3 files changed, 14 insertions, 1 deletions
diff --git a/compiler/GHC/Parser/Errors.hs b/compiler/GHC/Parser/Errors.hs
index 83812f7673..e48f04aae5 100644
--- a/compiler/GHC/Parser/Errors.hs
+++ b/compiler/GHC/Parser/Errors.hs
@@ -90,6 +90,9 @@ data PsErrorDesc
    = PsErrLambdaCase
       -- ^ LambdaCase syntax used without the extension enabled
 
+   | PsErrEmptyLambda
+      -- ^ A lambda requires at least one parameter
+
    | PsErrNumUnderscores !NumUnderscoreReason
       -- ^ Underscores in literals without the extension enabled
 
diff --git a/compiler/GHC/Parser/Errors/Ppr.hs b/compiler/GHC/Parser/Errors/Ppr.hs
index 7b9f2e64a0..0e83949a2e 100644
--- a/compiler/GHC/Parser/Errors/Ppr.hs
+++ b/compiler/GHC/Parser/Errors/Ppr.hs
@@ -141,6 +141,9 @@ 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"
diff --git a/compiler/GHC/Parser/PostProcess.hs b/compiler/GHC/Parser/PostProcess.hs
index 1de9f0cd53..6411df34d9 100644
--- a/compiler/GHC/Parser/PostProcess.hs
+++ b/compiler/GHC/Parser/PostProcess.hs
@@ -1629,6 +1629,11 @@ instance DisambECP (HsCmd GhcPs) where
 cmdFail :: SrcSpan -> SDoc -> PV a
 cmdFail loc e = addFatalError $ PsError (PsErrParseErrorInCmd e) [] loc
 
+checkLamMatchGroup :: SrcSpan -> MatchGroup GhcPs (LHsExpr GhcPs) -> PV ()
+checkLamMatchGroup l (MG { mg_alts = (L _ (matches:_))}) = do
+  when (null (hsLMatchPats matches)) $ addError $ PsError PsErrEmptyLambda [] l
+checkLamMatchGroup _ _ = return ()
+
 instance DisambECP (HsExpr GhcPs) where
   type Body (HsExpr GhcPs) = HsExpr
   ecpFromCmd' (L l c) = do
@@ -1640,7 +1645,9 @@ instance DisambECP (HsExpr GhcPs) where
     return $ mkRdrProjUpdate (noAnnSrcSpan l) fields arg isPun (EpAnn (spanAsAnchor l) anns cs)
   mkHsLamPV l mg = do
     cs <- getCommentsFor l
-    return $ L (noAnnSrcSpan l) (HsLam NoExtField (mg cs))
+    let mg' = mg cs
+    checkLamMatchGroup l mg'
+    return $ L (noAnnSrcSpan l) (HsLam NoExtField mg')
   mkHsLetPV l bs c anns = do
     cs <- getCommentsFor l
     return $ L (noAnnSrcSpan l) (HsLet (EpAnn (spanAsAnchor l) anns cs) bs c)