Fixes #7051 Detect typos in neg tests and give a warning

Author: ashwinbhaskar

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -658,20 +658,48 @@ trait ParallelTesting extends RunnerOrchestration { self =>
           if (errors > 0)
             errorMap.put(s"${file.getPath}:${lineNbr}", errors)
 
+
           val noposErrors = line.sliding("// nopos-error".length).count(_.mkString == "// nopos-error")
           if (noposErrors > 0) {
             val nopos = errorMap.get("nopos")
             val existing: Integer = if (nopos eq null) 0 else nopos
             errorMap.put("nopos", noposErrors + existing)
           }
 
+          maybeWarning(line).foreach(warning => echo(s"Possible typo in file ${file.getCanonicalPath} at line number $lineNbr \n$warning"))
+
           expectedErrors += noposErrors + errors
         }
       }
 
       (errorMap, expectedErrors)
     }
 
+    /**
+     * We want to warn the developer about some of the possible typos when trying to point "error" and "nopos-error"
+     * For example - A warning could be emitted if the developer mistakenly types in "//error" instead of "// error"
+     * or "//nopos-error" instead of "// nopos-error"
+     *
+     * @param line the line which will be checked for possible typos
+     * @return Some(warningMessage) or None
+     */
+    def maybeWarning(line : String) : Option[String] = {
+
+      def hasTypo(line :  String) : Boolean = line.contains("//error") || line.contains("//nopos-error")
+
+      def getWarning(line: String): String = if (line.contains("//error")) {
+        s"Wrong   : //error\nCorrect : // error"
+      } else if (line.contains("//nopos-error")) {
+        s"Wrong : //nopos-error\nCorrect : // nopos-error"
+      } else ""
+      
+      if(hasTypo(line)){
+        Some(getWarning(line))
+      }else {
+        None
+      }
+    }
+
     def getMissingExpectedErrors(errorMap: HashMap[String, Integer], reporterErrors: Iterator[MessageContainer]) = !reporterErrors.forall { error =>
       val key = if (error.pos.exists) {
         def toRelative(path: String): String =  // For some reason, absolute paths leak from the compiler itself...