Allow provided collections to be overridden in user config

index.js

@@ -1,5 +1,7 @@
 const { EleventyHtmlBasePlugin } = require('@11ty/eleventy')
 
+const addCollections = require('./lib/collections/index.js')
+
 module.exports = function (eleventyConfig, pluginOptions = {}) {
   const { pathPrefix } = eleventyConfig
 
@@ -11,16 +13,7 @@ module.exports = function (eleventyConfig, pluginOptions = {}) {
   eleventyConfig.setLibrary('njk', require('./lib/nunjucks.js')(eleventyConfig))
 
   // Collections
-  eleventyConfig.addCollection('all', require('./lib/collections/all.js'))
-  eleventyConfig.addCollection(
-    'ordered',
-    require('./lib/collections/ordered.js')
-  )
-  eleventyConfig.addCollection(
-    'sitemap',
-    require('./lib/collections/sitemap.js')
-  )
-  eleventyConfig.addCollection('tags', require('./lib/collections/tags.js'))
+  addCollections(eleventyConfig)
 
   // Extensions and template formats
   eleventyConfig.addExtension('scss', require('./lib/extensions/scss.js'))

layouts/sub-navigation.njk

@@ -11,7 +11,7 @@
   <div class="govuk-grid-row">
     <div class="govuk-grid-column-one-quarter-from-desktop">
       {{ xGovukSubNavigation({
-        items: collections.ordered | eleventyNavigation(sectionKey or options.homeKey) | itemsFromNavigation(page.url, { pathPrefix: options.pathPrefix })
+        items: collections.navigation | eleventyNavigation(sectionKey or options.homeKey) | itemsFromNavigation(page.url, { pathPrefix: options.pathPrefix })
       }) }}
     </div>
     <div class="govuk-grid-column-three-quarters-from-desktop">

lib/collections/index.js

@@ -0,0 +1,17 @@
+module.exports = function (eleventyConfig) {
+  if (!eleventyConfig.collections.all) {
+    eleventyConfig.addCollection('all', require('./all.js'))
+  }
+
+  if (!eleventyConfig.collections.navigation) {
+    eleventyConfig.addCollection('navigation', require('./navigation.js'))
+  }
+
+  if (!eleventyConfig.collections.sitemap) {
+    eleventyConfig.addCollection('sitemap', require('./sitemap.js'))
+  }
+
+  if (!eleventyConfig.collections.tag) {
+    eleventyConfig.addCollection('tags', require('./tags.js'))
+  }
+}