ghci should complain when the user imports non-existent modules

[dagit]

I was surprised today when I tried to import a module that wasn't installed locally and ghci didn't issue a warning so I assume it loaded. I didn't even notice that the prompt didn't change. I tried to use functions in the module I thought was imported and that's how I learned it didn't actually succeed at the import.

Here is an example to reproduce what I saw:

$ ghci
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> import Control.Monad.Pizza
Prelude> 

Thanks!

[creswick]

This appears to be a regression, in 7.2.1, the following happens:

GHCi, version 7.2.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Prelude> import Control.Monad.Pizza

<no location info>:
    Could not find module `Control.Monad.Pizza'
    Perhaps you meant
      Control.Monad.Fix (from base)
      Control.Monad.Zip (from base)
      Control.Monad.ST (from base)
    Use -v to see a list of the files searched for.
Prelude> 

[pcapriotti]

Duplicate of #5836.