* Update ghc-lib to speed up sdist generation
To incorporate https://github.com/digital-asset/ghc-lib/pull/379, which
is a more generic version of the changes introduced in
41ab1c2cba
to speed-up ghc-lib(-parser) sdist generation in Daml.
The slowest step in the ghc-lib(-parser) sdist generation is the
generation of `.hs` files from `.hsc` files via `hsc2hs` and from `.x`
or `.y` files via `alex` or `happy`. The reason that it's slow is that
`ghc-lib-gen` performs these through GHC's build system, hadrian, and
these steps require almost a full stage1 GHC build.
The `.hs` files are only needed to enable dependency discovery through
`ghc -M`, as it doesn't understand `.hsc|.x|.y` files. Apart from that
we can use the original `.hsc|.x|.y` files in the final sdist.
With this update `ghc-lib-gen` finds all relevant `.hsc|.x|.y` files
and replaces them with dummy `.hs` files that have the same module name
and the same imports. These dummy files are only used for the purposes
of dependency discovery via `ghc -M` and are not included in the final
sdist.
With this update the sdist generation is sped up between 4.3 to 4.5
times:
- ghc-lib-parser: 3m2s down to 42.04s (4.3x)
- ghc-lib: 3m5s down to 40.96s (4.5x)
I've applied `diffoscope` to the generated sdist tarballs with and
without this update to ensure that no unexpected differences are
introduced with this change.
https://github.com/digital-asset/ghc-lib/pull/379 reports a less
dramatic speed up of about a third reduction in build time for `stack
runhaskell CI.hs`. The reason for the discrepancy is that `CI.hs`
performs more steps than just the sdist generation, e.g. checking out
GHC's source tree, or building hadrian. These steps are not included in
the above benchmarks, because they are executed in separate Bazel
actions and can be cached separately.
CHANGELOG_BEGIN
CHANGELOG_END
* Update Cabal files
Co-authored-by: Andreas Herrmann <andreas.herrmann@tweag.io>
e8001fc4ff