Fix a case of unnecessary dependency rebuilding #3035

[mgsloan]

See #3035

I think it makes sense to include this in the release candidate, since it's the first version with custom-setup.

[sjakobi]

The change makes sense to me but it doesn't appear to fix the original issue. Even when I delete ~/.stack/snapshots and stack clean --full I still see the behavior described in #3035.

[borsboom]

Including in rc/v1.4.0 makes sense to me, so feel free to merge when ready.

[mgsloan]

@sjakobi Ah, good catch! Issue was that this computed info gets stored in a cache. Normally, we'd just bump the version tags.

However, when investigating this I noticed that the errors for peeking when both the version tag and format of the contents have changed are rather poor. Decode errors in the contents took priority over tag matching. I've released store-0.4.1, which handles this more gracefully, and encodes the tags at the beginning rather than the end.

There was also an encoding change with Map for this store release. If we delayed on updating store version, then this would cause further cache invalidation down the road. Best to avoid this when feasible!

[sjakobi]

OOM while building store with GHC-7.10.3: https://travis-ci.org/commercialhaskell/stack/jobs/207616671#L327

Not sure if this needs further investigation in store.

Here, we should probably switch to using the sudo-enabled Travis environment that has 7.5 GB memory instead of 4. (Yes, that environment has caching too now.)

[sjakobi]

Looks like the other build failures were caused because they weren't aware of store-0.4.1 yet.

[sjakobi]

Works on my machine though! Nice work, @mgsloan! 👍

[borsboom]

We should make sure the CI works before merging.

[borsboom]

@mgsloan: is the store upgrade actually necessary to fix the bug? I'm hesitant to do that for v1.4.0.

[mgsloan]

@borsboom Not strictly necessary. But if we don't do it now, then the cache for MiniBuildPlan will be invalidated for both this release and next release. It's straightforward to do it that way instead.

[mgsloan]

I've gone with the more conservative change. Will merge once the tests pass.

[borsboom]

Tests passed, so I merged it.