Revert "Normalize the element type of ListPat, fix #14547"

This reverts commit 361d23a8ebb44f5df5167306d7b98d8bd1724e06.

3 files changed, 1 insertions, 20 deletions

diff --git a/compiler/deSugar/Check.hs b/compiler/deSugar/Check.hs
index 7a5f889423..545aacef51 100644
--- a/compiler/deSugar/Check.hs
+++ b/compiler/deSugar/Check.hs
@@ -790,13 +790,10 @@ translatePat fam_insts pat = case pat of
   -- overloaded list
   ListPat (ListPatTc elem_ty (Just (pat_ty, _to_list))) lpats
     | Just e_ty <- splitListTyConApp_maybe pat_ty
-    , (_, norm_e_ty) <- normaliseType fam_insts Nominal e_ty
-         -- e_ty can be a type family instance, like
-         -- `It (List a)`, but we prefer `a`, see Trac #14547
     , (_, norm_elem_ty) <- normaliseType fam_insts Nominal elem_ty
          -- elem_ty is frequently something like
          -- `Item [Int]`, but we prefer `Int`
-    , norm_elem_ty `eqType` norm_e_ty ->
+    , norm_elem_ty `eqType` e_ty ->
         -- We have to ensure that the element types are exactly the same.
         -- Otherwise, one may give an instance IsList [Int] (more specific than
         -- the default IsList [a]) with a different implementation for `toList'
diff --git a/testsuite/tests/deSugar/should_compile/T14547.hs b/testsuite/tests/deSugar/should_compile/T14547.hs
deleted file mode 100644
index 02ff2e618c..0000000000
--- a/testsuite/tests/deSugar/should_compile/T14547.hs
+++ /dev/null
@@ -1,15 +0,0 @@
-{-# LANGUAGE OverloadedLists #-}
-{-# LANGUAGE TypeFamilies #-}
-
-module T14547 where
-
-class Foo f where
-        type It f
-        foo :: [It f] -> f
-
-data List a = Empty | a :! List a deriving Show
-
-instance Foo (List a) where
-        type It (List a) = a
-        foo [] = Empty
-        foo (x : xs) = x :! foo xs
diff --git a/testsuite/tests/deSugar/should_compile/all.T b/testsuite/tests/deSugar/should_compile/all.T
index 14140737d8..2d361464a6 100644
--- a/testsuite/tests/deSugar/should_compile/all.T
+++ b/testsuite/tests/deSugar/should_compile/all.T
@@ -100,7 +100,6 @@ test('T13290', normal, compile, [''])
 test('T13257', normal, compile, [''])
 test('T13870', normal, compile, [''])
 test('T14135', normal, compile, [''])
-test('T14547', normal, compile, ['-Wincomplete-patterns'])
 test('T14773a', normal, compile, ['-Wincomplete-patterns'])
 test('T14773b', normal, compile, ['-Wincomplete-patterns'])
 test('T14815', [], run_command, ['$MAKE -s --no-print-directory T14815'])