#649: better warning messages for why dependencies are missing / cannot be selected ---------------------------------+------------------------------------------ Reporter: duncan | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: cabal-install tool | Version: HEAD Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Comment(by duncan): Similarly, for installed constraints we should explain in error messages that an installed version is required and list any installed versions that were not suitable or were otherwise excluded. Consider for example: {{{ build-depends: base == 4.1.* }}} Suppose someone runs `cabal install` on this when the only available versions of base are 3.0.3 and 4.2.0 (ie using ghc-6.12.x). Currently we will report: {{{ cabal: cannot configure foo-1.0. It requires base ==4.1.* For the dependency on base ==4.1.* there are these packages: base-4.1.0.0. However none of them are available. base-4.1.0.0 was excluded because of the top level dependency base -any }}} This lists all the non-installed versions that satisfy the version constraint and tells us (badly) that they're no good because they're not installed. Instead in this situation it's probably better to say it needs an installed version and list the (hopefully) small number of installed versions, even if they do not satisfy the version constraint. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/649#comment:1 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects