Ensure package contents is namespaced to use govuk

Before:

package
├── assets
├── components
├── core
├── helpers
├── objects
├── overrides
├── settings
├── tools
├── utilities
├── vendor
├── README.md
├── all-ie8.scss
├── all.js
├── all.scss
├── common.js
├── govuk-prototype-kit.config.json
├── package.json
└── template.njk

After:

package
├── govuk
│   ├── assets
│   ├── components
│   ├── core
│   ├── helpers
│   ├── objects
│   ├── overrides
│   ├── settings
│   ├── tools
│   ├── utilities
│   ├── vendor
│   ├── all-ie8.scss
│   ├── all.js
│   ├── all.scss
│   ├── common.js
│   └── template.njk
├── README.md
├── govuk-prototype-kit.config.json
└── package.json

See proposal for more detail
https://github.com/alphagov/govuk-design-system-architecture/blob/master/proposals/005-namespace-govuk-frontend-nunjucks-sass-using-a-nested-folder-structure.md

tasks/gulp/__tests__/after-build-package.test.js

@@ -39,13 +39,15 @@ describe('package/', () => {
         '.DS_Store',
         '*.test.js',
         '*.yaml',
-        '*.snap'
+        '*.snap',
+        '*/govuk/README.md'
       ]
 
       const additionalFilesNotInSrc = [
         'package.json',
         'govuk-prototype-kit.config.json',
-        '**/macro-options.json'
+        '**/macro-options.json',
+        'README.md'
       ]
 
       return recursive(configPaths.src, filesToIgnore).then(
@@ -92,7 +94,7 @@ describe('package/', () => {
 
   describe('all.scss', () => {
     it('should compile without throwing an exception', async () => {
-      const allScssFile = path.join(configPaths.package, 'all.scss')
+      const allScssFile = path.join(configPaths.package, 'govuk', 'all.scss')
       await renderSass({ file: allScssFile })
     })
   })
@@ -101,7 +103,7 @@ describe('package/', () => {
     const componentNames = lib.allComponents.slice()
 
     it.each(componentNames)(`'%s' should have macro-options.json that contains JSON`, (name) => {
-      const filePath = path.join(configPaths.package, 'components', name, 'macro-options.json')
+      const filePath = path.join(configPaths.package, 'govuk', 'components', name, 'macro-options.json')
       return readFile(filePath, 'utf8')
         .then((data) => {
           var parsedData = JSON.parse(data)

tasks/gulp/compile-assets.js

@@ -142,6 +142,8 @@ gulp.task('scss:compile', () => {
 gulp.task('js:compile', () => {
   // for dist/ folder we only want compiled 'all.js' file
   let srcFiles = isDist ? configPaths.src + 'all.js' : configPaths.src + '**/*.js'
+  let destination = isDist ? taskArguments.destination : taskArguments.destination + '/govuk/'
+
   return gulp.src([
     srcFiles,
     '!' + configPaths.src + '**/*.test.js'
@@ -164,5 +166,5 @@ gulp.task('js:compile', () => {
       })
     ))
     .pipe(eol())
-    .pipe(gulp.dest(taskArguments.destination + '/'))
+    .pipe(gulp.dest(destination))
 })

tasks/gulp/copy-to-destination.js

@@ -60,5 +60,5 @@ gulp.task('copy-files', () => {
       path.extname = '.json'
     }))
     .pipe(yamlFiles.restore)
-    .pipe(gulp.dest(taskArguments.destination + '/'))
+    .pipe(gulp.dest(taskArguments.destination + '/govuk/'))
 })