cabal format update command to update list of modules

[gbaz]

The syntax is open to bikeshedding, but the idea is that cabal init auto-populates modules in a cabal file when it creates it. However, there's no way to auto-populate additional modules you may have since added.

It would be nice if we could add an update command that added to other-modules all modules in the source-dir not otherwise listed, so people didn't have to add them by hand as they added new modules to a project. We could even have a flag that controlled if they were added to exposed or other in the case of library stanzas.

Adding this as a subcommand of format makes sense imho because it uses the same round-tripping as format, and it also is blocked on public exposure by the same round-trip issues listed in : #2460

[23Skidoo]

Like all similar features, I think this requires comment-preserving exactprint to be implemented first.

[gbaz]

Hrm. Ok, so in #2460 we have a full correct data roundtrip almost there except for one encoding issue. However, I guess that still leaves comments out. I confess I don't still know the full state of things. Are we fully on the parsec parsers now? Are there plans for a comment-preserving exactprint or any tickets describing the issue more fully. Or is there just a desire for this?

(i guess related prior art is ghc-exactprint and also https://dorchard.wordpress.com/2017/09/20/scrap-your-reprinter/)

[hvr]

Are we fully on the parsec parsers now?

For .cabal files, yes; since cabal 2.2

for cabal.project / cabal.config not yet

Are there plans for a comment-preserving exactprint

Yes, definitely -- the ability to roundtrip .cabal files is essential to achieve some goals for hackage revisions! But as usual, it's a priority-scheduling / scarce resource issue... in hindsight, this could have been a great GSOC project...

/cc @phadej

[fgaz]

In the meantime, cabal-fmt can also update the module list. See here for how to use it: http://oleg.fi/gists/posts/2019-08-11-cabal-fmt.html#extra-expand-exposed-modules-and-other-modules