Enable tsserver global operations to be performed on all projects

src/compiler/core.ts

@@ -91,10 +91,10 @@ namespace ts {
         return undefined;
     }
 
-    export function contains<T>(array: T[], value: T): boolean {
+    export function contains<T>(array: T[], value: T, areEqual?: (a: T, b: T) => boolean): boolean {
         if (array) {
             for (const v of array) {
-                if (v === value) {
+                if (areEqual ? areEqual(v, value) : v === value) {
                     return true;
                 }
             }
@@ -156,12 +156,12 @@ namespace ts {
         return array1.concat(array2);
     }
 
-    export function deduplicate<T>(array: T[]): T[] {
+    export function deduplicate<T>(array: T[], areEqual?: (a: T, b: T) => boolean): T[] {
         let result: T[];
         if (array) {
             result = [];
             for (const item of array) {
-                if (!contains(result, item)) {
+                if (!contains(result, item, areEqual)) {
                     result.push(item);
                 }
             }

src/server/editorServices.ts

@@ -498,6 +498,14 @@ namespace ts.server {
         return copiedList;
     }
 
+    /**
+     * This helper funciton processes a list of projects and return the concatenated, sortd and deduplicated output of processing each project.
+     */
+    export function combineProjectOutput<T>(projects: Project[], action: (project: Project) => T[], comparer?: (a: T, b: T) => number, areEqual?: (a: T, b: T) => boolean) {
+        const result = projects.reduce<T[]>((previous, current) => concatenate(previous, action(current)), []).sort(comparer);
+        return projects.length > 1 ? deduplicate(result, areEqual) : result;
+    }
+
     export interface ProjectServiceEventHandler {
         (eventName: string, project: Project, fileName: string): void;
     }