Hi Timothy, thanks for your reply.
> On 12. Jun 2019, at 06:54, Timothy Sample <[email protected]> wrote: > > Hi Robert, > > I patched the “cabal-revision” stuff into the build system, so I suppose > I should weigh in here. :) > > Robert Vollmert <[email protected]> writes: > >> Hello all, >> >> I have a question regarding how cabal revisions are handled >> for haskell packages. Namely, would it make sense / is it >> possible to make the revised cabal file part of the source >> field in the package definition? > > Yes it makes sense, and yes it is possible. This is something I wanted > to do before, but I wasn’t sure how. The only idea I had was to make a > new download method, but that’s a very heavy solution for such a simple > task. […] >> Alternatively, could this be achieved through the snippet field? >> I couldn’t work out how, and none of the uses of snippet that I >> found used any file input. > > There is a way to do it through the mighty power of gexps! Behold: > > (origin > (method url-fetch) > (uri (string-append "https://hackage.haskell.org/package/"; > "tree-diff/tree-diff-0.0.1.tar.gz")) > (sha256 > (base32 > "049v44c520jy3icxlnrvbdblh3mjmvd7m6qmkzxbzkf02x63xqmz")) > (snippet > #~(copy-file > #+(origin > (method url-fetch) > (uri (string-append "https://hackage.haskell.org/package/"; > "tree-diff-0.0.1/revision/4.cabal")) > (sha256 > (base32 > "1rqxxyj6hqllahs11693g855cxz8mgnb490s7j1ksd300i5xgjsp"))) > "tree-diff.cabal"))) > > (I’m constantly amazed at how useful, composable, and empowering gexps > are.) This could be cleaned up with some procedures and made just as > nice as the current setup. What do you think? Lovely, thanks. The following works for me: (source (origin (method url-fetch) (uri (string-append "https://hackage.haskell.org/package/tree-diff/tree-diff-"; version ".tar.gz")) (sha256 (base32 "049v44c520jy3icxlnrvbdblh3mjmvd7m6qmkzxbzkf02x63xqmz")) (snippet (snippet-hackage-revision "tree-diff" version "4" (base32 "1rqxxyj6hqllahs11693g855cxz8mgnb490s7j1ksd300i5xgjsp"))))) with (define* (snippet-hackage-revision hackage-name version revision hash) #~(copy-file #+(origin (method url-fetch) (uri (string-append "https://hackage.haskell.org/package/"; hackage-name "-" version "/revision/" revision ".cabal")) (sha256 hash)) (string-append #+hackage-name ".cabal"))) Would this be a worthwhile change? What would be a good place (and name) for snippet-hackage-revision? One disadvantage that I see is that it moves the revision information from plain data in the arguments field to a rather opaque code snippet. >> (My reasons why using the source field instead of the argument >> field might be nicer: >> - all sources in one place >> - less special-casing for the haskell build system >> - simpler >> - maaaybe a useful abstraction that allows simplifying things >> like patching, too) I remembered one more: guix refresh. As far as I understand, it works only on the level of the source field, thus having the revision there would help make it revision-aware. I’m unsure though whether the snippet approach actually improves things here — probably the refresh code would see the resulting gexp and not the raw data. Cheers Rob
