feat: only load chat/notebook/mcp when their service overrides are used

rollup/plugins/feature-isolation-check-plugin.ts

@@ -0,0 +1,92 @@
+import type { Plugin, PluginContext } from 'rollup'
+
+interface FeatureIsolationCheckOptions {
+  /** Matches the modules of the optional features (e.g. chat, notebook, mcp) */
+  featureModules: RegExp
+  /** Matches the entry points that are allowed to load feature modules (their service overrides) */
+  allowedEntries: RegExp
+  /**
+   * Maximum size (in bytes of transformed code) of the feature modules statically reachable from
+   * the other entry points. It covers the known remaining dependencies, and fails the build when a
+   * VSCode update (or a change here) makes more of the features load unconditionally
+   */
+  maxSize: number
+}
+
+/**
+ * Checks that optional features are only loaded by their own service overrides, so that a workbench
+ * without them doesn't load (and bundle) their implementation
+ */
+export default ({
+  featureModules,
+  allowedEntries,
+  maxSize
+}: FeatureIsolationCheckOptions): Plugin => {
+  function getSize(context: PluginContext, id: string) {
+    return context.getModuleInfo(id)?.code?.length ?? 0
+  }
+
+  function collectStaticImports(context: PluginContext, from: string[]) {
+    const seen = new Set<string>(from)
+    const queue = [...from]
+    while (queue.length > 0) {
+      const id = queue.pop()!
+      for (const imported of context.getModuleInfo(id)?.importedIds ?? []) {
+        if (!seen.has(imported)) {
+          seen.add(imported)
+          queue.push(imported)
+        }
+      }
+    }
+    return seen
+  }
+
+  return {
+    name: 'feature-isolation-check',
+    buildEnd(error) {
+      if (error != null) {
+        return
+      }
+      const entries = Array.from(this.getModuleIds()).filter(
+        (id) => this.getModuleInfo(id)!.isEntry && !allowedEntries.test(id)
+      )
+      const reachable = collectStaticImports(this, entries)
+      const reachableFeatureModules = Array.from(reachable).filter((id) => featureModules.test(id))
+      const totalSize = reachableFeatureModules.reduce((acc, id) => acc + getSize(this, id), 0)
+
+      // Where the other modules start depending on the features, and how much each of them loads
+      const crossings = Array.from(reachable)
+        .filter((id) => !featureModules.test(id))
+        .flatMap((importer) =>
+          this.getModuleInfo(importer)!
+            .importedIds.filter((id) => featureModules.test(id))
+            .map((imported) => ({ importer, imported }))
+        )
+        .map(({ importer, imported }) => ({
+          importer,
+          imported,
+          size: Array.from(collectStaticImports(this, [imported]))
+            .filter((id) => featureModules.test(id))
+            .reduce((acc, id) => acc + getSize(this, id), 0)
+        }))
+        .sort((a, b) => b.size - a.size)
+
+      const kb = (size: number) => `${Math.round(size / 1024)}KB`
+      const shorten = (id: string) => id.replace(/^.*?\/(vs|src)\//, '$1/')
+      const report = [
+        `${reachableFeatureModules.length} feature modules (${kb(totalSize)}) are loaded without their service overrides (max ${kb(maxSize)})`,
+        ...crossings
+          .slice(0, 20)
+          .map(
+            ({ importer, imported, size }) =>
+              `  ${kb(size).padStart(7)}  ${shorten(importer)} -> ${shorten(imported)}`
+          )
+      ].join('\n')
+
+      if (totalSize > maxSize) {
+        this.error(report)
+      }
+      this.info(report)
+    }
+  }
+}

rollup/rollup.config.ts

@@ -20,6 +20,7 @@ import {
 import vscodeAssetGlobMetaUrl from './plugins/vscode-asset-glob-meta-url-plugin.js'
 import dynamicImportPolyfillPlugin from './plugins/dynamic-import-polyfill-plugin.js'
 import resolveAssetUrlPlugin from './plugins/resolve-asset-url-plugin.js'
+import featureIsolationCheckPlugin from './plugins/feature-isolation-check-plugin.js'
 import { typeDedupReplaceTransformer } from './tools/typeDedup.js'
 import {
   DIST_DIR_MAIN,
@@ -191,6 +192,15 @@ export default (args: Record<string, string>): rollup.RollupOptions => {
           return undefined
         }
       },
+      featureIsolationCheckPlugin({
+        // Service identifiers (`.service` files) are shared on purpose
+        featureModules: /\/vs\/workbench\/contrib\/(chat|notebook|mcp)\/(?!.*\.service\.js$)/,
+        // Service overrides that build on top of those features
+        allowedEntries:
+          /\/src\/service-override\/(chat|notebook|mcp|interactive|ai|speech|welcome)\.ts$/,
+        // ~910KB with VSCode 1.138: mostly dictation, go to symbol in chat, editor tabs and chat context keys
+        maxSize: 1000 * 1024
+      }),
       configuredSubpackagePlugin(),
       copy({
         hook: 'writeBundle',

scripts/check-unsupported-decorator.ts

@@ -1,11 +1,14 @@
 import { Project } from 'ts-morph'
 
 const project = new Project({ tsConfigFilePath: 'tsconfig.json' })
-const sourceFile = project.getSourceFileOrThrow('src/missing-services.ts')
+const sourceFiles = [
+  'src/missing-services.ts',
+  'src/service-override/tools/missingMainThreadCustomers.ts'
+].map((path) => project.getSourceFileOrThrow(path))
 
 const issues: string[] = []
 
-for (const cls of sourceFile.getClasses()) {
+for (const cls of sourceFiles.flatMap((sourceFile) => sourceFile.getClasses())) {
   for (const prop of cls.getProperties()) {
     const initText = prop.getInitializer()?.getText().trim()
     const usesUnsupported = initText === 'unsupported'
@@ -26,4 +29,4 @@ if (issues.length) {
   console.error(issues.join('\n'))
   process.exit(1)
 }
-console.log('✅ All consistent')
+console.log('✅ All consistent')

src/missing-services.ts

@@ -511,7 +511,7 @@ import {
   getBuiltInExtensionTranslationsUris,
   getExtensionIdProvidingCurrentLocale
 } from './l10n.js'
-import { unsupported } from './tools.js'
+import { Unsupported, unsupported } from './tools.js'
 
 import { NullAgentHostService } from 'vs/platform/agentHost/browser/nullAgentHostService'
 import { NullSSHRemoteAgentHostService } from 'vs/platform/agentHost/browser/nullSshRemoteAgentHostService'
@@ -543,7 +543,7 @@ import { IChatInputNotificationService } from 'vs/workbench/contrib/chat/browser
 import { IChatPhoneInputPresenter } from 'vs/workbench/contrib/chat/browser/widget/input/chatPhoneInputPresenter.service'
 import { IChatImageCarouselService } from 'vs/workbench/contrib/chat/browser/chatImageCarouselService.service.js'
 import { IChatDebugService } from 'vs/workbench/contrib/chat/common/chatDebugService.service.js'
-import { createVSCodeHarnessDescriptor } from 'vs/workbench/contrib/chat/common/customizationHarnessService'
+import type { IHarnessDescriptor } from 'vs/workbench/contrib/chat/common/customizationHarnessService'
 import { ICustomizationHarnessService } from 'vs/workbench/contrib/chat/common/customizationHarnessService.service'
 import type { IEnablementModel } from 'vs/workbench/contrib/chat/common/enablement.js'
 import { IPluginGitService } from 'vs/workbench/contrib/chat/common/plugins/pluginGitService.service.js'
@@ -583,29 +583,6 @@ import { IAgentHostCustomizationService } from 'vs/workbench/contrib/chat/browse
 import { IAgentHostActiveClientService } from 'vs/workbench/contrib/chat/browser/agentSessions/agentHost/agentHostActiveClientService.service'
 import { IGitHubService } from 'vs/platform/github/common/githubService.service.js'
 
-function Unsupported(target: object, propertyKey: string, descriptor?: PropertyDescriptor) {
-  function unsupported() {
-    throw new Error(
-      `Unsupported: ${target.constructor.name}.${propertyKey} is not supported. You are using a feature without registering the corresponding service override.`
-    )
-  }
-  if (descriptor != null) {
-    if (descriptor.value != null) {
-      descriptor.value = unsupported
-    } else if (descriptor.get != null) {
-      descriptor.get = unsupported
-    }
-  } else {
-    Object.defineProperty(target, propertyKey, {
-      get() {
-        unsupported()
-      },
-      set() {},
-      configurable: true,
-      enumerable: true
-    })
-  }
-}
 /**
  * Editor services: all editor service that are not defined in vs/editor/standalone/
  */
@@ -7270,8 +7247,15 @@ class CustomizationHarnessService implements ICustomizationHarnessService {
     URI.parse('chat-session://local/default')
   )
   activeHarness: ICustomizationHarnessService['activeHarness'] = constObservable(SessionType.Local)
-  availableHarnesses: ICustomizationHarnessService['availableHarnesses'] = constObservable([
-    createVSCodeHarnessDescriptor()
+  // Not using `createVSCodeHarnessDescriptor` on purpose: importing it loads most of the chat implementation
+  availableHarnesses: ICustomizationHarnessService['availableHarnesses'] = constObservable<
+    IHarnessDescriptor[]
+  >([
+    {
+      id: SessionType.Local,
+      label: 'Local',
+      icon: Codicon.vm
+    }
   ])
   onDidChangeSlashCommands: ICustomizationHarnessService['onDidChangeSlashCommands'] = Event.None
   onDidChangeCustomAgents: ICustomizationHarnessService['onDidChangeCustomAgents'] = Event.None

src/service-override/chat.ts

@@ -262,6 +262,7 @@ import 'vs/workbench/contrib/chat/browser/agentSessions/experiments/agentSession
 import 'vs/workbench/contrib/chat/browser/aiCustomization/aiCustomizationManagement.contribution'
 import 'vs/workbench/contrib/chat/browser/attachments/chatReferenceAttachmentWidget.contribution'
 import 'vs/workbench/contrib/chat/browser/attachments/transcriptContextAttachmentWidget.contribution'
+import 'vs/workbench/api/browser/extensionHost.chat.contribution'
 
 class DefaultAccountService implements IDefaultAccountService {
   declare _serviceBrand: undefined

src/service-override/extensions.ts

@@ -69,7 +69,8 @@ import {
 } from 'vs/platform/extensionManagement/common/extensionsScannerService.js'
 import * as platform from 'vs/base/common/platform'
 import { getBuiltInExtensionTranslationsUris } from '../l10n.js'
-import 'vs/workbench/api/browser/extensionHost.contribution'
+import 'vs/workbench/api/browser/extensionHost.base.contribution'
+import './tools/missingMainThreadCustomers.js'
 
 export interface WorkerConfig {
   url: string

src/service-override/mcp.ts

@@ -36,6 +36,7 @@ import { IWorkbenchMcpGatewayService } from 'vs/workbench/contrib/mcp/common/mcp
 import { BrowserMcpGatewayService } from 'vs/workbench/contrib/mcp/browser/mcpGatewayService'
 import 'vs/workbench/contrib/mcp/browser/mcp.contribution'
 import 'vs/workbench/contrib/mcp/browser/mcp.view.contribution'
+import 'vs/workbench/api/browser/extensionHost.mcp.contribution'
 
 export default function getServiceOverride(): IEditorOverrideServices {
   return {

src/service-override/notebook.ts

@@ -40,6 +40,7 @@ import { NotebookOutlineEntryFactory } from 'vs/workbench/contrib/notebook/brows
 import { INotebookOutlineEntryFactory } from 'vs/workbench/contrib/notebook/browser/viewModel/notebookOutlineEntryFactory.service'
 import 'vs/workbench/contrib/replNotebook/browser/repl.contribution'
 import 'vs/workbench/contrib/notebook/browser/notebook.contribution'
+import 'vs/workbench/api/browser/extensionHost.notebook.contribution'
 
 export default function getServiceOverride(): IEditorOverrideServices {
   return {