#326: Cabal should support Cabal-version-dependent Setup.hs ----------------------------+----------------------------------------------- Reporter: claus | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: Cabal library | Version: 1.2.3.0 Severity: normal | Resolution: Keywords: | Difficulty: normal Ghcversion: 6.8.2 | Platform: ----------------------------+----------------------------------------------- Comment (by claus): Replying to [comment:1 duncan]:

I'm not sure I understand why exact versions are needed and why testing lower bounds is not enough. Testing multi-component versions in CPP macro language is not very easy.

In this case, there is only one component to version-test: Cabal, as implicitly available in `Setup.hs` code. Exact versions are needed because later versions of Cabal are highly likely to break the code. A small example package with that issue is `ghc-paths`, I think. One version works with ghc head's Cabal (1.5?), another version works with hackage's Cabal (1.4?). So there is code that could be made to work with both, if Cabal provided its version as a CPP macro. But just as the 1.4 version doesn't work with 1.5, so I wouldn't bet on the 1.5 version working with 1.7. Hence the need for exact versions. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/326#comment:2 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects

#326: Cabal should support Cabal-version-dependent Setup.hs ----------------------------+----------------------------------------------- Reporter: claus | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: Cabal library | Version: 1.2.3.0 Severity: normal | Resolution: Keywords: | Difficulty: normal Ghcversion: 6.8.2 | Platform: ----------------------------+----------------------------------------------- Comment (by claus): shouldn't that be: {{{ #ifdef MIN_VERSION_CABAL #if MIN_VERSION_CABAL(1,6,0) && !MIN_VERSION_CABAL(1,7,0) -- stuff for 1.6 #else -- not supported/not yet tested #endif #else -- stuff for 1.4 #endif }}} But yes, those macros should help. So much so that it might be good to advertize their existence to library authors/hackage users, to start reducing `Setup` compile errors. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/326#comment:4 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects

#326: Cabal should support Cabal-version-dependent Setup.hs ----------------------------+----------------------------------------------- Reporter: claus | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: Cabal library | Version: 1.2.3.0 Severity: normal | Resolution: Keywords: | Difficulty: normal Ghcversion: 6.8.2 | Platform: ----------------------------+----------------------------------------------- Comment (by claus): Ah, I see - the macros are only temporarily available while building. I had assumed that Cabal would generate them permanently for each package, so that not only cabal-install could profit from them. A CABAL_VERSION macro could just as well be part of the cabal package, without auto-generation, but if cabal doesn't have an include directory yet, I certainly don't insist on a CPP-based solution, as long as we can find something else. What about the other suggestion? Standardise a format for including the Cabal-version in the `Setup` file name, and make cabal-install select the right one (that is something even users might manage to do manually, but it'd be nice if automated scripts could handle it as well). One could even code that up in Haskell, at the expense of interpreting `Setup-<version>`. However, Cabal should provide that code, and check that the required versions exist, just as it ought to provide a default `Setup` for build-type `Simple`. {{{ -- sketch of Cabal-version-dependent Setup: -- get Cabal version -- execute Setup-<version> }}} No CPP, and it can be started without changing Cabal, just standardizing the file name format. Since it is unlikely that the code for getting the Cabal version or for executing processes is going to be stable for long, such a `Setup.hs` file should really come with Cabal, for a build-type Setup-select or something, hiding the implementation details. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/326#comment:6 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects

#326: Cabal should support Cabal-version-dependent Setup.hs ----------------------------+----------------------------------------------- Reporter: claus | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: Cabal library | Version: 1.2.3.0 Severity: normal | Resolution: Keywords: | Difficulty: normal Ghcversion: 6.8.2 | Platform: ----------------------------+----------------------------------------------- Comment (by claus):

Cabal makes them available while building, a macro for testing the version of each dependency. It's not just cabal-install, it's done in the Cabal lib. I'm not sure what you're suggesting as an alternative, that we install the .h files too? I guess that would let packages that build without using Cabal to use the version macros of packages that were built with Cabal. Is that what you mean? Is that a major advantage?

Yes, I had assumed that the .h files would be installed with the package. Then it would be available to all importers, anytime, not just during building with Cabal. One might think that all Haskell code should be build via Cabal, always, but that isn't true, and `Setup.hs` seems to be our first exception to that scheme.

The problem with using these macros for compiling Setup.hs is that that would only help cabal-install and would actively hinder everyone else. `runghc Setup` would stop working.

I don't understand? If I have a pragma in `Setup.hs` that enables CPP, and there is a macro giving the version number for the installed cabal package that `Setup.hs` is using, why would `runhaskell Setup` not work? -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/326#comment:8 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects

It would not work for hugs or nhc98 because hugs does not grok the CPP

#326: Cabal should support Cabal-version-dependent Setup.hs ----------------------------+----------------------------------------------- Reporter: claus | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: Cabal library | Version: 1.2.3.0 Severity: normal | Resolution: Keywords: | Difficulty: normal Ghcversion: 6.8.2 | Platform: ----------------------------+----------------------------------------------- Comment (by claus): Replying to [comment:9 duncan]: pragma and neither let us specify extra info like `include-dirs` in the package resistration, so even if they did cpp they would not be able to find the header file. Interesting. How do hugs and nhc98 survive processing base without CPP and include-dir? Anyway, that brings us back to a CPP-less approach. Here is that sketch again, this time in code: {{{ import System.IO import System.Process import Text.Regex import System.Exit import Control.Monad import System.Directory die last_words = do hPrint stderr last_words exitFailure condition `orElse` action = do c <- condition unless c action main = do (_,o,_,_) <- runInteractiveCommand "ghc-pkg field Cabal version" field <- hGetContents o case matchRegex (mkRegex "version: ([0-9.]*)") field of Just [version] -> do let setup = "Setup-"++version++".hs" doesFileExist setup `orElse` die ("can't find version-specific Setup source: "++setup) runCommand $ "runhaskell "++setup _ -> die $ "can't determine Cabal version: "++field }}} I'm sure something less inelegant can be hacked up within Cabal, but I can never find what I'm looking for in `Distribution.*` (in spite of the many pieces of functionality available, it seems they are only really meant to be used in one specific context/order/framework, not in isolation). -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/326#comment:10 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects

#326: Cabal should support Cabal-version-dependent Setup.hs ----------------------------+----------------------------------------------- Reporter: claus | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: Cabal library | Version: 1.2.3.0 Severity: normal | Resolution: Keywords: | Difficulty: normal Ghcversion: 6.8.2 | Platform: ----------------------------+----------------------------------------------- Comment (by duncan): Yes, it could be done for nhc98 just as it is done for ghc if the `InstalledPackageInfo` files were installed. This depends on changes in nhc's build system to provide these files for all the libs that come with nhc98. It's all just work. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/326#comment:12 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects