Remove experimental image optimization feature (#34349)

This PR removes the experimental `optimizeImages` flag. This feature was designed to automatically add preload tags for images, but I was never able to get it to do a very good job of selecting the images that actually need preloading.

This feature never graduated from experimental and in fact we never even publicized it as an experimental feature for people to try.

Additionally, even if someone was using this feature, it wouldn't have a functional effect, only a performance effect (removal of some preloads).

For those reasons, I believe it is safe to remove this functionality and that it is not a breaking change.

packages/next/build/webpack-config.ts

@@ -1346,9 +1346,6 @@ export default async function getBaseWebpackConfig(
         'process.env.__NEXT_OPTIMIZE_FONTS': JSON.stringify(
           config.optimizeFonts && !dev
         ),
-        'process.env.__NEXT_OPTIMIZE_IMAGES': JSON.stringify(
-          config.experimental.optimizeImages
-        ),
         'process.env.__NEXT_OPTIMIZE_CSS': JSON.stringify(
           config.experimental.optimizeCss && !dev
         ),
@@ -1611,7 +1608,6 @@ export default async function getBaseWebpackConfig(
     reactStrictMode: config.reactStrictMode,
     reactMode: config.experimental.reactMode,
     optimizeFonts: config.optimizeFonts,
-    optimizeImages: config.experimental.optimizeImages,
     optimizeCss: config.experimental.optimizeCss,
     scrollRestoration: config.experimental.scrollRestoration,
     basePath: config.basePath,

packages/next/build/webpack/loaders/next-serverless-loader/page-handler.ts

@@ -191,7 +191,6 @@ export function getPageHandler(ctx: ServerlessHandlerCtx) {
           locale: detectedLocale,
           defaultLocale,
           domainLocales: i18n?.domains,
-          optimizeImages: process.env.__NEXT_OPTIMIZE_IMAGES,
           optimizeCss: process.env.__NEXT_OPTIMIZE_CSS,
           crossOrigin: process.env.__NEXT_CROSS_ORIGIN,
         },

packages/next/export/index.ts

@@ -385,7 +385,6 @@ export default async function exportApp(
       crossOrigin: nextConfig.crossOrigin,
       optimizeCss: nextConfig.experimental.optimizeCss,
       optimizeFonts: nextConfig.optimizeFonts,
-      optimizeImages: nextConfig.experimental.optimizeImages,
       reactRoot: nextConfig.experimental.reactRoot || false,
     }
 
@@ -583,7 +582,6 @@ export default async function exportApp(
             buildExport: options.buildExport,
             serverless: isTargetLikeServerless(nextConfig.target),
             optimizeFonts: nextConfig.optimizeFonts,
-            optimizeImages: nextConfig.experimental.optimizeImages,
             optimizeCss: nextConfig.experimental.optimizeCss,
             disableOptimizedLoading:
               nextConfig.experimental.disableOptimizedLoading,

packages/next/export/worker.ts

@@ -55,7 +55,6 @@ interface ExportPageInput {
   subFolders?: boolean
   serverless: boolean
   optimizeFonts: boolean
-  optimizeImages?: boolean
   optimizeCss: any
   disableOptimizedLoading: any
   parentSpanId: any
@@ -77,7 +76,6 @@ interface RenderOpts {
   ampValidatorPath?: string
   ampSkipValidation?: boolean
   optimizeFonts?: boolean
-  optimizeImages?: boolean
   disableOptimizedLoading?: boolean
   optimizeCss?: any
   fontManifest?: FontManifest
@@ -105,7 +103,6 @@ export default async function exportPage({
   subFolders,
   serverless,
   optimizeFonts,
-  optimizeImages,
   optimizeCss,
   disableOptimizedLoading,
   httpAgentOptions,
@@ -304,8 +301,6 @@ export default async function exportPage({
               /// @ts-ignore
               optimizeFonts,
               /// @ts-ignore
-              optimizeImages,
-              /// @ts-ignore
               optimizeCss,
               disableOptimizedLoading,
               distDir,
@@ -367,9 +362,6 @@ export default async function exportPage({
           if (optimizeFonts) {
             process.env.__NEXT_OPTIMIZE_FONTS = JSON.stringify(true)
           }
-          if (optimizeImages) {
-            process.env.__NEXT_OPTIMIZE_IMAGES = JSON.stringify(true)
-          }
           if (optimizeCss) {
             process.env.__NEXT_OPTIMIZE_CSS = JSON.stringify(true)
           }
@@ -379,7 +371,6 @@ export default async function exportPage({
             ampPath: renderAmpPath,
             params,
             optimizeFonts,
-            optimizeImages,
             optimizeCss,
             disableOptimizedLoading,
             fontManifest: optimizeFonts

packages/next/pages/_document.tsx

@@ -494,7 +494,6 @@ export class Head extends Component<
       useMaybeDeferContent,
       optimizeCss,
       optimizeFonts,
-      optimizeImages,
       runtime,
     } = this.context
 
@@ -737,7 +736,6 @@ export class Head extends Component<
               )}
               {!optimizeCss && this.getCssLinks(files)}
               {!optimizeCss && <noscript data-n-css={this.props.nonce ?? ''} />}
-              {optimizeImages && <meta name="next-image-preload" />}
 
               {!isDeferred && getDynamicScriptPreloads()}
 

packages/next/server/base-server.ts

@@ -152,7 +152,6 @@ export default abstract class Server {
     optimizeFonts: boolean
     images: ImageConfigComplete
     fontManifest?: FontManifest
-    optimizeImages: boolean
     disableOptimizedLoading?: boolean
     optimizeCss: any
     locale?: string
@@ -314,7 +313,6 @@ export default abstract class Server {
         this.nextConfig.optimizeFonts && !dev
           ? this.getFontManifest()
           : undefined,
-      optimizeImages: !!this.nextConfig.experimental.optimizeImages,
       optimizeCss: this.nextConfig.experimental.optimizeCss,
       disableOptimizedLoading: this.nextConfig.experimental.runtime
         ? true

packages/next/server/config-shared.ts

@@ -85,7 +85,6 @@ export interface ExperimentalConfig {
   reactMode?: 'legacy' | 'concurrent' | 'blocking'
   workerThreads?: boolean
   pageEnv?: boolean
-  optimizeImages?: boolean
   optimizeCss?: boolean
   scrollRestoration?: boolean
   externalDir?: boolean
@@ -454,7 +453,6 @@ export const defaultConfig: NextConfig = {
     isrFlushToDisk: true,
     workerThreads: false,
     pageEnv: false,
-    optimizeImages: false,
     optimizeCss: false,
     scrollRestoration: false,
     externalDir: false,

packages/next/server/next-server.ts

@@ -100,15 +100,11 @@ export default class NextNodeServer extends BaseServer {
     /**
      * This sets environment variable to be used at the time of SSR by head.tsx.
      * Using this from process.env allows targeting both serverless and SSR by calling
-     * `process.env.__NEXT_OPTIMIZE_IMAGES`.
-     * TODO(atcastle@): Remove this when experimental.optimizeImages are being cleaned up.
+     * `process.env.__NEXT_OPTIMIZE_CSS`.
      */
     if (this.renderOpts.optimizeFonts) {
       process.env.__NEXT_OPTIMIZE_FONTS = JSON.stringify(true)
     }
-    if (this.renderOpts.optimizeImages) {
-      process.env.__NEXT_OPTIMIZE_IMAGES = JSON.stringify(true)
-    }
     if (this.renderOpts.optimizeCss) {
       process.env.__NEXT_OPTIMIZE_CSS = JSON.stringify(true)
     }

packages/next/server/render.tsx

@@ -215,7 +215,6 @@ export type RenderOptsPartial = {
   unstable_JsPreload?: false
   optimizeFonts: boolean
   fontManifest?: FontManifest
-  optimizeImages: boolean
   optimizeCss: any
   devOnlyCacheBusterQueryString?: string
   resolvedUrl?: string
@@ -1406,7 +1405,6 @@ export async function renderToHTML(
     crossOrigin: renderOpts.crossOrigin,
     optimizeCss: renderOpts.optimizeCss,
     optimizeFonts: renderOpts.optimizeFonts,
-    optimizeImages: renderOpts.optimizeImages,
     runtime,
   }
 
@@ -1485,16 +1483,13 @@ export async function renderToHTML(
                 return html
               }
             : null,
-          !process.browser &&
-          (process.env.__NEXT_OPTIMIZE_FONTS ||
-            process.env.__NEXT_OPTIMIZE_IMAGES)
+          !process.browser && process.env.__NEXT_OPTIMIZE_FONTS
             ? async (html: string) => {
                 return await postProcess(
                   html,
                   { getFontDefinition },
                   {
                     optimizeFonts: renderOpts.optimizeFonts,
-                    optimizeImages: renderOpts.optimizeImages,
                   }
                 )
               }

packages/next/shared/lib/post-process.ts

@@ -1,14 +1,10 @@
-import { escapeStringRegexp } from './escape-regexp'
 import { parse, HTMLElement } from 'next/dist/compiled/node-html-parser'
 import { OPTIMIZED_FONT_PROVIDERS } from './constants'
 
 // const MIDDLEWARE_TIME_BUDGET = parseInt(process.env.__POST_PROCESS_MIDDLEWARE_TIME_BUDGET || '', 10) || 10
-const MAXIMUM_IMAGE_PRELOADS = 2
-const IMAGE_PRELOAD_SIZE_THRESHOLD = 2500
 
 type postProcessOptions = {
   optimizeFonts: boolean
-  optimizeImages: boolean
 }
 
 type renderOptions = {
@@ -169,103 +165,6 @@ class FontOptimizerMiddleware implements PostProcessMiddleware {
   }
 }
 
-class ImageOptimizerMiddleware implements PostProcessMiddleware {
-  inspect(originalDom: HTMLElement) {
-    const imgPreloads = []
-    const imgElements = originalDom.querySelectorAll('img')
-    let eligibleImages: Array<HTMLElement> = []
-    for (let i = 0; i < imgElements.length; i++) {
-      if (isImgEligible(imgElements[i])) {
-        eligibleImages.push(imgElements[i])
-      }
-      if (eligibleImages.length >= MAXIMUM_IMAGE_PRELOADS) {
-        break
-      }
-    }
-
-    for (const imgEl of eligibleImages) {
-      const src = imgEl.getAttribute('src')
-      if (src) {
-        imgPreloads.push(src)
-      }
-    }
-
-    return imgPreloads
-  }
-  mutate = async (markup: string, imgPreloads: string[]) => {
-    let result = markup
-    let imagePreloadTags = imgPreloads
-      .filter((imgHref) => !preloadTagAlreadyExists(markup, imgHref))
-      .reduce(
-        (acc, imgHref) =>
-          acc + `<link rel="preload" href="${imgHref}" as="image"/>`,
-        ''
-      )
-    return result.replace('<meta name="next-image-preload"/>', imagePreloadTags)
-  }
-}
-
-function isImgEligible(imgElement: HTMLElement): boolean {
-  let imgSrc = imgElement.getAttribute('src')
-  return (
-    !!imgSrc &&
-    sourceIsSupportedType(imgSrc) &&
-    imageIsNotTooSmall(imgElement) &&
-    imageIsNotHidden(imgElement)
-  )
-}
-
-function preloadTagAlreadyExists(html: string, href: string) {
-  const escapedHref = escapeStringRegexp(href)
-  const regex = new RegExp(`<link[^>]*href[^>]*${escapedHref}`)
-  return html.match(regex)
-}
-
-function imageIsNotTooSmall(imgElement: HTMLElement): boolean {
-  // Skip images without both height and width--we don't know enough to say if
-  // they are too small
-  if (
-    !(imgElement.hasAttribute('height') && imgElement.hasAttribute('width'))
-  ) {
-    return true
-  }
-  try {
-    const heightAttr = imgElement.getAttribute('height')
-    const widthAttr = imgElement.getAttribute('width')
-    if (!heightAttr || !widthAttr) {
-      return true
-    }
-
-    if (
-      parseInt(heightAttr) * parseInt(widthAttr) <=
-      IMAGE_PRELOAD_SIZE_THRESHOLD
-    ) {
-      return false
-    }
-  } catch (err) {
-    return true
-  }
-  return true
-}
-
-// Traverse up the dom from each image to see if it or any of it's
-// ancestors have the hidden attribute.
-function imageIsNotHidden(imgElement: HTMLElement): boolean {
-  let activeElement = imgElement
-  while (activeElement.parentNode) {
-    if (activeElement.hasAttribute('hidden')) {
-      return false
-    }
-    activeElement = activeElement.parentNode as HTMLElement
-  }
-  return true
-}
-
-// Currently only filters out svg images--could be made more specific in the future.
-function sourceIsSupportedType(imgSrc: string): boolean {
-  return !imgSrc.includes('.svg')
-}
-
 // Initialization
 registerPostProcessor(
   'Inline-Fonts',
@@ -275,11 +174,4 @@ registerPostProcessor(
   (options) => options.optimizeFonts || process.env.__NEXT_OPTIMIZE_FONTS
 )
 
-registerPostProcessor(
-  'Preload Images',
-  new ImageOptimizerMiddleware(),
-  // @ts-ignore
-  (options) => options.optimizeImages || process.env.__NEXT_OPTIMIZE_IMAGES
-)
-
 export default processHTML

packages/next/shared/lib/utils.ts

@@ -224,7 +224,6 @@ export type HtmlProps = {
   crossOrigin?: string
   optimizeCss?: boolean
   optimizeFonts?: boolean
-  optimizeImages?: boolean
   runtime?: 'edge' | 'nodejs'
 }