Update levity polymorphism

This commit implements the proposal in
https://github.com/ghc-proposals/ghc-proposals/pull/29 and
https://github.com/ghc-proposals/ghc-proposals/pull/35.

Here are some of the pieces of that proposal:

* Some of RuntimeRep's constructors have been shortened.

* TupleRep and SumRep are now parameterized over a list of RuntimeReps.
* This
means that two types with the same kind surely have the same
representation.
Previously, all unboxed tuples had the same kind, and thus the fact
above was
false.

* RepType.typePrimRep and friends now return a *list* of PrimReps. These
functions can now work successfully on unboxed tuples. This change is
necessary because we allow abstraction over unboxed tuple types and so
cannot
always handle unboxed tuples specially as we did before.

* We sometimes have to create an Id from a PrimRep. I thus split PtrRep
* into
LiftedRep and UnliftedRep, so that the created Ids have the right
strictness.

* The RepType.RepType type was removed, as it didn't seem to help with
* much.

* The RepType.repType function is also removed, in favor of typePrimRep.

* I have waffled a good deal on whether or not to keep VoidRep in
TyCon.PrimRep. In the end, I decided to keep it there. PrimRep is *not*
represented in RuntimeRep, and typePrimRep will never return a list
including
VoidRep. But it's handy to have in, e.g., ByteCodeGen and friends. I can
imagine another design choice where we have a PrimRepV type that is
PrimRep
with an extra constructor. That seemed to be a heavier design, though,
and I'm
not sure what the benefit would be.

* The last, unused vestiges of # (unliftedTypeKind) have been removed.

* There were several pretty-printing bugs that this change exposed;
* these are fixed.

* We previously checked for levity polymorphism in the types of binders.
* But we
also must exclude levity polymorphism in function arguments. This is
hard to check
for, requiring a good deal of care in the desugarer. See Note [Levity
polymorphism
checking] in DsMonad.

* In order to efficiently check for levity polymorphism in functions, it
* was necessary
to add a new bit of IdInfo. See Note [Levity info] in IdInfo.

* It is now safe for unlifted types to be unsaturated in Core. Core Lint
* is updated
accordingly.

* We can only know strictness after zonking, so several checks around
* strictness
in the type-checker (checkStrictBinds, the check for unlifted variables
under a ~
pattern) have been moved to the desugarer.

* Along the way, I improved the treatment of unlifted vs. banged
* bindings. See
Note [Strict binds checks] in DsBinds and #13075.

* Now that we print type-checked source, we must be careful to print
* ConLikes correctly.
This is facilitated by a new HsConLikeOut constructor to HsExpr.
Particularly troublesome
are unlifted pattern synonyms that get an extra void# argument.

* Includes a submodule update for haddock, getting rid of #.

* New testcases:
  typecheck/should_fail/StrictBinds
  typecheck/should_fail/T12973
  typecheck/should_run/StrictPats
  typecheck/should_run/T12809
  typecheck/should_fail/T13105
  patsyn/should_fail/UnliftedPSBind
  typecheck/should_fail/LevPolyBounded
  typecheck/should_compile/T12987
  typecheck/should_compile/T11736

* Fixed tickets:
  #12809
  #12973
  #11736
  #13075
  #12987

* This also adds a test case for #13105. This test case is
* "compile_fail" and
succeeds, because I want the testsuite to monitor the error message.
When #13105 is fixed, the test case will compile cleanly.

1 files changed, 15 insertions, 3 deletions

diff --git a/compiler/deSugar/Match.hs b/compiler/deSugar/Match.hs
index 672157e0d7..f5c3cf5066 100644
--- a/compiler/deSugar/Match.hs
+++ b/compiler/deSugar/Match.hs
@@ -444,7 +444,18 @@ tidy1 v (AsPat (L _ var) pat)
 -}
 
 tidy1 v (LazyPat pat)
-  = do  { (_,sel_prs) <- mkSelectorBinds [] pat (Var v)
+    -- This is a convenient place to check for unlifted types under a lazy pattern.
+    -- Doing this check during type-checking is unsatisfactory because we may
+    -- not fully know the zonked types yet. We sure do here.
+  = do  { let unlifted_bndrs = filter (isUnliftedType . idType) (collectPatBinders pat)
+        ; unless (null unlifted_bndrs) $
+          putSrcSpanDs (getLoc pat) $
+          errDs (hang (text "A lazy (~) pattern cannot bind variables of unlifted type." $$
+                       text "Unlifted variables:")
+                    2 (vcat (map (\id -> ppr id <+> dcolon <+> ppr (idType id))
+                                 unlifted_bndrs)))
+
+        ; (_,sel_prs) <- mkSelectorBinds [] pat (Var v)
         ; let sel_binds =  [NonRec b rhs | (b,rhs) <- sel_prs]
         ; return (mkCoreLets sel_binds, WildPat (idType v)) }
 
@@ -705,7 +716,7 @@ matchWrapper ctxt mb_scr (MG { mg_alts = L _ matches
         ; locn   <- getSrcSpanDs
 
         ; new_vars    <- case matches of
-                           []    -> mapM newSysLocalDs arg_tys
+                           []    -> mapM newSysLocalDsNoLP arg_tys
                            (m:_) -> selectMatchVars (map unLoc (hsLMatchPats m))
 
         ; eqns_info   <- mapM (mk_eqn_info new_vars) matches
@@ -951,6 +962,7 @@ viewLExprEq (e1,_) (e2,_) = lexp e1 e2
     -- we have to compare the wrappers
     exp (HsWrap h e) (HsWrap h' e') = wrap h h' && exp e e'
     exp (HsVar i) (HsVar i') =  i == i'
+    exp (HsConLikeOut c) (HsConLikeOut c') = c == c'
     -- the instance for IPName derives using the id, so this works if the
     -- above does
     exp (HsIPVar i) (HsIPVar i') = i == i'
@@ -1012,7 +1024,7 @@ viewLExprEq (e1,_) (e2,_) = lexp e1 e2
     --        equating different ways of writing a coercion)
     wrap WpHole WpHole = True
     wrap (WpCompose w1 w2) (WpCompose w1' w2') = wrap w1 w1' && wrap w2 w2'
-    wrap (WpFun w1 w2 _)   (WpFun w1' w2' _)   = wrap w1 w1' && wrap w2 w2'
+    wrap (WpFun w1 w2 _ _) (WpFun w1' w2' _ _) = wrap w1 w1' && wrap w2 w2'
     wrap (WpCast co)       (WpCast co')        = co `eqCoercion` co'
     wrap (WpEvApp et1)     (WpEvApp et2)       = et1 `ev_term` et2
     wrap (WpTyApp t)       (WpTyApp t')        = eqType t t'