feat: implement JIT component experiment

.circleci/workflows.yml

@@ -32,7 +32,7 @@ mainBuildFilters: &mainBuildFilters
         - 'update-v8-snapshot-cache-on-develop'
         - 'jquery-patch-remove-unload'
         - 'publish-binary'
-        - 'chore/use_build_docker_file_for_centos7'
+        - 'feat/experimentalJustInTimeCompile'
 
 # usually we don't build Mac app - it takes a long time
 # but sometimes we want to really confirm we are doing the right thing
@@ -43,7 +43,7 @@ macWorkflowFilters: &darwin-workflow-filters
     - equal: [ develop, << pipeline.git.branch >> ]
     # use the following branch as well to ensure that v8 snapshot cache updates are fully tested
     - equal: [ 'update-v8-snapshot-cache-on-develop', << pipeline.git.branch >> ]
-    - equal: [ 'fix/webpack-batteries-included-for-yarn-pnp', << pipeline.git.branch >> ]
+    - equal: [ 'feat/experimentalJustInTimeCompile', << pipeline.git.branch >> ]
     - matches:
         pattern: /^release\/\d+\.\d+\.\d+$/
         value: << pipeline.git.branch >>
@@ -54,8 +54,7 @@ linuxArm64WorkflowFilters: &linux-arm64-workflow-filters
     - equal: [ develop, << pipeline.git.branch >> ]
     # use the following branch as well to ensure that v8 snapshot cache updates are fully tested
     - equal: [ 'update-v8-snapshot-cache-on-develop', << pipeline.git.branch >> ]
-    - equal: [ 'chore/use_build_docker_file_for_centos7', << pipeline.git.branch >> ]
-    - equal: [ 'jquery-patch-remove-unload', << pipeline.git.branch >> ]
+    - equal: [ 'feat/experimentalJustInTimeCompile', << pipeline.git.branch >> ]
     - matches:
         pattern: /^release\/\d+\.\d+\.\d+$/
         value: << pipeline.git.branch >>
@@ -78,7 +77,7 @@ windowsWorkflowFilters: &windows-workflow-filters
     - equal: [ develop, << pipeline.git.branch >> ]
     # use the following branch as well to ensure that v8 snapshot cache updates are fully tested
     - equal: [ 'update-v8-snapshot-cache-on-develop', << pipeline.git.branch >> ]
-    - equal: [ 'fix/webpack-batteries-included-for-yarn-pnp', << pipeline.git.branch >> ]
+    - equal: [ 'feat/experimentalJustInTimeCompile', << pipeline.git.branch >> ]
     - matches:
         pattern: /^release\/\d+\.\d+\.\d+$/
         value: << pipeline.git.branch >>
@@ -154,7 +153,7 @@ commands:
           name: Set environment variable to determine whether or not to persist artifacts
           command: |
             echo "Setting SHOULD_PERSIST_ARTIFACTS variable"
-            echo 'if ! [[ "$CIRCLE_BRANCH" != "develop" && "$CIRCLE_BRANCH" != "release/"* && "$CIRCLE_BRANCH" != "chore/use_build_docker_file_for_centos7" ]]; then
+            echo 'if ! [[ "$CIRCLE_BRANCH" != "develop" && "$CIRCLE_BRANCH" != "release/"* && "$CIRCLE_BRANCH" != "feat/experimentalJustInTimeCompile" ]]; then
                 export SHOULD_PERSIST_ARTIFACTS=true
             fi' >> "$BASH_ENV"
   # You must run `setup_should_persist_artifacts` command and be using bash before running this command

cli/CHANGELOG.md

@@ -1,11 +1,17 @@
 <!-- See the ../guides/writing-the-cypress-changelog.md for details on writing the changelog. -->
-## 13.13.4
+## 13.14.0
 
 _Released 8/27/2024 (PENDING)_
 
 **Performance:**
 
-- Fixed a potential memory leak in the Cypress server when re-connecting to an unintentionally disconnected CDP connection. Fixes [#29744](https://github.com/cypress-io/cypress/issues/29744). Addressed in [#29988](https://github.com/cypress-io/cypress/pull/29988)
+- Fixed a potential memory leak in the Cypress server when re-connecting to an unintentionally disconnected CDP connection. Fixes [#29744](https://github.com/cypress-io/cypress/issues/29744). Addressed in [#29988](https://github.com/cypress-io/cypress/pull/29988).
+
+**Features:**
+
+- Added new
+  [`experimentalJustInTimeCompile`](/guides/references/experiments#Configuration)
+  configuration option for component testing. This option will only compile resources directly related to your spec, compiling them 'just-in-time' before spec execution. This should result in improved memory management and performance for component tests in `cypress open` and `cypress run` modes, in particular for large component testing suites. [`experimentalJustInTimeCompile`](/guides/references/experiments#Configuration) is currently supported for [`webpack`](https://www.npmjs.com/package/webpack) and [`vite`](https://www.npmjs.com/package/vite). Addresses [#29244](https://github.com/cypress-io/cypress/issues/29244).
 
 **Dependency Updates:**
 

cli/types/cypress.d.ts

@@ -3124,6 +3124,14 @@ declare namespace Cypress {
      * @default null
      */
     experimentalSkipDomainInjection: string[] | null
+    /**
+     * Allows for just-in-time compiling of a component test, which will only compile assets related to the component.
+     * This results in a smaller bundle under test, reducing resource constraints on a given machine. This option is recommended
+     * for users with large component testing projects and those who are running into webpack 'chunk load error' issues.
+     * Supported for vite and webpack. For component testing only.
+     * @see https://on.cypress.io/experiments#Configuration
+     */
+    experimentalJustInTimeCompile: boolean
     /**
      * Enables AST-based JS/HTML rewriting. This may fix issues caused by the existing regex-based JS/HTML replacement algorithm.
      * @default false

npm/vite-dev-server/src/devServer.ts

@@ -50,7 +50,12 @@ export async function devServer (config: ViteDevServerConfig): Promise<Cypress.R
     port,
     // Close is for unit testing only. We kill this child process which will handle the closing of the server
     close (cb) {
-      return server.close().then(() => cb?.()).catch(cb)
+      debug('closing dev server')
+
+      return server.close().then(() => {
+        debug('closed dev server')
+        cb?.()
+      }).catch(cb)
     },
   }
 }

npm/vite-dev-server/src/plugins/cypress.ts

@@ -43,6 +43,7 @@ export const Cypress = (
   let loader = fs.readFileSync(INIT_FILEPATH, 'utf8')
 
   devServerEvents.on('dev-server:specs:changed', (specs: Spec[]) => {
+    debug(`dev-server:secs:changed: ${specs.map((spec) => spec.relative)}`)
     specsPathsSet = getSpecsPathsSet(specs)
   })
 

npm/vite-dev-server/src/resolveConfig.ts

@@ -65,6 +65,7 @@ export const createViteDevServerConfig = async (config: ViteDevServerConfig, vit
 function makeCypressViteConfig (config: ViteDevServerConfig, vite: Vite): InlineConfig | InlineConfig {
   const {
     cypressConfig: {
+      experimentalJustInTimeCompile,
       port,
       projectRoot,
       devServerPublicPathRoute,
@@ -128,7 +129,8 @@ function makeCypressViteConfig (config: ViteDevServerConfig, vite: Vite): Inline
       port: vitePort,
       host: '127.0.0.1',
       // Disable file watching and HMR when executing tests in `run` mode
-      ...(isTextTerminal
+      // if experimentalJustInTimeCompile is configured, we need to watch for file changes as the spec entries are going to be updated per test in run mode
+      ...(isTextTerminal && !experimentalJustInTimeCompile
         ? { watch: { ignored: '**/*' }, hmr: false }
         : {}),
     },

npm/vite-dev-server/test/resolveConfig.spec.ts

@@ -109,5 +109,40 @@ describe('resolveConfig', function () {
         expect(viteConfig.server?.hmr).to.be.undefined
       })
     })
+
+    describe('experimentalJustInTimeCompile', () => {
+      let viteDevServerConfig: ViteDevServerConfig
+
+      beforeEach(async () => {
+        const projectRoot = await scaffoldSystemTestProject(`vite${version}-inspect`)
+
+        viteDevServerConfig = getViteDevServerConfig(projectRoot)
+        viteDevServerConfig.cypressConfig.experimentalJustInTimeCompile = true
+      })
+
+      describe('open mode', () => {
+        beforeEach(() => {
+          viteDevServerConfig.cypressConfig.isTextTerminal = false
+        })
+
+        it('enables hmr and watching', async () => {
+          const viteConfig = await createViteDevServerConfig(viteDevServerConfig, discoveredVite)
+
+          expect(viteConfig.server.watch).to.be.undefined
+        })
+      })
+
+      describe('run mode', () => {
+        beforeEach(() => {
+          viteDevServerConfig.cypressConfig.isTextTerminal = true
+        })
+
+        it('enables hmr and watching', async () => {
+          const viteConfig = await createViteDevServerConfig(viteDevServerConfig, discoveredVite)
+
+          expect(viteConfig.server.watch).to.be.undefined
+        })
+      })
+    })
   })
 })

npm/webpack-dev-server/src/devServer.ts

@@ -97,7 +97,7 @@ export function devServer (devServerConfig: WebpackDevServerConfig): Promise<Cyp
         return reject(new Error(`Expected port ${result.server.options.port} to be a number`))
       }
 
-      debug('Component testing webpack server 4 started on port %s', result.server.options.port)
+      debug(`Component testing webpack server ${result.version} started on port %s`, result.server.options.port)
 
       resolve({
         port: result.server.options.port as number,

npm/webpack-dev-server/src/makeDefaultWebpackConfig.ts

@@ -17,6 +17,7 @@ export function makeCypressWebpackConfig (
   const {
     devServerConfig: {
       cypressConfig: {
+        experimentalJustInTimeCompile,
         port,
         projectRoot,
         devServerPublicPathRoute,
@@ -98,7 +99,8 @@ export function makeCypressWebpackConfig (
     devtool: 'inline-source-map',
   } as any
 
-  if (isRunMode) {
+  // if experimentalJustInTimeCompile is configured, we need to watch for file changes as the spec entries are going to be updated per test
+  if (isRunMode && !experimentalJustInTimeCompile) {
     // Disable file watching when executing tests in `run` mode
     finalConfig.watchOptions = {
       ignored: '**/*',

npm/webpack-dev-server/test/makeWebpackConfig.spec.ts

@@ -437,4 +437,68 @@ describe('makeWebpackConfig', () => {
       })
     })
   })
+
+  describe('experimentalJustInTimeCompile', () => {
+    let devServerConfig: WebpackDevServerConfig
+
+    const WEBPACK_MATRIX: {
+      webpack: 4 | 5
+      wds: 3 | 4 | 5
+    }[] = [
+      {
+        webpack: 4,
+        wds: 3,
+      },
+      {
+        webpack: 4,
+        wds: 4,
+      },
+      {
+        webpack: 5,
+        wds: 4,
+      },
+      {
+        webpack: 5,
+        wds: 5,
+      },
+    ]
+
+    beforeEach(() => {
+      devServerConfig = {
+        specs: [],
+        cypressConfig: {
+          projectRoot: '.',
+          devServerPublicPathRoute: '/test-public-path',
+          experimentalJustInTimeCompile: true,
+          baseUrl: null,
+        } as Cypress.PluginConfigOptions,
+        webpackConfig: {
+          entry: { main: 'src/index.js' },
+        },
+        devServerEvents: new EventEmitter(),
+      }
+    })
+
+    WEBPACK_MATRIX.forEach(({ webpack, wds }) => {
+      describe(`webpack: v${webpack} with webpack-dev-server v${wds}`, () => {
+        describe('run mode', () => {
+          beforeEach(() => {
+            devServerConfig.cypressConfig.isTextTerminal = true
+          })
+
+          it('enables watching', async () => {
+            const actual = await makeWebpackConfig({
+              devServerConfig,
+              sourceWebpackModulesResult: createModuleMatrixResult({
+                webpack,
+                webpackDevServer: wds,
+              }),
+            })
+
+            expect(actual.watchOptions?.ignored).to.be.undefined
+          })
+        })
+      })
+    })
+  })
 })

packages/app/cypress/e2e/runner/runner-ct.experimentalJustInTimeCompile.cy.ts

@@ -0,0 +1,42 @@
+import type { fixtureDirs } from '@tooling/system-tests'
+
+type ProjectDirs = typeof fixtureDirs
+
+const EXPERIMENTAL_JIT_DIR: ProjectDirs[number] = 'experimental-JIT'
+
+const PROJECTS: {bundler: 'vite' | 'webpack'}[] = [
+  { bundler: 'vite' },
+  { bundler: 'webpack' },
+]
+
+for (const { bundler } of PROJECTS) {
+  const PROJECT_NAME = `${EXPERIMENTAL_JIT_DIR}/${bundler}`
+
+  describe(`CT experimentalJustInTimeCompile: ${bundler}`, { viewportWidth: 1500, defaultCommandTimeout: 30000 }, () => {
+    const visitComponentSpecAndVerifyPass = (specNumber: number) => {
+      cy.contains(`Component-${specNumber}.cy.jsx`).click()
+      cy.waitForSpecToFinish(undefined)
+      cy.get('[aria-label="Stats"] .passed > .num').should('contain', '1')
+      cy.get('[aria-label="Stats"] .failed > .num').should('contain', '--')
+    }
+
+    beforeEach(() => {
+      // @ts-expect-error
+      cy.scaffoldProject(PROJECT_NAME)
+      cy.findBrowsers()
+    }),
+
+    it(`can run multiple CT tests without interruption`, () => {
+      // @ts-expect-error
+      cy.openProject(PROJECT_NAME, ['--component'])
+      cy.startAppServer('component')
+      cy.visitApp()
+      cy.specsPageIsVisible()
+      visitComponentSpecAndVerifyPass(2)
+      cy.get('[data-cy="sidebar-link-specs-page"]').click()
+      visitComponentSpecAndVerifyPass(1)
+      cy.get('[data-cy="sidebar-link-specs-page"]').click()
+      visitComponentSpecAndVerifyPass(3)
+    })
+  })
+}

packages/app/src/runner/event-manager.ts

@@ -40,10 +40,10 @@ interface AddGlobalListenerOptions {
 }
 
 const driverToLocalAndReporterEvents = 'run:start run:end'.split(' ')
-const driverToSocketEvents = 'backend:request automation:request mocha recorder:frame'.split(' ')
+const driverToSocketEvents = 'backend:request automation:request mocha recorder:frame dev-server:on-spec-update'.split(' ')
 const driverToLocalEvents = 'viewport:changed config stop url:changed page:loading visit:failed visit:blank cypress:in:cypress:runner:event'.split(' ')
 const socketRerunEvents = 'runner:restart watched:file:changed'.split(' ')
-const socketToDriverEvents = 'net:stubbing:event request:event script:error cross:origin:cookies'.split(' ')
+const socketToDriverEvents = 'net:stubbing:event request:event script:error cross:origin:cookies dev-server:on-spec-updated'.split(' ')
 const localToReporterEvents = 'reporter:log:add reporter:log:state:changed reporter:log:remove'.split(' ')
 
 /**

packages/app/src/runner/index.ts

@@ -392,6 +392,18 @@ async function initialize () {
   window.UnifiedRunner.MobX.runInAction(() => setupRunner())
 }
 
+async function updateDevServerWithSpec (spec: SpecFile) {
+  return new Promise<void>((resolve, _reject) => {
+    // currently, we don't have criteria to reject the promise
+    // as the dev-server can take a long time to compile, which is variable per user.
+    Cypress.once('dev-server:on-spec-updated', () => {
+      resolve()
+    })
+
+    Cypress.emit('dev-server:on-spec-update', spec)
+  })
+}
+
 /**
  * This wraps all of the required interactions to run a spec.
  * Here are the things that happen:
@@ -437,6 +449,13 @@ async function executeSpec (spec: SpecFile, isRerun: boolean = false) {
   }
 
   if (window.__CYPRESS_TESTING_TYPE__ === 'component') {
+    if (config.experimentalJustInTimeCompile && !config.isTextTerminal) {
+      // If running with experimentalJustInTimeCompile enabled and in open mode,
+      // send a signal to the dev server to load the spec before running
+      // since the spec and related resources are not yet compiled.
+      await updateDevServerWithSpec(spec)
+    }
+
     return runSpecCT(config, spec)
   }
 

packages/config/__snapshots__/index.spec.ts.js

@@ -40,6 +40,7 @@ exports['config/src/index .getDefaultValues returns list of public config keys 1
   'experimentalMemoryManagement': false,
   'experimentalModifyObstructiveThirdPartyCode': false,
   'experimentalSkipDomainInjection': null,
+  'experimentalJustInTimeCompile': false,
   'experimentalOriginDependencies': false,
   'experimentalSourceRewriting': false,
   'experimentalSingleTabRunMode': false,
@@ -130,6 +131,7 @@ exports['config/src/index .getDefaultValues returns list of public config keys f
   'experimentalMemoryManagement': false,
   'experimentalModifyObstructiveThirdPartyCode': false,
   'experimentalSkipDomainInjection': null,
+  'experimentalJustInTimeCompile': false,
   'experimentalOriginDependencies': false,
   'experimentalSourceRewriting': false,
   'experimentalSingleTabRunMode': false,
@@ -216,6 +218,7 @@ exports['config/src/index .getPublicConfigKeys returns list of public config key
   'experimentalMemoryManagement',
   'experimentalModifyObstructiveThirdPartyCode',
   'experimentalSkipDomainInjection',
+  'experimentalJustInTimeCompile',
   'experimentalOriginDependencies',
   'experimentalSourceRewriting',
   'experimentalSingleTabRunMode',