#12518: Allow customizing immutable package dbs by stacking -------------------------------------+------------------------------------- Reporter: harendra | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Package system | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ezyang): So, what do you want to happen if a single package database has multiple exposed copies of a package; e.g. package.conf has both p-0.1 and p-0.2 (which are both exposed). Then do you want p-0.2? How about if it has two copies of p-0.2 (with different installed package IDs)? Which one is picked is left unspecified? It's also worth mentioning how the `exposed` flag ties into this. For the initial visibility calculation, you probably don't want not-exposed packages to be considered at all. So if we have pkg-0.1 (exposed), and then on the occluding package db, pkg-0.2 (not exposed), we should use pkg-0.1. (Maybe you don't care, because you never not expose? But the behavior needs to be ironed out.) If so, what should happen if I say `-package pkg`? The current behavior (without occlusion) is to pick the latest version in ANY database, no matter if it's exposed or not. So I guess we would then have to pick out pkg-0.2 from the top database, hiding pkg-0.1 in the process. I am also unsure about this comment:
If the package is broken it should report error rather than silently choosing from the next db.
OK I also need more clarification on this. So if I say `-package base` you still want to pick out `base` from the system package database, right? So do you want something like, "if you request a package `pkgname`, and it is occluded by a broken package, you want this to error. Do you also want this behavior for `-package pkg-1.0`? What if there are two copies of `pkg-1.0` in the top-most package db, one is broken and one isn't? How about if there is `pkg-0.9` which is broken and `pkg-1.0` which is not? Also, suppose there is no `-package` flag specified. If there are broken packages in the top-most database, should we immediately error? (I guess not?) (When you answer these, please edit the ticket description so that it's up-to-date.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12518#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler