[commit: ghc] master: Remove ASSERTion about increasing TcLevels (a754a42)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/a754a420b53cd2210ef60dcd695bf3334af2e400/ghc

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

commit a754a420b53cd2210ef60dcd695bf3334af2e400
Author: Richard Eisenberg <rae at cs.brynmawr.edu>
Date:   Thu Jul 12 16:10:34 2018 -0400

    Remove ASSERTion about increasing TcLevels
    
    This removes an ASSERTion that TcLevels should increase by
    exactly one in every implication. While this is a sensible
    goal, it's not true today, and we should not be crippling
    DEBUG for everyone while debugging this.
    
    The ASSERT was added in 261dd83cacec71edd551e9c581d05285c9ea3226


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

a754a420b53cd2210ef60dcd695bf3334af2e400
 compiler/typecheck/TcSimplify.hs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/compiler/typecheck/TcSimplify.hs b/compiler/typecheck/TcSimplify.hs
index 13a3f73..c57ef56 100644
--- a/compiler/typecheck/TcSimplify.hs
+++ b/compiler/typecheck/TcSimplify.hs
@@ -1495,7 +1495,8 @@ solveImplication imp@(Implic { ic_tclvl  = tclvl
   = do { inerts <- getTcSInerts
        ; traceTcS "solveImplication {" (ppr imp $$ text "Inerts" <+> ppr inerts)
 
-       ; when debugIsOn check_tc_level
+       -- commented out; see `where` clause below
+       -- ; when debugIsOn check_tc_level
 
          -- Solve the nested constraints
        ; (no_given_eqs, given_insols, residual_wanted)
@@ -1544,10 +1545,15 @@ solveImplication imp@(Implic { ic_tclvl  = tclvl
     -- TcLevels must be strictly increasing (see (ImplicInv) in
     -- Note [TcLevel and untouchable type variables] in TcType),
     -- and in fact I thinkthey should always increase one level at a time.
+
+    -- Though sensible, this check causes lots of testsuite failures. It is
+    -- remaining commented out for now.
+    {-
     check_tc_level = do { cur_lvl <- TcS.getTcLevel
                         ; MASSERT2( tclvl == pushTcLevel cur_lvl
                                   , text "Cur lvl =" <+> ppr cur_lvl $$
                                     text "Imp lvl =" <+> ppr tclvl ) }
+    -}
 
 ----------------------
 setImplicationStatus :: Implication -> TcS (Maybe Implication)