process.cwd()
   let files = glob.sync(globs, { caseSensitiveMatch: IS_WIN })
@@ -53,7 +66,13 @@ function loadGlobalMixin(helpers, globs) {
         addMixin(helpers, mixins, atrule, path)
       })
     } else {
-      mixins[name] = { mixin: require(path), file: path }
+      try {
+        mixins[name] = { mixin: require(path), file: path }
+        let module = require.cache[require.resolve(path)]
+        if (module) {
+          processModulesForHotReloadRecursively(module, helpers)
+        }
+      } catch {}
     }
   })
   return mixins

test/deps/f.js

@@ -0,0 +1 @@
+module.exports = require('./g')

test/deps/g.js

@@ -0,0 +1,3 @@
+module.exports = {
+  g: '5'
+}

test/index.test.js

@@ -341,6 +341,31 @@ test('loads mixins from file globs', async () => {
   })
 })
 
+test('loads mixins with dependencies', async () => {
+  let result = await run(
+    'a { @mixin f; }',
+    'a { g: 5; }',
+    {
+      mixinsFiles: join(__dirname, 'deps', 'f.js')
+    }
+  )
+  equal(
+    result.messages.sort((a, b) => a.file && a.file.localeCompare(b.file)),
+    [
+      {
+        file: join(__dirname, 'deps/f.js'),
+        type: 'dependency',
+        parent: ''
+      },
+      {
+        file: join(__dirname, 'deps/g.js'),
+        type: 'dependency',
+        parent: join(__dirname, 'deps/f.js')
+      }
+    ]
+  )
+})
+
 test('coverts mixins values', async () => {
   let processor = postcss(
     mixins({