typescript-eslint · nayounsang · Jun 21, 2025 · Jun 21, 2025 · Jun 30, 2025 · Jul 1, 2025
diff --git a/packages/typescript-estree/src/parseSettings/inferSingleRun.ts b/packages/typescript-estree/src/parseSettings/inferSingleRun.ts
@@ -18,13 +18,13 @@ export function inferSingleRun(options: TSESTreeOptions | undefined): boolean {
   // https://github.com/typescript-eslint/typescript-eslint/issues/9504
   // There's no support (yet?) for extraFileExtensions in single-run hosts.
   // Only watch program hosts and project service can support that.
-  if (options?.extraFileExtensions?.length) {
+  if (options?.extraFileExtensions?.length && !options.projectService) {
     return false;
   }
 
   if (
     // single-run implies type-aware linting - no projects means we can't be in single-run mode
-    options?.project == null ||
+    (options?.project == null && !options?.projectService) ||
     // programs passed via options means the user should be managing the programs, so we shouldn't
     // be creating our own single-run programs accidentally
     options.programs != null

diff --git a/packages/typescript-estree/tests/lib/inferSingleRun.test.ts b/packages/typescript-estree/tests/lib/inferSingleRun.test.ts
@@ -143,6 +143,17 @@ describe(inferSingleRun, () => {
     expect(actual).toBe(false);
   });
 
+  it('returns true when singleRun can be inferred options.extraFileExtensions contains entires with projectService', () => {
+    vi.stubEnv('CI', 'true');
+
+    const actual = inferSingleRun({
+      extraFileExtensions: ['.vue'],
+      projectService: true,
+    });
+
+    expect(actual).toBe(true);
+  });
+
   it('returns false when there is no way to infer singleRun', () => {
     const actual = inferSingleRun({
       programs: null,
@@ -157,4 +168,11 @@ describe(inferSingleRun, () => {
 
     expect(actual).toBe(false);
   });
+
+  it('returns true for project service in single run', () => {
+    vi.stubEnv('CI', 'true');
+    const actual = inferSingleRun({ projectService: true });
+
+    expect(actual).toBe(true);
+  });
 });
diff --git a/packages/typescript-estree/tests/lib/semanticInfo-singleRun.test.ts b/packages/typescript-estree/tests/lib/semanticInfo-singleRun.test.ts
@@ -260,4 +260,17 @@ describe('semanticInfo - singleRun', () => {
       );
     },
   );
+
+  it('should create program when extraFileExtensions is provided in projectService and singleRun mode', () => {
+    vi.stubEnv('TSESTREE_SINGLE_RUN', 'true');
+
+    const resultProgram = parseAndGenerateServices(code, {
+      ...options,
+      extraFileExtensions: ['.vue'],
+      project: null,
+      projectService: true,
+    }).services.program;
+
+    expect(resultProgram).not.toBeNull();
+  });
 });