.. _release-8-6-2:

Release notes for version 8.6.2
===============================

GHC 8.6.2 is a bug-fix release, fixing a few regressions found in 8.6.1.


Highlights
----------

The highlights, since the 8.6.1 release, are:

- A long-standing bug exposed in GHC 8.6.1, :ghc-ticket:`15696`, has been fixed.
  This issue resulted in undefined runtime behavior with some uses of the
  ``dataToTag#`` primop. Note that this issue, while less likely to manifest,
  has existed in some form in all GHC releases prior to this release and may
  result in silent, incorrect evaluation. For this reason, users are strongly
  encouraged to upgrade to 8.6.2.

- A long-standing bug in the LLVM code generator (:ghc-ticket:`14251`),
  resulting in incorrect floating point evaluation, has been fixed.

- Several compiler panics observed in GHC 8.6.1 have been fixed
  (:ghc-ticket:`15499`, :ghc-ticket:`15053`, :ghc-ticket:`15692`,
  :ghc-ticket:`15695`)

- GHC now runs without complaining when installed to a read-only location on
  Windows (:ghc-ticket:`15667`)

- An integer overflow, resulting in some ``encodeFloat`` uses returning
  incorrect results, has been fixed (:ghc-ticket:`15271`)


Known issues
------------

Note that the LLVM code generator (:ghc-flag:`-fllvm`) in GHC 8.6, as well as
all earlier releases, are affected by :ghc-ticket:`14251`, which can result in
miscompilation of some programs calling functions with unboxed floating-point
arguments. While originally scheduled to be fixed for this release, the fix
ended up being more difficult than anticipated and, given that issue is not a
strict regression from 8.4, we decided to proceed with the release.

Included libraries
------------------

The package database provided with this distribution also contains a number of
packages other than GHC itself. See the changelogs provided with these packages
for further change information.

.. ghc-package-list::

    libraries/array/array.cabal:             Dependency of ``ghc`` library
    libraries/base/base.cabal:               Core library
    libraries/binary/binary.cabal:           Dependency of ``ghc`` library
    libraries/bytestring/bytestring.cabal:   Deppendency of ``ghc`` library
    libraries/Cabal/Cabal/Cabal.cabal:       Dependency of ``ghc-pkg`` utility
    libraries/containers/containers.cabal:   Dependency of ``ghc`` library
    libraries/deepseq/deepseq.cabal:         Dependency of ``ghc`` library
    libraries/directory/directory.cabal:     Dependency of ``ghc`` library
    libraries/filepath/filepath.cabal:       Dependency of ``ghc`` library
    compiler/ghc.cabal:                      The compiler itself
    libraries/ghci/ghci.cabal:               The REPL interface
    libraries/ghc-boot/ghc-boot.cabal:       Internal compiler library
    libraries/ghc-compact/ghc-compact.cabal: Core library
    libraries/ghc-prim/ghc-prim.cabal:       Core library
    libraries/haskeline/haskeline.cabal:     Dependency of ``ghci`` executable
    libraries/hpc/hpc.cabal:                 Dependency of ``hpc`` executable
    libraries/integer-gmp/integer-gmp.cabal: Core library
    libraries/mtl/mtl.cabal:                 Dependency of ``Cabal`` library
    libraries/parsec/parsec.cabal:           Dependency of ``Cabal`` library
    libraries/process/process.cabal:         Dependency of ``ghc`` library
    libraries/template-haskell/template-haskell.cabal:     Core library
    libraries/text/text.cabal:               Dependency of ``Cabal`` library
    libraries/time/time.cabal:               Dependency of ``ghc`` library
    libraries/transformers/transformers.cabal: Dependency of ``ghc`` library
    libraries/unix/unix.cabal:               Dependency of ``ghc`` library
    libraries/Win32/Win32.cabal:             Dependency of ``ghc`` library
    libraries/xhtml/xhtml.cabal:             Dependency of ``haddock`` executable
