#2201: "ghc-pkg --user describe '*'" fails with empty user db
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Reporter: duncan | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.9 | Severity: normal
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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With ghc 6.9 and later Cabal uses the new "`ghc-pkg describe '*'`"
interface to get info out of `ghc-pkg` about all the installed packages.
It makes one call for each package db, for `--global` and `--user` (and
any other dbs the user specifies). The `--user` flag now means to list
only the packages from the user db and not the ones from the global one
too. It's quite possible that the user package db is empty (or
equivalently that the file does not exist yet).
So what goes wrong is that the new search feature treats an empty search
result as a failure. That's obviously a useful thing for some queries but
is extremely unhelpful for what Cabal wants. It means Cabal fails to
configure anything when the user package db is empty because it does not
expect ghc-pkg to fail. This blocks the current Cabal HEAD from working
with ghc HEAD.
I'd like to put in another request for the `ghc-pkg dump` feature that I
suggested originally. It would just dump all the packages in the
`describe` format. The difference is that it is not a query so we do not
fail if the result set is empty. Also, `dump` should not produce helpful
human readable error output like "{{{ghc-pkg: cannot find package matching
*}}}" because that will upset Cabal's parser.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2201>
GHC <http://www.haskell.org/ghc/>
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