add syncedKeys to proposed API

src/vs/vscode.proposed.d.ts

@@ -2179,4 +2179,22 @@ declare module 'vscode' {
 
 	}
 	//#endregion
+
+	//#region Syncing Extension's Global State https://github.com/microsoft/vscode/issues/95209 @sandy081
+
+	export interface ExtensionContext {
+		readonly syncedGlobalState: SyncedMemento;
+	}
+
+	export interface SyncedMemento extends Memento {
+
+		/**
+		 * List of keys whose values should be synced across devices when extensions synchronization is enabled .
+		 * Set synced keys to an empty array to unset the synced state.
+		 */
+		syncedKeys: ReadonlyArray<string>;
+
+	}
+
+	//#endregion
 }

src/vs/workbench/api/common/extHostExtensionService.ts

@@ -387,6 +387,7 @@ export abstract class AbstractExtHostExtensionService extends Disposable impleme
 			const that = this;
 			return Object.freeze<vscode.ExtensionContext>({
 				globalState,
+				get syncedGlobalState() { checkProposedApiEnabled(extensionDescription); return globalState; },
 				workspaceState,
 				subscriptions: [],
 				get extensionUri() { return extensionDescription.extensionLocation; },

src/vs/workbench/api/common/extHostMemento.ts

@@ -7,9 +7,11 @@ import type * as vscode from 'vscode';
 import { IDisposable } from 'vs/base/common/lifecycle';
 import { ExtHostStorage } from 'vs/workbench/api/common/extHostStorage';
 import { IExtensionDescription } from 'vs/platform/extensions/common/extensions';
+import { checkProposedApiEnabled } from 'vs/workbench/services/extensions/common/extensions';
 
-export class ExtensionMemento implements vscode.Memento {
+export class ExtensionMemento implements vscode.SyncedMemento {
 
+	private readonly _extension: IExtensionDescription;
 	private readonly _id: string;
 	private readonly _version: string;
 	private readonly _shared: boolean;
@@ -19,14 +21,19 @@ export class ExtensionMemento implements vscode.Memento {
 	private _value?: { [n: string]: any; };
 	private readonly _storageListener: IDisposable;
 
-	private _syncKeys: string[] = [];
-	get syncKeys(): ReadonlyArray<string> { return Object.freeze(this._syncKeys); }
-	set syncKeys(syncKeys: ReadonlyArray<string>) {
-		this._syncKeys = [...syncKeys];
-		this._storage.registerExtensionStorageKeysToSync({ id: this._id, version: this._version }, this._syncKeys);
+	private _syncedKeys: string[] = [];
+	get syncedKeys(): ReadonlyArray<string> { return Object.freeze(this._syncedKeys); }
+	set syncedKeys(syncKeys: ReadonlyArray<string>) {
+		checkProposedApiEnabled(this._extension);
+		if (!this._shared) {
+			throw new Error('Only global state is synchronized');
+		}
+		this._syncedKeys = [...syncKeys];
+		this._storage.registerExtensionStorageKeysToSync({ id: this._id, version: this._version }, this._syncedKeys);
 	}
 
 	constructor(extensionDescription: IExtensionDescription, global: boolean, storage: ExtHostStorage) {
+		this._extension = extensionDescription;
 		this._id = extensionDescription.identifier.value;
 		this._version = extensionDescription.version;
 		this._shared = global;