fix(gatsby-transformer-remark): wait for async subplugins (#12578)

* move eachPromise to utils file and add (failing) tests

* fix eachPromise

packages/gatsby-transformer-remark/src/__tests__/utils.js

@@ -0,0 +1,24 @@
+const { eachPromise } = require(`../utils`)
+
+test(`eachPromise`, async () => {
+  const args = [`foo`, `bar`, `baz`]
+
+  const cb = jest.fn()
+
+  await eachPromise(args, arg => {
+    cb(`Start`, arg)
+    return new Promise(resolve => {
+      setTimeout(() => {
+        cb(`Finish`, arg)
+        resolve()
+      }, 200)
+    })
+  })
+
+  expect(cb).toHaveBeenNthCalledWith(1, `Start`, `foo`)
+  expect(cb).toHaveBeenNthCalledWith(2, `Finish`, `foo`)
+  expect(cb).toHaveBeenNthCalledWith(3, `Start`, `bar`)
+  expect(cb).toHaveBeenNthCalledWith(4, `Finish`, `bar`)
+  expect(cb).toHaveBeenNthCalledWith(5, `Start`, `baz`)
+  expect(cb).toHaveBeenNthCalledWith(6, `Finish`, `baz`)
+})

packages/gatsby-transformer-remark/src/extend-node-type.js

@@ -29,6 +29,7 @@ const {
   cloneTreeUntil,
   findLastTextNode,
 } = require(`./hast-processing`)
+const { eachPromise } = require(`./utils`)
 
 let fileNodes
 let pluginsCacheStr = ``
@@ -68,19 +69,6 @@ const safeGetCache = ({ getCache, cache }) => id => {
   return getCache(id)
 }
 
-/**
- * @template T
- * @param {Array<T>} input
- * @param {(input: T) => Promise<void>} iterator
- * @return Promise<void>
- */
-const eachPromise = (input, iterator) =>
-  input.reduce(
-    (accumulatorPromise, nextValue) =>
-      accumulatorPromise.then(() => void iterator(nextValue)),
-    Promise.resolve()
-  )
-
 const HeadingType = new GraphQLObjectType({
   name: `MarkdownHeading`,
   fields: {

packages/gatsby-transformer-remark/src/utils.js

@@ -0,0 +1,12 @@
+/**
+ * @template T
+ * @param {Array<T>} input
+ * @param {(input: T) => Promise<void>} iterator
+ * @return Promise<void>
+ */
+exports.eachPromise = (input, iterator) =>
+  input.reduce(
+    (accumulatorPromise, nextValue) =>
+      accumulatorPromise.then(() => iterator(nextValue)),
+    Promise.resolve()
+  )