#10566: Move "package key" generation to GHC -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: bug | Status: new Priority: normal | Milestone: 7.12.1 Component: Package system | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by ezyang):
Sounds good in general terms. But up to now GHC has been primary a module-at-a-time compiler. To compute a package key it needs to know all about a package. Do you intend to do this by giving it a Backpack file describing the package? Or what?
So, actually, we can do this very nicely: if you compile a GHC module with `-hide-all-packages` and a list of `-package` flags, then GHC can infer the package key by just looking at each exposed package, and including their hash in the computed package key. So, in some since Cabal is still "calculating" many of the important parameters of the package key (the package name, version, and what dependencies are used), but GHC does the actual final calculation in the end. Here's how it looks without Backpack: 1. Cabal calls GHC with `-package-name foo-0.1 -hide-all-packages -package-id bar-0.1-ABCD ...` 2. GHC computes the package state with the package flags, getting a list of exposed packages with `PkgConfig`s 3. Compute the package key by hashing the source package ID and package key of each included exposed package. With Backpack it's a little trickier, because we don't necessarily want to hash the package key of included packages: instead, you want to hash the "version hash" of each package, which is like a package key but minus hole instantiation.
And how does Cabal get to know what key GHC computed?
My initial thought is a new major mode `ghc --package-key -package-name foo-0.1 -hide-all-packages -package bar-0.1-ABCD ...` which outputs the package key. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10566#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler