Implement deriving strategies

Allows users to explicitly request which approach to `deriving` to use
via keywords, e.g.,

```
newtype Foo = Foo Bar
  deriving Eq
  deriving stock    Ord
  deriving newtype Show
```

Fixes #10598. Updates haddock submodule.

Test Plan: ./validate

Reviewers: hvr, kosmikus, goldfire, alanz, bgamari, simonpj, austin,
erikd, simonmar

Reviewed By: alanz, bgamari, simonpj

Subscribers: thomie, mpickering, oerjan

Differential Revision: https://phabricator.haskell.org/D2280

GHC Trac Issues: #10598

1 files changed, 3 insertions, 3 deletions

diff --git a/testsuite/tests/generics/T5462No1.stderr b/testsuite/tests/generics/T5462No1.stderr
index 7c1aec8d79..c82f1b86ee 100644
--- a/testsuite/tests/generics/T5462No1.stderr
+++ b/testsuite/tests/generics/T5462No1.stderr
@@ -3,18 +3,18 @@
 
 T5462No1.hs:24:42: error:
     Can't make a derived instance of ‘GFunctor F’:
-      ‘GFunctor’ is not a standard derivable class (Eq, Show, etc.)
+      ‘GFunctor’ is not a stock derivable class (Eq, Show, etc.)
       Try GeneralizedNewtypeDeriving for GHC's newtype-deriving extension
     In the newtype declaration for ‘F’
 
 T5462No1.hs:26:23: error:
     Can't make a derived instance of ‘C1 G’:
-      ‘C1’ is not a standard derivable class (Eq, Show, etc.)
+      ‘C1’ is not a stock derivable class (Eq, Show, etc.)
       Try enabling DeriveAnyClass
     In the data declaration for ‘G’
 
 T5462No1.hs:27:23: error:
     Can't make a derived instance of ‘C2 H’:
-      ‘C2’ is not a standard derivable class (Eq, Show, etc.)
+      ‘C2’ is not a stock derivable class (Eq, Show, etc.)
       Try enabling DeriveAnyClass
     In the data declaration for ‘H’