[commit: ghc] master: Make use of boot TyThings during typechecking. (6998772)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/6998772043a7f0b0360116eb5ffcbaa5630b21fb/ghc

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

commit 6998772043a7f0b0360116eb5ffcbaa5630b21fb
Author: Edward Z. Yang <ezyang at fb.com>
Date:   Sun Oct 29 20:15:07 2017 -0400

    Make use of boot TyThings during typechecking.
    
    Summary:
    Suppose that you are typechecking A.hs, which transitively imports,
    via B.hs, A.hs-boot.  When we poke on B.hs and discover that it
    has a reference to a type from A, what TyThing should we wire
    it up with?  Clearly, if we have already typechecked A, we
    should use the most up-to-date TyThing: the one we freshly
    generated when we typechecked A.  But what if we haven't typechecked
    it yet?
    
    For the longest time, GHC adopted the policy that this was
    *an error condition*; that you MUST NEVER poke on B.hs's reference
    to a thing defined in A.hs until A.hs has gotten around to checking
    this.  However, actually ensuring this is the case has proven
    to be a bug farm.  The problem was especially poignant with
    type family consistency checks, which eagerly happen before
    any typechecking takes place.
    
    This patch takes a different strategy: if we ever try to access
    an entity from A which doesn't exist, we just fall back on the
    definition of A from the hs-boot file.  This means that you may
    end up with a mix of A.hs and A.hs-boot TyThings during the
    course of typechecking.
    
    Signed-off-by: Edward Z. Yang <ezyang at fb.com>
    
    Test Plan: validate
    
    Reviewers: simonpj, bgamari, austin, goldfire
    
    Subscribers: thomie, rwbarton
    
    GHC Trac Issues: #14396
    
    Differential Revision: https://phabricator.haskell.org/D4154


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

6998772043a7f0b0360116eb5ffcbaa5630b21fb
 compiler/iface/TcIface.hs                          |  65 +++++++----
 compiler/rename/RnSource.hs                        | 120 ---------------------
 compiler/typecheck/FamInst.hs                      |  78 +++-----------
 compiler/typecheck/TcRnDriver.hs                   |   4 +-
 compiler/typecheck/TcRnMonad.hs                    |   1 -
 compiler/typecheck/TcRnTypes.hs                    |   7 --
 compiler/typecheck/TcTyClsDecls.hs                 |   4 -
 testsuite/tests/typecheck/should_compile/T14396.hs |   4 +
 .../tests/typecheck/should_compile/T14396.hs-boot  |   2 +
 .../tests/typecheck/should_compile/T14396a.hs      |   5 +
 .../tests/typecheck/should_compile/T14396b.hs      |   4 +
 .../A.hs => typecheck/should_compile/T14396f.hs}   |   2 +-
 testsuite/tests/typecheck/should_compile/all.T     |   1 +
 .../tests/typecheck/should_fail/T12042.stderr      |  10 +-
 14 files changed, 85 insertions(+), 222 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 6998772043a7f0b0360116eb5ffcbaa5630b21fb