cast unsupported cabal version as warning

plugins/hls-cabal-plugin/src/Ide/Plugin/Cabal.hs

@@ -65,6 +65,7 @@ import           Text.Regex.TDFA
 
 
 import qualified Data.Text                                     ()
+import           Distribution.Parsec.Error
 import qualified Ide.Plugin.Cabal.CabalAdd                     as CabalAdd
 
 data Log
@@ -220,8 +221,9 @@ cabalRules recorder plId = do
     fields <- use_ ParseCabalFields file
     let commonSections = Maybe.mapMaybe (\case
           commonSection@(Syntax.Section (Syntax.Name _ "common") _ _) -> Just commonSection
-          _ -> Nothing)
-          fields
+                _ -> Nothing
+            )
+            fields
     pure ([], Just commonSections)
 
   define (cmapWithPrio LogShake recorder) $ \ParseCabalFile file -> do
@@ -247,7 +249,19 @@ cabalRules recorder plId = do
         let warningDiags = fmap (Diagnostics.warningDiagnostic file) pWarnings
         case pm of
           Left (_cabalVersion, pErrorNE) -> do
-            let errorDiags = NE.toList $ NE.map (Diagnostics.errorDiagnostic file) pErrorNE
+            let regex :: T.Text
+                -- We don't support the cabal version, this should not be an error, as the
+                -- user did not do anything wrong. Instead we cast it to a warning
+                regex = "Unsupported cabal-version [0-9]+.[0-9]*"
+                errorDiags =
+                  NE.toList $
+                    NE.map
+                      ( \pe@(PError pos text) ->
+                          if text =~ regex
+                            then Diagnostics.warningDiagnostic file (Syntax.PWarning Syntax.PWTOther pos text)
+                            else Diagnostics.errorDiagnostic file pe
+                      )
+                      pErrorNE
                 allDiags = errorDiags <> warningDiags
             pure (allDiags, Nothing)
           Right gpd -> do

plugins/hls-cabal-plugin/test/Main.hs

@@ -107,14 +107,14 @@ pluginTests =
                     length diags @?= 1
                     unknownLicenseDiag ^. L.range @?= Range (Position 3 24) (Position 4 0)
                     unknownLicenseDiag ^. L.severity @?= Just DiagnosticSeverity_Error
-            ,   runCabalTestCaseSession "Publishes Diagnostics on Error in the first line" "" $ do
+            ,   runCabalTestCaseSession "Publishes Diagnostics on unsupported cabal version as Warning" "" $ do
                 _ <- openDoc "unsupportedVersion.cabal" "cabal"
                 diags <- cabalCaptureKick
                 unknownVersionDiag <- liftIO $ inspectDiagnostic diags ["Unsupported cabal-version 99999.0"]
                 liftIO $ do
                     length diags @?= 1
                     unknownVersionDiag ^. L.range @?= Range (Position 0 0) (Position 1 0)
-                    unknownVersionDiag ^. L.severity @?= Just DiagnosticSeverity_Error
+                    unknownVersionDiag ^. L.severity @?= Just DiagnosticSeverity_Warning
             , runCabalTestCaseSession "Clears diagnostics" "" $ do
                 doc <- openDoc "invalid.cabal" "cabal"
                 diags <- cabalCaptureKick