cabal run creates a build folder if dist-newstyle is already present

[ffaf1]

Describe the bug
cabal run creates a build folder if dist-newstyle is already present.
Offspring of #10686.

To Reproduce

1. Create new folder, cd into it.
2. Create a dist-newstyle folder inside it.
3. Create a minimal script.hs.

   #! /usr/bin/env cabal
   
   {- cabal:
   build-depends: base
                , acme-missiles
   -}
   
   import Acme.Missiles
   
   main :: IO ()
   main = launchMissiles
   

4. Make it executable, run it.
5. Modify the script slightly (e.g. add a putStrLn), run it again
6. ls -l
7. There is a build folder.
   Expected behavior
   build/ is not created.

System information
Debian bookworm. cabal 3.15.

Additional context
This is not fixed by #10771 , but neither is a regression and once #10771 lands, not urgent.

[alt-romes]

FWIW, I've observed with head and 3.14 that the build folder is created regardless of whether dist-newstyle exists

[ffaf1]

that the build folder is created regardless of whether dist-newstyle exists

Thanks.

While bisecting, this — weirdly enough — happened only at times, while always when dist-newstyle was present.

[Bodigrim]

Additional context This is not fixed by #10771 , but neither is a regression and once #10771 lands, not urgent.

I use single-file scripts quite a lot and I don't think I ever encountered this bug with Cabal 3.12, so it's likely to be a regression as well, just an older one.

[ulysses4ever]

@ffaf1 maybe you could leave the dist-newstyle directory be and try to bisect it that way? It does sound believable that it's a regression in 3.14. Does it not reproduce on the 3.14 branch for you at all now?

[ffaf1]

I believe it is more complicated that a simple dist-newstyle folder. For once I have to modify the script, so the issue title is incorrect.

I will try to write a reasoned reproducer soon™.

[Bodigrim]

Here is a reproducer:

$ ll build/*/ghc*; echo '#!/usr/bin/env cabal\n{- cabal:\nbuild-depends: base\n-}\nmain :: IO ()\nmain = pure () -- '$(date) > Main.hs && chmod +x Main.hs && ./Main.hs && ll build/*/ghc*
zsh: no matches found: build/*/ghc*
drwxr-xr-x  3 andrew  staff  96 Feb  3 19:11 ./
drwxr-xr-x  3 andrew  staff  96 Feb  3 19:11 ../
drwxr-xr-x  3 andrew  staff  96 Feb  3 19:11 fake-package-0/

There was no build/*/ghc*/fake-package-0 folder before, but there is one after.

git bisect says that

7b9058328e162a4cb707b5d5b25cd1d2df66680e is the first bad commit
commit 7b9058328e162a4cb707b5d5b25cd1d2df66680e
Author: sheaf <[email protected]>
Date:   Fri Mar 29 15:19:27 2024 +0100

    Make Cabal agnostic about working directory

CC @sheaf