--haddock-lib is not used for dependencies

[FinleyMcIlwaine]

Describe the bug
I have a Haddock built outside of the GHC tree at /my/haddock and a Haddock resource directory at /my/haddock/resources. In a cabal project with a dependency, running

cabal v2-haddock -v2 --with-haddock=/my/haddock --haddock-lib=/my/haddock/resources

Causes building documentation to fail with Haddock's resource directory does not exist! in the build logs for the dependency.

I think --haddock-lib=/my/haddock/resources should cause a --lib=/my/haddock/resources argument to be provided to all invocations of Haddock, including those for dependencies.

To Reproduce
lib.cabal contents:

cabal-version:   3.8
name:            scratch
version:         0.1.0
build-type:      Simple

library
    build-depends:
        base
      , acme-missiles
    default-language: Haskell2010

In same directory as lib.cabal, run (substituting paths appropriately):

cabal v2-haddock -v2 --with-haddock=/my/haddock --haddock-lib=/my/haddock/resources

It will fail to build documentation for the acme-missiles dependency. cat the resulting build log and see output ending with something like:

Running: /my/haddock '@dist/doc/html/acme-missiles/haddock-response97139-1.txt'
[1 of 2] Compiling Acme.Missiles    ( Acme/Missiles.hs, nothing )
[2 of 2] Compiling Acme.Missiles.STM ( Acme/Missiles/STM.hs, nothing )
Haddock's resource directory does not exist!

Haddock coverage:
 100% (  2 /  2) in 'Acme.Missiles'
  75% (  3 /  4) in 'Acme.Missiles.STM'
  Missing documentation for:
    Module header

Expected behavior
Building documentation with a haddock built outside the GHC tree and a specific --haddock-lib should succeed.

System information

• Operating system: macOS Monterey
• cabal, ghc versions: cabal version 3.11.0.0 (commit e1a10bd), haddock version 2.28.0 (commit 710e1ea119a566a8f704b07bfa4375ab50a94dec on the ghc mirror, ghc version 9.8.20230619.

I suspect this occurs with any version of Haddock built outside of the GHC tree with any version of GHC, but I have not verified that.

[FinleyMcIlwaine]

I now realize the correct way to do this is with:

package *
  haddock-lib: ...

But that was not clear since the haddock-lib option is not included in the users guide. I will be adding an entry for it in #9177