Allow unsaturated uses of unlifted types in Core

Currently Core Lint checks for unsaturated uses of unlifted types in . These are easily produced in the new type-indexed Typeable scheme. For instance, consider solving for Typeable # (Array# Int):

• We decompose the application into wanteds Typeable (* -> #) Array# and Typeable * Int
• We construct dictionaries for both, giving us a term typeRepArray# :: TypeRep (* -> #) Array#

While nothing seems to blow up with this patch,

diff --git a/compiler/coreSyn/CoreLint.hs b/compiler/coreSyn/CoreLint.hs
index 99625c9..2c401de 100644
--- a/compiler/coreSyn/CoreLint.hs
+++ b/compiler/coreSyn/CoreLint.hs
@@ -1040,7 +1040,7 @@ lintType ty@(TyConApp tc tys)
   = lintType ty'   -- Expand type synonyms, so that we do not bogusly complain
                    --  about un-saturated type synonyms
 
-  | isUnliftedTyCon tc || isTypeSynonymTyCon tc || isTypeFamilyTyCon tc
+  | isTypeSynonymTyCon tc || isTypeFamilyTyCon tc
        -- Also type synonyms and type families
   , length tys < tyConArity tc
   = failWithL (hang (text "Un-saturated type application") 2 (ppr ty))

I otherwise have no reason to believe that this is safe.

Trac metadata

Trac field	Value
Version	8.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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CC	goldfire, simonpj
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