Allow to use @vue/component to set type of file to vue

fixes vuejs#109

Author: armano2

lib/utils/index.js

@@ -341,15 +341,26 @@ module.exports = {
       })
   },
 
+  /**
+   * Check whether the given node is a Vue component based
+   * @param {RuleContext} context The ESLint rule context object.
+   * @returns {boolean}
+   */
+  hasVueComponentComment (context) {
+    const sourceCode = context.getSourceCode()
+    return Boolean(sourceCode.getAllComments().find(item => /@vue\/component/g.test(item.value)))
+  },
+
   /**
    * Check whether the given node is a Vue component based
    * on the filename and default export type
    * export default {} in .vue || .jsx
    * @param {ASTNode} node Node to check
    * @param {string} path File name with extension
+   * @param {RuleContext} context The ESLint rule context object.
    * @returns {boolean}
    */
-  isVueComponentFile (node, path) {
+  isVueComponentFile (node, path, context) {
     const isVueFile = path.endsWith('.vue') || path.endsWith('.jsx')
     return isVueFile &&
       node.type === 'ExportDefaultDeclaration' &&
@@ -435,8 +446,8 @@ module.exports = {
 
     return {
       'ExportDefaultDeclaration:exit' (node) {
-        // export default {} in .vue || .jsx
-        if (!_this.isVueComponentFile(node, filePath)) return
+        // export default {} in .vue || .jsx or comment with @vue/component
+        if (!_this.isVueComponentFile(node, filePath, context) && !_this.hasVueComponentComment(context)) return
         cb(node.declaration)
       },
       'CallExpression:exit' (node) {

tests/lib/rules/no-dupe-keys.js

@@ -77,8 +77,8 @@ ruleTester.run('no-dupe-keys', rule, {
 
   invalid: [
     {
-      filename: 'test.vue',
-      code: `
+      // filename: 'test.vue',
+      code: `/* @vue/component */
         export default {
           props: ['foo'],
           computed: {
@@ -109,8 +109,8 @@ ruleTester.run('no-dupe-keys', rule, {
       }]
     },
     {
-      filename: 'test.vue',
-      code: `
+      // filename: 'test.vue',
+      code: `// @vue/component
         export default {
           props: {
             foo: String