Tell the user that a boot package was pruned

[Rufflewind]

I use Stack on CI and sometimes override dependencies intentionally. Recently, they started failing, but the error message isn't particularly descriptive:

Error: While constructing the build plan, the following exceptions were
encountered:
In the dependencies for directory-1.3.3.2:
    time must match >=1.4 && <1.10, but the stack configuration has no specified
         version  (latest matching version is 1.9.3)
needed since directory is a build target.

stack ls dependencies shows time 1.6.0.1, and similarly on Stackage. Therefore, I was left very confused why Stack suddenly forgot time existed.

It took me a while but I eventually figured I should check the release notes in case it was intentional. I saw this:

Overriding GHC boot packages results in any other GHC boot
packages depending on it being no longer available as a dependency,
such packages need to be added explicitly when needed. See
[#4510] (#4510).

So that explained a lot, but figuring this out wasted a lot of time. Could the error message be made a little more detailed? It at least state that a package was pruned behind the scenes, and preferably include a reason for doing so and/or link to #4510 for rationale.

[dbaynard]

Could the error message be made a little more detailed?

Yeah, that's a good idea. I knew about the issue and still got bitten yesterday (at least I was able to identify the solution quickly). There might be a straightforward way to indicate in that error that a boot package has been overriden. @Rufflewind would you be interested in implementing such a change?

[simonmichael]

Sorry to tell you @Rufflewind, but the newer error message is not much clearer. Here's a newcomer hitting it: https://www.reddit.com/r/haskell/comments/pcf9be/i_cant_find_a_solution_to_this_problem_involving/

Instead of "this GHC boot package has been pruned (issue #4510)", how about:
"this GHC boot package has been overridden, which in effect hides any other GHC boot packages depending on it; usually this is something you should not do. See stack issue #4897 for more." (or, less future proof but much more friendly, provide the full url: https://github.com/commercialhaskell/stack/issues/4897).