`cabal new-install --lib` adds process-1.6.5.1 to GHC's environment

[trajafri]

Describe the bug Running cabal new-install --lib will silently add process-1.6.5.1 to GHC's environment listing. This causes issues with running new-install in the future:

To Reproduce

1. Create a new cabal package (I used cabal init)
2. cabal new-install --lib
3. cabal new-install --lib

Step 3 should fail.

$ cabal init 
$ cabal new-install --lib
Resolving dependencies...
Up to date

$ cabal new-install --lib
Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] trying: base-4.12.0.0/installed-4.1... (user goal)
[__1] trying: ghc-8.6.5/installed-8.6... (user goal)
[__2] next goal: process (user goal)
[__2] rejecting: process-1.6.5.1 (conflict: ghc =>
process==1.6.5.0/installed-1.6...)
[__2] rejecting: process-1.6.5.0/installed-1.6..., process-1.6.5.0,
process-1.6.4.0, process-1.6.3.0, process-1.6.2.0, process-1.6.1.0,
process-1.6.0.0, process-1.5.0.0, process-1.4.3.0, process-1.4.2.0,
process-1.4.1.0, process-1.4.0.0, process-1.3.0.0, process-1.2.3.0,
process-1.2.2.0, process-1.2.1.0, process-1.2.0.0, process-1.1.0.2,
process-1.1.0.1, process-1.1.0.0, process-1.0.1.5, process-1.0.1.4,
process-1.0.1.3, process-1.0.1.2, process-1.0.1.1, process-1.0.0.0 (constraint
from user target requires ==1.6.5.1)
[__2] fail (backjumping, conflict set: ghc, process)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: base, process, ghc, ghc:buildable

Expected behavior I am new to cabal so new-install failing to install tools like hlint was confusing. Thankfully, folks at #haskell were able to deduce what could have gone wrong.

System informataion

• Operating system: Manjaro Linux x86_64
• cabal: 2.4.1.0 , ghc versions: 8.6.5

Additional context In this case, the solution was to delete the process listing under environments/default

[23Skidoo]

/cc @typedrat

[typedrat]

There's not a satisfying answer here, since I'm currently rebuilding how the command works, but it should end up fixing this problem among many others. :)

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On Mon, Jul 29th, 2019 at 12:16 AM, Mikhail Glushenkov [email protected] wrote:

/cc @typedrat ( https://github.com/typedrat )

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[ulysses4ever]

This looks like a more egregious instance of #5559, which literally starts with: "Because new-install wants to keep every package that GHC bundles in the environment…". So, not sure if this ticket needs to be open. It's a good reproducer for #5559, though.

With GHC 9.0.2 and cabal 3.8 it fails with analogous error but for directory rather than process.