cabal can't find modules from private package - error message is unhelpful

[cheater]

Describe the bug
I have a test suite which imports modules from a private library. Those modules are not found, even though the private library is added as build-depends.

The cabal file is here: foo.cabal.txt
(I had to add .txt so GitHub would take it)

Expected behavior

after a bunch of time spent experimenting, this seems to be alleviated by doing build-depends: foo:foo-test-lib. The error message should be more helpful. If I am in a package quux that contains baz as a private library, and I do build-depends: baz, then the error message should tell me to instead do build-depends: quux:baz. As in, "did you mean ...?" etc. Otherwise, the behavior is perceived as a bug - no one on IRC knew that the prefix (quux:) should be done, for example. Please include the actual name of the library or package in the error message.

System information

cabal-install version 3.8.1.0
compiled using version 3.8.1.0 of the Cabal library
The Glorious Glasgow Haskell Compilation System, version 9.0.2

Additional context
Add any other context about the problem here.

[Mikolaj]

PR welcome. Related: #8573