Subsections in custom-setup

[phadej]

By reading http://cabal.readthedocs.io/en/latest/developing-packages.html#custom-setup-scripts it's not clear whether subsections e.g. if os(windows) are supported. IIRC they aren't, but IMHO it's good idea to explicitly mention this (and the reasoning behind).

Also: if such section is added, cabal crashes:

'parseField' called on a non-field. This is possibly a bug in Cabal.
Please report it to the developers:
https://github.com/haskell/cabal/issues/new
CallStack (from HasCallStack):
error, called at ./Distribution/PackageDescription/Utils.hs:21:16 in

(I'm not sure what parsec variant does).

[23Skidoo]

I think the idea was to make custom-setup as simple as possible, so it's probably deliberate, but the error message should be improved.

/cc @dcoutts

[phadej]

FWIW: I guess it should crash, but (and) parser should warn about this. I can look into the code issue, but I don't know about the reasons to improve the documentation.

[ezyang]

See also #4047 which is a proposal to allow a custom setup to be an external executable, in which case the current setup stanza restrictions do not apply. CC @Ericson2314

[grayjay]

#3085 (comment) and #4852 are related.