Refactor SuggestExtension constructor in GhcHint

This commit refactors the SuggestExtension type constructor of the
GhcHint to be more powerful and flexible. In particular, we can now
embed extra user information (essentially "sugar") to help clarifying
the suggestion. This makes the following possible:

Suggested fix: Perhaps you intended to use GADTs
               or a similar language extension to enable syntax: data T where

We can still give to IDEs and tools a `LangExt.Extension` they can use,
but in the pretty-printed message we can tell the user a bit more on why
such extension is needed.

On top of that, we now have the ability to express conjuctions and
disjunctons, for those cases where GHC suggests to enable "X or Y" and
for the cases where we need "X and Y".

16 files changed, 153 insertions, 78 deletions

diff --git a/compiler/GHC/HsToCore/Errors/Ppr.hs b/compiler/GHC/HsToCore/Errors/Ppr.hs
index b0d2b16409..6c65b14e20 100644
--- a/compiler/GHC/HsToCore/Errors/Ppr.hs
+++ b/compiler/GHC/HsToCore/Errors/Ppr.hs
@@ -282,7 +282,9 @@ instance Diagnostic DsMessage where
       -> case (bounds, usingNegLiterals) of
           (Just (MinBound minB, MaxBound _), NotUsingNegLiterals)
             | minB == -i -- Note [Suggest NegativeLiterals]
-            , i > 0 -> [SuggestExtension LangExt.NegativeLiterals]
+            , i > 0
+            -> [ suggestExtensionWithInfo (text "If you are trying to write a large negative literal")
+                                          LangExt.NegativeLiterals ]
           _ -> noHints
     DsRedundantBangPatterns{}                   -> noHints
     DsOverlappingPatterns{}                     -> noHints
diff --git a/compiler/GHC/Parser/Errors/Ppr.hs b/compiler/GHC/Parser/Errors/Ppr.hs
index 048605a225..2cc8b4a113 100644
--- a/compiler/GHC/Parser/Errors/Ppr.hs
+++ b/compiler/GHC/Parser/Errors/Ppr.hs
@@ -183,15 +183,7 @@ instance Diagnostic PsMessage where
     PsErrOverloadedRecordUpdateNoQualifiedFields
       -> mkSimpleDecorated $ text "Fields cannot be qualified when OverloadedRecordUpdate is enabled"
     PsErrExplicitForall is_unicode
-      -> mkSimpleDecorated $ vcat
-           [ text "Illegal symbol" <+> quotes (forallSym is_unicode) <+> text "in type"
-           , text "Perhaps you intended to use RankNTypes or a similar language"
-           , text "extension to enable explicit-forall syntax:" <+>
-             forallSym is_unicode <+> text "<tvs>. <type>"
-           ]
-         where
-          forallSym True  = text "∀"
-          forallSym False = text "forall"
+      -> mkSimpleDecorated $ text "Illegal symbol" <+> quotes (forallSym is_unicode) <+> text "in type"
     PsErrIllegalQualifiedDo qdoDoc
       -> mkSimpleDecorated $
            text "Illegal qualified" <+> quotes qdoDoc <+> text "block"
@@ -358,12 +350,7 @@ instance Diagnostic PsMessage where
       -> mkSimpleDecorated $
            text "Malformed head of type or class declaration:" <+> ppr ty
     PsErrIllegalWhereInDataDecl
-      -> mkSimpleDecorated $
-           vcat
-              [ text "Illegal keyword 'where' in data declaration"
-              , text "Perhaps you intended to use GADTs or a similar language"
-              , text "extension to enable syntax: data T where"
-              ]
+      -> mkSimpleDecorated $ text "Illegal keyword 'where' in data declaration"
     PsErrIllegalDataTypeContext c
       -> mkSimpleDecorated $
            text "Illegal datatype context:"
@@ -607,18 +594,18 @@ instance Diagnostic PsMessage where
     PsWarnStarIsType                              -> [SuggestUseTypeFromDataKind]
     PsWarnUnrecognisedPragma                      -> noHints
     PsWarnImportPreQualified                      -> [ SuggestQualifiedAfterModuleName
-                                                     , SuggestExtension LangExt.ImportQualifiedPost]
+                                                     , suggestExtension LangExt.ImportQualifiedPost]
     PsErrLexer{}                                  -> noHints
     PsErrCmmLexer                                 -> noHints
     PsErrCmmParser{}                              -> noHints
     PsErrParse token PsErrParseDetails{..}        -> case token of
       ""                         -> []
-      "$"  | not ped_th_enabled  -> [SuggestExtension LangExt.TemplateHaskell]   -- #7396
-      "<-" | ped_mdo_in_last_100 -> [SuggestExtension LangExt.RecursiveDo]
+      "$"  | not ped_th_enabled  -> [suggestExtension LangExt.TemplateHaskell]   -- #7396
+      "<-" | ped_mdo_in_last_100 -> [suggestExtension LangExt.RecursiveDo]
            | otherwise           -> [SuggestMissingDo]
       "="  | ped_do_in_last_100  -> [SuggestLetInDo]                             -- #15849
       _    | not ped_pat_syn_enabled
-           , ped_pattern_parsed  -> [SuggestExtension LangExt.PatternSynonyms]   -- #12429
+           , ped_pattern_parsed  -> [suggestExtension LangExt.PatternSynonyms]   -- #12429
            | otherwise           -> []
     PsErrTypeAppWithoutSpace{}                    -> noHints
     PsErrLazyPatWithoutSpace{}                    -> noHints
@@ -628,18 +615,21 @@ instance Diagnostic PsMessage where
     PsErrSpaceInSCC                               -> noHints
     PsErrEmptyDoubleQuotes th_on | th_on          -> [SuggestThQuotationSyntax]
                                  | otherwise      -> noHints
-    PsErrLambdaCase{}                             -> [SuggestExtension LangExt.LambdaCase]
+    PsErrLambdaCase{}                             -> [suggestExtension LangExt.LambdaCase]
     PsErrEmptyLambda{}                            -> noHints
-    PsErrLinearFunction{}                         -> [SuggestExtension LangExt.LinearTypes]
-    PsErrMultiWayIf{}                             -> [SuggestExtension LangExt.MultiWayIf]
-    PsErrOverloadedRecordUpdateNotEnabled{}       -> [SuggestExtension LangExt.OverloadedRecordUpdate]
-    PsErrNumUnderscores{}                         -> [SuggestExtension LangExt.NumericUnderscores]
-    PsErrIllegalBangPattern{}                     -> [SuggestExtension LangExt.BangPatterns]
+    PsErrLinearFunction{}                         -> [suggestExtension LangExt.LinearTypes]
+    PsErrMultiWayIf{}                             -> [suggestExtension LangExt.MultiWayIf]
+    PsErrOverloadedRecordUpdateNotEnabled{}       -> [suggestExtension LangExt.OverloadedRecordUpdate]
+    PsErrNumUnderscores{}                         -> [suggestExtension LangExt.NumericUnderscores]
+    PsErrIllegalBangPattern{}                     -> [suggestExtension LangExt.BangPatterns]
     PsErrOverloadedRecordDotInvalid{}             -> noHints
-    PsErrIllegalPatSynExport                      -> [SuggestExtension LangExt.PatternSynonyms]
+    PsErrIllegalPatSynExport                      -> [suggestExtension LangExt.PatternSynonyms]
     PsErrOverloadedRecordUpdateNoQualifiedFields  -> noHints
-    PsErrExplicitForall{}                         -> noHints
-    PsErrIllegalQualifiedDo{}                     -> [SuggestExtension LangExt.QualifiedDo]
+    PsErrExplicitForall is_unicode                ->
+      let info = text "or a similar language extension to enable explicit-forall syntax:" <+>
+                 forallSym is_unicode <+> text "<tvs>. <type>"
+      in [ suggestExtensionWithInfo info LangExt.RankNTypes ]
+    PsErrIllegalQualifiedDo{}                     -> [suggestExtension LangExt.QualifiedDo]
     PsErrQualifiedDoInCmd{}                       -> noHints
     PsErrRecordSyntaxInPatSynDecl{}               -> noHints
     PsErrEmptyWhereInPatSynDecl{}                 -> noHints
@@ -647,9 +637,9 @@ instance Diagnostic PsMessage where
     PsErrNoSingleWhereBindInPatSynDecl{}          -> noHints
     PsErrDeclSpliceNotAtTopLevel{}                -> noHints
     PsErrMultipleNamesInStandaloneKindSignature{} -> noHints
-    PsErrIllegalExplicitNamespace                 -> [SuggestExtension LangExt.ExplicitNamespaces]
+    PsErrIllegalExplicitNamespace                 -> [suggestExtension LangExt.ExplicitNamespaces]
     PsErrUnallowedPragma{}                        -> noHints
-    PsErrImportPostQualified                      -> [SuggestExtension LangExt.ImportQualifiedPost]
+    PsErrImportPostQualified                      -> [suggestExtension LangExt.ImportQualifiedPost]
     PsErrImportQualifiedTwice                     -> noHints
     PsErrIllegalImportBundleForm                  -> noHints
     PsErrInvalidRuleActivationMarker              -> noHints
@@ -692,20 +682,22 @@ instance Diagnostic PsMessage where
     PsErrIfInFunAppExpr{}                         -> suggestParensAndBlockArgs
     PsErrProcInFunAppExpr{}                       -> suggestParensAndBlockArgs
     PsErrMalformedTyOrClDecl{}                    -> noHints
-    PsErrIllegalWhereInDataDecl                   -> noHints
-    PsErrIllegalDataTypeContext{}                 -> [SuggestExtension LangExt.DatatypeContexts]
+    PsErrIllegalWhereInDataDecl                   ->
+      [ suggestExtensionWithInfo (text "or a similar language extension to enable syntax: data T where")
+                                 LangExt.GADTs ]
+    PsErrIllegalDataTypeContext{}                 -> [suggestExtension LangExt.DatatypeContexts]
     PsErrPrimStringInvalidChar                    -> noHints
     PsErrSuffixAT                                 -> noHints
     PsErrPrecedenceOutOfRange{}                   -> noHints
-    PsErrSemiColonsInCondExpr{}                   -> [SuggestExtension LangExt.DoAndIfThenElse]
-    PsErrSemiColonsInCondCmd{}                    -> [SuggestExtension LangExt.DoAndIfThenElse]
+    PsErrSemiColonsInCondExpr{}                   -> [suggestExtension LangExt.DoAndIfThenElse]
+    PsErrSemiColonsInCondCmd{}                    -> [suggestExtension LangExt.DoAndIfThenElse]
     PsErrAtInPatPos                               -> noHints
     PsErrParseErrorOnInput{}                      -> noHints
     PsErrMalformedDecl{}                          -> noHints
     PsErrUnexpectedTypeAppInDecl{}                -> noHints
     PsErrNotADataCon{}                            -> noHints
     PsErrInferredTypeVarNotAllowed                -> noHints
-    PsErrIllegalTraditionalRecordSyntax{}         -> [SuggestExtension LangExt.TraditionalRecordSyntax]
+    PsErrIllegalTraditionalRecordSyntax{}         -> [suggestExtension LangExt.TraditionalRecordSyntax]
     PsErrParseErrorInCmd{}                        -> noHints
     PsErrInPat _ details                          -> case details of
       PEIP_RecPattern args YesPatIsRecursive ctx
@@ -714,18 +706,18 @@ instance Diagnostic PsMessage where
       PEIP_OtherPatDetails ctx -> catMaybes [sug_missingdo ctx]
       _                        -> []
       where
-        sug_recdo                                           = Just (SuggestExtension LangExt.RecursiveDo)
+        sug_recdo                                           = Just (suggestExtension LangExt.RecursiveDo)
         sug_missingdo (ParseContext _ YesIncompleteDoBlock) = Just SuggestMissingDo
         sug_missingdo _                                     = Nothing
     PsErrParseRightOpSectionInPat{}               -> noHints
     PsErrIllegalRoleName _ nearby                 -> [SuggestRoles nearby]
     PsErrInvalidTypeSignature lhs                 ->
         if | foreign_RDR `looks_like` lhs
-           -> [SuggestExtension LangExt.ForeignFunctionInterface]
+           -> [suggestExtension LangExt.ForeignFunctionInterface]
            | default_RDR `looks_like` lhs
-           -> [SuggestExtension LangExt.DefaultSignatures]
+           -> [suggestExtension LangExt.DefaultSignatures]
            | pattern_RDR `looks_like` lhs
-           -> [SuggestExtension LangExt.PatternSynonyms]
+           -> [suggestExtension LangExt.PatternSynonyms]
            | otherwise
            -> [SuggestTypeSignatureForm]
       where
@@ -782,7 +774,7 @@ psHeaderMessageHints = \case
 
 suggestParensAndBlockArgs :: [GhcHint]
 suggestParensAndBlockArgs =
-  [SuggestParentheses, SuggestExtension LangExt.BlockArguments]
+  [SuggestParentheses, suggestExtension LangExt.BlockArguments]
 
 pp_unexpected_fun_app :: Outputable a => SDoc -> a -> SDoc
 pp_unexpected_fun_app e a =
@@ -791,3 +783,7 @@ pp_unexpected_fun_app e a =
 
 parse_error_in_pat :: SDoc
 parse_error_in_pat = text "Parse error in pattern:"
+
+forallSym :: Bool -> SDoc
+forallSym True  = text "∀"
+forallSym False = text "forall"
diff --git a/compiler/GHC/Tc/Errors/Ppr.hs b/compiler/GHC/Tc/Errors/Ppr.hs
index 97d0a40413..73ef9d9470 100644
--- a/compiler/GHC/Tc/Errors/Ppr.hs
+++ b/compiler/GHC/Tc/Errors/Ppr.hs
@@ -171,13 +171,13 @@ instance Diagnostic TcRnMessage where
     TcRnEmptyRecordUpdate{}
       -> noHints
     TcRnIllegalFieldPunning{}
-      -> [SuggestExtension LangExt.NamedFieldPuns]
+      -> [suggestExtension LangExt.NamedFieldPuns]
     TcRnIllegalWildcardsInRecord{}
-      -> [SuggestExtension LangExt.RecordWildCards]
+      -> [suggestExtension LangExt.RecordWildCards]
     TcRnDuplicateFieldName{}
       -> noHints
     TcRnIllegalViewPattern{}
-      -> [SuggestExtension LangExt.ViewPatterns]
+      -> [suggestExtension LangExt.ViewPatterns]
     TcRnCharLiteralOutOfRange{}
       -> noHints
     TcRnIllegalWildcardsInConstructor{}
diff --git a/compiler/GHC/Types/Error.hs b/compiler/GHC/Types/Error.hs
index bb27b568bb..b1814e8fb1 100644
--- a/compiler/GHC/Types/Error.hs
+++ b/compiler/GHC/Types/Error.hs
@@ -33,6 +33,13 @@ module GHC.Types.Error
 
    -- * Hints and refactoring actions
    , GhcHint (..)
+   , LanguageExtensionHint(..)
+   , suggestExtension
+   , suggestExtensionWithInfo
+   , suggestExtensions
+   , suggestExtensionsWithInfo
+   , suggestAnyExtension
+   , suggestAnyExtensionWithInfo
    , noHints
 
     -- * Rendering Messages
diff --git a/compiler/GHC/Types/Hint.hs b/compiler/GHC/Types/Hint.hs
index e1ed317753..364bad8355 100644
--- a/compiler/GHC/Types/Hint.hs
+++ b/compiler/GHC/Types/Hint.hs
@@ -1,8 +1,15 @@
 {-# LANGUAGE ExistentialQuantification #-}
 
 module GHC.Types.Hint (
-  GhcHint(..),
-  InstantiationSuggestion(..)
+    GhcHint(..)
+  , InstantiationSuggestion(..)
+  , LanguageExtensionHint(..)
+  , suggestExtension
+  , suggestExtensionWithInfo
+  , suggestExtensions
+  , suggestExtensionsWithInfo
+  , suggestAnyExtension
+  , suggestAnyExtensionWithInfo
   ) where
 
 import GHC.Prelude
@@ -19,6 +26,52 @@ import {-# SOURCE #-} Language.Haskell.Syntax.Expr
   -- This {-# SOURCE #-} import should be removable once
   -- 'Language.Haskell.Syntax.Bind' no longer depends on 'GHC.Tc.Types.Evidence'.
 
+
+data LanguageExtensionHint
+  = -- | Suggest to enable the input extension. If the input 'SDoc'
+    -- is not empty, it will contain some extra information about the
+    -- why the extension is required, but it's totally irrelevant/redundant
+    -- for IDEs and other tools.
+     SuggestSingleExtension !SDoc !LangExt.Extension
+    -- | Suggest to enable the input extensions. The list
+    -- is to be intended as /disjuctive/ i.e. the user is
+    -- suggested to enable /any/ of the extensions listed. If
+    -- the input 'SDoc' is not empty, it will contain some extra
+    -- information about the why the extensions are required, but
+    -- it's totally irrelevant/redundant for IDEs and other tools.
+  | SuggestAnyExtension !SDoc [LangExt.Extension]
+    -- | Suggest to enable the input extensions. The list
+    -- is to be intended as /conjunctive/ i.e. the user is
+    -- suggested to enable /all/ the extensions listed. If
+    -- the input 'SDoc' is not empty, it will contain some extra
+    -- information about the why the extensions are required, but
+    -- it's totally irrelevant/redundant for IDEs and other tools.
+  | SuggestExtensions !SDoc [LangExt.Extension]
+
+-- | Suggests a single extension without extra user info.
+suggestExtension :: LangExt.Extension -> GhcHint
+suggestExtension ext = SuggestExtension (SuggestSingleExtension empty ext)
+
+-- | Like 'suggestExtension' but allows supplying extra info for the user.
+suggestExtensionWithInfo :: SDoc -> LangExt.Extension -> GhcHint
+suggestExtensionWithInfo extraInfo ext = SuggestExtension (SuggestSingleExtension extraInfo ext)
+
+-- | Suggests to enable /every/ extension in the list.
+suggestExtensions :: [LangExt.Extension] -> GhcHint
+suggestExtensions exts = SuggestExtension (SuggestExtensions empty exts)
+
+-- | Like 'suggestExtensions' but allows supplying extra info for the user.
+suggestExtensionsWithInfo :: SDoc -> [LangExt.Extension] -> GhcHint
+suggestExtensionsWithInfo extraInfo exts = SuggestExtension (SuggestExtensions extraInfo exts)
+
+-- | Suggests to enable /any/ extension in the list.
+suggestAnyExtension :: [LangExt.Extension] -> GhcHint
+suggestAnyExtension exts = SuggestExtension (SuggestAnyExtension empty exts)
+
+-- | Like 'suggestAnyExtension' but allows supplying extra info for the user.
+suggestAnyExtensionWithInfo :: SDoc -> [LangExt.Extension] -> GhcHint
+suggestAnyExtensionWithInfo extraInfo exts = SuggestExtension (SuggestAnyExtension extraInfo exts)
+
 -- | A type for hints emitted by GHC.
 -- A /hint/ suggests a possible way to deal with a particular warning or error.
 data GhcHint
@@ -39,7 +92,7 @@ data GhcHint
                       parser/should_fail/T18251e, ... (and many more)
 
     -}
-  | SuggestExtension !LangExt.Extension
+  | SuggestExtension !LanguageExtensionHint
     {-| Suggests that a monadic code block is probably missing a \"do\" keyword.
 
         Example:
diff --git a/compiler/GHC/Types/Hint/Ppr.hs b/compiler/GHC/Types/Hint/Ppr.hs
index 24e0da427d..abb30d55d8 100644
--- a/compiler/GHC/Types/Hint/Ppr.hs
+++ b/compiler/GHC/Types/Hint/Ppr.hs
@@ -15,17 +15,23 @@ import GHC.Types.Hint
 import GHC.Hs.Expr ()   -- instance Outputable
 import GHC.Types.Id
 import GHC.Utils.Outputable
-import qualified GHC.LanguageExtensions as LangExt
+
+import Data.List (intersperse)
 
 instance Outputable GhcHint where
   ppr = \case
     UnknownHint m
       -> ppr m
-    SuggestExtension ext
-      -> case ext of
-          LangExt.NegativeLiterals
-            -> text "If you are trying to write a large negative literal, use NegativeLiterals"
-          _ -> text "Perhaps you intended to use" <+> ppr ext
+    SuggestExtension extHint
+      -> case extHint of
+          SuggestSingleExtension extraUserInfo ext ->
+            (text "Perhaps you intended to use" <+> ppr ext) $$ extraUserInfo
+          SuggestAnyExtension extraUserInfo exts ->
+            let header = text "Enable any of the following extensions:"
+            in  header <+> hsep (intersperse (char ',') (map ppr exts)) $$ extraUserInfo
+          SuggestExtensions extraUserInfo exts ->
+            let header = text "Enable all of the following extensions:"
+            in  header <+> hsep (intersperse (char ',') (map ppr exts)) $$ extraUserInfo
     SuggestMissingDo
       -> text "Possibly caused by a missing 'do'?"
     SuggestLetInDo
diff --git a/testsuite/tests/dependent/should_fail/T16326_Fail7.stderr b/testsuite/tests/dependent/should_fail/T16326_Fail7.stderr
index c5aba0b06d..edb1c1c8f5 100644
--- a/testsuite/tests/dependent/should_fail/T16326_Fail7.stderr
+++ b/testsuite/tests/dependent/should_fail/T16326_Fail7.stderr
@@ -1,5 +1,6 @@
 
 T16326_Fail7.hs:9:13: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
diff --git a/testsuite/tests/numeric/should_compile/T8542.stderr b/testsuite/tests/numeric/should_compile/T8542.stderr
index fb6ddf7a72..2d12b9fd7f 100644
--- a/testsuite/tests/numeric/should_compile/T8542.stderr
+++ b/testsuite/tests/numeric/should_compile/T8542.stderr
@@ -2,4 +2,5 @@
 T8542.hs:9:5: warning: [-Woverflowed-literals (in -Wdefault)]
     Literal 128 is out of the Int8 range -128..127
     Suggested fix:
-      If you are trying to write a large negative literal, use NegativeLiterals
+      Perhaps you intended to use NegativeLiterals
+      If you are trying to write a large negative literal
diff --git a/testsuite/tests/parser/should_fail/ParserNoForallUnicode.stderr b/testsuite/tests/parser/should_fail/ParserNoForallUnicode.stderr
index 81286aa49d..0d8841c676 100644
--- a/testsuite/tests/parser/should_fail/ParserNoForallUnicode.stderr
+++ b/testsuite/tests/parser/should_fail/ParserNoForallUnicode.stderr
@@ -1,5 +1,6 @@
 
 ParserNoForallUnicode.hs:6:8: error:
     Illegal symbol ‘∀’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: ∀ <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: ∀ <tvs>. <type>
diff --git a/testsuite/tests/parser/should_fail/T16270.stderr b/testsuite/tests/parser/should_fail/T16270.stderr
index 578add9682..e928638539 100644
--- a/testsuite/tests/parser/should_fail/T16270.stderr
+++ b/testsuite/tests/parser/should_fail/T16270.stderr
@@ -37,8 +37,8 @@ T16270.hs:19:5: error:
 
 T16270.hs:21:6: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix: Perhaps you intended to use RankNTypes
+                   or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
 
 T16270.hs:22:8: error:
     Unexpected semi-colons in conditional:
@@ -47,8 +47,8 @@ T16270.hs:22:8: error:
 
 T16270.hs:24:10: error:
     Illegal keyword 'where' in data declaration
-    Perhaps you intended to use GADTs or a similar language
-    extension to enable syntax: data T where
+    Suggested fix: Perhaps you intended to use GADTs
+                   or a similar language extension to enable syntax: data T where
 
 T16270.hs:26:12: error:
     Illegal bang-pattern
diff --git a/testsuite/tests/parser/should_fail/T3095.stderr b/testsuite/tests/parser/should_fail/T3095.stderr
index 599579deb0..ebb42b5be1 100644
--- a/testsuite/tests/parser/should_fail/T3095.stderr
+++ b/testsuite/tests/parser/should_fail/T3095.stderr
@@ -1,8 +1,9 @@
 
 T3095.hs:8:12: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
 
 T3095.hs:8:12: error:
     Unexpected type ‘forall x. x :: Type’
diff --git a/testsuite/tests/parser/should_fail/T8258NoGADTs.stderr b/testsuite/tests/parser/should_fail/T8258NoGADTs.stderr
index ecf3f7e11b..8e0cce6f54 100644
--- a/testsuite/tests/parser/should_fail/T8258NoGADTs.stderr
+++ b/testsuite/tests/parser/should_fail/T8258NoGADTs.stderr
@@ -1,5 +1,6 @@
 
 T8258NoGADTs.hs:4:8: error:
     Illegal keyword 'where' in data declaration
-    Perhaps you intended to use GADTs or a similar language
-    extension to enable syntax: data T where
+    Suggested fix:
+      Perhaps you intended to use GADTs
+      or a similar language extension to enable syntax: data T where
diff --git a/testsuite/tests/rename/should_fail/rnfail052.stderr b/testsuite/tests/rename/should_fail/rnfail052.stderr
index b818a4b6be..242fb70fd6 100644
--- a/testsuite/tests/rename/should_fail/rnfail052.stderr
+++ b/testsuite/tests/rename/should_fail/rnfail052.stderr
@@ -1,15 +1,18 @@
 
 rnfail052.hs:7:6: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
 
 rnfail052.hs:10:14: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
 
 rnfail052.hs:13:15: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
diff --git a/testsuite/tests/typecheck/should_fail/T3155.stderr b/testsuite/tests/typecheck/should_fail/T3155.stderr
index e82803fd22..ed7c4160e2 100644
--- a/testsuite/tests/typecheck/should_fail/T3155.stderr
+++ b/testsuite/tests/typecheck/should_fail/T3155.stderr
@@ -1,5 +1,6 @@
 
 T3155.hs:14:9: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
diff --git a/testsuite/tests/typecheck/should_fail/tcfail166.stderr b/testsuite/tests/typecheck/should_fail/tcfail166.stderr
index ab8805183d..5866cacd77 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail166.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail166.stderr
@@ -1,5 +1,6 @@
 
 tcfail166.hs:6:13: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>
diff --git a/testsuite/tests/typecheck/should_fail/tcfail183.stderr b/testsuite/tests/typecheck/should_fail/tcfail183.stderr
index 96245ce100..fc6fcfdcac 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail183.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail183.stderr
@@ -1,5 +1,6 @@
 
 tcfail183.hs:5:30: error:
     Illegal symbol ‘forall’ in type
-    Perhaps you intended to use RankNTypes or a similar language
-    extension to enable explicit-forall syntax: forall <tvs>. <type>
+    Suggested fix:
+      Perhaps you intended to use RankNTypes
+      or a similar language extension to enable explicit-forall syntax: forall <tvs>. <type>