• Ryan Scott's avatar
    Suppress redundant givens during error reporting · c552feea
    Ryan Scott authored
    Summary:
    When GHC reports that it cannot solve a constraint in error
    messages, it often reports what given constraints it has in scope.
    Unfortunately, sometimes redundant constraints (like `* ~ *`, from
    #15361) can sneak in. The fix is simple: blast away these redundant
    constraints using `mkMinimalBySCs`.
    
    Test Plan: make test TEST=T15361
    
    Reviewers: simonpj, bgamari
    
    Subscribers: rwbarton, thomie, carter
    
    GHC Trac Issues: #15361
    
    Differential Revision: https://phabricator.haskell.org/D5002
    c552feea
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