racket package is different for every build

[bmwiedemann]

Originally filed a bug at http://bugs.racket-lang.org/query/?cmd=view&pr=15439 but cannot read that now.

While working on the reproducible builds effort, I found that
when building the racket package for openSUSE Linux, there were many differences between each build.

See https://reproducible-builds.org/ for why this matters.

A full diff is at
http://rb.zq1.de/compare.factory-20180228/racket-compare.out

e.g. it includes

/usr/bin/racket
/usr/lib64/libracket3m-6.11.so
/usr/share/doc/packages/racket/2d/stamp.sxref
/usr/share/doc/packages/racket/db/query-api.html
/usr/share/doc/packages/racket/docindex.sqlite
/usr/share/doc/packages/racket/math/pict_24.png
/usr/share/doc/packages/racket/math/pict_25.png
/usr/share/doc/packages/racket/math/pict_28.png
/usr/share/racket/pkgs/drracket/scribblings/drracket/compiled/extending_scrbl.dep
/usr/share/racket/pkgs/web-server-lib/web-server/formlets/compiled/stateless_rkt.dep
/usr/share/racket/pkgs/web-server-lib/web-server/formlets/compiled/stateless_rkt.zo
/usr/share/doc/packages/racket/teachpack/pict.svg

and some statistics:

grep -o "^-/[^ ]*" racket-compare.out | grep -o '[^./]*$'|sort|uniq -c|sort -rn
   2390 dep
    276 zo
    205 svg
    158 sxref
     27 html
      9 png
      1 sqlite
      1 so
      1 racket

[SuzanneSoy]

This issue has popped up for the NixOS package too.

See a short IRC discussion between me and @henrytill at https://botbot.me/freenode/nixos/2016-01-26/?msg=58715198&page=7 about this:

henrytill       georges-duperon: there's some seeming non-determinism in the doc building step
                georges-duperon: which meant that hydra routinely failed the build when under load
                georges-duperon: which is why we ultimately disabled them
georges-duperon henrytill: Oh, so you mean the hash isn't constant ?
henrytill       georges-duperon: no even deeper
                georges-duperon: there were random SQL failures

In the history for the NixOS racket package, we can see that building the docs was disabled in September 2, 2015, and was re-enabled in November 12, 2017.

@gebner Do you remember what made it possible to re-enable the Racket docs by default in the NixOS package ?

I don't see much in the diff between the two commits mentioned above: aside from version changes and dependencies, the most noticeable change is that the environment variable for ar was unset.

[gebner]

The NixOS change is explained in this PR: NixOS/nixpkgs#31556
As far as I could tell, this commit in racket fixed the issue.

[SuzanneSoy]

@gebner Thanks a lot for the feedback!