Filter out yarn.lock files when displaying diffs (#18)

We have a few spurious historic diffs in yarn.lock
due to the changes in the way lockfile seeding
works in create-app. These diffs are never
relevant for upgraders - they're not expected to
update their yarn.lock file in response to seed
changes. With that in mind, it makes sense to
always filter out any changes in yarn.lock in the
diff.

Co-authored-by: Vincenzo Scamporlino <[email protected]>

src/hooks/fetch-diff.js

@@ -5,8 +5,11 @@ import { useSettings } from '../SettingsProvider'
 
 const delay = ms => new Promise(res => setTimeout(res, ms))
 
-const movePackageJsonToTop = parsedDiff =>
-  parsedDiff.sort(({ newPath }) => (newPath.includes('package.json') ? -1 : 1))
+const excludeYarnLock = ({ oldPath, newPath, ...rest }) =>
+  !(oldPath.includes('yarn.lock') || newPath.includes('yarn.lock'))
+
+const packageJsonFirst = ({ newPath }) =>
+  newPath.includes('package.json') ? -1 : 1
 
 export const useFetchDiff = ({
   shouldShowDiff,
@@ -42,7 +45,11 @@ export const useFetchDiff = ({
 
       const diff = await response.text()
 
-      setDiff(movePackageJsonToTop(parseDiff(diff)))
+      setDiff(
+        parseDiff(diff)
+          .filter(excludeYarnLock)
+          .sort(packageJsonFirst)
+      )
 
       setIsLoading(false)
       setIsDone(true)