[ANNOUNCE] GHC 8.0.1 release candidate 2

[Ben Gamari]

Hello everyone,

The GHC Team is very pleased to announce the second release candidate of
the Glasgow Haskell Compiler 8.0.1 release. Source and binary
distributions as well as the newly revised users guide and Haddock
documentation can be found at

    http://downloads.haskell.org/~ghc/8.0.1-rc2/

This is the second in a series of release candidates leading up to the 8.0.1
release and fixes many of the issues reported in -rc1. These fixes
include,

  * A re-rewrite of the pattern checker by George Karachalias. The new
    checker should have far more predictable performance characteristics
    while sacrificing minimal reasoning power. This should resolve a
    large number of the issues felt in -rc1.

  * Richard Eisenberg has been hammering out all manner of
    type-application- and TypeInType-related issues (#11335, #11416,
    #11405). There is still more work to do here, however (e.g. #11471).

  * Matthew Pickering has restored support for multi-clause pattern
    synonyms (#11367)

  * A latent bug in the constraint solver which popped up as a build
    failure in xmonad-contrib in -rc1 has been fixed (#11379)

  * Dimitrios Vytiniotis and Simon Peyton Jones has been squashing a
    variety of older type-checker bugs at a furious rate (#11458,
    #11248, #11330, #11408)

  * Simon Peyton Jones has taught demand analysis to more precisely
    handle exceptions (#11222)

  * Tamar Christina has added support for remote GHCi on Windows
    and resolved a long-standing linking issue (#11223)

  * Loading of compiled modules needing shared library symbols now works
    in GHCi thanks to Peter Trommler (#10458)

  * A variety of limitations in our implementation of Typeable
    implementation have been fixed (#11120) although there is still more
    to be done (#11334).

  * A terrible failure of type inference due to visible type application has
    been fixed (#11458)

  * InjectiveTypeFamilies has been renamed to TypeFamilyDependencies

  * Custom type errors are now more robust (#11391) although there is
    still more work to be done (#11541)

  * We now have a more conservative default warning set, as well as
    better mechanisms for managing warning changes in the future.
    (#11429, #11370)

  * Compatibility with earlier Cabal versions should be a bit more
    robust.

  * The user-facing interface of the (formerly "implicit") CallStack
    functionality has been reworked, hiding the implicit callstack
    parameter behind a constraint synonym.

  * Online haddock documentation has been restored (#11419)

  * We now offer xz archives exclusively

  * A variety of miscellaneous bug-fixes have also been merged.

All of these changes add up to nearly 200 commits in total. Given the
large amount of churn between this candidate and -rc1, as well as the
fact that there is at least one more significant patch pending (D1891,
to fix #11471 and others), we will be releasing a third release
candidate in a few weeks which should address more of the issues listed
on the release status page [1]. Assuming things go well, we should be
able to cut a final release by early March at the latest.

All of the builds above were produced from the ghc-8.0.1-rc2 tag (commit
e2230228906a1c0fa1f86a0c1aa18d87de3cc49d) *with the exception of the
Windows builds*. Unfortunately, it was realized only too late that the
tagged commit is broken on Windows. Consequently, the Windows builds
were produced from the ghc-8.0.1-rc2 tag with two additional patches
(commit 5b35c5509adb1311856faa0bc9767aec9ad5e9b7). While this would of
course be completely unacceptable for a proper release, time constraints
have meant that this was unfortunately the only viable option for this
release candidate. We apologize for any confusion this may cause.

At this point we are working very hard to nail the remaining bugs
labelled as "highest" priority on the 8.0.1 status page [1]. If you have
an issue which you'd like to see addressed in the release that does not
appear in this list, please bring it to our attention.

As always, we look forward to hearing about any issues that you
encounter with this candidate. Thanks to everyone who has contributed so
far!

Cheers,

 - Ben


[1] https://ghc.haskell.org/trac/ghc/wiki/Status/GHC-8.0.1
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