deprecation warnings are reported too often

Not so much a bug, more an annoyance.

In some code which is designed to work on multiple compiler platforms, there are some system dependencies such as the name/location of non-standard libraries. Accordingly, I gather all such deps into a single module SysDeps.hs, which is heavily reliant on cpp #ifdefs, but whose only purpose is to re-export the non-standard entities needed by the rest of the project. So far so good. Now it turns out that ghc-6.6 has deprecated some of the non-standard libraries. Fair enough, I would expect to see the deprecation warnings when I compile SysDeps.hs. But in fact, I see multiple deprecation warnings - one for every deprecated entity, used in any module. So instead of seeing 5 or so warnings, nicely localised to a single module, I see 40 or so, smeared out across the whole project.

An example:

Import.hs:9:28:
    Warning: Deprecated use of `unpackPS'
	     (imported from SysDeps, but defined in Data.PackedString):
	     use Data.ByteString, Data.ByteString.Char8, or plain String.

As you can see, the warning mechanism is aware that it is doing a transitive closure over imports. But really, I'd prefer it not to, and instead to report the deprecation only in the directly-importing module.

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Multiple
Architecture	Multiple