[bug#48999] [PATCH] import: hackage: Accept local source for package.

[Xinglu Chen]

On Wed, Jun 30 2021, Ludovic Courtès wrote:

> Hi,
>
> Xinglu Chen <public@yoctocell.xyz> skribis:
>
>> On Tue, Jun 29 2021, Ludovic Courtès wrote:
>>
>>> Hi,
>>>
>>> Xinglu Chen <public@yoctocell.xyz> skribis:
>>>
>>>> When developing a Haskell package it is often useful to have a Guix package
>>>> definition for that package, previously one would have to write that 
>>>> package
>>>> definition by hand, and if the .cabal file changed one would manually 
>>>> update
>>>> the Guix package definition.
>>>>
>>>> This commit allows one to specify a custom source for their package, 
>>>> meaning
>>>> that one could programatically generate a Guix package definition for their
>>>> local Haskell package.  If the .cabal file changes, the generated package
>>>> definition will also change accordingly.  One could for instance write the
>>>> following in a guix.scm file:
>>>>
>>>>   (define-values (ghc-haskeme deps)
>>>>     (call-with-input-file "haskeme.cabal"
>>>>       (lambda (port)
>>>>         (hackage->guix-package
>>>>          "haskeme"
>>>>          #:port port
>>>>          #:source (local-file "." "haskeme-checkout"
>>>>                               #:recursive? #t
>>>>                               #:select? hg-predicate)))))
>>>>
>>>>   ghc-haskeme
>>>>
>>>> Invoking ‘guix build -f guix.scm’ would then always build an up-to-date
>>>> version of the package.
>>>>
>>>> * guix/import/hackage.scm (hackage-module->sexp): Add optional keyword
>>>> argument ‘source’
>>>> (hackage->guix-package): Likewise.
>>>> * tests/hackage.scm (eval-test-with-cabal): Likewise.
>>>> ("hackage->guix-package local source"): New test.
>>>
>>> Looks like a nice improvement.
>>>
>>> What I don’t get is that this functionality doesn’t seem to be available
>>> from the CLI, which the patch doesn’t change.  Or am I missing
>>> something?
>>
>> No, I don’t think this functionality is available from the CLI since
>> ‘hackage->guix-package’ is not called with the #:source keyword
>> argument.
>
> IOW, this functionality is not accessible, unless you use the Scheme API
> as in the example above, right?

Yes.

>> Once all the other importers (or those where it makes sense to do
>> this) get this functionality, it would be a good idea to add an option
>> for reading a .cabal/setup.py/whatever file and generating a package
>> definition from that.
>
> ‘guix import hackage’ could support it even if other importers don’t
> have equivalent functionality, no?

Sure, that could work too.

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