[json-loader] dont recompile on data change - part 2 (#4837)

* prevent adding duplicate redirects

* don't write new `redirects.json` if redirects didn't change

prevents webpack recompilation on data change

packages/gatsby/src/internal-plugins/query-runner/redirects-writer.js

@@ -1,8 +1,11 @@
 import _ from "lodash"
+import crypto from "crypto"
 import fs from "fs-extra"
 import { store, emitter } from "../../redux/"
 import { joinPath } from "../../utils/path"
 
+let lastHash = null
+
 const writeRedirects = async () => {
  bootstrapFinished = true
 
@@ -11,6 +14,17 @@ const writeRedirects = async () => {
  // Filter for redirects that are meant for the browser.
  const browserRedirects = redirects.filter(r => r.redirectInBrowser)
 
+ const newHash = crypto
+ .createHash(`md5`)
+ .update(JSON.stringify(browserRedirects))
+ .digest(`hex`)
+
+ if (newHash === lastHash) {
+ return Promise.resolve()
+ }
+
+ lastHash = newHash
+
  await fs.writeFile(
  joinPath(program.directory, `.cache/redirects.json`),
  JSON.stringify(browserRedirects, null, 2)

packages/gatsby/src/redux/reducers/redirects.js

@@ -1,7 +1,15 @@
+const _ = require(`lodash`)
+
 module.exports = (state = [], action) => {
  switch (action.type) {
- case `CREATE_REDIRECT`:
- return [...state, action.payload]
+ case `CREATE_REDIRECT`: {
+ if (!state.some(redirect => _.isEqual(redirect, action.payload))) {
+ // Add redirect only if it wasn't yet added to prevent duplicates
+ return [...state, action.payload]
+ }
+ return state
+ }
+
  default:
  return state
  }