Include parse-error in output-not-valid error message

source/library/Language/Haskell/Brittany/Internal.hs

@@ -144,7 +144,7 @@ pPrintModuleAndCheck traceFunc conf inlineConf parsedModule = do
                                                (\_ -> return $ Right ())
                                                (TextL.unpack output)
   let errs' = errs ++ case parseResult of
-        Left{}  -> [ErrorOutputCheck]
+        Left x  -> [ErrorOutputCheck x]
         Right{} -> []
   return (errs', output)
 
@@ -195,7 +195,7 @@ parsePrintModuleTests conf filename input = do
     LayoutWarning str         -> str
     ErrorUnknownNode str _    -> str
     ErrorMacroConfig str _    -> "when parsing inline config: " ++ str
-    ErrorOutputCheck          -> "Output is not syntactically valid."
+    ErrorOutputCheck str      -> "Output is not syntactically valid: " ++ str
 -- this approach would for if there was a pure GHC.parseDynamicFilePragma.
 -- Unfortunately that does not exist yet, so we cannot provide a nominally
 -- pure interface.

source/library/Language/Haskell/Brittany/Internal/Types.hs

@@ -52,7 +52,7 @@ data BrittanyError
   | forall ast . (Data.Data.Data (XRec GhcPs ast), Outputable (Anno ast)) => ErrorUnknownNode String (XRec GhcPs ast)
     -- ^ internal error: pretty-printing is not implemented for type of node
     --   in the syntax-tree
-  | ErrorOutputCheck
+  | ErrorOutputCheck String
     -- ^ checking the output for syntactic validity failed