make sure activeParameter isn't larger then aviablable parameters, fixes #4618

extensions/typescript/src/features/signatureHelpProvider.ts

@@ -38,7 +38,15 @@ export default class TypeScriptSignatureHelpProvider implements SignatureHelpPro
 			result.activeSignature = info.selectedItemIndex;
 			result.activeParameter = info.argumentIndex;
 
-			info.items.forEach(item => {
+			if (info.items[info.selectedItemIndex].isVariadic) {
+			}
+
+			info.items.forEach((item, i) => {
+
+				// keep active parameter in bounds
+				if (i === info.selectedItemIndex && item.isVariadic) {
+					result.activeParameter = Math.min(info.argumentIndex, item.parameters.length - 1);
+				}
 
 				let signature = new SignatureInformation('');
 				signature.label += Previewer.plain(item.prefixDisplayParts);