Implement -Wredundant-record-wildcards and -Wunused-record-wildcardswip/wildcards-warn

-Wredundant-record-wildcards warns when a .. pattern binds no variables.

-Wunused-record-wildcards warns when none of the variables bound by a ..
pattern are used.

These flags are not enabled by `-Wall` currently. If people think it
is appropuiate to add them then that is an easy change.

1 files changed, 45 insertions, 3 deletions

diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst
index 03ca184531..396bc2b1bc 100644
--- a/docs/users_guide/using-warnings.rst
+++ b/docs/users_guide/using-warnings.rst
@@ -1565,9 +1565,9 @@ of ``-W(no-)*``.
 
     When :extension:`ExplicitForAll` is enabled, explicitly quantified type
     variables may also be identified as unused. For instance: ::
-      
+
         type instance forall x y. F x y = []
-    
+
     would still report ``x`` and ``y`` as unused on the right hand side
 
     Unlike :ghc-flag:`-Wunused-matches`, :ghc-flag:`-Wunused-type-patterns` is
@@ -1575,7 +1575,7 @@ of ``-W(no-)*``.
     unlike term-level pattern names, type names are often chosen expressly for
     documentation purposes, so using underscores in type names can make the
     documentation harder to read.
-    
+
 .. ghc-flag:: -Wunused-foralls
     :shortdesc: warn about type variables in user-written
         ``forall``\\s that are unused
@@ -1594,6 +1594,48 @@ of ``-W(no-)*``.
 
     would report ``a`` and ``c`` as unused.
 
+.. ghc-flag:: -Wunused-record-wildcards
+    :shortdesc: Warn about record wildcard matches when none of the bound variables
+      are used.
+    :type: dynamic
+    :reverse: -Wno-unused-record-wildcards
+    :category:
+
+    .. index::
+       single: unused, warning, record wildcards
+
+    Report all record wildcards where none of the variables bound implicitly
+    are used. For instance: ::
+
+
+	data P = P { x :: Int, y :: Int }
+
+        f1 :: P -> Int
+        f1 P{..} = 1 + 3
+
+    would report that the ``P{..}`` match is unused.
+
+.. ghc-flag:: -Wredundant-record-wildcards
+    :shortdesc: Warn about record wildcard matches when the wildcard binds no patterns.
+    :type: dynamic
+    :reverse: -Wno-redundant-record-wildcards
+    :category:
+
+    .. index::
+       single: unused, warning, record wildcards
+
+    Report all record wildcards where the wild card match binds no patterns.
+    For instance: ::
+
+
+	data P = P { x :: Int, y :: Int }
+
+        f1 :: P -> Int
+        f1 P{x,y,..} = x + y
+
+    would report that the ``P{x, y, ..}`` match has a redundant use of ``..``.
+
+
 .. ghc-flag:: -Wwrong-do-bind
     :shortdesc: warn about do bindings that appear to throw away monadic values
         that you should have bound instead