Subdir field of source-repository-package should accept multiple arguments.

[merijn]

I'm playing around with the freshly merged source-repository-package (#2189, #5351), after searching the cabal-install source to figure out all the field names, I noticed an annoyance. The implementation of remote dependencies was prescient enough to allow me to specify a subdirectory to look for a cabal file in, but sadly only allows me to list a single subdirectory to look in.

I have several related packages in a single repository, these depend on each other, but some haven't been released yet, so I need to depend on multiple package from the same repo. Unfortunately, I can only specify one subdir to look in for cabal files. I've worked around this by listing the same repo multiple times, but this super ugly:

source-repository-package
  type: git
  location: https://github.com/merijn/broadcast-chan.git
  tag: 996aecdacc2eb8501a1a27c8559153d93ed3d6d2
  subdir: broadcast-chan

source-repository-package
  type: git
  location: https://github.com/merijn/broadcast-chan.git
  tag: 996aecdacc2eb8501a1a27c8559153d93ed3d6d2
  subdir: broadcast-chan-conduit

source-repository-package
  type: git
  location: https://github.com/merijn/broadcast-chan.git
  tag: 996aecdacc2eb8501a1a27c8559153d93ed3d6d2
  subdir: broadcast-chan-tests

Ideally subdir should just take a list of subdirectories so I can instead simply write:

source-repository-package
  type: git
  location: https://github.com/merijn/broadcast-chan.git
  tag: 996aecdacc2eb8501a1a27c8559153d93ed3d6d2
  subdir: broadcast-chan broadcast-chan-conduit broadcast-chan-tests

[hvr]

I have to cringe at a singular subdir taking multiple args ;-)

other than that, I think that's a reasonable request (and indeed it's been suggested to @dcoutts already iirc)

@typedrat do you think you could look into this one?

[merijn]

@hvr Well, we could just change it to subdirs instead of subdir, since it's not in any officially released version of cabal-install. Alternatively, change it to subdirs and keep subdir as backwards compat alternative.

[hvr]

@merijn I like the idea to introduce a subdirs fieldname; but isn't the parser for source-repository-package shared with the one for source-repos in the .cabal pkg description? If so, we'd need to make sure that subdirs is only allowed for source-repository-package but not for source-repositorys

Generally, there's likely more fields we'd want to add to source-repository-package but which makes no sense for the source-repository declaration in .cabal files.

[hvr]

IMPORTANT: Due to #5487 there's a minor added complexity: we'd need to resolve the multiple subdirs to a unique a subdir in the plan.json output for the respective package

[mpickering]

This would be a good feature.

[erikd]

Just hit this myself. Is there a workaround?

[dcoutts]

@hvr I really think this is just a case of expanding it out at the syntax layer. The underlying mechanisms already have support for subdir and doing only a single download even when there are multiple uses of the same repo (including for git when different uses use different commits/branches).

For @erikd and others: yes the workaround is just list the repo multiple times, once for each subdir. It only gets downloaded once.

[patrickt]

Would love this!

[phadej]

Implementation comment: the SourceRepo type in Cabal the lib should not be changed,
as that would change .cabal file format. That type need to be forked into cabal-install.

[michaelpj]

This would be nice!

[int-index]

The lack of this feature has definitely been annoying for me. I have the following lines in my cabal.project:

source-repository-package
  type: git
  location: https://github.com/int-index/slay
  tag: 69b533004637319c2f210dfb17f44acfce3f59d2
  subdir: core

source-repository-package
  type: git
  location: https://github.com/int-index/slay
  tag: 69b533004637319c2f210dfb17f44acfce3f59d2
  subdir: combinators

source-repository-package
  type: git
  location: https://github.com/int-index/slay
  tag: 69b533004637319c2f210dfb17f44acfce3f59d2
  subdir: cairo

And each time the tag: field changes, I have to update it in three places instead of one place.