deprecate writeSync

src/browser/TestUtils.test.ts

@@ -21,6 +21,9 @@ export class TestTerminal extends Terminal {
   public get curAttrData(): IAttributeData { return (this as any)._inputHandler._curAttrData; }
   public keyDown(ev: any): boolean | undefined { return this._keyDown(ev); }
   public keyPress(ev: any): boolean { return this._keyPress(ev); }
+  public writeP(data: string | Uint8Array): Promise<void> {
+    return new Promise(r => this.write(data, r));
+  }
 }
 
 export class MockTerminal implements ITerminal {

src/common/CoreTerminal.ts

@@ -125,7 +125,17 @@ export abstract class CoreTerminal extends Disposable implements ICoreTerminal {
     this._writeBuffer.write(data, callback);
   }
 
+  /**
+   * Write data to terminal synchonously.
+   * 
+   * This method is unreliable with async parser handlers, thus should not
+   * be used anymore. If you need blocking semantics on data input consider
+   * `write` with a callback instead.
+   * 
+   * @deprecated Unreliable, will be removed soon.
+   */
   public writeSync(data: string | Uint8Array): void {
+    console.error('writeSync is unreliable and will be removed soon.');
     this._writeBuffer.writeSync(data);
   }