Add PatternGuards flag

compiler/main/DynFlags.hs

@@ -193,6 +193,7 @@ data DynFlag
    | Opt_ParallelListComp
    | Opt_GeneralizedNewtypeDeriving
    | Opt_RecursiveDo
+   | Opt_PatternGuards
 
    -- optimisation opts
    | Opt_Strictness
@@ -1102,6 +1103,7 @@ fFlags = [
 -- These -X<blah> flags can all be reversed with -Xno-<blah>
 xFlags :: [(String, DynFlag)]
 xFlags = [
+  ( "PatternGuards",                    Opt_PatternGuards ),
   ( "MagicHash",                        Opt_MagicHash ),
   ( "KindSignatures",                   Opt_KindSignatures ),
   ( "EmptyDataDecls",                   Opt_EmptyDataDecls ),
@@ -1160,6 +1162,7 @@ glasgowExtsFlags = [ Opt_GlasgowExts
            , Opt_MultiParamTypeClasses
            , Opt_FunctionalDependencies
 		   , Opt_MagicHash
+           , Opt_PatternGuards
            , Opt_RecursiveDo
            , Opt_ParallelListComp
            , Opt_EmptyDataDecls

compiler/rename/RnBinds.lhs

@@ -596,11 +596,11 @@ rnGRHS :: HsMatchContext Name -> LGRHS RdrName -> RnM (LGRHS Name, FreeVars)
 rnGRHS ctxt = wrapLocFstM (rnGRHS' ctxt)
 
 rnGRHS' ctxt (GRHS guards rhs)
-  = do	{ opt_GlasgowExts <- doptM Opt_GlasgowExts
+  = do	{ pattern_guards_allowed <- doptM Opt_PatternGuards
 	; ((guards', rhs'), fvs) <- rnStmts (PatGuard ctxt) guards $
 				    rnLExpr rhs
 
-	; checkM (opt_GlasgowExts || is_standard_guard guards')
+	; checkM (pattern_guards_allowed || is_standard_guard guards')
 	  	 (addWarn (nonStdGuardErr guards'))
 
 	; return (GRHS guards' rhs', fvs) }
@@ -653,6 +653,6 @@ bindsInHsBootFile mbinds
        2 (ppr mbinds)
 
 nonStdGuardErr guards
-  = hang (ptext SLIT("accepting non-standard pattern guards (-fglasgow-exts to suppress this message)"))
+  = hang (ptext SLIT("accepting non-standard pattern guards (use -XPatternGuards to suppress this message)"))
        4 (interpp'SP guards)
 \end{code}