fixes #4608

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

@@ -324,7 +324,12 @@ export class CallStackRenderer implements tree.IRenderer {
 		data.label.textContent = stackFrame.name;
 		data.label.title = stackFrame.name;
 		data.fileName.textContent = getSourceName(stackFrame.source, this.contextService);
-		data.lineNumber.textContent = (stackFrame.source.available && stackFrame.lineNumber !== undefined) ? `${ stackFrame.lineNumber }` : '';
+		if (stackFrame.source.available && stackFrame.lineNumber !== undefined) {
+			data.lineNumber.textContent = `${ stackFrame.lineNumber }`;
+			dom.removeClass(data.lineNumber, 'unavailable');
+		} else {
+			dom.addClass(data.lineNumber, 'unavailable');
+		}
 	}
 
 	public disposeTemplate(tree: tree.ITree, templateId: string, templateData: any): void {

src/vs/workbench/parts/debug/browser/media/debugViewlet.css

@@ -142,6 +142,10 @@
 	float: right;
 }
 
+.debug-viewlet .debug-call-stack .stack-frame > .file > .line-number.unavailable {
+	display: none;
+}
+
 .debug-viewlet .debug-call-stack > .monaco-tree-row:not(.selected) .stack-frame > .file {
 	color: rgba(108, 108, 108, 0.8);
 }

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

@@ -15,6 +15,7 @@ import debug = require('vs/workbench/parts/debug/common/debug');
 import { Source } from 'vs/workbench/parts/debug/common/debugSource';
 
 const MAX_REPL_LENGTH = 10000;
+const UNKNOWN_SOURCE_LABEL = nls.localize('unknownSource', "Unknown Source");
 
 function resolveChildren(debugService: debug.IDebugService, parent: debug.IExpressionContainer): TPromise<Variable[]> {
 	const session = debugService.getActiveSession();
@@ -144,10 +145,10 @@ export class Thread implements debug.IThread {
 			this.stoppedDetails.totalFrames = response.body.totalFrames;
 			return response.body.stackFrames.map((rsf, level) => {
 				if (!rsf) {
-					return new StackFrame(this.threadId, 0, new Source({ name: 'unknown' }, false), nls.localize('unknownStack', "Unknown stack location"), undefined, undefined);
+					return new StackFrame(this.threadId, 0, new Source({ name: UNKNOWN_SOURCE_LABEL }, false), nls.localize('unknownStack', "Unknown stack location"), undefined, undefined);
 				}
 
-				return new StackFrame(this.threadId, rsf.id, rsf.source ? new Source(rsf.source) : new Source({ name: 'unknown' }, false), rsf.name, rsf.line, rsf.column);
+				return new StackFrame(this.threadId, rsf.id, rsf.source ? new Source(rsf.source) : new Source({ name: UNKNOWN_SOURCE_LABEL }, false), rsf.name, rsf.line, rsf.column);
 			});
 		});
 	}