add some utilities functions

src/Error/Diagnose/Diagnostic.hs

@@ -21,7 +21,10 @@ import Error.Diagnose.Diagnostic.Internal as Export
     addFile,
     addReport,
     def,
+    errorsToWarnings,
+    hasReports,
     prettyDiagnostic,
     printDiagnostic,
+    warningsToErrors,
   )
 import System.IO as Export (stderr, stdout)

src/Error/Diagnose/Diagnostic/Internal.hs

@@ -29,7 +29,7 @@ import Data.Foldable (fold, toList)
 import qualified Data.HashMap.Lazy as HashMap
 import Data.List (intersperse)
 import Error.Diagnose.Report (Report)
-import Error.Diagnose.Report.Internal (FileMap, prettyReport)
+import Error.Diagnose.Report.Internal (FileMap, errorToWarning, prettyReport, warningToError)
 import Error.Diagnose.Style (Annotation, Style)
 import Prettyprinter (Doc, Pretty, hardline, unAnnotate)
 import Prettyprinter.Render.Terminal (hPutDoc)
@@ -67,6 +67,19 @@ instance ToJSON msg => ToJSON (Diagnostic msg) where
                ]
 #endif
 
+-- | Checks whether the given diagnostic has any report or not (if it is effectively empty).
+hasReports :: Diagnostic msg -> Bool
+hasReports (Diagnostic DL.Nil _) = True
+hasReports _ = False
+
+-- | Transforms every warning report in this diagnostic into an error report.
+warningsToErrors :: Diagnostic msg -> Diagnostic msg
+warningsToErrors (Diagnostic reports files) = Diagnostic (warningToError <$> reports) files
+
+-- | Transforms every error report in this diagnostic into a warning report.
+errorsToWarnings :: Diagnostic msg -> Diagnostic msg
+errorsToWarnings (Diagnostic reports files) = Diagnostic (errorToWarning <$> reports) files
+
 -- | Pretty prints a 'Diagnostic' into a 'Doc'ument that can be output using 'hPutDoc'.
 --
 --   Colors are put by default.

src/Error/Diagnose/Report.hs

@@ -11,4 +11,4 @@ module Error.Diagnose.Report
   )
 where
 
-import Error.Diagnose.Report.Internal as Export (Marker (..), Note (..), Report, err, warn)
+import Error.Diagnose.Report.Internal as Export (Marker (..), Note (..), Report, err, errorToWarning, warn, warningToError)

src/Error/Diagnose/Report/Internal.hs

@@ -160,6 +160,16 @@ warn = Report False
 err = Report True
 {-# INLINE err #-}
 
+-- | Transforms a warning report into an error report.
+warningToError :: Report msg -> Report msg
+warningToError (Report False code msg markers notes) = Report True code msg markers notes
+warningToError r@(Report True _ _ _ _) = r
+
+-- | Transforms an error report into a warning report.
+errorToWarning :: Report msg -> Report msg
+errorToWarning (Report True code msg markers notes) = Report False code msg markers notes
+errorToWarning r@(Report False _ _ _ _) = r
+
 -- | Pretty prints a report to a 'Doc' handling colors.
 prettyReport ::
   Pretty msg =>