src/vs/workbench/api/common/extHostTypes.ts/Diagnostic/isEqual
class Diagnostic:	static isEqual(a: Diagnostic | undefined, b: Diagnostic | undefined): boolean {
		if (a === b) {
			return true;
		}
		if (!a || !b) {
			return false;
		}
		return a.message === b.message
			&& a.severity === b.severity
			&& a.code === b.code
			&& a.severity === b.severity
			&& a.source === b.source
			&& a.range.isEqual(b.range)
			&& equals(a.tags, b.tags)
			&& equals(a.relatedInformation, b.relatedInformation, DiagnosticRelatedInformation.isEqual);
	}