[commit: ghc] ghc-8.2: Fix incorrect ambiguity error on identically-named data constructors (343cb32)

[git at git.haskell.org]

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

On branch  : ghc-8.2
Link       : http://ghc.haskell.org/trac/ghc/changeset/343cb32d0983f576d344a2d04a35c3fd6eecf2c5/ghc

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commit 343cb32d0983f576d344a2d04a35c3fd6eecf2c5
Author: Soham Chowdhury <chow.soham at gmail.com>
Date:   Thu May 11 15:40:18 2017 -0400

    Fix incorrect ambiguity error on identically-named data constructors
    
    Given multiple in-scope constructors with the same name, say `A`, and a
    function of type `A -> Int`, say, the compiler reports both a "type `A`
    is not in scope" and (incorrectly) an ambiguity error. The latter
    shouldn't be there if `DataKinds` isn't enabled.
    
    This issue was recommended to me by @mpickering as a suitable first
    task, and the fix was also outlined in the original Trac ticket. It
    involved a simple reordering of the steps taken in `lookup_demoted` in
    `RnEnv.hs`. The fix is to make the `DataKinds` check happen earlier,
    ensuring that the ambiguity check doesn't happen at all if we know the
    constructors couldn't have been promoted.
    
    Signed-off-by: Soham Chowdhury <chow.soham at gmail.com>
    
    Reviewers: mpickering, austin, bgamari
    
    Reviewed By: mpickering, bgamari
    
    Subscribers: rwbarton, thomie
    
    GHC Trac Issues: #13568
    
    Differential Revision: https://phabricator.haskell.org/D3547
    
    (cherry picked from commit 1381c142cd8d030f9997cdc206dcad006c028bbb)


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343cb32d0983f576d344a2d04a35c3fd6eecf2c5
 compiler/rename/RnEnv.hs                            | 21 +++++++++++----------
 testsuite/tests/module/mod122.stderr                |  4 +++-
 testsuite/tests/module/mod123.stderr                |  4 +++-
 testsuite/tests/module/mod124.stderr                |  1 +
 testsuite/tests/module/mod127.stderr                |  1 +
 testsuite/tests/module/mod29.stderr                 |  1 +
 testsuite/tests/module/mod50.stderr                 |  4 +++-
 .../tests/parser/should_fail/readFail001.stderr     |  1 +
 .../tests/rename/prog003/rename.prog003.stderr      |  4 +++-
 testsuite/tests/rename/should_fail/T13568.hs        |  8 ++++++++
 testsuite/tests/rename/should_fail/T13568.stderr    |  4 ++++
 testsuite/tests/rename/should_fail/T13568a.hs       |  3 +++
 testsuite/tests/rename/should_fail/T1595a.stderr    |  4 +++-
 testsuite/tests/rename/should_fail/T5745.stderr     |  4 +++-
 testsuite/tests/rename/should_fail/all.T            |  1 +
 testsuite/tests/typecheck/should_fail/T1595.stderr  |  6 ++++--
 .../tests/typecheck/should_fail/tcfail048.stderr    |  4 +++-
 .../tests/typecheck/should_fail/tcfail053.stderr    |  4 +++-
 18 files changed, 59 insertions(+), 20 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 343cb32d0983f576d344a2d04a35c3fd6eecf2c5