[test] Restore nextjs cache for size snapshot (#20155)

Author: eps1lon

azure-pipelines.yml

@@ -10,11 +10,14 @@ trigger:
 pr:
   branches:
     include:
-    - '*' 
+      - '*'
 
 pool:
   vmImage: 'ubuntu-latest'
 
+variables:
+  DOCS_NEXT_CACHE_FOLDER: $(Build.SourcesDirectory)/docs/.next/cache
+
 steps:
   - task: NodeTool@0
     inputs:
@@ -54,6 +57,15 @@ steps:
       artifactName: 'canaries'
       targetPath: 'material-ui-core.tgz'
 
+  - task: Cache@2
+    inputs:
+      key: 'yarn | "$(Agent.OS)" | yarn.lock'
+      restoreKeys: |
+        yarn | "$(Agent.OS)"
+        yarn
+      path: $(DOCS_NEXT_CACHE_FOLDER)
+    displayName: Cache nextjs build
+
   - script: |
       set -o pipefail
       mkdir -p scripts/sizeSnapshot/build	

docs/package.json

@@ -5,7 +5,8 @@
   "author": "Material-UI Team",
   "license": "MIT",
   "scripts": {
-    "build": "rimraf .next && cross-env NODE_ENV=production next build",
+    "build": "cross-env NODE_ENV=production next build",
+    "build:clean": "rimraf .next && yarn build",
     "build-sw": "node ./scripts/buildServiceWorker.js",
     "dev": "rimraf ./node_modules/.cache/babel-loader && next dev",
     "deploy": "git push material-ui-docs master:latest",