complain when ghc-pkg doesn't find any matching packages in a given database

Currently, ghc-pkg list will print something like the following when no package matches a query:

$ ghc-pkg list blargle
/usr/local/lib/ghc-7.4.1/package.conf.d

This is a deceptive answer for newcomers, because they assume that this means the package was successfully found, and lives in /usr/local/lib/ghc-7.4.1/package.conf.d. It would be nice if the message explicitly mentioned that the result list was actually empty; for example:

$ ghc-pkg list blargle
/usr/local/lib/ghc-7.4.1/package.conf.d
    (no matching packages found in this database)

Trac metadata

Trac field	Value
Version	7.4.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture