Ability to build a cabal script into executable

[ethercrow]

When I have a haskell program in a form of a single file script like

#!/usr/bin/env cabal
{- cabal:
build-depends: base, lens, shake, ...
-}
main = putStrLn "All done."

I'd like to be able to build it into a standalone executable.

Currently it seems like you can only build something with cabal v2-build if there is a cabal file and/or a project file, but building single file scripts is not supported:

> cabal v2-build Main.hs
No cabal.project file or cabal file matching the default glob './*.cabal' was found.
Please create a package description file ...

Creating a package description file is exactly what I'd like to avoid for small programs, since all the necessary information is already contained in the source file.

[jneira]

In fact cabal generates an executable when you does a cabal v2-run whatever.hs, it is under dist-newstyle\build\x86_64-windows\ghc-x.x.x\fake-package-0\x\script\build\script\script.exe in my windows system (the precise path can be different in other os). Maybe it would not be a final solution but maybe a working workaround.

[phadej]

@jneira as if I remembered that cabal script should just use runghc. Whether it should first compiler and run executable, or just interpret is better left to the choice of user. (I think that interpreting is more reasonable default for scripts).

[bacchanalia]

I think #7851 resolved this issue.

[Mikolaj]

It seems so. @ethercrow (and other interested parties), could you kindly confirm if it solves your use case? Ideally by compiling the master branch and trying it out.

[georgefst]

#7851 certainly improves the situation. But there's no easy way to find the resulting binary. It would be great if list-bin worked for scripts (and/or install, but I've always had issues with that one).

[bacchanalia]

There are so many cabal sub commands I didn't even realize list-bin was a thing. Adding list-bin support for scripts seems reasonable. I think installing a script going against the spirit of a script, though.

[georgefst]

There are so many cabal sub commands I didn't even realize list-bin was a thing.

Not unreasonably: #7774.

Adding list-bin support for scripts seems reasonable. I think installing a script going against the spirit of a script, though.

Well, if you have list-bin then I was thinking cabal install Script.hs is just a shortcut for (roughly) cabal build Script.hs && cabal list-bin Script.hs | cp ~/.local/bin. But I seem to remember that install isn't defined like that, and I've never understood why.

[bacchanalia]

can we close this?

[georgefst]

can we close this?

I'm happy. Thanks for #7925!

[Mikolaj]

Tada!