WIBNI: edit data file for installed program

[geekosaur]

Describe the feature request
Simple ability to list and/or edit data files for installed programs

Additional context
data-files live in cabal's store, for very good reasons. But this makes them not very discoverable when someone needs to edit one.

I propose a new command cabal [v2-]edit <package[-version]> [--list|<filename>] (the default action would be to list, --list would just make it explicit) to show or edit such files. The guts of this wouldn't be much different from cabal install with a package already installed into the store.

Whether it would do anything useful for a package not already installed would be something to discuss before implementation: on the face of it it doesn't look very useful, but on the other hand it's probably difficult to not have cabal install the requested package/version when it's not already present.

[geekosaur]

I should add that the original intent of data-files was for things like templates that aren't normally edited, but increasingly these are done using file-embed or similar that use TH tricks to embed resources in binaries. Pretty much the only things that don't use that method any more are ghc boot packages that can't rely on TH (e.g. happy's parser skeleton). And we currently have no support to speak of for things like config files, which are much more common: we expect programs to create them in reasonable locations that we don't specify on first use.