Warn on all out-of-range literals in pats/exprs

Summary:
These changes were motivated by #13256. While poking around, I
realized we weren't very consistent in our "-Woverflowed-literals"
warnings. This patch fixes that by:

  * warning earlier on in the pipeline (ie. before we've desugared
    'Int' patterns into 'I# Int#')
  * handling 'HsLit' as well as 'HsOverLit' (this covers unboxed
    literals)
  * covering more pattern / expression forms

4/6 of the warnings in the 'Overflow' test are due to this patch. The
other two are mostly for completeness.

Also fixed a missing empty-enumeration warning for 'Natural'.

This warnings were tripped up by the 'Bounded Word' instance (see #9505),
but the fix was obvious and simple: use unboxed word literals.

Test Plan: make TEST=Overflow && make TEST=T10930

Reviewers: hvr, bgamari, RyanGlScott

Reviewed By: RyanGlScott

Subscribers: RyanGlScott, rwbarton, carter

GHC Trac Issues: #13256, #10930

Differential Revision: https://phabricator.haskell.org/D5181

1 files changed, 20 insertions, 6 deletions

diff --git a/compiler/deSugar/DsMonad.hs b/compiler/deSugar/DsMonad.hs
index 5d597912e5..7742f8cd76 100644
--- a/compiler/deSugar/DsMonad.hs
+++ b/compiler/deSugar/DsMonad.hs
@@ -66,6 +66,7 @@ import PrelNames
 import RdrName
 import HscTypes
 import Bag
+import BasicTypes ( Origin )
 import DataCon
 import ConLike
 import TyCon
@@ -104,14 +105,27 @@ instance Outputable DsMatchContext where
   ppr (DsMatchContext hs_match ss) = ppr ss <+> pprMatchContext hs_match
 
 data EquationInfo
-  = EqnInfo { eqn_pats :: [Pat GhcTc],  -- The patterns for an eqn
-                -- NB: We have /already/ applied decideBangHood to
-                -- these patterns.  See Note [decideBangHood] in DsUtils
-
-              eqn_rhs  :: MatchResult } -- What to do after match
+  = EqnInfo { eqn_pats :: [Pat GhcTc]
+              -- ^ The patterns for an equation
+              --
+              -- NB: We have /already/ applied 'decideBangHood' to
+              -- these patterns.  See Note [decideBangHood] in "DsUtils"
+
+            , eqn_orig :: Origin
+              -- ^ Was this equation present in the user source?
+              --
+              -- This helps us avoid warnings on patterns that GHC elaborated.
+              --
+              -- For instance, the pattern @-1 :: Word@ gets desugared into
+              -- @W# -1## :: Word@, but we shouldn't warn about an overflowed
+              -- literal for /both/ of these cases.
+
+            , eqn_rhs  :: MatchResult
+              -- ^ What to do after match
+            }
 
 instance Outputable EquationInfo where
-    ppr (EqnInfo pats _) = ppr pats
+    ppr (EqnInfo pats _ _) = ppr pats
 
 type DsWrapper = CoreExpr -> CoreExpr
 idDsWrapper :: DsWrapper