Improved to-directory-tree

[mmhat]

• Added a new command line flag --allow-path-separators for the
  to-directory-tree command. This flag controls whether path separators
  in names are allowed. In that case we also create all parent
  directories of a file.
• Added a new way building directory trees using a fixpoint approach.
  Using it allows one to set the user, group and permissions (for some OS).
  The values accepted need to have the type given in the issue description of Allow users to set ownership and permissions in to-directory-tree #2436 .
• Added unix-compat as a new dependency of the dhall package
• Added some tests for to-directory-tree
• Added a FromDhall instance for Identity

Fixes #2436
Fixes #1633

[mmhat]

If this one gets merged, I also suggest we add the types of the issue description of #2436 to the Dhall prelude.

[mmhat]

Not sure what happened here: Hydra failed very early and I have no clue what went wrong...

[sjakobi]

Not sure what happened here: Hydra failed very early and I have no clue what went wrong...

Just an instance of #2313. I've restarted the build.

[mmhat]

@sjakobi It failed again. How can I trigger a re-run of the job?

[mmhat]

Ok, this is blocked by #2313 for now 😞

[Gabriella439]

Looks great! Just a few comments

Also, would it be possible to create a small Dhall package within this repository for working with the new tree type?

[mmhat]

@Gabriella439 I added a commented example to the examples directory of the dhall package. I also think that adding the used types and some useful functions/constants to the Dhall Prelude; What do you think?

[Gabriella439]

Oh yeah, you can try to add it to the Prelude. At first I was a bit hesitant to add a type that is a bit specific to the Haskell implementation, but we actually already do that in at least one other place in the Prelude, which Prelude.JSON.Nesting: https://store.dhall-lang.org/Prelude-v21.1.0/JSON/Nesting.dhall.html