Add support for metalsmith builder hooks (#428)

* Add support for metalsmith builder hooks

Close #427

* Fix style

* Fix documentation sentence

* Add e2e test for metalsmith custom plugin

* Enhance e2e tests for metalsmith custom plugin

Author: Toilal

Diff for: README.md

@@ -77,6 +77,8 @@ vue init ~/fs/path/to-custom-template my-project
   - `prompts`: used to collect user options data;
 
   - `filters`: used to conditional filter files to render.
+  
+  - `metalsmith`: used to add custom metalsmith plugins in the chain.
 
   - `completeMessage`: the message to be displayed to the user when the template has been generated. You can include custom instruction here.
 
@@ -179,6 +181,36 @@ The `skipInterpolation` field in the metadata file should be a [minimatch glob p
 }
 ```
 
+#### Metalsmith
+
+`vue-cli` uses [metalsmith](https://github.com/segmentio/metalsmith) to generate the project.
+
+You may customize the metalsmith builder created by vue-cli to register custom plugins.
+
+```js
+{
+  "metalsmith": function (metalsmith, opts, helpers) {
+    function customMetalsmithPlugin (files, metalsmith, done) {
+      // Implement something really custom here.
+      done(null, files)
+    }
+    
+    metalsmith.use(customMetalsmithPlugin)
+  }
+}
+```
+
+If you need to hook metalsmith before questions are asked, you may use an object with `before` key.
+
+```js
+{
+  "metalsmith": {
+    before: function (metalsmith, opts, helpers) {},
+    after: function (metalsmith, opts, helpers) {}
+  }
+}
+```
+
 #### Additional data available in meta.{js,json}
 
 - `destDirName` - destination directory name
@@ -204,7 +236,7 @@ Arguments:
 - `data`: the same data you can access in `completeMessage`:
   ```js
   {
-    complete(data) {
+    complete (data) {
       if (!data.inPlace) {
         console.log(`cd ${data.destDirName}`)
       }
@@ -218,7 +250,7 @@ Arguments:
   - `files`: An array of generated files
   ```js
   {
-    complete(data, {logger, chalk}) {
+    complete (data, {logger, chalk}) {
       if (!data.inPlace) {
         logger.log(`cd ${chalk.yellow(data.destDirName)}`)
       }

Diff for: lib/generate.js

@@ -43,11 +43,24 @@ module.exports = function generate (name, src, dest, done) {
   opts.helpers && Object.keys(opts.helpers).map(function (key) {
     Handlebars.registerHelper(key, opts.helpers[key])
   })
-  metalsmith
-    .use(askQuestions(opts.prompts))
+
+  var helpers = {chalk, logger}
+
+  if (opts.metalsmith && typeof opts.metalsmith.before === 'function') {
+    opts.metalsmith.before(metalsmith, opts, helpers)
+  }
+
+  metalsmith.use(askQuestions(opts.prompts))
     .use(filterFiles(opts.filters))
     .use(renderTemplateFiles(opts.skipInterpolation))
-    .clean(false)
+
+  if (typeof opts.metalsmith === 'function') {
+    opts.metalsmith(metalsmith, opts, helpers)
+  } else if (opts.metalsmith && typeof opts.metalsmith.after === 'function') {
+    opts.metalsmith.after(metalsmith, opts, helpers)
+  }
+
+  metalsmith.clean(false)
     .source('.') // start from template root instead of `./src` which is Metalsmith's default for `source`
     .destination(dest)
     .build(function (err, files) {

Diff for: test/e2e/mock-metalsmith-custom-before-after/meta.js

@@ -0,0 +1,21 @@
+module.exports = {
+  "metalsmith": {
+    before: function (metalsmith, opts, helpers) {
+      metalsmith.metadata().before = "Before";
+    },
+    after: function (metalsmith, opts, helpers) {
+      metalsmith.metadata().after  = "After";
+      function customMetalsmithPlugin (files, metalsmith, done) {
+        // Implement something really custom here.
+
+        var readme = files['readme.md']
+        delete files['readme.md']
+        files['custom-before-after/readme.md'] = readme
+
+        done(null, files)
+      }
+
+      metalsmith.use(customMetalsmithPlugin)
+    }
+  }
+}

Diff for: test/e2e/mock-metalsmith-custom-before-after/template/readme.md

@@ -0,0 +1 @@
+Metalsmith {{after}} and {{before}} hooks

Diff for: test/e2e/mock-metalsmith-custom/meta.js

@@ -0,0 +1,16 @@
+module.exports = {
+  "metalsmith": function (metalsmith, opts, helpers) {
+    metalsmith.metadata().custom = "Custom";
+    function customMetalsmithPlugin (files, metalsmith, done) {
+      // Implement something really custom here.
+
+      var readme = files['readme.md']
+      delete files['readme.md']
+      files['custom/readme.md'] = readme
+
+      done(null, files)
+    }
+
+    metalsmith.use(customMetalsmithPlugin)
+  }
+}

Diff for: test/e2e/mock-metalsmith-custom/template/readme.md

@@ -0,0 +1 @@
+Metalsmith {{custom}}

Diff for: test/e2e/test.js

@@ -13,6 +13,8 @@ const metadata = require('../../lib/options')
 const { isLocalPath, getTemplatePath } = require('../../lib/local-path')
 
 const MOCK_META_JSON_PATH = path.resolve('./test/e2e/mock-meta-json')
+const MOCK_METALSMITH_CUSTOM_PATH = path.resolve('./test/e2e/mock-metalsmith-custom')
+const MOCK_METALSMITH_CUSTOM_BEFORE_AFTER_PATH = path.resolve('./test/e2e/mock-metalsmith-custom-before-after')
 const MOCK_TEMPLATE_REPO_PATH = path.resolve('./test/e2e/mock-template-repo')
 const MOCK_TEMPLATE_BUILD_PATH = path.resolve('./test/e2e/mock-template-build')
 const MOCK_METADATA_REPO_JS_PATH = path.resolve('./test/e2e/mock-metadata-repo-js')
@@ -120,6 +122,46 @@ describe('vue-cli', () => {
     })
   })
 
+  it('supports custom metalsmith plugins', done => {
+    generate('test', MOCK_METALSMITH_CUSTOM_PATH, MOCK_TEMPLATE_BUILD_PATH, err => {
+      if (err) done(err)
+
+      expect(exists(`${MOCK_TEMPLATE_BUILD_PATH}/custom/readme.md`)).to.equal(true)
+
+      async.eachSeries([
+        'readme.md'
+      ], function (file, next) {
+        const template = fs.readFileSync(`${MOCK_METALSMITH_CUSTOM_PATH}/template/${file}`, 'utf8')
+        const generated = fs.readFileSync(`${MOCK_TEMPLATE_BUILD_PATH}/custom/${file}`, 'utf8')
+        render(template, {custom: 'Custom'}, (err, res) => {
+          if (err) return next(err)
+          expect(res).to.equal(generated)
+          next()
+        })
+      }, done)
+    })
+  })
+
+  it('supports custom metalsmith plugins with after/before object keys', done => {
+    generate('test', MOCK_METALSMITH_CUSTOM_BEFORE_AFTER_PATH, MOCK_TEMPLATE_BUILD_PATH, err => {
+      if (err) done(err)
+
+      expect(exists(`${MOCK_TEMPLATE_BUILD_PATH}/custom-before-after/readme.md`)).to.equal(true)
+
+      async.eachSeries([
+        'readme.md'
+      ], function (file, next) {
+        const template = fs.readFileSync(`${MOCK_METALSMITH_CUSTOM_BEFORE_AFTER_PATH}/template/${file}`, 'utf8')
+        const generated = fs.readFileSync(`${MOCK_TEMPLATE_BUILD_PATH}/custom-before-after/${file}`, 'utf8')
+        render(template, {before: 'Before', after: 'After'}, (err, res) => {
+          if (err) return next(err)
+          expect(res).to.equal(generated)
+          next()
+        })
+      }, done)
+    })
+  })
+
   it('generate a vaild package.json with escaped author', done => {
     monkeyPatchInquirer(escapedAnswers)
     generate('test', MOCK_TEMPLATE_REPO_PATH, MOCK_TEMPLATE_BUILD_PATH, err => {
@@ -254,7 +296,7 @@ describe('vue-cli', () => {
     expect(getTemplatePath('../template')).to.equal(path.join(__dirname, '/../../../template'))
   })
 
-  it.only('points out the file in the error', done => {
+  it('points out the file in the error', done => {
     monkeyPatchInquirer(answers)
     generate('test', MOCK_ERROR, MOCK_TEMPLATE_BUILD_PATH, err => {
       expect(err.message).to.match(/^\[readme\.md\] Parse error/)