feat: cache .next/cache between builds

helpers/cacheBuild.js

@@ -0,0 +1,32 @@
+const path = require('path')
+
+const DEFAULT_DIST_DIR = '.next'
+
+// Account for possible custom distDir
+const getPath = (distDir, source) => {
+  return path.join(distDir || DEFAULT_DIST_DIR, source)
+}
+
+const restoreCache = async ({ cache, distDir }) => {
+  const cacheDir = getPath(distDir, 'cache')
+  if (await cache.restore(cacheDir)) {
+    console.log('Next.js cache restored.')
+  } else {
+    console.log('No Next.js cache to restore.')
+  }
+}
+
+const saveCache = async ({ cache, distDir }) => {
+  const cacheDir = getPath(distDir, 'cache')
+  const buildManifest = getPath(distDir, 'build-manifest.json')
+  if (await cache.save(cacheDir, { digests: [buildManifest] })) {
+    console.log('Next.js cache saved.')
+  } else {
+    console.log('No Next.js cache to save.')
+  }
+}
+
+module.exports = {
+  restoreCache,
+  saveCache,
+}

helpers/getNextConfig.js

@@ -1,24 +1,32 @@
 'use strict'
 
+const { cwd: getCwd } = require('process')
 const { resolve } = require('path')
 
 const moize = require('moize')
 
-// Load next.config.js
-const getNextConfig = async function (failBuild = defaultFailBuild) {
+// We used to cache nextConfig for any cwd. Now we pass process.cwd() to cache
+// (or memoize) nextConfig per cwd.
+const getNextConfig = async function (failBuild = defaultFailBuild, cwd = getCwd()) {
   // We cannot load `next` at the top-level because we validate whether the
   // site is using `next` inside `onPreBuild`.
   const { PHASE_PRODUCTION_BUILD } = require('next/constants')
   const loadConfig = require('next/dist/next-server/server/config').default
 
   try {
-    return await loadConfig(PHASE_PRODUCTION_BUILD, resolve('.'))
+    return await loadConfig(PHASE_PRODUCTION_BUILD, cwd)
   } catch (error) {
     return failBuild('Error loading your next.config.js.', { error })
   }
 }
 
-const moizedGetNextConfig = moize(getNextConfig, { maxSize: 1e3, isPromise: true })
+const moizedGetNextConfig = moize(getNextConfig, {
+  maxSize: 1e3,
+  isPromise: true,
+  // Memoization cache key. We need to use `transformArgs` so `process.cwd()`
+  // default value is assigned
+  transformArgs: ([, cwd = getCwd()]) => [cwd],
+})
 
 const defaultFailBuild = function (message, { error }) {
   throw new Error(`${message}\n${error.stack}`)

helpers/isStaticExportProject.js

@@ -17,7 +17,7 @@ const isStaticExportProject = ({ build, scripts }) => {
 
   if (isStaticExport) {
     console.log(
-      `Static HTML export Next.js projects do not require this plugin. Check your project's build command for 'next export'.`,
+      'NOTE: Static HTML export Next.js projects (projects that use `next export`) do not require most of this plugin. For these sites, this plugin *only* caches builds.',
     )
   }
 

index.js

@@ -9,6 +9,7 @@ const validateNextUsage = require('./helpers/validateNextUsage')
 const doesNotNeedPlugin = require('./helpers/doesNotNeedPlugin')
 const getNextConfig = require('./helpers/getNextConfig')
 const copyUnstableIncludedDirs = require('./helpers/copyUnstableIncludedDirs')
+const { restoreCache, saveCache } = require('./helpers/cacheBuild')
 
 const pWriteFile = util.promisify(fs.writeFile)
 
@@ -27,6 +28,9 @@ module.exports = {
       return failBuild('Could not find a package.json for this project')
     }
 
+    const nextConfig = await getNextConfig(utils.failBuild)
+    await restoreCache({ cache: utils.cache, distDir: nextConfig.distDir })
+
     if (await doesNotNeedPlugin({ netlifyConfig, packageJson, failBuild })) {
       return
     }
@@ -60,12 +64,14 @@ module.exports = {
 
     await nextOnNetlify({ functionsDir: FUNCTIONS_SRC, publishDir: PUBLISH_DIR })
   },
+
   async onPostBuild({ netlifyConfig, packageJson, constants: { FUNCTIONS_DIST }, utils }) {
     if (await doesNotNeedPlugin({ netlifyConfig, packageJson, utils })) {
       return
     }
 
     const nextConfig = await getNextConfig(utils.failBuild)
+    await saveCache({ cache: utils.cache, distDir: nextConfig.distDir })
     copyUnstableIncludedDirs({ nextConfig, functionsDist: FUNCTIONS_DIST })
   },
 }

test/fixtures/dist_dir_next_config/next.config.js

@@ -0,0 +1,4 @@
+module.exports = {
+  target: 'serverless',
+  distDir: 'build',
+}

test/index.js

@@ -18,6 +18,10 @@ const utils = {
       throw new Error(message)
     },
   },
+  cache: {
+    save() {},
+    restore() {},
+  },
 }
 
 // Temporary switch cwd
@@ -155,6 +159,29 @@ describe('preBuild()', () => {
       }),
     ).rejects.toThrow(`Error loading your next.config.js.`)
   })
+
+  test('restores cache with right paths', async () => {
+    await useFixture('dist_dir_next_config')
+
+    let distPath
+    const utils_ = {
+      ...utils,
+      cache: {
+        restore: (x) => (distPath = x),
+      },
+    }
+    const spy = jest.spyOn(utils_.cache, 'restore')
+
+    await plugin.onPreBuild({
+      netlifyConfig,
+      packageJson: DUMMY_PACKAGE_JSON,
+      utils: utils_,
+      constants: { FUNCTIONS_SRC: 'out_functions' },
+    })
+
+    expect(spy).toHaveBeenCalled()
+    expect(path.normalize(distPath)).toBe(path.normalize('build/cache'))
+  })
 })
 
 describe('onBuild()', () => {
@@ -229,3 +256,33 @@ describe('onBuild()', () => {
     expect(await pathExists(`${resolvedFunctions}/next_api_test/next_api_test.js`)).toBeTruthy()
   })
 })
+
+describe('onPostBuild', () => {
+  test('saves cache with right paths', async () => {
+    await useFixture('dist_dir_next_config')
+
+    let distPath
+    let manifestPath
+    const utils_ = {
+      ...utils,
+      cache: {
+        save: (x, y) => {
+          distPath = x
+          manifestPath = y
+        },
+      },
+    }
+    const spy = jest.spyOn(utils_.cache, 'save')
+
+    await plugin.onPostBuild({
+      netlifyConfig,
+      packageJson: DUMMY_PACKAGE_JSON,
+      utils: utils_,
+      constants: { FUNCTIONS_SRC: 'out_functions' },
+    })
+
+    expect(spy).toHaveBeenCalled()
+    expect(path.normalize(distPath)).toBe(path.normalize('build/cache'))
+    expect(path.normalize(manifestPath.digests[0])).toBe(path.normalize('build/build-manifest.json'))
+  })
+})