Implement -f[no-]print-unicode-syntax flag for unicode syntax output (#8959)

There is currently no way to separate whether UnicodeSyntax is accepted
for input from the corresponding output syntax using unicode symbols.
This patch implements a separate flag for affecting ghc(i)'s output.
Signed-off-by: Bertram Felgenhauer <int-e@gmx.de>

Reviewed By: nomeata, austin

Differential Revision: https://phabricator.haskell.org/D807

GHC Trac Issues: #8959

compiler/main/DynFlags.hs

@@ -329,6 +329,7 @@ data GeneralFlag
 
    | Opt_PrintExplicitForalls
    | Opt_PrintExplicitKinds
+   | Opt_PrintUnicodeSyntax
 
    -- optimisation opts
    | Opt_CallArity
@@ -1767,8 +1768,9 @@ lang_set dflags lang =
             extensionFlags = flattenExtensionFlags lang (extensions dflags)
           }
 
+-- | Check whether to use unicode syntax for output
 useUnicodeSyntax :: DynFlags -> Bool
-useUnicodeSyntax = xopt Opt_UnicodeSyntax
+useUnicodeSyntax = gopt Opt_PrintUnicodeSyntax
 
 -- | Set the Haskell language standard to use
 setLanguage :: Language -> DynP ()
@@ -2972,6 +2974,7 @@ fFlags = [
   flagGhciSpec "print-evld-with-show"         Opt_PrintEvldWithShow,
   flagSpec "print-explicit-foralls"           Opt_PrintExplicitForalls,
   flagSpec "print-explicit-kinds"             Opt_PrintExplicitKinds,
+  flagSpec "print-unicode-syntax"             Opt_PrintUnicodeSyntax,
   flagSpec "prof-cafs"                        Opt_AutoSccsOnIndividualCafs,
   flagSpec "prof-count-entries"               Opt_ProfCountEntries,
   flagSpec "regs-graph"                       Opt_RegsGraph,

docs/users_guide/flags.xml

@@ -37,16 +37,22 @@
           </row>
           <row>
             <entry><option>-fprint-explicit-foralls</option></entry>
-            <entry>print explicit <literal>forall</literal> quantification in types</entry>
+            <entry>Print explicit <literal>forall</literal> quantification in types. See also <option>-XExplicitForAll</option></entry>
             <entry>dynamic</entry>
             <entry>-fno-print-explicit-foralls</entry>
           </row>
           <row>
             <entry><option>-fprint-explicit-kinds</option></entry>
-            <entry>print explicit kind foralls and kind arguments in types</entry>
+            <entry>Print explicit kind foralls and kind arguments in types. See also <option>-XKindSignature</option></entry>
             <entry>dynamic</entry>
             <entry>-fno-print-explicit-kinds</entry>
           </row>
+          <row>
+            <entry><option>-fprint-unicode-syntax</option></entry>
+            <entry>Use unicode syntax when printing expressions, types and kinds. See also <option>-XUnicodeSyntax</option></entry>
+            <entry>dynamic</entry>
+            <entry>-fno-print-unicode-syntax</entry>
+          </row>
           <row>
             <entry><option>-ferror-spans</option></entry>
             <entry>output full span in error messages</entry>

docs/users_guide/using.xml

@@ -896,12 +896,13 @@ ghc -c Foo.hs
 
 
       <varlistentry>
-        <term><option>--fprint-explicit-foralls, -fprint-explicit-kinds</option>
+        <term><option>--fprint-explicit-foralls, -fprint-explicit-kinds, -fprint-unicode-syntax</option>
           <indexterm><primary><option>-fprint-explicit-foralls</option></primary></indexterm>
           <indexterm><primary><option>-fprint-explicit-kinds</option></primary></indexterm>
+          <indexterm><primary><option>-fprint-unicode-syntax</option></primary></indexterm>
         </term>
         <listitem>
-          <para>These two flags control the way in which GHC displays types, in error messages and in GHCi.
+          <para>These three flags control the way in which GHC displays types, in error messages and in GHCi.
           Using <option>-fprint-explicit-foralls</option> makes GHC print explicit <literal>forall</literal>
           quantification at the top level of a type; normally this is suppressed.  For example, in GHCi:
 <screen>
@@ -944,6 +945,15 @@ MkT :: forall (k :: BOX) (a :: k). T a
 ghci> :set -fprint-explicit-foralls
 ghci> :t MkT
 MkT :: forall (k :: BOX) (a :: k). T k a
+</screen>
+         </para>
+         <para>
+          When <option>-fprint-unicode-syntax</option> is enabled, GHC prints type signatures using
+          the unicode symbols from the <option>-XUnicodeSyntax</option> extension.
+<screen>
+ghci> :set -fprint-unicode-syntax
+ghci> :t (>>)
+(>>) :: &forall; (m :: * &rarr; *) a b. Monad m &rArr; m a &rarr; m b &rarr; m b
 </screen>
          </para>
         </listitem>

ghc/InteractiveUI.hs

@@ -2073,6 +2073,7 @@ showDynFlags show_all dflags = do
                                         DynFlags.fFlags
         flgs = [ Opt_PrintExplicitForalls
                , Opt_PrintExplicitKinds
+               , Opt_PrintUnicodeSyntax
                , Opt_PrintBindResult
                , Opt_BreakOnException
                , Opt_BreakOnError

testsuite/tests/ghci/scripts/T8959.script

@@ -5,14 +5,14 @@
 :t () >- () -< () >>- () -<< ()
 let fun foo | True <- () = ()
 
-:set -XUnicodeSyntax
+:set -fprint-unicode-syntax
 
 :t lookup
 :t undefined :: (forall a. a -> a) -> a
 :t () >- () -< () >>- () -<< ()
 let fun foo | True <- () = ()
 
-:set -XNoUnicodeSyntax
+:set -fno-print-unicode-syntax
 
 :t lookup
 :t undefined :: (forall a. a -> a) -> a

testsuite/tests/ghci/scripts/T8959b.script

+:set -fprint-unicode-syntax
 :l T8959b.hs

testsuite/tests/ghci/scripts/all.T

@@ -187,7 +187,7 @@ test('T8831', normal, ghci_script, ['T8831.script'])
 test('T8917', normal, ghci_script, ['T8917.script'])
 test('T8931', normal, ghci_script, ['T8931.script'])
 test('T8959', normal, ghci_script, ['T8959.script'])
-test('T8959b', expect_broken(8959), ghci_script, ['T8959b.script'])
+test('T8959b', normal, ghci_script, ['T8959b.script'])
 test('T9181', normal, ghci_script, ['T9181.script'])
 test('T9086b', normal, ghci_script, ['T9086b.script'])
 test('T9140', combined_output, ghci_script, ['T9140.script'])