Dear Henning,

Your advice indeed forced Cabal to perform but it choked on 'mingw/bin/ld.exe' when building 'zlib'. So, I cannot comment whether that merry run is able to produce working library, just because of ignoring dependency constraints.
Stack has built zlib in ghc-8.8.3 which for the above purpose is useless ...unless somebody will offer a solution to my main question: how to include old GHC Stack builds in current GHC work?

Cabal: Building library for zlib-0.6.2.2..
[1 of 5] Compiling Codec.Compression.Zlib.Stream ( dist\build\Codec\Compression\Zlib\Stream.hs, dist\build\Codec\Compression\Zlib\Stream.o )
ghc.exe: could not execute: C:/GitLabRunner/builds/2WeHDSFP/0/ghc/ghc/inplace/mingw/bin/ld.exe
cabal.exe: Failed to build zlib-0.6.2.2

Regards:-)

On Fri, Aug 28, 2020 at 1:14 AM Henning Thielemann <lemming@henning-thielemann.de> wrote:

On Fri, 28 Aug 2020, Sylvester Hazel via Haskell-Cafe wrote:

> The command 'stack ghci' configured older GHCi version 8.6.3 with all the needed packages.
> It is possible to reason about this library now.
> However, how to extend/modify this library and incorporate in my target (non-trivial) project is still beyond me.
> There must be some way of reverse engineering this binary library to .hs scripts, so I could add this modified to
> my project?

There might be a set of versions of all libraries to build your project,
but one library may have too restrictive version bounds.

Cabal is more flexible than Stack in choosing sets of versions. You may
use cabal's option --allow-newer=pkg1,pkg2,pkg3 and check whether Cabal
can build your project anyway.