bug#43061: freedink package is needlessly complex

[Jesse Gibbons <jgibbons2357@gmail.com>]

TL;DR The freedink package is defined in a complex way that breaks 
guix's custom source build features and the GUI wrapper.

The freedink package wraps the freedink-engine and freedink-data 
packages so the resulting executable bin/freedink runs the freedink 
engine pointed at the output of freedink-data. The wrapped packages are 
not exported from gnu/packages/games.scm. Because of these two design 
choices,

-> guix build --sources=all freedink does not list the freedink-data source.

-> the only way to get the freedink-data source is to run guix build 
--sources=transitive freedink. This is not ideas because it gets the 
source for bash as well.

-> "guix build --with-source=freedink-data=..." has no effect on 
freedink, so guix cannot be used to facilitate freedoms 1 and 3 with 
freedink, unlike most other packages. To be clear,  freedoms 1 (to 
modify the software) and 3 (to distribute the modified software) are not 
violated, but a very nice feature of guix that makes them less complex 
does not work with freedink. To achieve a guix install or pack of 
freedink as it is currently defined with custom sources and/or data, one 
must define new freedink packages, which is more work than one or two 
simple command-line flags.

-> freedink-dfarc does not find "dinkedit" or "dink", which are links to 
binaries built in freedink-engine. Once again, freedoms 1 and 3 are a 
little more difficult to exercise than reasonably expected given what 
guix provides, but not violated. To point freedink-dfarc to the correct 
binaries, one must copy the store location in the wrapper script 
produced by freedink. Obviously, this store location will not 
automatically be updated when freedink-engine is upgraded.

-> Because the wrapper hard-codes a location to look for the data, I 
suspect (but have yet to confirm) that an attempt to use freedink-dfarc 
to build a modified version of freedink will ultimately throw an error.

There must be a way to re-package freedink such that:

1) It works with the custom source build features provided by guix.

2) The guix wrapper freedink-dfarc is neither necessary for running 
freedink, nor broken when used to run freedink.

The solution could be as simple as publicly exposing freedink-engine and 
freedink-data, and redefining the freedink package to simply take the 
two packages as inputs and produce a wrapper script. The script should 
probably have a name other than "freedink" or "dink" so all three 
packages can optionally co-exist in the same profile without a name 
conflict. I will try this solution and send a patch if it passes the 
following tests:

-> The sources for all freedink-related packages can be produced with 
"guix build --source" or "guix build --sources=all"

-> all freedink-related packages can be installed and packed with 
modified local sources specified by --with-source

-> installing freedink does not add anything to the profile other than a 
wrapper script.

-> There is no name conflict between the executables provided by 
freedink-engine and freedink

If anyone knows why freedink is packaged the way it is and thinks it is 
better that way, I want to know your reasons before I begin to attempt 
to fix this issue, because those reasons could lead me to a different 
approach.

I suspect freedink is not the only package with these issues.

-Jesse