cabal-install: cannot depend on public sublibrary when the package does not contain a main library too

[fgaz]

Repro:

cabal.project:

packages: d, p

d.cabal:

cabal-version: 3.0
name: d
version: 0.1.0.0

library sublib
  visibility: public
  default-language: Haskell2010

p.cabal:

cabal-version: 3.0
name: p
version: 0.1.0.0

library
  build-depends: d:sublib
  default-language: Haskell2010

cabal v2-build p output:

cabal: Could not resolve dependencies:
[__0] trying: d-0.1.0.0 (user goal)
[__1] next goal: p (user goal)
[__1] rejecting: p-0.1.0.0 (requires library from d, but the component does
not exist)
[__1] fail (backjumping, conflict set: d, p)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: d, p

Adding an empty main library to d fixes it.:w

[23Skidoo]

Why not just prohibit such packages?

[23Skidoo]

(At least for now, the restriction could be relaxed in a later spec version)

[fgaz]

Good idea! It should be an easy to implement stopgap