Make templateHaskell flag manual

So it isn't triggered by cabal-solver automatically.

This patch also makes use of TemplateHaskellQuotes extension on GHC-8.0+
https://downloads.haskell.org/ghc/latest/docs/html/users_guide/glasgow_exts.html?highlight=templatehaskellquotes#extension-TemplateHaskellQuotes

This extension allows to make some quotes, even
when GHC doesn't support TemplateHaskell (e.g. ghc-stage1).

This way template haskell functionality can be always compiled.

This way making `templateHaskell` flag manual doesn't hurt,
as its default `True` value shouldn't pose problems.

QuickCheck.cabal

@@ -62,10 +62,12 @@ source-repository this
 flag templateHaskell
   Description: Build Test.QuickCheck.All, which uses Template Haskell.
   Default: True
+  Manual: True
 
 flag old-random
   Description: Build against a pre-1.2.0 version of the random package.
   Default: False
+  Manual: False
 
 library
   Hs-source-dirs: src
@@ -114,7 +116,10 @@ library
 
   if impl(ghc) && flag(templateHaskell) && !impl(haste)
     Build-depends: template-haskell >= 2.4
-    Other-Extensions: TemplateHaskell
+    if impl(ghc >=8.0)
+      Other-Extensions: TemplateHaskellQuotes
+    else
+      Other-Extensions: TemplateHaskell
     Exposed-Modules: Test.QuickCheck.All
   else
     cpp-options: -DNO_TEMPLATE_HASKELL

src/Test/QuickCheck/All.hs

@@ -1,4 +1,9 @@
-{-# LANGUAGE TemplateHaskell, Rank2Types, CPP #-}
+{-# LANGUAGE Rank2Types, CPP #-}
+#if __GLASGOW_HASKELL__ >= 800
+{-# LANGUAGE TemplateHaskellQuotes #-}
+#else
+{-# LANGUAGE TemplateHaskell #-}
+#endif
 #ifndef NO_SAFE_HASKELL
 {-# LANGUAGE Trustworthy #-}
 #endif
@@ -44,7 +49,7 @@ import qualified System.IO as S
 -- property, the same scoping problems pop up as in 'quickCheckAll':
 -- see the note there about @return []@.
 polyQuickCheck :: Name -> ExpQ
-polyQuickCheck x = [| quickCheck $(monomorphic x) |]
+polyQuickCheck x = [| quickCheck |] `appE` monomorphic x
 
 -- | Test a polymorphic property, defaulting all type variables to 'Integer'.
 -- This is just a convenience function that combines 'verboseCheck' and 'monomorphic'.
@@ -53,7 +58,7 @@ polyQuickCheck x = [| quickCheck $(monomorphic x) |]
 -- property, the same scoping problems pop up as in 'quickCheckAll':
 -- see the note there about @return []@.
 polyVerboseCheck :: Name -> ExpQ
-polyVerboseCheck x = [| verboseCheck $(monomorphic x) |]
+polyVerboseCheck x = [| verboseCheck |] `appE` monomorphic x
 
 type Error = forall a. String -> a
 
@@ -132,7 +137,7 @@ monomorphiseType err mono ty = return ty
 -- 'forAllProperties' has the same issue with scoping as 'quickCheckAll':
 -- see the note there about @return []@.
 forAllProperties :: Q Exp -- :: (Property -> IO Result) -> IO Bool
-forAllProperties = [| runQuickCheckAll $allProperties |]
+forAllProperties = [| runQuickCheckAll |] `appE` allProperties
 
 -- | List all properties in the current module.
 --
@@ -155,10 +160,15 @@ allProperties = do
       quickCheckOne :: (Int, String) -> Q [Exp]
       quickCheckOne (l, x) = do
         exists <- (warning x >> return False) `recover` (reify (mkName x) >> return True)
-        if exists then sequence [ [| ($(stringE $ x ++ " from " ++ filename ++ ":" ++ show l),
-                                     property $(monomorphic (mkName x))) |] ]
+        if exists
+         then sequence
+          [ tupE
+            [ stringE $ x ++ " from " ++ filename ++ ":" ++ show l
+            , [| property |] `appE` monomorphic (mkName x)
+            ]
+          ]
          else return []
-  [| $(fmap (ListE . concat) (mapM quickCheckOne idents)) :: [(String, Property)] |]
+  fmap (ListE . concat) (mapM quickCheckOne idents) `sigE` [t| [(String, Property)] |]
 
 readUTF8File name = S.openFile name S.ReadMode >>=
                     set_utf8_io_enc >>=
@@ -195,15 +205,15 @@ set_utf8_io_enc h = return h
 -- of the module, which means that the later call to 'quickCheckAll'
 -- can see everything that was defined before the @return []@. Yikes!
 quickCheckAll :: Q Exp
-quickCheckAll = [| $(forAllProperties) quickCheckResult |]
+quickCheckAll = forAllProperties `appE` [| quickCheckResult |]
 
 -- | Test all properties in the current module.
 -- This is just a convenience function that combines 'quickCheckAll' and 'verbose'.
 --
 -- 'verboseCheckAll' has the same issue with scoping as 'quickCheckAll':
 -- see the note there about @return []@.
 verboseCheckAll :: Q Exp
-verboseCheckAll = [| $(forAllProperties) verboseCheckResult |]
+verboseCheckAll = forAllProperties `appE` [| verboseCheckResult |]
 
 runQuickCheckAll :: [(String, Property)] -> (Property -> IO Result) -> IO Bool
 runQuickCheckAll ps qc =