#1839: need ghc-pkg dump feature
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Reporter: duncan | Owner:
Type: feature request | Status: new
Priority: normal | Milestone: 6.10 branch
Component: Compiler | Version: 6.8.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Comment (by duncan):
I know we've made changes to ghc-pkg in the HEAD branch. I'd still very
much like to see a simple dump feature included in ghc-pkg in time for
ghc-6.8.3.
Cabal does not need any complex query interface but it does at a minimum
need to know what versions of what dependencies each existing package
uses. This is necessary to avoid or at least detect problems where we
build a package that uses two other packages that were built against
different versions of another common package.
The most common example in the wild at the moment is people adding
bytestring-0.9.0.4 in addition to the bytestring-0.9.0.1 that came with
ghc-6.8.2 and then half their packages are built against one version and
half against the other and when we try to use packages built against
different versions we get a type error about
{{{bytestring-0.9.0.1:Data.ByteString.ByteString}}} not being the same as
{{{bytestring-0.9.0.4:Data.ByteString.ByteString}}}.
Cabal could and should detect this situation, and cabal-install should
plan around it in its dependency resolution algorithm. However in both
cases we require the dependency information of the existing installed
packages.
Not that many people are triping up over this just yet, but I think with
more hackage automation we will. Especially with automated hackage QA
where we want to build every version of every package to see if it works.
As I say, I think we want this on the 6.8.3 timescale, rather than having
to wait for 6.10. If this 'bulk' feature is going to go in for 6.8.3 then
fine, otherwise I suggest the simple 'dump' command that I suggested
originally.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1839#comment:7>
GHC <http://www.haskell.org/ghc/>
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