Expose enabled language extensions to TH

This exposes `template-haskell` functions for querying the language
extensions which are enabled when compiling a module,

- an `isExtEnabled` function to check whether an extension is enabled
- an `extsEnabled` function to obtain a full list of enabled extensions

To avoid code duplication this adds a `GHC.LanguageExtensions` module to
`ghc-boot` and moves `DynFlags.ExtensionFlag` into it. A happy
consequence of this is that the ungainly `DynFlags` lost around 500
lines. Moreover, flags corresponding to language extensions are now
clearly distinguished from other flags due to the `LangExt.*` prefix.

Updates haddock submodule.

This fixes #10820.

Test Plan: validate

Reviewers: austin, spinda, hvr, goldfire, alanz

Reviewed By: goldfire

Subscribers: mpickering, RyanGlScott, hvr, simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1200

GHC Trac Issues: #10820

2 files changed, 7 insertions, 5 deletions

diff --git a/ghc/InteractiveUI.hs b/ghc/InteractiveUI.hs
index 0727d6b629..43c789b26e 100644
--- a/ghc/InteractiveUI.hs
+++ b/ghc/InteractiveUI.hs
@@ -62,6 +62,7 @@ import Maybes ( orElse, expectJust )
 import NameSet
 import Panic hiding ( showException )
 import Util
+import qualified GHC.LanguageExtensions as LangExt
 
 -- Haskell Libraries
 import System.Console.Haskeline as Haskeline
@@ -380,8 +381,8 @@ interactiveUI config srcs maybe_exprs = do
    -- as the global DynFlags, plus -XExtendedDefaultRules and
    -- -XNoMonomorphismRestriction.
    dflags <- getDynFlags
-   let dflags' = (`xopt_set` Opt_ExtendedDefaultRules)
-               . (`xopt_unset` Opt_MonomorphismRestriction)
+   let dflags' = (`xopt_set` LangExt.ExtendedDefaultRules)
+               . (`xopt_unset` LangExt.MonomorphismRestriction)
                $ dflags
    GHC.setInteractiveDynFlags dflags'
 
@@ -859,7 +860,7 @@ checkInputForLayout :: String -> InputT GHCi (Maybe String)
                     -> InputT GHCi (Maybe String)
 checkInputForLayout stmt getStmt = do
    dflags' <- getDynFlags
-   let dflags = xopt_set dflags' Opt_AlternativeLayoutRule
+   let dflags = xopt_set dflags' LangExt.AlternativeLayoutRule
    st0 <- getGHCiState
    let buf'   =  stringToStringBuffer stmt
        loc    = mkRealSrcLoc (fsLit (progname st0)) (line_number st0) 1
@@ -1962,7 +1963,7 @@ setGHCContextFromGHCiState = do
   iidecls <- filterM (tryBool.checkAdd) (transient_ctx st ++ remembered_ctx st)
   dflags <- GHC.getSessionDynFlags
   GHC.setContext $
-     if xopt Opt_ImplicitPrelude dflags && not (any isPreludeImport iidecls)
+     if xopt LangExt.ImplicitPrelude dflags && not (any isPreludeImport iidecls)
         then iidecls ++ [implicitPreludeImport]
         else iidecls
     -- XXX put prel at the end, so that guessCurrentModule doesn't pick it up.
@@ -2371,7 +2372,7 @@ showImports = do
 
       prel_imp
         | any isPreludeImport (rem_ctx ++ trans_ctx) = []
-        | not (xopt Opt_ImplicitPrelude dflags)      = []
+        | not (xopt LangExt.ImplicitPrelude dflags)      = []
         | otherwise = ["import Prelude -- implicit"]
 
       trans_comment s = s ++ " -- added automatically"
diff --git a/ghc/ghc-bin.cabal.in b/ghc/ghc-bin.cabal.in
index 4f67e479c7..90b8a55e5b 100644
--- a/ghc/ghc-bin.cabal.in
+++ b/ghc/ghc-bin.cabal.in
@@ -33,6 +33,7 @@ Executable ghc
                    directory  >= 1   && < 1.3,
                    process    >= 1   && < 1.5,
                    filepath   >= 1   && < 1.5,
+                   ghc-boot,
                    ghc
     if os(windows)
         Build-Depends: Win32