Cabal checks with ghc-pkg for where the .haddock file of dependent packages should be. However even though ghc-pkg says it's there, it very often isn't there. In this case we still ask haddock to use it, and haddock justifiably complains.
Cabal should check that the .haddock file actually exists. If it does not, Cabal should warn that links to this dependent package will not be generated because the docs for this dependent package are not installed. It should then not tell haddock to use that package.
Current behavior:
{{
$ runghc Setup.lhs haddock
Preprocessing library bytestring-0.9...
Running Haddock for bytestring-0.9...
haddock: /usr/share/doc/ghc-6.4.2/html/libraries/base/base.haddock: openBinaryFile: does not exist (No such file or directory)
}}
Desired behavior:
{{
$ runghc Setup.lhs haddock
Preprocessing library bytestring-0.9...
Running Haddock for bytestring-0.9...
Warning: Documentation for package base is not installed. No links will be generated.
Documentation created: dist/doc/html/bytestring/index.html
}}
Or something like that, I'm sure someone can think of a clear friendly warning message
This should be an easy bug for some new Cabal hacker to have a go at. It should just require modifying makeReadInterface in the Distribution.Simple.Haddock module.
