#2201: "ghc-pkg --user describe '*'" fails with empty user db
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Reporter: duncan | Owner:
Type: bug | Status: new
Priority: low | Milestone: 6.10 branch
Component: Compiler | Version: 6.9
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Comment (by duncan):
Though I should note that we need to have this fixed in the 6.10 release
or Cabal will not play nicely with it. The workaround is quite horrible.
So the question is, how should we get the info from ghc-pkg, bearing in
mind that in future we expect the package databases to be really quite
large, in the 100's of packages.
In some ways the current system cabal-install uses for the hackage package
index is quite nice. It loads the entire index into memory but it does not
parse each entry immediately. Instead it does that lazily so that if we
only inspect a small number of the packages then it's quite cheap.
I think we could do a similar trick with ghc-pkg. If it can dump all the
info to stdout sufficiently quickly (even for large databases) then so
long as we can identify each record without parsing the whole thing then
we can probably make it quick enough.
Splitting just based on seeing "\nname:" is probably quick enough and is
probably unambiguous. Or we could consider using some other way to
delineate records.
So on balance I think `ghc-pkg dump` is a sensible way to go, though I'd
prefer a better way of identifying record boundaries.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2201#comment:3>
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