This is same GHC version, but newer other packages, which we need after
updating for yesod-1.6. The 11.5 yaml is equivalent to stack.yaml, but
we'll keep it distinct for when we update our default development
resolver.
I just can't get the older LTS to solve after updating for yesod-1.6. I
will not in the CHANGELOG that, from this point, it may work on that
version, but we aren't explicitly testing it anymore.
8.4 is about to release, so it seems OK to start phasing out anyway, if
we're following a reasonable "current and one back" policy.
Checksumming stack.yaml was a cargo-cult of interpreted languages, where
"build" artifacts are uniquely determined by the dependency lock file.
This approach would result in us refusing to store a new cache after
changing code (as long as it was the same resolver), and forever
recompiling any altered modules.
Computing a digest of all git-tracked files seems like the simplest way
to key compilation for now.
