an empty target is an empty string

[fgaz]

without this cabal new-run without targets errors with an irrefutable pattern

[mention-bot]

@fgaz, thanks for your PR! By analyzing the history of the files in this pull request, we identified @dcoutts, @ezyang and @23Skidoo to be potential reviewers.

[23Skidoo]

/cc @dcoutts

[23Skidoo]

Looks OK to me, by the way.

[23Skidoo]

So I looked at all use sites of showTargetSelector and it looks like it is only used in error messages. So the change seems to be safe to apply; however, from looking at the TargetSelector definition I don't understand in which cases we can get an empty list here.

[23Skidoo]

Anyhoozle, I think I'm going to merge this.

[ezyang]

I'm generally down on using empty strings as a sigil. Does turning the return type into Maybe cause lots of knock on changes?

[23Skidoo]

I don't think using Maybe here makes sense, because this function is used during error message formatting, so you'll just end up with a fromMaybe "" at every use site. Maybe it should return something like "<empty>" instead of an empty string.

[fgaz]

+1, it's called show TargetSelector after all.

The run command is for running a single executable at once. The target '' refers to the package MultipleExes-1.0 which includes the executables foo and bar.
vs
The run command is for running a single executable at once. The target '<empty>' refers to the package MultipleExes-1.0 which includes the executables foo and bar.
The second does look nicer, but the quotes imply <empty> is literally the target.
Of course nobody would interpret it like that. I hope.

(On the other hand with Maybe we could do
The run command is for running a single executable at once. The empty target refers to the package MultipleExes-1.0 which includes the executables foo and bar.)

[ezyang]

OK, I trust your judgment :)