Implement caching for dependency expansion

[Bo98]

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This adds opt-in caching to Dependency.expand and Requirement.expand.

This massively increases the speed of those functions, if a cache key is passed. I've adjusted Formula#rescursive_dependencies and Formula#recursive_requirements to do this if no block is passed.

This massively improves the brew uses runtime from ~40s on Linux to about 6s, with most of that remaining time now being the actual Formula.to_a file loading.

Care is needed when choosing a cache key - the block is not re-evaulated on cache hits and so the cache key should be constructed depending on what variables might require rerunning the block.

I tried to be careful to clear the cache where it might be necessary - hopefully I haven't missed an edge case.

If successful, this should also speed up the test default formula (Linux) CI step.

[BrewTestBot]

Review period will end on 2021-03-22 at 03:31:58 UTC.

[MikeMcQuaid]

Makes sense, nice work! The only thing I'd be tempted to do here is make the interface a bit more similar to the existing uses caching i.e. Formulary.enable_factory_cache! or something similar/shared which allows the cache keys to be set inside the relevant methods.

[Bo98]

something similar/shared which allows the cache keys to be set inside the relevant methods.

The hard bit is that the return value of Dependency.expand depends on the block passed, which varies from caller to caller.

[Bo98]

If successful, this should also speed up the test default formula (Linux) CI step.

About 12 minutes -> less than 2 minutes

[MikeMcQuaid]

About 12 minutes -> less than 2 minutes

🤯

The hard bit is that the return value of Dependency.expand depends on the block passed, which varies from caller to caller.

Ah, I see. No worries, then.

[BrewTestBot]

Review period ended.