next.js/packages/next/src/build/webpack/plugins/next-drop-client-page-plugin.ts

import type { webpack } from 'next/dist/compiled/webpack/webpack'
import { STRING_LITERAL_DROP_BUNDLE } from '../../../shared/lib/constants'

export const ampFirstEntryNamesMap: WeakMap<webpack.Compilation, string[]> =
  new WeakMap()

const PLUGIN_NAME = 'DropAmpFirstPagesPlugin'

// Prevents outputting client pages when they are not needed
export class DropClientPage implements webpack.WebpackPluginInstance {
  ampPages = new Set()

  apply(compiler: webpack.Compiler) {
    compiler.hooks.compilation.tap(
      PLUGIN_NAME,
      (compilation: any, { normalModuleFactory }: any) => {
        // Recursively look up the issuer till it ends up at the root
        function findEntryModule(mod: any): webpack.Module | null {
          const queue = new Set([mod])
          for (const module of queue) {
            const incomingConnections =
              compilation.moduleGraph.getIncomingConnections(module)

            for (const incomingConnection of incomingConnections) {
              if (!incomingConnection.originModule) return module
              queue.add(incomingConnection.originModule)
            }
          }

          return null
        }

        function handler(parser: any) {
          function markAsAmpFirst() {
            const entryModule = findEntryModule(parser.state.module)

            if (!entryModule) {
              return
            }

            // @ts-ignore buildInfo exists on Module
            entryModule.buildInfo.NEXT_ampFirst = true
          }

          parser.hooks.preDeclarator.tap(PLUGIN_NAME, (declarator: any) => {
            if (declarator?.id?.name === STRING_LITERAL_DROP_BUNDLE) {
              markAsAmpFirst()
            }
          })
        }

        normalModuleFactory.hooks.parser
          .for('javascript/auto')
          .tap(PLUGIN_NAME, handler)

        normalModuleFactory.hooks.parser
          .for('javascript/esm')
          .tap(PLUGIN_NAME, handler)

        normalModuleFactory.hooks.parser
          .for('javascript/dynamic')
          .tap(PLUGIN_NAME, handler)

        if (!ampFirstEntryNamesMap.has(compilation)) {
          ampFirstEntryNamesMap.set(compilation, [])
        }

        const ampFirstEntryNamesItem = ampFirstEntryNamesMap.get(
          compilation
        ) as string[]

        compilation.hooks.seal.tap(PLUGIN_NAME, () => {
          for (const [name, entryData] of compilation.entries) {
            for (const dependency of entryData.dependencies) {
              const module = compilation.moduleGraph.getModule(dependency)
              if (module?.buildInfo?.NEXT_ampFirst) {
                ampFirstEntryNamesItem.push(name)
                compilation.entries.delete(name)
              }
            }
          }
        })
      }
    )
  }
}