[commit: ghc] master: Fix solveOneFromTheOther for RecursiveSuperclasses (6506980)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/65069806ea3637882d584e785dcb9e650271e4b6/ghc

>---------------------------------------------------------------

commit 65069806ea3637882d584e785dcb9e650271e4b6
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Wed Feb 7 11:57:40 2018 +0000

    Fix solveOneFromTheOther for RecursiveSuperclasses
    
    This patch fixes the redundant superclass expansion
    in Trac #14774.
    
    The main change is to fix TcInterac.solveOneFromTheOther, so
    that it does not prefer a work-item with a binding if that binding
    transitively depends on the inert item we are comparing it with.
    
    Explained in Note [Replacement vs keeping] in TcInert, esp
    item (c) of the "Constraints coming from the same level" part.
    
    To make this work I refactored out a new function
    TcEvidence.findNeededEvVars, which was previously buried
    inside TcSimplify.neededEvVars.
    
    I added quite a few more comments and signposts about superclass
    expansion.


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65069806ea3637882d584e785dcb9e650271e4b6
 compiler/typecheck/TcCanonical.hs                  | 43 +++++++++++++++-----
 compiler/typecheck/TcEvidence.hs                   | 29 ++++++++++++-
 compiler/typecheck/TcInteract.hs                   | 47 ++++++++++++++--------
 compiler/typecheck/TcSimplify.hs                   | 22 +++-------
 testsuite/tests/typecheck/should_compile/Makefile  |  4 ++
 testsuite/tests/typecheck/should_compile/T14774.hs | 13 ++++++
 .../tests/typecheck/should_compile/T14774.stdout   |  3 ++
 testsuite/tests/typecheck/should_compile/all.T     |  1 +
 8 files changed, 119 insertions(+), 43 deletions(-)

Diff suppressed because of size. To see it, use:

    git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc 65069806ea3637882d584e785dcb9e650271e4b6