Fix debug widget dropdown is changed unnecessarily when continuing/stepping

fixes #16761

src/vs/base/browser/ui/actionbar/actionbar.ts

@@ -705,7 +705,7 @@ export class SelectActionItem extends BaseActionItem {
 		this.registerListeners();
 	}
 
-	public setOptions(options: string[], selected: number): void {
+	public setOptions(options: string[], selected?: number): void {
 		this.selectBox.setOptions(options, selected);
 	}
 

src/vs/base/browser/ui/selectBox/selectBox.ts

@@ -9,6 +9,7 @@ import { IDisposable, dispose } from 'vs/base/common/lifecycle';
 import Event, { Emitter } from 'vs/base/common/event';
 import { Widget } from 'vs/base/browser/ui/widget';
 import * as dom from 'vs/base/browser/dom';
+import * as arrays from 'vs/base/common/arrays';
 
 export class SelectBox extends Widget {
 
@@ -40,13 +41,15 @@ export class SelectBox extends Widget {
 		return this._onDidSelect.event;
 	}
 
-	public setOptions(options: string[], selected: number): void {
-		this.options = options;
+	public setOptions(options: string[], selected?: number): void {
+		if (!arrays.equals(this.options, options)) {
+			this.options = options;
 
-		this.selectElement.options.length = 0;
-		this.options.forEach((option) => {
-			this.selectElement.add(this.createOption(option));
-		});
+			this.selectElement.options.length = 0;
+			this.options.forEach((option) => {
+				this.selectElement.add(this.createOption(option));
+			});
+		}
 		this.select(selected);
 	}
 

src/vs/workbench/parts/debug/browser/debugActionItems.ts

@@ -130,8 +130,14 @@ export class FocusProcessActionItem extends SelectActionItem {
 
 		this.debugService.getViewModel().onDidFocusStackFrame(() => {
 			const process = this.debugService.getViewModel().focusedProcess;
-			const names = this.debugService.getModel().getProcesses().map(p => p.name);
-			this.setOptions(names, process ? names.indexOf(process.name) : 0);
+			if (process) {
+				const names = this.debugService.getModel().getProcesses().map(p => p.name);
+				this.select(names.indexOf(process.name));
+			}
+		});
+
+		this.debugService.getModel().onDidChangeCallStack(() => {
+			this.setOptions(this.debugService.getModel().getProcesses().map(p => p.name));
 		});
 	}
 }