• Edward Z. Yang's avatar
    Correctly account for -package-db ordering when picking packages. · e0eaea91
    Edward Z. Yang authored
    Summary:
    When I originally implemented ABI-based shadowing as per
    ee4e1654, I switched our strategy
    from pasting together lists to creating a map of all units first,
    and then selecting packages from this.  However, what I did
    not realize when doing this was that we actually depended
    on the *ordering* of these lists later, when we selected
    a preferred package to use.
    
    The crux is if I have -package-db db1 -package-db db2 -package p-0.1,
    and p-0.1 is provided by both db1 and db2, which one does the
    -package flag select?  Previously, this was undetermined; now
    we always select the instance from the LATEST package database.
    (If p-0.1 shows up multiple times in the same database, once again
    the chosen package is undefined.)
    
    The reason why cabal08 intermittently failed was that, in practice,
    we were sorting on the UnitId, so when we bumped version numbers,
    that often wibbled the UnitIds so that they compared oppositely.
    I've extended the test so that we check that the relation is
    antisymmetric.
    
    Fixes #13313
    Signed-off-by: default avatarEdward Z. Yang <ezyang@cs.stanford.edu>
    
    Test Plan: validate
    
    Reviewers: bgamari, austin
    
    Subscribers: rwbarton, thomie
    
    Differential Revision: https://phabricator.haskell.org/D3369
    e0eaea91
Packages.hs 83.9 KB