Extend functionality of 'expand src' to also delete missing module names

[Simre1]

Hi, i am mainly using cabal-fmt for its capabilities to add newly created modules to exposed-modules.

However, it does not work so well when I am moving modules around. cabal-fmt correctly adds the new name of the module to exposed-modules. The old name still persists and I have to delete it manually. It would be nice if cabal-fmt could also delete modules that no longer exist.

I am not sure about the specifics of the implementation. A solution would be to create an additional setting like -- cabal-fmt: expand src but for deleting module names; maybe -- cabal-fmt: clean src.

What do you think?

[phadej]

When formatting a stdin, we don't know the location of the .cabal file, so we cannot read contents of (correct) directories either.

The current adding behavior is consequence of that. If we succeed to read anything from filesystem, it's added, but nothing is ever removed.

I don't yet know whether allowing machinery to know whether there are filesystem reading functions is good thing to do.

[chris-martin]

If I understand correctly, it seems like the behavior of cabal-fmt already varies based on the way it is used?

Current behavior:

• When formatting stdin, no modules are added
• When formatting a file path, modules may be added

Desired behavior:

• When formatting stdin, no modules are added or removed
• When formatting a file path, modules may be added or removed

I haven't looked at the code here yet, but as a user of this program it's difficult to understand in what sense "machinery to know whether there are filesystem reading functions" doesn't already exist, given that the program's output does depend upon whether it has been called with context sufficient to let it find module files.