alex-3.1.5 doesn't declare its dependency on happy

[peti]

Citing from http://hydra.cryp.to/build/1389306/nixlog/1/raw:

Building alex-3.1.5...
Preprocessing executable 'alex' for alex-3.1.5...
Setup: The program 'happy' is required but it could not be found

Apparently a build-tools: happy attribute is missing from the Cabal file.

[peti]

And while I am at it ... perl seems to be missing, too.

[simonmar]

Sigh, alex is not supposed to depend on Happy because it comes with the Happy-generated files. But this functionality in Cabal seems to break all the time. Let me check and see what happened.

[simonmar]

Uploaded 3.1.6 without the problem, and filed an issue with cabal: haskell/cabal#2940

[hvr]

Cabal should have never attempted to regenerate the parsers if build-tools: happy is not specified

[simonmar]

Do you mean "should" as in "it doesn't behave like that right now, but someone should fix it", or "I believe it behaves like that now, so if it doesn't it's a bug"?

If Cabal never runs Happy unless build-tools: happy is present, then I would need to have a -f devel flag to alex to enable the build-tools: happy line when modifying the parser or building the source distribution.