@Override
    public List<ValidationEvent> evaluate(Differences differences) {
        return differences.changedMetadata()
                .map(metadata -> ValidationEvent.builder()
                        .id(getEventId())
                        .severity(Severity.WARNING)
                        .sourceLocation(metadata)
                        .message(String.format(
                                "Metadata key `%s` was changed from %s to %s",
                                metadata.getKey(),
                                Node.prettyPrintJson(metadata.getOldValue()),
                                Node.prettyPrintJson(metadata.getNewValue())))
                        .build())
                .collect(Collectors.toList());
    }
Creates a WARNING event when metadata is changed.
smithy-diff/src/main/java/software/amazon/smithy/diff/evaluators/ChangedMetadata.java