feat(gatsby-source-drupal): Add ability to use JSON API filters when querying. (#12508)

Author: eojthebrave

packages/gatsby-source-drupal/README.md

@@ -34,6 +34,46 @@ module.exports = {
 }
 ```
 
+### Filters
+
+You can use the `filters` option to limit the data that is retrieved from Drupal. Filters are applied per JSON API collection. You can use any [valid JSON API filter query](https://www.drupal.org/docs/8/modules/jsonapi/filtering). For large data sets this can reduce the build time of your application by allowing Gatsby to skip content you'll never use.
+
+As an example, if your JSON API endpoint (https://live-contentacms.pantheonsite.io/api) returns the following collections list, then `articles` and `recipes` are both collections that can have a filters applied:
+
+```json
+{
+  ...
+  links: {
+    articles: "https://live-contentacms.pantheonsite.io/api/articles",
+    recipes: "https://live-contentacms.pantheonsite.io/api/recipes",
+    ...
+  }
+}
+```
+
+To retrieve only recipes with a specific tag you could do something like the following where the key (recipe) is the collection from above, and the value is the filter you want to apply.
+
+```javascript
+// In your gatsby-config.js
+module.exports = {
+  plugins: [
+    {
+      resolve: `gatsby-source-drupal`,
+      options: {
+        baseUrl: `https://live-contentacms.pantheonsite.io/`,
+        apiBase: `api`,
+        filters: {
+          // collection : filter
+          recipe: "filter[tags.name][value]=British",
+        },
+      },
+    },
+  ],
+}
+```
+
+Which would result in Gatsby using the filtered collection https://live-contentacms.pantheonsite.io/api/recipes?filter[tags.name][value]=British to retrieve data.
+
 ### Basic Auth
 
 You can use `basicAuth` option if your site is protected by basicauth.

packages/gatsby-source-drupal/src/gatsby-node.js

@@ -14,7 +14,7 @@ const createContentDigest = obj =>
 
 exports.sourceNodes = async (
   { actions, getNode, hasNodeChanged, store, cache, createNodeId },
-  { baseUrl, apiBase, basicAuth }
+  { baseUrl, apiBase, basicAuth, filters }
 ) => {
   const { createNode } = actions
 
@@ -50,6 +50,15 @@ exports.sourceNodes = async (
         if (typeof url === `object`) {
           // url can be string or object containing href field
           url = url.href
+
+          // Apply any filters configured in gatsby-config.js. Filters
+          // can be any valid JSON API filter query string.
+          // See https://www.drupal.org/docs/8/modules/jsonapi/filtering
+          if (typeof filters === `object`) {
+            if (filters.hasOwnProperty(type)) {
+              url = url + `?${filters[type]}`
+            }
+          }
         }
 
         let d