Disallow unboxed string literals in patterns (#13260)

Signed-off-by: Rupert Horlick <ruperthorlick@gmail.com>

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3286

compiler/parser/RdrHsSyn.hs

@@ -829,6 +829,9 @@ checkAPat msg loc e0 = do
  case e0 of
    EWildPat -> return (WildPat placeHolderType)
    HsVar x  -> return (VarPat x)
+   HsLit (HsStringPrim _ _) -- (#13260)
+       -> parseErrorSDoc loc (text "Illegal unboxed string literal in pattern:" $$ ppr e0)
+
    HsLit l  -> return (LitPat l)
 
    -- Overloaded numeric patterns (e.g. f 0 x = x)

testsuite/tests/parser/should_fail/T13260.hs

+{-# LANGUAGE MagicHash #-}
+
+module T13260 where
+
+  g y = case y of
+    "a"# -> True
+    _    -> False

testsuite/tests/parser/should_fail/T13260.stderr

+
+T13260.hs:6:5: error:
+    Illegal unboxed string literal in pattern:
+    "a"#

testsuite/tests/parser/should_fail/all.T

@@ -96,3 +96,4 @@ test('T10498b', normal, compile_fail, [''])
 test('T12051', normal, compile_fail, [''])
 test('T12429', normal, compile_fail, [''])
 test('T12811', normal, compile_fail, [''])
+test('T13260', normal, compile_fail, [''])