On Mon, 2011-10-03 at 13:18 +0200, Joachim Breitner wrote:
Hi,
I’d like to propose that the package (shown by "ghc-pkg field <pkg> id" and used by "ghc-pkg field <pkg> depends") should only consist of the first three components of the package version, not all of them.
So I agree with your aims but I suggest a different approach. Also, we're conflating issues here: The "id" field (or the InstalledPackageId in Cabal parlance) is used to uniquely identify each package. This is not the same thing as an ABI. Note that currently, confusingly, the package id that Cabal creates (for ghc) is made up of the package name, version and abi hash. This makes people think it is an abi identifier when it is not. We need (in future) to be able to distinguish different packages that share the same ABI. So what needs to happen is that we include the ABI as a separate field in the package db. That abi need not contain the version number at all, it can be just some abi hash. Then whether the dependencies should then use an installed package id or a package abi is an interesting question. I think the right thing is to use installed package ids. Just because it would be possible to update a dependency to use the latest-ABI compatible version doesn't mean that it should be immediate and automatic. Indeed it would prevent us from having a persistent package database, as adding new packages would change the meaning of existing packages. Switching to a later ABI-compatible version of a dependency should be a deliberate act. Hence we should use installed package ids for dependencies. Duncan