[commit: ghc] master: Add `PatSynSigSkol` and modify `PatSynCtxt` (997312b)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/997312b04c56017197250096d61f3e8fab502319/ghc

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

commit 997312b04c56017197250096d61f3e8fab502319
Author: Rik Steenkamp <rik at ewps.nl>
Date:   Wed Mar 23 16:17:27 2016 +0100

    Add `PatSynSigSkol` and modify `PatSynCtxt`
    
    As the type of a pattern synonym cannot in general be represented by a
    value of type Type, we cannot use a value `SigSkol (PatSynCtxt n) (Check
    ty)` to represent the signature of a pattern synonym (this causes
    incorrect signatures to be printed in error messages). Therefore we now
    represent it by a value `PatSynSigSkol n` (instead of incorrect
    signatures we simply print no explicit signature).
    
    Furthermore, we rename `PatSynCtxt` to `PatSynBuilderCtxt`, and use
    `SigSkol (PatSynBuilderCtxt n) (Check ty)` to represent the type of a
    bidirectional pattern synonym when used in an expression context.
    Before, this type was represented by a value `SigSkol (PatSynCtxt n)
    (Check ty)`, which caused incorrect error messages.
    
    Also, in `mk_dict_err` of `typecheck\TcErrors.hs` we now distinguish
    between all enclosing implications and "useful" enclosing implications,
    for better error messages concerning pattern synonyms. See `Note [Useful
    implications]`.
    
    See the Phabricator page for examples.
    
    Reviewers: mpickering, goldfire, simonpj, austin, bgamari
    
    Reviewed By: bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D1967
    
    GHC Trac Issues: #11667


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997312b04c56017197250096d61f3e8fab502319
 compiler/basicTypes/PatSyn.hs                    | 15 ++++
 compiler/typecheck/TcErrors.hs                   | 88 ++++++++++++++++--------
 compiler/typecheck/TcPatSyn.hs                   |  5 +-
 compiler/typecheck/TcRnTypes.hs                  |  7 ++
 compiler/typecheck/TcSimplify.hs                 |  4 +-
 compiler/typecheck/TcType.hs                     | 17 ++---
 compiler/typecheck/TcValidity.hs                 | 38 +++++-----
 testsuite/tests/patsyn/should_fail/T10873.stderr |  9 ++-
 testsuite/tests/patsyn/should_fail/T11039.stderr |  4 +-
 testsuite/tests/patsyn/should_fail/T11667.hs     | 31 +++++++++
 testsuite/tests/patsyn/should_fail/T11667.stderr | 43 ++++++++++++
 testsuite/tests/patsyn/should_fail/all.T         |  1 +
 12 files changed, 194 insertions(+), 68 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 997312b04c56017197250096d61f3e8fab502319