[Hackage] #725: Distinguish speculative and required build-depends upper bound
#725: Distinguish speculative and required build-depends upper bound ---------------------------------+------------------------------------------ Reporter: ezyang | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: cabal-install tool | Version: 1.6.0.3 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ When a package adds a build-dependency on another package, it's good form to follow the Package Versioning Policy and add a speculative upper bound that is x.(y+1), if the current version is x.y. This is great, but in many cases the next version will /not/ break compatibility with your package. In that case, once you have tested that the dependency is fine, you can bump the upper bound. As the list of dependencies for any respectable Cabal package can be quite long, it may be useful to have some sort of 'cabal whatsnew' command which checks the upper bounds of your build dependencies and notifies you when there are newer versions than your upper bounds availble. Furthermore, there should be a mechanism for telling Cabal that the upper bound is required, and that the package will break if you try to bump it. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/725 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects
#725: Distinguish speculative and required build-depends upper bound ---------------------------------+------------------------------------------ Reporter: ezyang | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: cabal-install tool | Version: 1.6.0.3 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Comment(by duncan): I agree we should have tools that can help with checking if packages will in fact build with later versions of their deps. I'm not convinced at this stage that we need to record extra information in the .cabal file to distinguish "conservative" from "known" upper bounds. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/725#comment:1 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects
#725: Distinguish speculative and required build-depends upper bound ---------------------------------+------------------------------------------ Reporter: ezyang | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: cabal-install tool | Version: 1.6.0.3 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Comment(by wk): For testing whether a GHC bug had been fixed in HEAD, I just went through blindly bumping quite a few upper bounds in cabal dependency declarations in Agda and the packages it requires, since GHC HEAD of course contains versions that not everybody has tested against, yet. (The resulting Agda actually works.) Abstractly, for each package in the dependencies of a another package, there is a dependently-typed function {{{ status : \Pi version : Version . \powerset (flags version) -> {KnownToWork, KnownToBreak, Unknown} }}} (assuming no interaction between dependencies). This function is only very poorly approximated by the current range sets. The current scheme does not distinguish between {{{KnownToBreak}}} and {{{UnKnown}}}, and conservatively refuses to build for any version outside the declared range. This is a real hassle for the use case described above, namely trying out new versions of anything very deep down the dependency graph (like the packages that come with GHC...). If the dependency declaration allowed to distinguish between {{{KnownToBreak}}} and {{{UnKnown}}}, cabal could just issue a warning when compiling against a version with {{{UnKnown}}} status, and refuse (with an improved error message) when only finding {{{KnownToBreak}}} versions. By the way, an automatic tool run can only be used to obtain {{{KnownToBreak}}}, but (almost) never {{{KnownToWork}}} --- a "{{{KnownToCompile}}}" is in general only an {{{UnKnown}}}, and in the best case might, via {{{*Check}}}, be turned into {{{KnownToBreak}}}. I therefore strongly recommend to require a distinction between {{{KnownToBreak}}} and {{{UnKnown}}} in Cabal dependency declarations. Wolfram -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/725#comment:2 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects
#725: Distinguish speculative and required build-depends upper bound ---------------------------------+------------------------------------------ Reporter: ezyang | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: cabal-install tool | Version: 1.6.0.3 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Comment(by igloo): FWIW, this could make hackage regression testing with the GHC HEAD more useful. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/725#comment:3 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects
#725: Distinguish speculative and required build-depends upper bound ---------------------------------+------------------------------------------ Reporter: ezyang | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: cabal-install tool | Version: 1.6.0.3 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Comment(by duncan): Recording this extra information in the context of hackage is much easier. For one thing it can be discovered automatically. Adding this information to .cabal files is more tricky, we need a syntax for it and users have to specify it. -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/725#comment:4 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects
#725: Distinguish speculative and required build-depends upper bound ---------------------------------+------------------------------------------ Reporter: ezyang | Owner: Type: enhancement | Status: new Priority: normal | Milestone: Component: cabal-install tool | Version: 1.6.0.3 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Comment(by wk):
Recording this extra information in the context of hackage is much easier.
I don't understand exactly what you mean, but it seems to exclude recording this "extra information" for unpublished packages and local developments?
For one thing it can be discovered automatically.
You can discover automatically whether it compiles. You cannot, in general, discover automatically whether it works correctly.
Adding this information to .cabal files is more tricky, we need a syntax for it and users have to specify it.
I don't think the syntax question is tricky --- if you know the semantics you want to enable, you have tons of options. One particularly easy option would interpret the current ranges as establishing mappings to {{{KnownToWork}}}, and add a separate notation (perhaps using a {{{!}}} prefix) to establish mappings to {{{KnownToBreak}}}. Versions not mentioned in either would be interpreted as being mapped to {{{UnKnown}}}. I estimate that most currently-listed excluded upper bounds are intended to mean {{{UnKnown}}} and not {{{KnownToBreak}}}. Therefore, this would even be backwards-compatible. (The semantics of sequences of such positive or negative ranges would most naturally be {{{Map.foldWithKey Map.insert}}}, that is, a right-biased version of {{{Map.union}}}.) If {{{UnKnown}}} gives rise only to a warning instead of to a refusal to even attempt compilation (as it does now), that will make it also much easier for package authors to be honest about old versions they did not check against. Wolfram -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/725#comment:5 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects
#725: Distinguish speculative and required build-depends upper bound ---------------------------------+------------------------------------------ Reporter: ezyang | Owner: Type: enhancement | Status: new Priority: normal | Milestone: cabal-install-0.16 Component: cabal-install tool | Version: 1.6.0.3 Severity: normal | Keywords: Difficulty: unknown | Ghcversion: Platform: | ---------------------------------+------------------------------------------ Changes (by kosmikus): * milestone: => cabal-install-0.16 -- Ticket URL: http://hackage.haskell.org/trac/hackage/ticket/725#comment:6 Hackage http://haskell.org/cabal/ Hackage: Cabal and related projects
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