Parenthesise TypeOperator in import hints

When a constructor was mistakenly imported directly instead of as a
constructor of a data type, a hint will be shown on how to correctly
import
it. Just like the constructor, the data type should be surrounded in
parentheses if it is an operator (TypeOperator in this case).

Instead of:

    error:
        In module ‘Data.Type.Equality’:
          ‘Refl’ is a data constructor of ‘:~:’
        To import it use
          ‘import’ Data.Type.Equality( :~:( Refl ) )
        or
          ‘import’ Data.Type.Equality( :~:(..) )

Print:

    error:
        In module ‘Data.Type.Equality’:
          ‘Refl’ is a data constructor of ‘(:~:)’
        To import it use
          ‘import’ Data.Type.Equality( (:~:)( Refl ) )
        or
          ‘import’ Data.Type.Equality( (:~:)(..) )

Test Plan: pass new test

Reviewers: austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1093

GHC Trac Issues: #10668

4 files changed, 17 insertions, 4 deletions

diff --git a/compiler/rename/RnNames.hs b/compiler/rename/RnNames.hs
index 2818db82e4..58a743e08e 100644
--- a/compiler/rename/RnNames.hs
+++ b/compiler/rename/RnNames.hs
@@ -1631,25 +1631,26 @@ badImportItemErrDataCon :: OccName
                         -> ImpDeclSpec
                         -> IE RdrName
                         -> SDoc
-badImportItemErrDataCon dataType is_boot decl_spec ie
+badImportItemErrDataCon dataType_occ is_boot decl_spec ie
   = vcat [ ptext (sLit "In module")
              <+> quotes (ppr (is_mod decl_spec))
              <+> source_import <> colon
          , nest 2 $ quotes datacon
              <+> ptext (sLit "is a data constructor of")
-             <+> quotes (ppr dataType)
+             <+> quotes dataType
          , ptext (sLit "To import it use")
          , nest 2 $ quotes (ptext (sLit "import"))
              <+> ppr (is_mod decl_spec)
-             <> parens_sp (ppr dataType <> parens_sp datacon)
+             <> parens_sp (dataType <> parens_sp datacon)
          , ptext (sLit "or")
          , nest 2 $ quotes (ptext (sLit "import"))
              <+> ppr (is_mod decl_spec)
-             <> parens_sp (ppr dataType <> ptext (sLit "(..)"))
+             <> parens_sp (dataType <> ptext (sLit "(..)"))
          ]
   where
     datacon_occ = rdrNameOcc $ ieName ie
     datacon = parenSymOcc datacon_occ (ppr datacon_occ)
+    dataType = parenSymOcc dataType_occ (ppr dataType_occ)
     source_import | is_boot       = ptext (sLit "(hi-boot interface)")
                   | otherwise     = Outputable.empty
     parens_sp d = parens (space <> d <> space)  -- T( f,g )
diff --git a/testsuite/tests/rename/should_fail/T10668.hs b/testsuite/tests/rename/should_fail/T10668.hs
new file mode 100644
index 0000000000..111637b19b
--- /dev/null
+++ b/testsuite/tests/rename/should_fail/T10668.hs
@@ -0,0 +1,3 @@
+module T10668 where
+
+import Data.Type.Equality(Refl)
diff --git a/testsuite/tests/rename/should_fail/T10668.stderr b/testsuite/tests/rename/should_fail/T10668.stderr
new file mode 100644
index 0000000000..8c96fad1a8
--- /dev/null
+++ b/testsuite/tests/rename/should_fail/T10668.stderr
@@ -0,0 +1,8 @@
+
+T10668.hs:3:27: error:
+    In module ‘Data.Type.Equality’:
+      ‘Refl’ is a data constructor of ‘(:~:)’
+    To import it use
+      ‘import’ Data.Type.Equality( (:~:)( Refl ) )
+    or
+      ‘import’ Data.Type.Equality( (:~:)(..) )
diff --git a/testsuite/tests/rename/should_fail/all.T b/testsuite/tests/rename/should_fail/all.T
index 2aeee2f6fc..69ad1a31ac 100644
--- a/testsuite/tests/rename/should_fail/all.T
+++ b/testsuite/tests/rename/should_fail/all.T
@@ -132,3 +132,4 @@ test('T9032',
      normal,
      run_command,
      ['$MAKE -s --no-print-directory T9032'])
+test('T10668', normal, compile_fail, [''])