Support new parser types in GHC

This commit converts the lexers and all the parser machinery to use the
new parser types and diagnostics infrastructure. Furthermore, it cleans
up the way the parser code was emitting hints.

As a result of this systematic approach, the test output of the
`InfixAppPatErr` and `T984` tests have been changed. Previously they
would emit a `SuggestMissingDo` hint, but this was not at all helpful in
resolving the error, and it was even confusing by just looking at the
original program that triggered the errors.

Update haddock submodule

1 files changed, 677 insertions, 533 deletions

diff --git a/compiler/GHC/Parser/Errors/Ppr.hs b/compiler/GHC/Parser/Errors/Ppr.hs
index 4cc8da75f4..6a2152f3f7 100644
--- a/compiler/GHC/Parser/Errors/Ppr.hs
+++ b/compiler/GHC/Parser/Errors/Ppr.hs
@@ -1,528 +1,479 @@
+{-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE FlexibleContexts #-}
 
 {-# OPTIONS_GHC -fno-warn-orphans #-} -- instance Diagnostic PsMessage
 
-module GHC.Parser.Errors.Ppr
-   ( mkParserWarn
-   , mkParserErr
-   , pprPsError
-   )
-where
+module GHC.Parser.Errors.Ppr where
 
 import GHC.Prelude
 import GHC.Driver.Flags
-import GHC.Parser.Errors
 import GHC.Parser.Errors.Types
 import GHC.Parser.Types
 import GHC.Types.Basic
 import GHC.Types.Error
-import GHC.Types.Hint (perhapsAsPat)
 import GHC.Types.SrcLoc
-import GHC.Types.Name.Reader (starInfo, rdrNameOcc, mkUnqual)
+import GHC.Types.Name.Reader (opIsAt, starInfo, rdrNameOcc, mkUnqual)
 import GHC.Types.Name.Occurrence (isSymOcc, occNameFS, varName)
 import GHC.Utils.Outputable
 import GHC.Utils.Misc
 import GHC.Data.FastString
+import GHC.Data.Maybe (catMaybes)
 import GHC.Hs.Expr (prependQualified,HsExpr(..))
 import GHC.Hs.Type (pprLHsContext)
 import GHC.Builtin.Names (allNameStrings)
 import GHC.Builtin.Types (filterCTuple)
-import GHC.Driver.Session (DynFlags)
-import GHC.Utils.Error (diagReasonSeverity)
+import qualified GHC.LanguageExtensions as LangExt
 
-instance Diagnostic PsMessage where
-  diagnosticMessage (PsUnknownMessage m) = diagnosticMessage m
-  diagnosticReason  (PsUnknownMessage m) = diagnosticReason m
-  -- FIXME(adinapoli) Fix it properly for #18516.
-  -- The reason why we temporarily set 'diagnosticHints' to be
-  -- the empty list is because currently the parser types does
-  -- not integrate tightly with the new diagnostic infrastructure
-  -- and as such hints and bundled together with the rendereded
-  -- diagnostic, and the same 'PsErrorDesc' is sometimes emitted
-  -- twice but with a different hint, which makes it hard to
-  -- untangle the two. Therefore, to smooth out the integration,
-  -- we provisionally tuck the hints directly into a 'PsUnknownMessage'
-  -- and we rendered them inside 'diagnosticMessage'.
-  diagnosticHints   (PsUnknownMessage _m) = []
-
-mk_parser_err :: [GhcHint] -> SrcSpan -> SDoc -> MsgEnvelope PsMessage
-mk_parser_err hints span doc = MsgEnvelope
-   { errMsgSpan        = span
-   , errMsgContext     = alwaysQualify
-   , errMsgDiagnostic  = PsUnknownMessage $ mkPlainError hints doc
-   , errMsgSeverity    = SevError
-   }
-
-mk_parser_warn :: DynFlags -> WarningFlag -> SrcSpan -> SDoc -> MsgEnvelope PsMessage
-mk_parser_warn df flag span doc = MsgEnvelope
-   { errMsgSpan        = span
-   , errMsgContext     = alwaysQualify
-   , errMsgDiagnostic  = PsUnknownMessage $ mkPlainDiagnostic reason noHints doc
-   , errMsgSeverity    = diagReasonSeverity df reason
-   }
-  where
-    reason :: DiagnosticReason
-    reason = WarningWithFlag flag
 
-mkParserWarn :: DynFlags -> PsWarning -> MsgEnvelope PsMessage
-mkParserWarn df = \case
-   PsWarnTab loc tc
-      -> mk_parser_warn df Opt_WarnTabs loc $
-          text "Tab character found here"
-            <> (if tc == 1
-                then text ""
-                else text ", and in" <+> speakNOf (fromIntegral (tc - 1)) (text "further location"))
-            <> text "."
-            $+$ text "Please use spaces instead."
-
-   PsWarnTransitionalLayout loc reason
-      -> mk_parser_warn df Opt_WarnAlternativeLayoutRuleTransitional loc $
+instance Diagnostic PsMessage where
+  diagnosticMessage = \case
+    PsUnknownMessage m
+      -> diagnosticMessage m
+
+    PsWarnHaddockInvalidPos
+       -> mkSimpleDecorated $ text "A Haddock comment cannot appear in this position and will be ignored."
+    PsWarnHaddockIgnoreMulti
+       -> mkSimpleDecorated $
+            text "Multiple Haddock comments for a single entity are not allowed." $$
+            text "The extraneous comment will be ignored."
+    PsWarnTab tc
+      -> mkSimpleDecorated $
+           text "Tab character found here"
+             <> (if tc == 1
+                 then text ""
+                 else text ", and in" <+> speakNOf (fromIntegral (tc - 1)) (text "further location"))
+             <> text "."
+    PsWarnTransitionalLayout reason
+      -> mkSimpleDecorated $
             text "transitional layout will not be accepted in the future:"
             $$ text (case reason of
                TransLayout_Where -> "`where' clause at the same depth as implicit layout block"
                TransLayout_Pipe  -> "`|' at the same depth as implicit layout block"
             )
-
-   PsWarnUnrecognisedPragma loc
-      -> mk_parser_warn df Opt_WarnUnrecognisedPragmas loc $
-            text "Unrecognised pragma"
-
-   PsWarnHaddockInvalidPos loc
-      -> mk_parser_warn df Opt_WarnInvalidHaddock loc $
-            text "A Haddock comment cannot appear in this position and will be ignored."
-
-   PsWarnHaddockIgnoreMulti loc
-      -> mk_parser_warn df Opt_WarnInvalidHaddock loc $
-            text "Multiple Haddock comments for a single entity are not allowed." $$
-            text "The extraneous comment will be ignored."
-
-   PsWarnStarBinder loc
-      -> mk_parser_warn df Opt_WarnStarBinder loc $
-            text "Found binding occurrence of" <+> quotes (text "*")
-            <+> text "yet StarIsType is enabled."
-         $$ text "NB. To use (or export) this operator in"
-            <+> text "modules with StarIsType,"
-         $$ text "    including the definition module, you must qualify it."
-
-   PsWarnStarIsType loc
-      -> mk_parser_warn df Opt_WarnStarIsType loc $
-             text "Using" <+> quotes (text "*")
-             <+> text "(or its Unicode variant) to mean"
-             <+> quotes (text "Data.Kind.Type")
-          $$ text "relies on the StarIsType extension, which will become"
-          $$ text "deprecated in the future."
-          $$ text "Suggested fix: use" <+> quotes (text "Type")
-           <+> text "from" <+> quotes (text "Data.Kind") <+> text "instead."
-
-   PsWarnImportPreQualified loc
-      -> mk_parser_warn df Opt_WarnPrepositiveQualifiedModule loc $
-            text "Found" <+> quotes (text "qualified")
-             <+> text "in prepositive position"
-         $$ text "Suggested fix: place " <+> quotes (text "qualified")
-             <+> text "after the module name instead."
-         $$ text "To allow this, enable language extension 'ImportQualifiedPost'"
-
-   PsWarnOperatorWhitespaceExtConflict loc sym
-      -> mk_parser_warn df Opt_WarnOperatorWhitespaceExtConflict loc $
-         let mk_prefix_msg operator_symbol extension_name syntax_meaning =
+    PsWarnOperatorWhitespaceExtConflict sym
+      -> let mk_prefix_msg operator_symbol extension_name syntax_meaning =
                   text "The prefix use of a" <+> quotes (text operator_symbol)
                     <+> text "would denote" <+> text syntax_meaning
                $$ nest 2 (text "were the" <+> text extension_name <+> text "extension enabled.")
                $$ text "Suggested fix: add whitespace after the"
                     <+> quotes (text operator_symbol) <> char '.'
-         in
+         in mkSimpleDecorated $
          case sym of
            OperatorWhitespaceSymbol_PrefixPercent -> mk_prefix_msg "%" "LinearTypes" "a multiplicity annotation"
            OperatorWhitespaceSymbol_PrefixDollar -> mk_prefix_msg "$" "TemplateHaskell" "an untyped splice"
            OperatorWhitespaceSymbol_PrefixDollarDollar -> mk_prefix_msg "$$" "TemplateHaskell" "a typed splice"
-
-
-   PsWarnOperatorWhitespace loc sym occ_type
-      -> mk_parser_warn df Opt_WarnOperatorWhitespace loc $
-         let mk_msg occ_type_str =
+    PsWarnOperatorWhitespace sym occ_type
+      -> let mk_msg occ_type_str =
                   text "The" <+> text occ_type_str <+> text "use of a" <+> quotes (ftext sym)
                     <+> text "might be repurposed as special syntax"
                $$ nest 2 (text "by a future language extension.")
                $$ text "Suggested fix: add whitespace around it."
-         in
+         in mkSimpleDecorated $
          case occ_type of
            OperatorWhitespaceOccurrence_Prefix -> mk_msg "prefix"
            OperatorWhitespaceOccurrence_Suffix -> mk_msg "suffix"
            OperatorWhitespaceOccurrence_TightInfix -> mk_msg "tight infix"
+    PsWarnStarBinder
+      -> mkSimpleDecorated $
+            text "Found binding occurrence of" <+> quotes (text "*")
+            <+> text "yet StarIsType is enabled."
+         $$ text "NB. To use (or export) this operator in"
+            <+> text "modules with StarIsType,"
+         $$ text "    including the definition module, you must qualify it."
+    PsWarnStarIsType
+      -> mkSimpleDecorated $
+             text "Using" <+> quotes (text "*")
+             <+> text "(or its Unicode variant) to mean"
+             <+> quotes (text "Data.Kind.Type")
+          $$ text "relies on the StarIsType extension, which will become"
+          $$ text "deprecated in the future."
+          $$ text "Suggested fix: use" <+> quotes (text "Type")
+           <+> text "from" <+> quotes (text "Data.Kind") <+> text "instead."
+    PsWarnUnrecognisedPragma
+      -> mkSimpleDecorated $ text "Unrecognised pragma"
+    PsWarnImportPreQualified
+      -> mkSimpleDecorated $
+            text "Found" <+> quotes (text "qualified")
+             <+> text "in prepositive position"
+         $$ text "Suggested fix: place " <+> quotes (text "qualified")
+             <+> text "after the module name instead."
+         $$ text "To allow this, enable language extension 'ImportQualifiedPost'"
 
-mkParserErr :: PsError -> MsgEnvelope PsMessage
-mkParserErr err = mk_parser_err (errHints err) (errLoc err) $
-                  pprPsError (errDesc err) (errHints err)
-
--- | Render a 'PsErrorDesc' into an 'SDoc', with its 'Hint's.
-pprPsError :: PsErrorDesc -> [GhcHint] -> SDoc
-pprPsError desc hints = vcat (pp_err desc : map ppr hints)
-
-pp_err :: PsErrorDesc -> SDoc
-pp_err = \case
-   PsErrLambdaCase
-      -> text "Illegal lambda-case (use LambdaCase)"
-
-   PsErrEmptyLambda
-      -> text "A lambda requires at least one parameter"
-
-   PsErrNumUnderscores reason
-      -> text $ case reason of
-            NumUnderscore_Integral -> "Use NumericUnderscores to allow underscores in integer literals"
-            NumUnderscore_Float    -> "Use NumericUnderscores to allow underscores in floating literals"
-
-   PsErrPrimStringInvalidChar
-      -> text "primitive string literal must contain only characters <= \'\\xFF\'"
-
-   PsErrMissingBlock
-      -> text "Missing block"
-
-   PsErrLexer err kind
-      -> hcat
-         [ text $ case err of
-            LexError               -> "lexical error"
-            LexUnknownPragma       -> "unknown pragma"
-            LexErrorInPragma       -> "lexical error in pragma"
-            LexNumEscapeRange      -> "numeric escape sequence out of range"
-            LexStringCharLit       -> "lexical error in string/character literal"
-            LexStringCharLitEOF    -> "unexpected end-of-file in string/character literal"
-            LexUnterminatedComment -> "unterminated `{-'"
-            LexUnterminatedOptions -> "unterminated OPTIONS pragma"
-            LexUnterminatedQQ      -> "unterminated quasiquotation"
-
-
-         , text $ case kind of
-            LexErrKind_EOF    -> " at end of input"
-            LexErrKind_UTF8   -> " (UTF-8 decoding error)"
-            LexErrKind_Char c -> " at character " ++ show c
-         ]
-
-   PsErrSuffixAT
-      -> text "Suffix occurrence of @. For an as-pattern, remove the leading whitespace."
-
-   PsErrParse token
+    PsErrLexer err kind
+      -> mkSimpleDecorated $ hcat
+           [ text $ case err of
+              LexError               -> "lexical error"
+              LexUnknownPragma       -> "unknown pragma"
+              LexErrorInPragma       -> "lexical error in pragma"
+              LexNumEscapeRange      -> "numeric escape sequence out of range"
+              LexStringCharLit       -> "lexical error in string/character literal"
+              LexStringCharLitEOF    -> "unexpected end-of-file in string/character literal"
+              LexUnterminatedComment -> "unterminated `{-'"
+              LexUnterminatedOptions -> "unterminated OPTIONS pragma"
+              LexUnterminatedQQ      -> "unterminated quasiquotation"
+
+           , text $ case kind of
+              LexErrKind_EOF    -> " at end of input"
+              LexErrKind_UTF8   -> " (UTF-8 decoding error)"
+              LexErrKind_Char c -> " at character " ++ show c
+           ]
+    PsErrParse token _details
       | null token
-      -> text "parse error (possibly incorrect indentation or mismatched brackets)"
-
+      -> mkSimpleDecorated $ text "parse error (possibly incorrect indentation or mismatched brackets)"
       | otherwise
-      -> text "parse error on input" <+> quotes (text token)
-
-   PsErrCmmLexer
-      -> text "Cmm lexical error"
-
-   PsErrUnsupportedBoxedSumExpr s
-      -> hang (text "Boxed sums not supported:") 2
-              (pprSumOrTuple Boxed s)
-
-   PsErrUnsupportedBoxedSumPat s
-      -> hang (text "Boxed sums not supported:") 2
-              (pprSumOrTuple Boxed s)
-
-   PsErrUnexpectedQualifiedConstructor v
-      -> hang (text "Expected an unqualified type constructor:") 2
-              (ppr v)
-
-   PsErrTupleSectionInPat
-      -> text "Tuple section in pattern context"
-
-   PsErrIllegalBangPattern e
-      -> text "Illegal bang-pattern (use BangPatterns):" $$ ppr e
-
-   PsErrOpFewArgs (StarIsType star_is_type) op
-      -> text "Operator applied to too few arguments:" <+> ppr op
-         $$ starInfo star_is_type op
-
-   PsErrImportQualifiedTwice
-      -> text "Multiple occurrences of 'qualified'"
-
-   PsErrImportPostQualified
-      -> text "Found" <+> quotes (text "qualified")
-          <+> text "in postpositive position. "
-         $$ text "To allow this, enable language extension 'ImportQualifiedPost'"
-
-   PsErrIllegalExplicitNamespace
-      -> text "Illegal keyword 'type' (use ExplicitNamespaces to enable)"
-
-   PsErrVarForTyCon name
-      -> text "Expecting a type constructor but found a variable,"
-           <+> quotes (ppr name) <> text "."
-         $$ if isSymOcc $ rdrNameOcc name
-            then text "If" <+> quotes (ppr name) <+> text "is a type constructor"
-                  <+> text "then enable ExplicitNamespaces and use the 'type' keyword."
-            else empty
-
-   PsErrIllegalPatSynExport
-      -> text "Illegal export form (use PatternSynonyms to enable)"
-
-   PsErrMalformedEntityString
-      -> text "Malformed entity string"
-
-   PsErrDotsInRecordUpdate
-      -> text "You cannot use `..' in a record update"
-
-   PsErrPrecedenceOutOfRange i
-      -> text "Precedence out of range: " <> int i
-
-   PsErrOverloadedRecordDotInvalid
-      -> text "Use of OverloadedRecordDot '.' not valid ('.' isn't allowed when constructing records or in record patterns)"
-
-   PsErrOverloadedRecordUpdateNoQualifiedFields
-      -> text "Fields cannot be qualified when OverloadedRecordUpdate is enabled"
-
-   PsErrOverloadedRecordUpdateNotEnabled
-      -> text "OverloadedRecordUpdate needs to be enabled"
-
-   PsErrInvalidDataCon t
-      -> hang (text "Cannot parse data constructor in a data/newtype declaration:") 2
-              (ppr t)
-
-   PsErrInvalidInfixDataCon lhs tc rhs
-      -> hang (text "Cannot parse an infix data constructor in a data/newtype declaration:")
-            2 (ppr lhs <+> ppr tc <+> ppr rhs)
-
-   PsErrUnpackDataCon
-      -> text "{-# UNPACK #-} cannot be applied to a data constructor."
-
-   PsErrUnexpectedKindAppInDataCon lhs ki
-      -> hang (text "Unexpected kind application in a data/newtype declaration:") 2
-              (ppr lhs <+> text "@" <> ppr ki)
-
-   PsErrInvalidRecordCon p
-      -> text "Not a record constructor:" <+> ppr p
-
-   PsErrIllegalUnboxedStringInPat lit
-      -> text "Illegal unboxed string literal in pattern:" $$ ppr lit
-
-   PsErrDoNotationInPat
-      -> text "do-notation in pattern"
-
-   PsErrIfTheElseInPat
-      -> text "(if ... then ... else ...)-syntax in pattern"
-
-   PsErrLambdaCaseInPat
-      -> text "(\\case ...)-syntax in pattern"
-
-   PsErrCaseInPat
-      -> text "(case ... of ...)-syntax in pattern"
-
-   PsErrLetInPat
-      -> text "(let ... in ...)-syntax in pattern"
-
-   PsErrLambdaInPat
-      -> text "Lambda-syntax in pattern."
-         $$ text "Pattern matching on functions is not possible."
-
-   PsErrArrowExprInPat e
-      -> text "Expression syntax in pattern:" <+> ppr e
-
-   PsErrArrowCmdInPat c
-      -> text "Command syntax in pattern:" <+> ppr c
-
-   PsErrArrowCmdInExpr c
-      -> vcat
-         [ text "Arrow command found where an expression was expected:"
-         , nest 2 (ppr c)
-         ]
-
-   PsErrViewPatInExpr a b
-      -> sep [ text "View pattern in expression context:"
-             , nest 4 (ppr a <+> text "->" <+> ppr b)
-             ]
-
-   PsErrTypeAppWithoutSpace v e
-      -> sep [ text "@-pattern in expression context:"
-             , nest 4 (pprPrefixOcc v <> text "@" <> ppr e)
-             ]
-         $$ text "Type application syntax requires a space before '@'"
-
-
-   PsErrLazyPatWithoutSpace e
-      -> sep [ text "Lazy pattern in expression context:"
-             , nest 4 (text "~" <> ppr e)
-             ]
-         $$ text "Did you mean to add a space after the '~'?"
-
-   PsErrBangPatWithoutSpace e
-      -> sep [ text "Bang pattern in expression context:"
-             , nest 4 (text "!" <> ppr e)
-             ]
-         $$ text "Did you mean to add a space after the '!'?"
-
-   PsErrUnallowedPragma prag
-      -> hang (text "A pragma is not allowed in this position:") 2
-              (ppr prag)
-
-   PsErrQualifiedDoInCmd m
-      -> hang (text "Parse error in command:") 2 $
-            text "Found a qualified" <+> ppr m <> text ".do block in a command, but"
-            $$ text "qualified 'do' is not supported in commands."
-
-   PsErrParseErrorInCmd s
-      -> hang (text "Parse error in command:") 2 s
-
-   PsErrParseErrorInPat s
-      -> text "Parse error in pattern:" <+> s
-
+      -> mkSimpleDecorated $ text "parse error on input" <+> quotes (text token)
+    PsErrCmmLexer
+      -> mkSimpleDecorated $ text "Cmm lexical error"
+    PsErrCmmParser cmm_err -> mkSimpleDecorated $ case cmm_err of
+      CmmUnknownPrimitive name     -> text "unknown primitive" <+> ftext name
+      CmmUnknownMacro fun          -> text "unknown macro" <+> ftext fun
+      CmmUnknownCConv cconv        -> text "unknown calling convention:" <+> text cconv
+      CmmUnrecognisedSafety safety -> text "unrecognised safety" <+> text safety
+      CmmUnrecognisedHint hint     -> text "unrecognised hint:" <+> text hint
 
-   PsErrInvalidInfixHole
-      -> text "Invalid infix hole, expected an infix operator"
+    PsErrTypeAppWithoutSpace v e
+      -> mkSimpleDecorated $
+           sep [ text "@-pattern in expression context:"
+               , nest 4 (pprPrefixOcc v <> text "@" <> ppr e)
+               ]
+           $$ text "Type application syntax requires a space before '@'"
+    PsErrLazyPatWithoutSpace e
+      -> mkSimpleDecorated $
+           sep [ text "Lazy pattern in expression context:"
+               , nest 4 (text "~" <> ppr e)
+               ]
+           $$ text "Did you mean to add a space after the '~'?"
+    PsErrBangPatWithoutSpace e
+      -> mkSimpleDecorated $
+           sep [ text "Bang pattern in expression context:"
+               , nest 4 (text "!" <> ppr e)
+               ]
+           $$ text "Did you mean to add a space after the '!'?"
+    PsErrInvalidInfixHole
+      -> mkSimpleDecorated $ text "Invalid infix hole, expected an infix operator"
+    PsErrExpectedHyphen
+      -> mkSimpleDecorated $ text "Expected a hyphen"
+    PsErrSpaceInSCC
+      -> mkSimpleDecorated $ text "Spaces are not allowed in SCCs"
+    PsErrEmptyDoubleQuotes th_on
+      -> mkSimpleDecorated $ if th_on then vcat (msg ++ th_msg) else vcat msg
+         where
+            msg    = [ text "Parser error on `''`"
+                     , text "Character literals may not be empty"
+                     ]
+            th_msg = [ text "Or perhaps you intended to use quotation syntax of TemplateHaskell,"
+                     , text "but the type variable or constructor is missing"
+                     ]
 
-   PsErrSemiColonsInCondExpr c st t se e
-      -> text "Unexpected semi-colons in conditional:"
-         $$ nest 4 expr
-         $$ text "Perhaps you meant to use DoAndIfThenElse?"
+    PsErrLambdaCase
+      -> mkSimpleDecorated $ text "Illegal lambda-case (use LambdaCase)"
+    PsErrEmptyLambda
+       -> mkSimpleDecorated $ text "A lambda requires at least one parameter"
+    PsErrLinearFunction
+      -> mkSimpleDecorated $ text "Enable LinearTypes to allow linear functions"
+    PsErrOverloadedRecordUpdateNotEnabled
+      -> mkSimpleDecorated $ text "OverloadedRecordUpdate needs to be enabled"
+    PsErrMultiWayIf
+      -> mkSimpleDecorated $ text "Multi-way if-expressions need MultiWayIf turned on"
+    PsErrNumUnderscores reason
+      -> mkSimpleDecorated $
+           text $ case reason of
+             NumUnderscore_Integral -> "Use NumericUnderscores to allow underscores in integer literals"
+             NumUnderscore_Float    -> "Use NumericUnderscores to allow underscores in floating literals"
+    PsErrIllegalBangPattern e
+      -> mkSimpleDecorated $ text "Illegal bang-pattern (use BangPatterns):" $$ ppr e
+    PsErrOverloadedRecordDotInvalid
+      -> mkSimpleDecorated $
+           text "Use of OverloadedRecordDot '.' not valid ('.' isn't allowed when constructing records or in record patterns)"
+    PsErrIllegalPatSynExport
+      -> mkSimpleDecorated $ text "Illegal export form (use PatternSynonyms to enable)"
+    PsErrOverloadedRecordUpdateNoQualifiedFields
+      -> mkSimpleDecorated $ text "Fields cannot be qualified when OverloadedRecordUpdate is enabled"
+    PsErrExplicitForall is_unicode
+      -> mkSimpleDecorated $ vcat
+           [ text "Illegal symbol" <+> quotes (forallSym is_unicode) <+> text "in type"
+           , text "Perhaps you intended to use RankNTypes or a similar language"
+           , text "extension to enable explicit-forall syntax:" <+>
+             forallSym is_unicode <+> text "<tvs>. <type>"
+           ]
+         where
+          forallSym True  = text "∀"
+          forallSym False = text "forall"
+    PsErrIllegalQualifiedDo qdoDoc
+      -> mkSimpleDecorated $ vcat
+           [ text "Illegal qualified" <+> quotes qdoDoc <+> text "block"
+           , text "Perhaps you intended to use QualifiedDo"
+           ]
+    PsErrQualifiedDoInCmd m
+      -> mkSimpleDecorated $
+           hang (text "Parse error in command:") 2 $
+             text "Found a qualified" <+> ppr m <> text ".do block in a command, but"
+             $$ text "qualified 'do' is not supported in commands."
+    PsErrRecordSyntaxInPatSynDecl pat
+      -> mkSimpleDecorated $
+           text "record syntax not supported for pattern synonym declarations:"
+           $$ ppr pat
+    PsErrEmptyWhereInPatSynDecl patsyn_name
+      -> mkSimpleDecorated $
+           text "pattern synonym 'where' clause cannot be empty"
+           $$ text "In the pattern synonym declaration for: "
+              <+> ppr (patsyn_name)
+    PsErrInvalidWhereBindInPatSynDecl patsyn_name decl
+      -> mkSimpleDecorated $
+           text "pattern synonym 'where' clause must bind the pattern synonym's name"
+           <+> quotes (ppr patsyn_name) $$ ppr decl
+    PsErrNoSingleWhereBindInPatSynDecl _patsyn_name decl
+      -> mkSimpleDecorated $
+           text "pattern synonym 'where' clause must contain a single binding:"
+           $$ ppr decl
+    PsErrDeclSpliceNotAtTopLevel d
+      -> mkSimpleDecorated $
+           hang (text "Declaration splices are allowed only"
+                 <+> text "at the top level:")
+             2 (ppr d)
+    PsErrMultipleNamesInStandaloneKindSignature vs
+      -> mkSimpleDecorated $
+           vcat [ hang (text "Standalone kind signatures do not support multiple names at the moment:")
+                  2 (pprWithCommas ppr vs)
+                , text "See https://gitlab.haskell.org/ghc/ghc/issues/16754 for details."
+                ]
+    PsErrIllegalExplicitNamespace
+      -> mkSimpleDecorated $
+           text "Illegal keyword 'type' (use ExplicitNamespaces to enable)"
+
+    PsErrUnallowedPragma prag
+      -> mkSimpleDecorated $
+           hang (text "A pragma is not allowed in this position:") 2
+                (ppr prag)
+    PsErrImportPostQualified
+      -> mkSimpleDecorated $
+           text "Found" <+> quotes (text "qualified")
+             <+> text "in postpositive position. "
+           $$ text "To allow this, enable language extension 'ImportQualifiedPost'"
+    PsErrImportQualifiedTwice
+      -> mkSimpleDecorated $ text "Multiple occurrences of 'qualified'"
+    PsErrIllegalImportBundleForm
+      -> mkSimpleDecorated $
+           text "Illegal import form, this syntax can only be used to bundle"
+           $+$ text "pattern synonyms with types in module exports."
+    PsErrInvalidRuleActivationMarker
+      -> mkSimpleDecorated $ text "Invalid rule activation marker"
+
+    PsErrMissingBlock
+      -> mkSimpleDecorated $ text "Missing block"
+    PsErrUnsupportedBoxedSumExpr s
+      -> mkSimpleDecorated $
+           hang (text "Boxed sums not supported:") 2
+                (pprSumOrTuple Boxed s)
+    PsErrUnsupportedBoxedSumPat s
+      -> mkSimpleDecorated $
+           hang (text "Boxed sums not supported:") 2
+                (pprSumOrTuple Boxed s)
+    PsErrUnexpectedQualifiedConstructor v
+      -> mkSimpleDecorated $
+           hang (text "Expected an unqualified type constructor:") 2
+                (ppr v)
+    PsErrTupleSectionInPat
+      -> mkSimpleDecorated $ text "Tuple section in pattern context"
+    PsErrOpFewArgs (StarIsType star_is_type) op
+      -> mkSimpleDecorated $
+           text "Operator applied to too few arguments:" <+> ppr op
+           $$ starInfo star_is_type op
+    PsErrVarForTyCon name
+      -> mkSimpleDecorated $
+           text "Expecting a type constructor but found a variable,"
+             <+> quotes (ppr name) <> text "."
+           $$ if isSymOcc $ rdrNameOcc name
+              then text "If" <+> quotes (ppr name) <+> text "is a type constructor"
+                    <+> text "then enable ExplicitNamespaces and use the 'type' keyword."
+              else empty
+    PsErrMalformedEntityString
+      -> mkSimpleDecorated $ text "Malformed entity string"
+    PsErrDotsInRecordUpdate
+      -> mkSimpleDecorated $ text "You cannot use `..' in a record update"
+    PsErrInvalidDataCon t
+      -> mkSimpleDecorated $
+           hang (text "Cannot parse data constructor in a data/newtype declaration:") 2
+                (ppr t)
+    PsErrInvalidInfixDataCon lhs tc rhs
+      -> mkSimpleDecorated $
+           hang (text "Cannot parse an infix data constructor in a data/newtype declaration:") 2
+                (ppr lhs <+> ppr tc <+> ppr rhs)
+    PsErrUnpackDataCon
+      -> mkSimpleDecorated $ text "{-# UNPACK #-} cannot be applied to a data constructor."
+    PsErrUnexpectedKindAppInDataCon lhs ki
+      -> mkSimpleDecorated $
+           hang (text "Unexpected kind application in a data/newtype declaration:") 2
+                (ppr lhs <+> text "@" <> ppr ki)
+    PsErrInvalidRecordCon p
+      -> mkSimpleDecorated $ text "Not a record constructor:" <+> ppr p
+    PsErrIllegalUnboxedStringInPat lit
+      -> mkSimpleDecorated $ text "Illegal unboxed string literal in pattern:" $$ ppr lit
+    PsErrDoNotationInPat
+      -> mkSimpleDecorated $ text "do-notation in pattern"
+    PsErrIfThenElseInPat
+      -> mkSimpleDecorated $ text "(if ... then ... else ...)-syntax in pattern"
+    PsErrLambdaCaseInPat
+      -> mkSimpleDecorated $ text "(\\case ...)-syntax in pattern"
+    PsErrCaseInPat
+      -> mkSimpleDecorated $ text "(case ... of ...)-syntax in pattern"
+    PsErrLetInPat
+      -> mkSimpleDecorated $ text "(let ... in ...)-syntax in pattern"
+    PsErrLambdaInPat
+      -> mkSimpleDecorated $
+           text "Lambda-syntax in pattern."
+           $$ text "Pattern matching on functions is not possible."
+    PsErrArrowExprInPat e
+      -> mkSimpleDecorated $ text "Expression syntax in pattern:" <+> ppr e
+    PsErrArrowCmdInPat c
+      -> mkSimpleDecorated $ text "Command syntax in pattern:" <+> ppr c
+    PsErrArrowCmdInExpr c
+      -> mkSimpleDecorated $
+           vcat
+           [ text "Arrow command found where an expression was expected:"
+           , nest 2 (ppr c)
+           ]
+    PsErrViewPatInExpr a b
+      -> mkSimpleDecorated $
+           sep [ text "View pattern in expression context:"
+               , nest 4 (ppr a <+> text "->" <+> ppr b)
+               ]
+    PsErrLambdaCmdInFunAppCmd a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "lambda command") a
+    PsErrCaseCmdInFunAppCmd a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "case command") a
+    PsErrIfCmdInFunAppCmd a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "if command") a
+    PsErrLetCmdInFunAppCmd a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "let command") a
+    PsErrDoCmdInFunAppCmd a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "do command") a
+    PsErrDoInFunAppExpr m a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (prependQualified m (text "do block")) a
+    PsErrMDoInFunAppExpr m a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (prependQualified m (text "mdo block")) a
+    PsErrLambdaInFunAppExpr a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "lambda expression") a
+    PsErrCaseInFunAppExpr a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "case expression") a
+    PsErrLambdaCaseInFunAppExpr a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "lambda-case expression") a
+    PsErrLetInFunAppExpr a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "let expression") a
+    PsErrIfInFunAppExpr a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "if expression") a
+    PsErrProcInFunAppExpr a
+      -> mkSimpleDecorated $ pp_unexpected_fun_app (text "proc expression") a
+    PsErrMalformedTyOrClDecl ty
+      -> 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"
+              ]
+    PsErrIllegalDataTypeContext c
+      -> mkSimpleDecorated $
+           text "Illegal datatype context (use DatatypeContexts):"
+             <+> pprLHsContext (Just c)
+    PsErrPrimStringInvalidChar
+      -> mkSimpleDecorated $ text "primitive string literal must contain only characters <= \'\\xFF\'"
+    PsErrSuffixAT
+      -> mkSimpleDecorated $
+           text "Suffix occurrence of @. For an as-pattern, remove the leading whitespace."
+    PsErrPrecedenceOutOfRange i
+      -> mkSimpleDecorated $ text "Precedence out of range: " <> int i
+    PsErrSemiColonsInCondExpr c st t se e
+      -> mkSimpleDecorated $
+           text "Unexpected semi-colons in conditional:"
+           $$ nest 4 expr
+           $$ text "Perhaps you meant to use DoAndIfThenElse?"
          where
             pprOptSemi True  = semi
             pprOptSemi False = empty
             expr = text "if"   <+> ppr c <> pprOptSemi st <+>
                    text "then" <+> ppr t <> pprOptSemi se <+>
                    text "else" <+> ppr e
-
-   PsErrSemiColonsInCondCmd c st t se e
-      -> text "Unexpected semi-colons in conditional:"
-         $$ nest 4 expr
-         $$ text "Perhaps you meant to use DoAndIfThenElse?"
+    PsErrSemiColonsInCondCmd c st t se e
+      -> mkSimpleDecorated $
+           text "Unexpected semi-colons in conditional:"
+           $$ nest 4 expr
+           $$ text "Perhaps you meant to use DoAndIfThenElse?"
          where
             pprOptSemi True  = semi
             pprOptSemi False = empty
             expr = text "if"   <+> ppr c <> pprOptSemi st <+>
                    text "then" <+> ppr t <> pprOptSemi se <+>
                    text "else" <+> ppr e
-
-
-   PsErrAtInPatPos
-      -> text "Found a binding for the"
-         <+> quotes (text "@")
-         <+> text "operator in a pattern position."
-         $$ perhapsAsPat
-
-   PsErrLambdaCmdInFunAppCmd a
-      -> pp_unexpected_fun_app (text "lambda command") a
-
-   PsErrCaseCmdInFunAppCmd a
-      -> pp_unexpected_fun_app (text "case command") a
-
-   PsErrIfCmdInFunAppCmd a
-      -> pp_unexpected_fun_app (text "if command") a
-
-   PsErrLetCmdInFunAppCmd a
-      -> pp_unexpected_fun_app (text "let command") a
-
-   PsErrDoCmdInFunAppCmd a
-      -> pp_unexpected_fun_app (text "do command") a
-
-   PsErrDoInFunAppExpr m a
-      -> pp_unexpected_fun_app (prependQualified m (text "do block")) a
-
-   PsErrMDoInFunAppExpr m a
-      -> pp_unexpected_fun_app (prependQualified m (text "mdo block")) a
-
-   PsErrLambdaInFunAppExpr a
-      -> pp_unexpected_fun_app (text "lambda expression") a
-
-   PsErrCaseInFunAppExpr a
-      -> pp_unexpected_fun_app (text "case expression") a
-
-   PsErrLambdaCaseInFunAppExpr a
-      -> pp_unexpected_fun_app (text "lambda-case expression") a
-
-   PsErrLetInFunAppExpr a
-      -> pp_unexpected_fun_app (text "let expression") a
-
-   PsErrIfInFunAppExpr a
-      -> pp_unexpected_fun_app (text "if expression") a
-
-   PsErrProcInFunAppExpr a
-      -> pp_unexpected_fun_app (text "proc expression") a
-
-   PsErrMalformedTyOrClDecl ty
-      -> text "Malformed head of type or class declaration:"
-         <+> ppr ty
-
-   PsErrIllegalWhereInDataDecl
-      -> 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"
-            ]
-
-   PsErrIllegalTraditionalRecordSyntax s
-      -> text "Illegal record syntax (use TraditionalRecordSyntax):"
-         <+> s
-
-   PsErrParseErrorOnInput occ
-      -> text "parse error on input" <+> ftext (occNameFS occ)
-
-   PsErrIllegalDataTypeContext c
-      -> text "Illegal datatype context (use DatatypeContexts):"
-         <+> pprLHsContext (Just c)
-
-   PsErrMalformedDecl what for
-      -> text "Malformed" <+> what
-         <+> text "declaration for" <+> quotes (ppr for)
-
-   PsErrUnexpectedTypeAppInDecl ki what for
-      -> vcat [ text "Unexpected type application"
-                <+> text "@" <> ppr ki
-              , text "In the" <+> what
-                <+> text "declaration for"
-                <+> quotes (ppr for)
-              ]
-
-   PsErrNotADataCon name
-      -> text "Not a data constructor:" <+> quotes (ppr name)
-
-   PsErrRecordSyntaxInPatSynDecl pat
-      -> text "record syntax not supported for pattern synonym declarations:"
-         $$ ppr pat
-
-   PsErrEmptyWhereInPatSynDecl patsyn_name
-      -> text "pattern synonym 'where' clause cannot be empty"
-         $$ text "In the pattern synonym declaration for: "
-            <+> ppr (patsyn_name)
-
-   PsErrInvalidWhereBindInPatSynDecl patsyn_name decl
-      -> text "pattern synonym 'where' clause must bind the pattern synonym's name"
-         <+> quotes (ppr patsyn_name) $$ ppr decl
-
-   PsErrNoSingleWhereBindInPatSynDecl _patsyn_name decl
-      -> text "pattern synonym 'where' clause must contain a single binding:"
-         $$ ppr decl
-
-   PsErrDeclSpliceNotAtTopLevel d
-      -> hang (text "Declaration splices are allowed only"
-               <+> text "at the top level:")
-           2 (ppr d)
-
-   PsErrInferredTypeVarNotAllowed
-      -> text "Inferred type variables are not allowed here"
-
-   PsErrIllegalRoleName role nearby
-      -> text "Illegal role name" <+> quotes (ppr role)
-         $$ case nearby of
-             []  -> empty
-             [r] -> text "Perhaps you meant" <+> quotes (ppr r)
-             -- will this last case ever happen??
-             _   -> hang (text "Perhaps you meant one of these:")
-                         2 (pprWithCommas (quotes . ppr) nearby)
-
-   PsErrMultipleNamesInStandaloneKindSignature vs
-      -> vcat [ hang (text "Standalone kind signatures do not support multiple names at the moment:")
-                2 (pprWithCommas ppr vs)
-              , text "See https://gitlab.haskell.org/ghc/ghc/issues/16754 for details."
-              ]
-
-   PsErrIllegalImportBundleForm
-      -> text "Illegal import form, this syntax can only be used to bundle"
-         $+$ text "pattern synonyms with types in module exports."
-
-   PsErrInvalidTypeSignature lhs
-      -> text "Invalid type signature:"
-         <+> ppr lhs
-         <+> text ":: ..."
-         $$ text hint
+    PsErrAtInPatPos
+      -> mkSimpleDecorated $
+           text "Found a binding for the"
+           <+> quotes (text "@")
+           <+> text "operator in a pattern position."
+           $$ perhapsAsPat
+    PsErrParseErrorOnInput occ
+      -> mkSimpleDecorated $ text "parse error on input" <+> ftext (occNameFS occ)
+    PsErrMalformedDecl what for
+      -> mkSimpleDecorated $
+           text "Malformed" <+> what
+           <+> text "declaration for" <+> quotes (ppr for)
+    PsErrUnexpectedTypeAppInDecl ki what for
+      -> mkSimpleDecorated $
+           vcat [ text "Unexpected type application"
+                  <+> text "@" <> ppr ki
+                , text "In the" <+> what
+                  <+> text "declaration for"
+                  <+> quotes (ppr for)
+                ]
+    PsErrNotADataCon name
+      -> mkSimpleDecorated $ text "Not a data constructor:" <+> quotes (ppr name)
+    PsErrInferredTypeVarNotAllowed
+      -> mkSimpleDecorated $ text "Inferred type variables are not allowed here"
+    PsErrIllegalTraditionalRecordSyntax s
+      -> mkSimpleDecorated $
+           text "Illegal record syntax (use TraditionalRecordSyntax):" <+> s
+    PsErrParseErrorInCmd s
+      -> mkSimpleDecorated $ hang (text "Parse error in command:") 2 s
+    PsErrInPat s details
+      -> let msg  = parse_error_in_pat
+             body = case details of
+                 PEIP_NegApp -> text "-" <> ppr s
+                 PEIP_TypeArgs peipd_tyargs
+                   | not (null peipd_tyargs) -> ppr s <+> vcat [
+                               hsep [text "@" <> ppr t | t <- peipd_tyargs]
+                             , text "Type applications in patterns are only allowed on data constructors."
+                             ]
+                   | otherwise -> ppr s
+                 PEIP_OtherPatDetails (ParseContext (Just fun) _)
+                  -> ppr s <+> text "In a function binding for the"
+                                     <+> quotes (ppr fun)
+                                     <+> text "operator."
+                                  $$ if opIsAt fun
+                                        then perhapsAsPat
+                                        else empty
+                 _  -> ppr s
+         in mkSimpleDecorated $ msg <+> body
+    PsErrParseRightOpSectionInPat infixOcc s
+      -> mkSimpleDecorated $ parse_error_in_pat <+> pprInfixOcc infixOcc <> ppr s
+    PsErrIllegalRoleName role nearby
+      -> mkSimpleDecorated $
+           text "Illegal role name" <+> quotes (ppr role)
+           $$ case nearby of
+               []  -> empty
+               [r] -> text "Perhaps you meant" <+> quotes (ppr r)
+               -- will this last case ever happen??
+               _   -> hang (text "Perhaps you meant one of these:")
+                           2 (pprWithCommas (quotes . ppr) nearby)
+    PsErrInvalidTypeSignature lhs
+      -> mkSimpleDecorated $
+           text "Invalid type signature:"
+           <+> ppr lhs
+           <+> text ":: ..."
+           $$ text hint
          where
          hint | foreign_RDR `looks_like` lhs
               = "Perhaps you meant to use ForeignFunctionInterface?"
@@ -537,7 +488,7 @@ pp_err = \case
          -- so check for that, and suggest.  cf #3805
          -- Sadly 'foreign import' still barfs 'parse error' because
          --  'import' is a keyword
-         -- looks_like :: RdrName -> LHsExpr GhcPs -> Bool -- AZ
+         -- looks_like :: RdrName -> LHsExpr GhcPsErr -> Bool -- AZ
          looks_like s (L _ (HsVar _ (L _ v))) = v == s
          looks_like s (L _ (HsApp _ lhs _))   = looks_like s lhs
          looks_like _ _                       = False
@@ -545,83 +496,276 @@ pp_err = \case
          foreign_RDR = mkUnqual varName (fsLit "foreign")
          default_RDR = mkUnqual varName (fsLit "default")
          pattern_RDR = mkUnqual varName (fsLit "pattern")
-
-   PsErrUnexpectedTypeInDecl t what tc tparms equals_or_where
-      -> vcat [ text "Unexpected type" <+> quotes (ppr t)
-              , text "In the" <+> what
-                <+> text "declaration for" <+> quotes tc'
-              , vcat[ (text "A" <+> what
-                       <+> text "declaration should have form")
-              , nest 2
-                (what
-                 <+> tc'
-                 <+> hsep (map text (takeList tparms allNameStrings))
-                 <+> equals_or_where) ] ]
-          where
-            -- Avoid printing a constraint tuple in the error message. Print
-            -- a plain old tuple instead (since that's what the user probably
-            -- wrote). See #14907
-            tc' = ppr $ filterCTuple tc
-
-   PsErrCmmParser cmm_err -> case cmm_err of
-      CmmUnknownPrimitive name     -> text "unknown primitive" <+> ftext name
-      CmmUnknownMacro fun          -> text "unknown macro" <+> ftext fun
-      CmmUnknownCConv cconv        -> text "unknown calling convention:" <+> text cconv
-      CmmUnrecognisedSafety safety -> text "unrecognised safety" <+> text safety
-      CmmUnrecognisedHint hint     -> text "unrecognised hint:" <+> text hint
-
-   PsErrExpectedHyphen
-      -> text "Expected a hyphen"
-
-   PsErrSpaceInSCC
-      -> text "Spaces are not allowed in SCCs"
-
-   PsErrEmptyDoubleQuotes th_on
-      -> if th_on then vcat (msg ++ th_msg) else vcat msg
-         where
-            msg    = [ text "Parser error on `''`"
-                     , text "Character literals may not be empty"
-                     ]
-            th_msg = [ text "Or perhaps you intended to use quotation syntax of TemplateHaskell,"
-                     , text "but the type variable or constructor is missing"
-                     ]
-
-   PsErrInvalidPackageName pkg
-      -> vcat
+    PsErrUnexpectedTypeInDecl t what tc tparms equals_or_where
+       -> mkSimpleDecorated $
+            vcat [ text "Unexpected type" <+> quotes (ppr t)
+                 , text "In the" <+> what
+                   <+> text "declaration for" <+> quotes tc'
+                 , vcat[ (text "A" <+> what
+                          <+> text "declaration should have form")
+                 , nest 2
+                   (what
+                    <+> tc'
+                    <+> hsep (map text (takeList tparms allNameStrings))
+                    <+> equals_or_where) ] ]
+           where
+             -- Avoid printing a constraint tuple in the error message. Print
+             -- a plain old tuple instead (since that's what the user probably
+             -- wrote). See #14907
+             tc' = ppr $ filterCTuple tc
+    PsErrInvalidPackageName pkg
+      -> mkSimpleDecorated $ vcat
             [ text "Parse error" <> colon <+> quotes (ftext pkg)
             , text "Version number or non-alphanumeric" <+>
               text "character in package name"
             ]
 
-   PsErrInvalidRuleActivationMarker
-      -> text "Invalid rule activation marker"
-
-   PsErrLinearFunction
-      -> text "Enable LinearTypes to allow linear functions"
-
-   PsErrMultiWayIf
-      -> text "Multi-way if-expressions need MultiWayIf turned on"
-
-   PsErrExplicitForall is_unicode
-      -> 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"
-
-   PsErrIllegalQualifiedDo qdoDoc
-      -> vcat
-         [ text "Illegal qualified" <+> quotes qdoDoc <+> text "block"
-         , text "Perhaps you intended to use QualifiedDo"
-         ]
+  diagnosticReason  = \case
+    PsUnknownMessage m                            -> diagnosticReason m
+    PsWarnTab{}                                   -> WarningWithFlag Opt_WarnTabs
+    PsWarnTransitionalLayout{}                    -> WarningWithFlag Opt_WarnAlternativeLayoutRuleTransitional
+    PsWarnOperatorWhitespaceExtConflict{}         -> WarningWithFlag Opt_WarnOperatorWhitespaceExtConflict
+    PsWarnOperatorWhitespace{}                    -> WarningWithFlag Opt_WarnOperatorWhitespace
+    PsWarnHaddockInvalidPos                       -> WarningWithFlag Opt_WarnInvalidHaddock
+    PsWarnHaddockIgnoreMulti                      -> WarningWithFlag Opt_WarnInvalidHaddock
+    PsWarnStarBinder                              -> WarningWithFlag Opt_WarnStarBinder
+    PsWarnStarIsType                              -> WarningWithFlag Opt_WarnStarIsType
+    PsWarnUnrecognisedPragma                      -> WarningWithFlag Opt_WarnUnrecognisedPragmas
+    PsWarnImportPreQualified                      -> WarningWithFlag Opt_WarnPrepositiveQualifiedModule
+    PsErrLexer{}                                  -> ErrorWithoutFlag
+    PsErrCmmLexer                                 -> ErrorWithoutFlag
+    PsErrCmmParser{}                              -> ErrorWithoutFlag
+    PsErrParse{}                                  -> ErrorWithoutFlag
+    PsErrTypeAppWithoutSpace{}                    -> ErrorWithoutFlag
+    PsErrLazyPatWithoutSpace{}                    -> ErrorWithoutFlag
+    PsErrBangPatWithoutSpace{}                    -> ErrorWithoutFlag
+    PsErrInvalidInfixHole                         -> ErrorWithoutFlag
+    PsErrExpectedHyphen                           -> ErrorWithoutFlag
+    PsErrSpaceInSCC                               -> ErrorWithoutFlag
+    PsErrEmptyDoubleQuotes{}                      -> ErrorWithoutFlag
+    PsErrLambdaCase{}                             -> ErrorWithoutFlag
+    PsErrEmptyLambda{}                            -> ErrorWithoutFlag
+    PsErrLinearFunction{}                         -> ErrorWithoutFlag
+    PsErrMultiWayIf{}                             -> ErrorWithoutFlag
+    PsErrOverloadedRecordUpdateNotEnabled{}       -> ErrorWithoutFlag
+    PsErrNumUnderscores{}                         -> ErrorWithoutFlag
+    PsErrIllegalBangPattern{}                     -> ErrorWithoutFlag
+    PsErrOverloadedRecordDotInvalid{}             -> ErrorWithoutFlag
+    PsErrIllegalPatSynExport                      -> ErrorWithoutFlag
+    PsErrOverloadedRecordUpdateNoQualifiedFields  -> ErrorWithoutFlag
+    PsErrExplicitForall{}                         -> ErrorWithoutFlag
+    PsErrIllegalQualifiedDo{}                     -> ErrorWithoutFlag
+    PsErrQualifiedDoInCmd{}                       -> ErrorWithoutFlag
+    PsErrRecordSyntaxInPatSynDecl{}               -> ErrorWithoutFlag
+    PsErrEmptyWhereInPatSynDecl{}                 -> ErrorWithoutFlag
+    PsErrInvalidWhereBindInPatSynDecl{}           -> ErrorWithoutFlag
+    PsErrNoSingleWhereBindInPatSynDecl{}          -> ErrorWithoutFlag
+    PsErrDeclSpliceNotAtTopLevel{}                -> ErrorWithoutFlag
+    PsErrMultipleNamesInStandaloneKindSignature{} -> ErrorWithoutFlag
+    PsErrIllegalExplicitNamespace                 -> ErrorWithoutFlag
+    PsErrUnallowedPragma{}                        -> ErrorWithoutFlag
+    PsErrImportPostQualified                      -> ErrorWithoutFlag
+    PsErrImportQualifiedTwice                     -> ErrorWithoutFlag
+    PsErrIllegalImportBundleForm                  -> ErrorWithoutFlag
+    PsErrInvalidRuleActivationMarker              -> ErrorWithoutFlag
+    PsErrMissingBlock                             -> ErrorWithoutFlag
+    PsErrUnsupportedBoxedSumExpr{}                -> ErrorWithoutFlag
+    PsErrUnsupportedBoxedSumPat{}                 -> ErrorWithoutFlag
+    PsErrUnexpectedQualifiedConstructor{}         -> ErrorWithoutFlag
+    PsErrTupleSectionInPat{}                      -> ErrorWithoutFlag
+    PsErrOpFewArgs{}                              -> ErrorWithoutFlag
+    PsErrVarForTyCon{}                            -> ErrorWithoutFlag
+    PsErrMalformedEntityString                    -> ErrorWithoutFlag
+    PsErrDotsInRecordUpdate                       -> ErrorWithoutFlag
+    PsErrInvalidDataCon{}                         -> ErrorWithoutFlag
+    PsErrInvalidInfixDataCon{}                    -> ErrorWithoutFlag
+    PsErrUnpackDataCon                            -> ErrorWithoutFlag
+    PsErrUnexpectedKindAppInDataCon{}             -> ErrorWithoutFlag
+    PsErrInvalidRecordCon{}                       -> ErrorWithoutFlag
+    PsErrIllegalUnboxedStringInPat{}              -> ErrorWithoutFlag
+    PsErrDoNotationInPat{}                        -> ErrorWithoutFlag
+    PsErrIfThenElseInPat                          -> ErrorWithoutFlag
+    PsErrLambdaCaseInPat                          -> ErrorWithoutFlag
+    PsErrCaseInPat                                -> ErrorWithoutFlag
+    PsErrLetInPat                                 -> ErrorWithoutFlag
+    PsErrLambdaInPat                              -> ErrorWithoutFlag
+    PsErrArrowExprInPat{}                         -> ErrorWithoutFlag
+    PsErrArrowCmdInPat{}                          -> ErrorWithoutFlag
+    PsErrArrowCmdInExpr{}                         -> ErrorWithoutFlag
+    PsErrViewPatInExpr{}                          -> ErrorWithoutFlag
+    PsErrLambdaCmdInFunAppCmd{}                   -> ErrorWithoutFlag
+    PsErrCaseCmdInFunAppCmd{}                     -> ErrorWithoutFlag
+    PsErrIfCmdInFunAppCmd{}                       -> ErrorWithoutFlag
+    PsErrLetCmdInFunAppCmd{}                      -> ErrorWithoutFlag
+    PsErrDoCmdInFunAppCmd{}                       -> ErrorWithoutFlag
+    PsErrDoInFunAppExpr{}                         -> ErrorWithoutFlag
+    PsErrMDoInFunAppExpr{}                        -> ErrorWithoutFlag
+    PsErrLambdaInFunAppExpr{}                     -> ErrorWithoutFlag
+    PsErrCaseInFunAppExpr{}                       -> ErrorWithoutFlag
+    PsErrLambdaCaseInFunAppExpr{}                 -> ErrorWithoutFlag
+    PsErrLetInFunAppExpr{}                        -> ErrorWithoutFlag
+    PsErrIfInFunAppExpr{}                         -> ErrorWithoutFlag
+    PsErrProcInFunAppExpr{}                       -> ErrorWithoutFlag
+    PsErrMalformedTyOrClDecl{}                    -> ErrorWithoutFlag
+    PsErrIllegalWhereInDataDecl                   -> ErrorWithoutFlag
+    PsErrIllegalDataTypeContext{}                 -> ErrorWithoutFlag
+    PsErrPrimStringInvalidChar                    -> ErrorWithoutFlag
+    PsErrSuffixAT                                 -> ErrorWithoutFlag
+    PsErrPrecedenceOutOfRange{}                   -> ErrorWithoutFlag
+    PsErrSemiColonsInCondExpr{}                   -> ErrorWithoutFlag
+    PsErrSemiColonsInCondCmd{}                    -> ErrorWithoutFlag
+    PsErrAtInPatPos                               -> ErrorWithoutFlag
+    PsErrParseErrorOnInput{}                      -> ErrorWithoutFlag
+    PsErrMalformedDecl{}                          -> ErrorWithoutFlag
+    PsErrUnexpectedTypeAppInDecl{}                -> ErrorWithoutFlag
+    PsErrNotADataCon{}                            -> ErrorWithoutFlag
+    PsErrInferredTypeVarNotAllowed                -> ErrorWithoutFlag
+    PsErrIllegalTraditionalRecordSyntax{}         -> ErrorWithoutFlag
+    PsErrParseErrorInCmd{}                        -> ErrorWithoutFlag
+    PsErrInPat{}                                  -> ErrorWithoutFlag
+    PsErrIllegalRoleName{}                        -> ErrorWithoutFlag
+    PsErrInvalidTypeSignature{}                   -> ErrorWithoutFlag
+    PsErrUnexpectedTypeInDecl{}                   -> ErrorWithoutFlag
+    PsErrInvalidPackageName{}                     -> ErrorWithoutFlag
+    PsErrParseRightOpSectionInPat{}               -> ErrorWithoutFlag
+
+  diagnosticHints  = \case
+    PsUnknownMessage m                            -> diagnosticHints m
+    PsWarnTab{}                                   -> [SuggestUseSpaces]
+    PsWarnTransitionalLayout{}                    -> noHints
+    PsWarnOperatorWhitespaceExtConflict{}         -> noHints
+    PsWarnOperatorWhitespace{}                    -> noHints
+    PsWarnHaddockInvalidPos                       -> noHints
+    PsWarnHaddockIgnoreMulti                      -> noHints
+    PsWarnStarBinder                              -> noHints
+    PsWarnStarIsType                              -> noHints
+    PsWarnUnrecognisedPragma                      -> noHints
+    PsWarnImportPreQualified                      -> noHints
+    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]
+           | otherwise           -> [SuggestMissingDo]
+      "="  | ped_do_in_last_100  -> [SuggestLetInDo]                             -- #15849
+      _    | not ped_pat_syn_enabled
+           , ped_pattern_parsed  -> [SuggestExtension LangExt.PatternSynonyms]   -- #12429
+           | otherwise           -> []
+    PsErrTypeAppWithoutSpace{}                    -> noHints
+    PsErrLazyPatWithoutSpace{}                    -> noHints
+    PsErrBangPatWithoutSpace{}                    -> noHints
+    PsErrInvalidInfixHole                         -> noHints
+    PsErrExpectedHyphen                           -> noHints
+    PsErrSpaceInSCC                               -> noHints
+    PsErrEmptyDoubleQuotes{}                      -> noHints
+    PsErrLambdaCase{}                             -> noHints
+    PsErrEmptyLambda{}                            -> noHints
+    PsErrLinearFunction{}                         -> noHints
+    PsErrMultiWayIf{}                             -> noHints
+    PsErrOverloadedRecordUpdateNotEnabled{}       -> noHints
+    PsErrNumUnderscores{}                         -> noHints
+    PsErrIllegalBangPattern{}                     -> noHints
+    PsErrOverloadedRecordDotInvalid{}             -> noHints
+    PsErrIllegalPatSynExport                      -> noHints
+    PsErrOverloadedRecordUpdateNoQualifiedFields  -> noHints
+    PsErrExplicitForall{}                         -> noHints
+    PsErrIllegalQualifiedDo{}                     -> noHints
+    PsErrQualifiedDoInCmd{}                       -> noHints
+    PsErrRecordSyntaxInPatSynDecl{}               -> noHints
+    PsErrEmptyWhereInPatSynDecl{}                 -> noHints
+    PsErrInvalidWhereBindInPatSynDecl{}           -> noHints
+    PsErrNoSingleWhereBindInPatSynDecl{}          -> noHints
+    PsErrDeclSpliceNotAtTopLevel{}                -> noHints
+    PsErrMultipleNamesInStandaloneKindSignature{} -> noHints
+    PsErrIllegalExplicitNamespace                 -> noHints
+    PsErrUnallowedPragma{}                        -> noHints
+    PsErrImportPostQualified                      -> noHints
+    PsErrImportQualifiedTwice                     -> noHints
+    PsErrIllegalImportBundleForm                  -> noHints
+    PsErrInvalidRuleActivationMarker              -> noHints
+    PsErrMissingBlock                             -> noHints
+    PsErrUnsupportedBoxedSumExpr{}                -> noHints
+    PsErrUnsupportedBoxedSumPat{}                 -> noHints
+    PsErrUnexpectedQualifiedConstructor{}         -> noHints
+    PsErrTupleSectionInPat{}                      -> noHints
+    PsErrOpFewArgs{}                              -> noHints
+    PsErrVarForTyCon{}                            -> noHints
+    PsErrMalformedEntityString                    -> noHints
+    PsErrDotsInRecordUpdate                       -> noHints
+    PsErrInvalidDataCon{}                         -> noHints
+    PsErrInvalidInfixDataCon{}                    -> noHints
+    PsErrUnpackDataCon                            -> noHints
+    PsErrUnexpectedKindAppInDataCon{}             -> noHints
+    PsErrInvalidRecordCon{}                       -> noHints
+    PsErrIllegalUnboxedStringInPat{}              -> noHints
+    PsErrDoNotationInPat{}                        -> noHints
+    PsErrIfThenElseInPat                          -> noHints
+    PsErrLambdaCaseInPat                          -> noHints
+    PsErrCaseInPat                                -> noHints
+    PsErrLetInPat                                 -> noHints
+    PsErrLambdaInPat                              -> noHints
+    PsErrArrowExprInPat{}                         -> noHints
+    PsErrArrowCmdInPat{}                          -> noHints
+    PsErrArrowCmdInExpr{}                         -> noHints
+    PsErrViewPatInExpr{}                          -> noHints
+    PsErrLambdaCmdInFunAppCmd{}                   -> suggestParensAndBlockArgs
+    PsErrCaseCmdInFunAppCmd{}                     -> suggestParensAndBlockArgs
+    PsErrIfCmdInFunAppCmd{}                       -> suggestParensAndBlockArgs
+    PsErrLetCmdInFunAppCmd{}                      -> suggestParensAndBlockArgs
+    PsErrDoCmdInFunAppCmd{}                       -> suggestParensAndBlockArgs
+    PsErrDoInFunAppExpr{}                         -> suggestParensAndBlockArgs
+    PsErrMDoInFunAppExpr{}                        -> suggestParensAndBlockArgs
+    PsErrLambdaInFunAppExpr{}                     -> suggestParensAndBlockArgs
+    PsErrCaseInFunAppExpr{}                       -> suggestParensAndBlockArgs
+    PsErrLambdaCaseInFunAppExpr{}                 -> suggestParensAndBlockArgs
+    PsErrLetInFunAppExpr{}                        -> suggestParensAndBlockArgs
+    PsErrIfInFunAppExpr{}                         -> suggestParensAndBlockArgs
+    PsErrProcInFunAppExpr{}                       -> suggestParensAndBlockArgs
+    PsErrMalformedTyOrClDecl{}                    -> noHints
+    PsErrIllegalWhereInDataDecl                   -> noHints
+    PsErrIllegalDataTypeContext{}                 -> noHints
+    PsErrPrimStringInvalidChar                    -> noHints
+    PsErrSuffixAT                                 -> noHints
+    PsErrPrecedenceOutOfRange{}                   -> noHints
+    PsErrSemiColonsInCondExpr{}                   -> noHints
+    PsErrSemiColonsInCondCmd{}                    -> noHints
+    PsErrAtInPatPos                               -> noHints
+    PsErrParseErrorOnInput{}                      -> noHints
+    PsErrMalformedDecl{}                          -> noHints
+    PsErrUnexpectedTypeAppInDecl{}                -> noHints
+    PsErrNotADataCon{}                            -> noHints
+    PsErrInferredTypeVarNotAllowed                -> noHints
+    PsErrIllegalTraditionalRecordSyntax{}         -> noHints
+    PsErrParseErrorInCmd{}                        -> noHints
+    PsErrInPat _ details                          -> case details of
+      PEIP_RecPattern args YesPatIsRecursive ctx
+       | length args /= 0 -> catMaybes [sug_recdo, sug_missingdo ctx]
+       | otherwise        -> catMaybes [sug_missingdo ctx]
+      PEIP_OtherPatDetails ctx -> catMaybes [sug_missingdo ctx]
+      _                        -> []
+      where
+        sug_recdo                                           = Just (SuggestExtension LangExt.RecursiveDo)
+        sug_missingdo (ParseContext _ YesIncompleteDoBlock) = Just SuggestMissingDo
+        sug_missingdo _                                     = Nothing
+    PsErrParseRightOpSectionInPat{}               -> noHints
+    PsErrIllegalRoleName{}                        -> noHints
+    PsErrInvalidTypeSignature{}                   -> noHints
+    PsErrUnexpectedTypeInDecl{}                   -> noHints
+    PsErrInvalidPackageName{}                     -> noHints
+
+suggestParensAndBlockArgs :: [GhcHint]
+suggestParensAndBlockArgs =
+  [SuggestParentheses, SuggestExtension LangExt.BlockArguments]
 
 pp_unexpected_fun_app :: Outputable a => SDoc -> a -> SDoc
 pp_unexpected_fun_app e a =
    text "Unexpected " <> e <> text " in function application:"
     $$ nest 4 (ppr a)
-    $$ text "You could write it with parentheses"
-    $$ text "Or perhaps you meant to enable BlockArguments?"
+
+parse_error_in_pat :: SDoc
+parse_error_in_pat = text "Parse error in pattern:"
+
+perhapsAsPat :: SDoc
+perhapsAsPat = text "Perhaps you meant an as-pattern, which must not be surrounded by whitespace"