feat(typescript-estree): add EXPERIMENTAL_useProjectService option to use TypeScript project service

.github/workflows/ci.yml

@@ -192,6 +192,38 @@ jobs:
           # Sadly 1 day is the minimum
           retention-days: 1
 
+  unit_tests_tsserver:
+    name: Run Unit Tests with Experimental TSServer
+    needs: [build]
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        package:
+          [
+            'eslint-plugin',
+            'eslint-plugin-internal',
+            'eslint-plugin-tslint',
+            'typescript-estree',
+          ]
+    env:
+      COLLECT_COVERAGE: false
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 2
+      - name: Install
+        uses: ./.github/actions/prepare-install
+        with:
+          node-version: 18
+      - name: Build
+        uses: ./.github/actions/prepare-build
+      - name: Run unit tests for ${{ matrix.package }}
+        run: npx nx test ${{ matrix.package }} --coverage=false
+        env:
+          CI: true
+          TYPESCRIPT_ESLINT_EXPERIMENTAL_TSSERVER: true
+
   website_build:
     name: Build Website
     needs: [install, build]

docs/architecture/TypeScript-ESTree.mdx

@@ -147,6 +147,15 @@ interface ParseAndGenerateServicesOptions extends ParseOptions {
    */
   errorOnTypeScriptSyntacticAndSemanticIssues?: boolean;
 
+  /**
+   * ***EXPERIMENTAL FLAG*** - Use this at your own risk.
+   *
+   * Whether to create a shared TypeScript server to power program creation.
+   *
+   * @see https://github.com/typescript-eslint/typescript-eslint/issues/6575
+   */
+  EXPERIMENTAL_useProjectService?: boolean;
+
   /**
    * ***EXPERIMENTAL FLAG*** - Use this at your own risk.
    *
@@ -155,7 +164,7 @@ interface ParseAndGenerateServicesOptions extends ParseOptions {
    *
    * This flag REQUIRES at least TS v3.9, otherwise it does nothing.
    *
-   * See: https://github.com/typescript-eslint/typescript-eslint/issues/2094
+   * @see https://github.com/typescript-eslint/typescript-eslint/issues/2094
    */
   EXPERIMENTAL_useSourceOfProjectReferenceRedirect?: boolean;
 

packages/types/src/parser-options.ts

@@ -47,6 +47,7 @@ interface ParserOptions {
   debugLevel?: DebugLevel;
   errorOnTypeScriptSyntacticAndSemanticIssues?: boolean;
   errorOnUnknownASTType?: boolean;
+  EXPERIMENTAL_useProjectService?: boolean; // purposely undocumented for now
   EXPERIMENTAL_useSourceOfProjectReferenceRedirect?: boolean; // purposely undocumented for now
   extraFileExtensions?: string[];
   filePath?: string;

packages/typescript-estree/src/create-program/createProjectProgram.ts

@@ -5,7 +5,6 @@ import * as ts from 'typescript';
 import { firstDefined } from '../node-utils';
 import type { ParseSettings } from '../parseSettings';
 import { describeFilePath } from './describeFilePath';
-import { getWatchProgramsForProjects } from './getWatchProgramsForProjects';
 import type { ASTAndDefiniteProgram } from './shared';
 import { getAstFromProgram } from './shared';
 
@@ -28,10 +27,10 @@ const DEFAULT_EXTRA_FILE_EXTENSIONS = [
  */
 function createProjectProgram(
   parseSettings: ParseSettings,
+  programsForProjects: readonly ts.Program[],
 ): ASTAndDefiniteProgram | undefined {
   log('Creating project program for: %s', parseSettings.filePath);
 
-  const programsForProjects = getWatchProgramsForProjects(parseSettings);
   const astAndProgram = firstDefined(programsForProjects, currentProgram =>
     getAstFromProgram(currentProgram, parseSettings),
   );

packages/typescript-estree/src/create-program/createProjectService.ts

@@ -0,0 +1,55 @@
+import * as tsserver from 'typescript/lib/tsserverlibrary';
+
+const doNothing = (): void => {};
+
+const createStubFileWatcher = (): tsserver.FileWatcher => ({
+  close: doNothing,
+});
+
+export function createProjectService(): tsserver.server.ProjectService {
+  // TODO: see getWatchProgramsForProjects
+  // We don't watch the disk, we just refer to these when ESLint calls us
+  // there's a whole separate update pass in maybeInvalidateProgram at the bottom of getWatchProgramsForProjects
+  // (this "goes nuclear on TypeScript")
+  const system: tsserver.server.ServerHost = {
+    ...tsserver.sys,
+    clearImmediate,
+    clearTimeout,
+    setImmediate,
+    setTimeout,
+    watchDirectory: createStubFileWatcher,
+    watchFile: createStubFileWatcher,
+  };
+
+  const projectService = new tsserver.server.ProjectService({
+    host: system,
+    cancellationToken: { isCancellationRequested: (): boolean => false },
+    useSingleInferredProject: false,
+    useInferredProjectPerProjectRoot: false,
+    // TODO: https://github.com/microsoft/TypeScript/issues/53803
+    typingsInstaller: {
+      attach: (): void => {},
+      enqueueInstallTypingsRequest: (): void => {},
+      installPackage: (): Promise<never> => {
+        throw new Error('This should never be called.');
+      },
+      isKnownTypesPackageName: () => false,
+      onProjectClosed: (): void => {},
+      globalTypingsCacheLocation: '',
+    },
+    logger: {
+      close: doNothing,
+      endGroup: doNothing,
+      getLogFileName: () => undefined,
+      hasLevel: () => false,
+      info: doNothing,
+      loggingEnabled: () => false,
+      msg: doNothing,
+      perftrc: doNothing,
+      startGroup: doNothing,
+    },
+    session: undefined,
+  });
+
+  return projectService;
+}

packages/typescript-estree/src/parseSettings/createParseSettings.ts

@@ -1,6 +1,7 @@
 import debug from 'debug';
 import type * as ts from 'typescript';
 
+import { createProjectService } from '../create-program/createProjectService';
 import { ensureAbsolutePath } from '../create-program/shared';
 import type { TSESTreeOptions } from '../parser-options';
 import { isSourceFile } from '../source-files';
@@ -20,6 +21,9 @@ const log = debug(
 
 let TSCONFIG_MATCH_CACHE: ExpiringCache<string, string> | null;
 
+let TSSERVER_PROJECT_SERVICE: ReturnType<typeof createProjectService> | null =
+  null;
+
 export function createParseSettings(
   code: string | ts.SourceFile,
   options: Partial<TSESTreeOptions> = {},
@@ -47,6 +51,11 @@ export function createParseSettings(
         : new Set(),
     errorOnTypeScriptSyntacticAndSemanticIssues: false,
     errorOnUnknownASTType: options.errorOnUnknownASTType === true,
+    EXPERIMENTAL_projectService:
+      options.EXPERIMENTAL_useProjectService === true ||
+      process.env.TYPESCRIPT_ESLINT_EXPERIMENTAL_TSSERVER === 'true'
+        ? (TSSERVER_PROJECT_SERVICE ??= createProjectService())
+        : undefined,
     EXPERIMENTAL_useSourceOfProjectReferenceRedirect:
       options.EXPERIMENTAL_useSourceOfProjectReferenceRedirect === true,
     extraFileExtensions:

packages/typescript-estree/src/parseSettings/index.ts

@@ -1,4 +1,5 @@
 import type * as ts from 'typescript';
+import type * as tsserverlibrary from 'typescript/lib/tsserverlibrary';
 
 import type { CanonicalPath } from '../create-program/shared';
 import type { TSESTree } from '../ts-estree';
@@ -57,6 +58,13 @@ export interface MutableParseSettings {
    */
   errorOnUnknownASTType: boolean;
 
+  /**
+   * Experimental: TypeScript server to power program creation.
+   */
+  EXPERIMENTAL_projectService:
+    | tsserverlibrary.server.ProjectService
+    | undefined;
+
   /**
    * Whether TS should use the source files for referenced projects instead of the compiled .d.ts files.
    *

packages/typescript-estree/src/parser-options.ts

@@ -94,6 +94,15 @@ interface ParseAndGenerateServicesOptions extends ParseOptions {
    */
   errorOnTypeScriptSyntacticAndSemanticIssues?: boolean;
 
+  /**
+   * ***EXPERIMENTAL FLAG*** - Use this at your own risk.
+   *
+   * Whether to create a shared TypeScript server to power program creation.
+   *
+   * @see https://github.com/typescript-eslint/typescript-eslint/issues/6575
+   */
+  EXPERIMENTAL_useProjectService?: boolean;
+
   /**
    * ***EXPERIMENTAL FLAG*** - Use this at your own risk.
    *
@@ -102,7 +111,7 @@ interface ParseAndGenerateServicesOptions extends ParseOptions {
    *
    * This flag REQUIRES at least TS v3.9, otherwise it does nothing.
    *
-   * See: https://github.com/typescript-eslint/typescript-eslint/issues/2094
+   * @see https://github.com/typescript-eslint/typescript-eslint/issues/2094
    */
   EXPERIMENTAL_useSourceOfProjectReferenceRedirect?: boolean;
 

packages/typescript-estree/src/parser.ts

@@ -10,6 +10,7 @@ import {
   createNoProgram,
   createSourceFile,
 } from './create-program/createSourceFile';
+import { getWatchProgramsForProjects } from './create-program/getWatchProgramsForProjects';
 import type { ASTAndProgram, CanonicalPath } from './create-program/shared';
 import {
   createProgramFromConfigFile,
@@ -25,6 +26,7 @@ import type { ParseSettings } from './parseSettings';
 import { createParseSettings } from './parseSettings/createParseSettings';
 import { getFirstSemanticOrSyntacticError } from './semantic-or-syntactic-errors';
 import type { TSESTree } from './ts-estree';
+import { useProgramFromProjectService } from './useProgramFromProjectService';
 
 const log = debug('typescript-eslint:typescript-estree:parser');
 
@@ -57,27 +59,40 @@ function getProgramAndAST(
     }
   }
 
-  if (hasFullTypeInformation) {
-    const fromProjectProgram = createProjectProgram(parseSettings);
-    if (fromProjectProgram) {
-      return fromProjectProgram;
+  // no need to waste time creating a program as the caller didn't want parser services
+  // so we can save time and just create a lonesome source file
+  if (!hasFullTypeInformation) {
+    return createNoProgram(parseSettings);
+  }
+
+  if (parseSettings.EXPERIMENTAL_projectService) {
+    const fromProjectService = useProgramFromProjectService(
+      parseSettings.EXPERIMENTAL_projectService,
+      parseSettings,
+    );
+    if (fromProjectService) {
+      return fromProjectService;
     }
+  }
 
+  const fromProjectProgram = createProjectProgram(
+    parseSettings,
+    getWatchProgramsForProjects(parseSettings),
+  );
+  if (fromProjectProgram) {
+    return fromProjectProgram;
+  }
+
+  // eslint-disable-next-line deprecation/deprecation -- will be cleaned up with the next major
+  if (parseSettings.DEPRECATED__createDefaultProgram) {
     // eslint-disable-next-line deprecation/deprecation -- will be cleaned up with the next major
-    if (parseSettings.DEPRECATED__createDefaultProgram) {
-      // eslint-disable-next-line deprecation/deprecation -- will be cleaned up with the next major
-      const fromDefaultProgram = createDefaultProgram(parseSettings);
-      if (fromDefaultProgram) {
-        return fromDefaultProgram;
-      }
+    const fromDefaultProgram = createDefaultProgram(parseSettings);
+    if (fromDefaultProgram) {
+      return fromDefaultProgram;
     }
-
-    return createIsolatedProgram(parseSettings);
   }
 
-  // no need to waste time creating a program as the caller didn't want parser services
-  // so we can save time and just create a lonesome source file
-  return createNoProgram(parseSettings);
+  return createIsolatedProgram(parseSettings);
 }
 
 interface EmptyObject {}

packages/typescript-estree/src/useProgramFromProjectService.ts

@@ -0,0 +1,34 @@
+import type * as ts from 'typescript';
+import type { server } from 'typescript/lib/tsserverlibrary';
+
+import { createProjectProgram } from './create-program/createProjectProgram';
+import type { ASTAndDefiniteProgram } from './create-program/shared';
+import type { MutableParseSettings } from './parseSettings';
+
+export function useProgramFromProjectService(
+  projectService: server.ProjectService,
+  parseSettings: Readonly<MutableParseSettings>,
+): ASTAndDefiniteProgram | undefined {
+  projectService.setCompilerOptionsForInferredProjects({
+    rootDir: parseSettings.tsconfigRootDir,
+  });
+
+  projectService.openClientFile(
+    parseSettings.filePath,
+    parseSettings.codeFullText,
+    /* scriptKind */ undefined,
+    parseSettings.tsconfigRootDir,
+  );
+
+  const scriptInfo = projectService.getScriptInfo(parseSettings.filePath);
+  const program = projectService
+    .getDefaultProjectForFile(scriptInfo!.fileName, true)!
+    .getLanguageService(/*ensureSynchronized*/ true)
+    .getProgram();
+
+  if (!program) {
+    return undefined;
+  }
+
+  return createProjectProgram(parseSettings, [program as ts.Program]);
+}

packages/website/src/components/linter/config.ts

@@ -13,6 +13,7 @@ export const defaultParseSettings: ParseSettings = {
   DEPRECATED__createDefaultProgram: false,
   errorOnTypeScriptSyntacticAndSemanticIssues: false,
   errorOnUnknownASTType: false,
+  EXPERIMENTAL_projectService: undefined,
   EXPERIMENTAL_useSourceOfProjectReferenceRedirect: false,
   extraFileExtensions: [],
   filePath: '',