src/vs/workbench/api/common/extHostTypes.ts/Diagnostic/constructor
class Diagnostic:	constructor(range: Range, message: string, severity: DiagnosticSeverity = DiagnosticSeverity.Error) {
		if (!Range.isRange(range)) {
			throw new TypeError('range must be set');
		}
		if (!message) {
			throw new TypeError('message must be set');
		}
		this.range = range;
		this.message = message;
		this.severity = severity;
	}