GHC 8.0.1 plans

[Ben Gamari]

tl;dr: The march towards 8.0.1 continues. Release candidate 2 will likely
       be cut late next week. If you have a ticket which you'd like to
       see addressed but suspect we aren't working on then please say so.


Hello again GHC-ers,

As you likely know, we are currently in the stabilization period of
GHC's 8.0.1 release. Release candidate 1 has been out for nearly two
weeks now and issues have been steadily trickling in.

The problems we've heard about thusfar have largely fallen into a few
broad categories,

  * OS X linker issues due to botched preparation of the first binary
    distribution (#11423)

  * pattern match checker performance. These we largely knew about prior
    to the release, although it has been surprising to see how easily
    one can wander into the new checker's performance abyss. (#11374,
    #11276, #11163, #11302, #11303, #11195)

  * Regressions due to visible type applications (#11329, #11458)

  * Issues uncovered by generalizations allowed under TypeInType
    (#11429, #11334, #11473, #11405, #11407, #11399)

  * Trouble caused by new warnings (#11370, #11316, #11474)

Since the release, there has been significant progress on many of these
fronts:

  * George Karachalias has been hard at work further improving the
    pattern checker. The result should have far more predictable
    performance characteristics at less cost in reasoning power.

  * Simon Peyton Jones has been squashing bugs at a furious rate,
    including a variety of long-standing issues (#11248, #11330 and many
    others)

  * Tamar Christina has added support for remote GHCi on Windows
    and resolved a long-standing linking issue (#11223, #11100)

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

  * InjectiveTypeFamilies has been renamed to TypeFamiliesDependencies

  * Custom type errors are now more robust (#11391)

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

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

Given how much progress has been made, we approaching the point where we
can begin planning the next candidate. At this point the plan is to wait
until we have landed George's pattern checker rework, as this has been
one of the more visible issues in practice. This may be merged as early as
the latter half of next week. If this happens then we hope to have the
next release candidate out late next week.

In the interim we will continue to work on paring down the bug list,
focusing on the highest priority tickets listed on the 8.0.1 status
page. In particular, those with owners are most likely to be dealt with
soon. If you see a ticket which you would like to see addressed in 8.0.1
but is unowned or lower than "highest" priority, please bring this to
our attention.

Given the large amount of churn still being felt in the `ghc-8.0` branch
(with over 150 comments in the two weeks since -rc1) and the size of
some of the patches that have yet to land, it's unclear whether two
release candidates will be sufficient to ensure the stability of the
branch. Consequently, unless -rc2 yields a particularly small number of
new tickets it's likely that it will be followed by a third candidate
before the release.

As always, let us know if you have any questions or concerns about the
release process.

Thanks to everyone who has contributed to -rc1!

Cheers,

- Ben
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