debug: if there is a thread running focusedThread should not be null

fixes #15165

src/vs/workbench/parts/debug/common/debugViewModel.ts

@@ -10,6 +10,7 @@ export class ViewModel implements debug.IViewModel {
 
 	private _focusedStackFrame: debug.IStackFrame;
 	private _focusedProcess: debug.IProcess;
+	private _focusedThread: debug.IThread;
 	private selectedExpression: debug.IExpression;
 	private selectedFunctionBreakpoint: debug.IFunctionBreakpoint;
 	private _onDidFocusStackFrame: Emitter<debug.IStackFrame>;
@@ -38,16 +39,17 @@ export class ViewModel implements debug.IViewModel {
 	}
 
 	public get focusedThread(): debug.IThread {
-		return this._focusedStackFrame ? this._focusedStackFrame.thread : null;
+		return this._focusedThread;
 	}
 
 	public get focusedStackFrame(): debug.IStackFrame {
 		return this._focusedStackFrame;
 	}
 
-	public setFocusedStackFrame(stackFrame: debug.IStackFrame, process: debug.IProcess): void {
+	public setFocusedStackFrame(stackFrame: debug.IStackFrame, thread: debug.IThread, process: debug.IProcess): void {
 		this._focusedStackFrame = stackFrame;
 		this._focusedProcess = process;
+		this._focusedThread = thread;
 		this._onDidFocusStackFrame.fire(stackFrame);
 		this._onDidFocusProcess.fire(process);
 	}

src/vs/workbench/parts/debug/electron-browser/debugService.ts

@@ -445,13 +445,13 @@ export class DebugService implements debug.IDebugService {
 		if (!process) {
 			process = focusedStackFrame ? focusedStackFrame.thread.process : processes.length ? processes[0] : null;
 		}
-		if (process && !focusedStackFrame) {
-			const thread = process.getAllThreads().pop();
-			const callStack = thread ? thread.getCachedCallStack() : null;
+		const thread = focusedStackFrame ? focusedStackFrame.thread : (process ? process.getAllThreads().pop() : null);
+		if (thread && !focusedStackFrame) {
+			const callStack = thread.getCachedCallStack();
 			focusedStackFrame = callStack && callStack.length ? callStack[0] : null;
 		}
 
-		this.viewModel.setFocusedStackFrame(focusedStackFrame, process);
+		this.viewModel.setFocusedStackFrame(focusedStackFrame, thread, process);
 		this._onDidChangeState.fire();
 
 		return this.model.evaluateWatchExpressions(process, focusedStackFrame);
@@ -645,7 +645,7 @@ export class DebugService implements debug.IDebugService {
 				this.viewModel.setMultiProcessView(true);
 			}
 			if (!this.viewModel.focusedProcess) {
-				this.viewModel.setFocusedStackFrame(null, process);
+				this.viewModel.setFocusedStackFrame(null, null, process);
 				this._onDidChangeState.fire();
 			}
 			this.toDisposeOnSessionEnd[session.getId()] = [];

src/vs/workbench/parts/debug/test/common/debugViewModel.test.ts

@@ -26,7 +26,7 @@ suite('Debug - View Model', () => {
 		const process = new Process('mockProcess', mockSession);
 		const thread = new Thread(process, 'myThread', 1);
 		const frame = new StackFrame(thread, 1, null, 'app.js', 1, 1);
-		model.setFocusedStackFrame(frame, process);
+		model.setFocusedStackFrame(frame, thread, process);
 
 		assert.equal(model.focusedStackFrame, frame);
 		assert.equal(model.focusedThread.threadId, 1);