Implement -Wredundant-record-wildcards and -Wunused-record-wildcards

-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 enabled by `-Wall`.

2 files changed, 92 insertions, 3 deletions

diff --git a/docs/users_guide/8.10.1-notes.rst b/docs/users_guide/8.10.1-notes.rst
new file mode 100644
index 0000000000..cf67246abf
--- /dev/null
+++ b/docs/users_guide/8.10.1-notes.rst
@@ -0,0 +1,45 @@
+.. _release-8-10-1:
+
+Release notes for version 8.10.1
+===============================
+
+The significant changes to the various parts of the compiler are listed in the
+following sections.
+
+
+Highlights
+----------
+
+Full details
+------------
+
+Language
+~~~~~~~~
+
+Compiler
+~~~~~~~~
+
+- Add new flags :ghc-flag:`-Wunused-record-wildcards` and
+  :ghc-flag:`-Wredundant-record-wildcards`  which warn users when they have
+  redundant or unused uses of a record wildcard match.
+
+Runtime system
+~~~~~~~~~~~~~~
+
+Template Haskell
+~~~~~~~~~~~~~~~~
+
+``ghc-prim`` library
+~~~~~~~~~~~~~~~~~~~~
+
+``ghc`` library
+~~~~~~~~~~~~~~~
+
+``base`` library
+~~~~~~~~~~~~~~~~
+
+Build system
+~~~~~~~~~~~~
+
+Included libraries
+------------------
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst
index 03ca184531..c392ab38df 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 +1594,50 @@ 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
+    :since: 8.10.1
+    :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
+    :since: 8.10.1
+    :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