Discussion: Consider adding a buildStep.markNonHermetic() api for targeting builders that can't easily be written with good behavior

[natebosch]

If we end up with some build behavior which is annoying or impossible to base only on buildStep.readAs* inputs it might be nice to have some API to indicate that a particular builder is non hermetic and therefore must always be run on every build.

We would either make this a setting in the builder definition (and always run the builder), or give an API to mark a build step as non-hermetic dynamically so builder authors may be able to do some hermetic work and make a decision if further non-hermetic work is necessary.

[jakemac53]

Just throwing out random ideas here, but what if we exposed an api where the builder was allowed to return some sort of state object, which was required to be serializable and comparable, and we would use that to determine if we need to re-run the builder or not.

We would have to call this api on every build for sure, but I think in most scenarios this could be just once per builder, not per builder+input combo?

[natebosch]

Closing in favor of #967