Cache transitive dependencies

[felixSchl]

The call to getTransitiveDeps can get quite slow for larger projects, even on a decent machine.

I found at least one relevant reference to this here: #110 (comment).

I am wondering if we could not simply cache the transitive deps based on the hash of the dhall files, perhaps, or even take the hash of the PackageSet type, if at all possible.

[f-f]

@felixSchl yeah, great points! I think it would be ok to cache things based on the hash of Dhall files, but it might not be necessary if we had a faster implementation. I think the current implementation is fairly naive and there might be lots of space for improvement, as noted in the comment you linked

[justinwoo]

my other question for this is would this work with a function written in dhall?

[f-f]

@justinwoo as I understood it they did not mean to write the function in Dhall, but to use the hash of spago.dhall or packages.dhall to identify the right cache to use for caching the list of transitive dependencies for every package