Implement independent goals #2500
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It turns out not to be the right solution for general private dependencies and is just complicated. However we keep qualified goals, just much simpler. Now dependencies simply inherit the qualification of their parent goal. This gets us closer to the intended behaviour for the --independent-goals feature, and for the simpler case of private dependencies for setup scripts. When not using --independent-goals, the solver behaves exactly as before (tested by comparing solver logs for a hard hackage goal). When using --independent-goals, now every dep of each independent goal is qualified, so the dependencies are solved completely independently (which is actually too much still).
POption annotates a package choice with a "linked to" field. This commit just introduces the datatype and deals with the immediate fallout, it doesn't actually use the field for anything.
This is implemented as a separate pass so that it can be understood independently of the rest of the solver.
In particular, in the definition of dependencyInconsistencies. One slightly annoying thing is that in order to validate an install plan, we need to know if the goals are to be considered independent. This means we need to pass an additional Bool to a few functions; to limit the number of functions where this is necessary, also recorded whether or not goals are independent as part of the InstallPlan itself.
Since we didn't really have a unit test setup for the solver yet, this introduces some basic tests for solver, as well as tests for independent goals specifically.
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Oops, sorry, forgot to add a module to |
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I'll try to review this early next week. Please ping me again if you don't hear back then. |
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There are some failures on 7.4.2/7.6.3: Leaving this PR for @kosmikus to review. |
This address @23Skidoo's comment #2500 (comment)
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BTW, I very much enjoyed reading your blog post and I think that the work you're doing on Cabal is very cool. |
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I see you've fixed the compatibility problems by adding a |
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@kosmikus Only reason I felt okay to add it as a dependency is because it's only necessary for the test suite, not for cabal-install itself (and since the test suite already depends on tasty, which depends on tagged, it's not actually a new dependency). |
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@23Skidoo Thanks! Glad you liked the blogpost :) |
This is the next PR in the quest for setup dependencies, and implements independent goals and linking, as described in detail in the blog post
Qualified Goals in the Cabal Solver
This does not change any user observable behaviour -- in particular, we do not make independent goals available to the user as a command line argument (though we could); but having the infrastructure there will be essential for treating setup dependencies as independent, as well as a number of other features that can be built on top of this. One of those features will be base-3-shim support, so that we can change away from using the top-down solver as a default under certain circumstances. That however will be the topic of a later PR.