Re-export Word from Prelude (re #9531)

The original proposal text can be found at

  http://www.haskell.org/pipermail/libraries/2014-August/023491.html

The proposal passed with a clear majority, and was additionally
confirmed by the core libraries committee.

*Compatibility Note*

Only code that imports `Data.Word` for the sole purpose of using `Word`
*and* requires to be `-Werror`-clean (due to `-fwarn-unused-imports`)
is affected by this change.

In order to write warning-free forward/backward compatible against `base`,
a variant of the following CPP-based snippet can be used:

  -- Starting with base>4.7.0 or GHC>7.8 Prelude re-exports 'Word'
  -- The following is needed, if 'Word' is the *only* entity needed from Data.Word
  #ifdef MIN_VERSION_base
  # if !MIN_VERSION_base(4,7,1)
  import Data.Word (Word)
  # endif
  -- no cabal_macros.h -- fallback to __GLASGOW_HASKELL__
  #elif __GLASGOW_HASKELL__ < 709
  import Data.Word (Word)
  #endif

This also updates the haddock submodule in order to avoid a compile warning

8 files changed, 19 insertions, 5 deletions

diff --git a/compiler/coreSyn/MkCore.lhs b/compiler/coreSyn/MkCore.lhs
index 3ba8b1d6ee..08c3eedc53 100644
--- a/compiler/coreSyn/MkCore.lhs
+++ b/compiler/coreSyn/MkCore.lhs
@@ -92,7 +92,9 @@ import DynFlags
 import Data.Char        ( ord )
 import Data.List
 import Data.Ord
-import Data.Word
+#if __GLASGOW_HASKELL__ < 709
+import Data.Word        ( Word )
+#endif
 
 infixl 4 `mkCoreApp`, `mkCoreApps`
 \end{code}
diff --git a/libraries/base/Prelude.hs b/libraries/base/Prelude.hs
index 9b1119e155..3a3cc4dcc2 100644
--- a/libraries/base/Prelude.hs
+++ b/libraries/base/Prelude.hs
@@ -48,7 +48,7 @@ module Prelude (
 
     -- *** Numeric types
     Int, Integer, Float, Double,
-    Rational,
+    Rational, Word,
 
     -- *** Numeric type classes
     Num((+), (-), (*), negate, abs, signum, fromInteger),
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index 28005f8986..b9768119be 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -20,6 +20,8 @@
 
   * Make `abs` and `signum` handle (-0.0) correctly per IEEE-754.
 
+  * Re-export `Data.Word.Word` from `Prelude`
+
 ## 4.7.0.1  *Jul 2014*
 
   * Bundled with GHC 7.8.3
diff --git a/mk/validate-settings.mk b/mk/validate-settings.mk
index 4ccef07f7f..bd3e3bc937 100644
--- a/mk/validate-settings.mk
+++ b/mk/validate-settings.mk
@@ -96,6 +96,9 @@ libraries/containers_dist-install_EXTRA_HC_OPTS += -fno-warn-incomplete-patterns
 # Temporarily turn off pointless-pragma warnings for containers
 libraries/containers_dist-install_EXTRA_HC_OPTS += -fno-warn-pointless-pragmas
 
+# Temporarily turn off unused-imports warnings for containers
+libraries/containers_dist-install_EXTRA_HC_OPTS += -fno-warn-unused-imports
+
 # bytestring has identities at the moment
 libraries/bytestring_dist-install_EXTRA_HC_OPTS += -fno-warn-identities
 
diff --git a/testsuite/tests/lib/integer/IntegerConversionRules.hs b/testsuite/tests/lib/integer/IntegerConversionRules.hs
index cb5269f360..56949e7bf1 100644
--- a/testsuite/tests/lib/integer/IntegerConversionRules.hs
+++ b/testsuite/tests/lib/integer/IntegerConversionRules.hs
@@ -1,7 +1,10 @@
+{-# LANGUAGE CPP #-}
 
 module IntegerConversionRules where
 
-import Data.Word
+#if __GLASGOW_HASKELL__ < 709
+import Data.Word (Word)
+#endif
 
 f1 :: Int -> Double
 f1 = fi
diff --git a/testsuite/tests/numeric/should_run/T7014.hs b/testsuite/tests/numeric/should_run/T7014.hs
index 82375389d7..222b33bd59 100644
--- a/testsuite/tests/numeric/should_run/T7014.hs
+++ b/testsuite/tests/numeric/should_run/T7014.hs
@@ -1,7 +1,11 @@
+{-# LANGUAGE CPP #-}
+
 module Main where
 
 import Data.Bits
-import Data.Word
+#if __GLASGOW_HASKELL__ < 705
+import Data.Word (Word)
+#endif
 
 test_and1 :: Word -> Word
 test_and1 x = x .&. 0
diff --git a/testsuite/tests/typecheck/should_fail/T5095.stderr b/testsuite/tests/typecheck/should_fail/T5095.stderr
index e8d2b712cd..55342cdf33 100644
--- a/testsuite/tests/typecheck/should_fail/T5095.stderr
+++ b/testsuite/tests/typecheck/should_fail/T5095.stderr
@@ -53,7 +53,7 @@ T5095.hs:9:11:
       instance Eq Float -- Defined in ‘GHC.Classes’
       instance Eq Int -- Defined in ‘GHC.Classes’
       instance Eq Ordering -- Defined in ‘GHC.Classes’
-      instance Eq GHC.Types.Word -- Defined in ‘GHC.Classes’
+      instance Eq Word -- Defined in ‘GHC.Classes’
       instance Eq a => Eq [a] -- Defined in ‘GHC.Classes’
       instance Eq Integer
         -- Defined in ‘integer-gmp-0.5.1.0:GHC.Integer.Type’
diff --git a/utils/haddock b/utils/haddock
-Subproject b2a807da55d197c648fd2df1f156f9862711d92
+Subproject eee52f697233f99e23c1d8183511229fb93e3f3