The State of GHC 8.10

[Zubin Duggal]

Hi all,

GHC 8.10.6 was released last week, with high hopes of finally putting an
end to the long running saga of the GHC 8.10 series. Unfortunately, this
was not to be the case as we soon discovered #19950, an issue that we
claimed to have fixed in the 8.10.6 release, was still affecting the
released compiler.

#19950 is caused by a bug in newer Apple toolchains (specifically XCode
12) where programs compiled with affected versions of XCode are not
backwards compatible with configurations running older version of XCode
(certain versions of XCode 11). It surfaced in GHC 8.10.5 since we
upgraded the toolchain on our Darwin builders to one of the affected
versions.

The original fix/workaround for #19950 was tested on the master and
GHC-9.2 branches and found to be working, and so backported to the 8.10
branch. Unfortunately, Darwin releases for 8.10 are still done using
the Make build system, which did not pick up the extra linker options
needed to work around the issue. 

It places a heavy burden on developers to have so many active branches
of the compiler to keep in mind, and the current situation with 4 active
branches is simply not sustainable. As the oldest currently active
branch, it is currently a priority to retire the 8.10 branch of GHC from
active development as soon as possible.

We have now fixed and verified the fix for #19950 on the 8.10 branch
and prepared a GHC 8.10.7 release including it. As of now, the only
change in GHC 8.10.7 is to link the x86_64 darwin release build with a
few extra linker options to work around #19950.

If you have any other critical issues that prevent you from using GHC
8.10(.6), please raise them soon by either pointing to existing tickets
on the tracker or creating a new one. We are planning to cut the new
release as soon as early next week, and we are really hoping that this
would be the final release in the 8.10 series.

Cheers,
Zubin.
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