base: Document the fact that Typeable is automatically "derived"

This fixes #17060.

2 files changed, 5 insertions, 1 deletions

diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst
index de0aabbbbb..60f708284a 100644
--- a/docs/users_guide/glasgow_exts.rst
+++ b/docs/users_guide/glasgow_exts.rst
@@ -4603,7 +4603,7 @@ The class ``Typeable`` is very special:
    :extension:`DeriveDataTypeable` extension is enabled, but they are ignored,
    and they may be reported as an error in a later version of the compiler.
 
--  The rules for solving \`Typeable\` constraints are as follows:
+-  The rules for solving ``Typeable`` constraints are as follows:
 
    -  A concrete type constructor applied to some types. ::
 
diff --git a/libraries/base/Data/Typeable.hs b/libraries/base/Data/Typeable.hs
index ba0650c8f2..2b4d63b271 100644
--- a/libraries/base/Data/Typeable.hs
+++ b/libraries/base/Data/Typeable.hs
@@ -33,6 +33,10 @@
 -- index, providing an interface very similar to the "Typeable" notion seen in
 -- previous releases. For the type-indexed interface, see "Type.Reflection".
 --
+-- Since GHC 7.10, all types automatically have 'Typeable' instances derived.
+-- This is in contrast to previous releases where 'Typeable' had to be
+-- explicitly derived using the @DeriveDataTypeable@ language extension.
+--
 -- Since GHC 7.8, 'Typeable' is poly-kinded. The changes required for this might
 -- break some old programs involving 'Typeable'. More details on this, including
 -- how to fix your code, can be found on the