Unduplicate enrich{,ed}ErrorMessage

Having a same-named enrichement will cause the original to be called
if/when explicit nulls is switched off - which leads to the original
method to be called, meaning an NPE will be thrown.

So, instead, move all the functionality as an extension method, so we
don't need mangled names.

Author: dwijnand

compiler/src/dotty/tools/dotc/Run.scala

@@ -175,19 +175,11 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
 
   private var myEnrichedErrorMessage = false
 
-  def enrichedErrorMessage: Boolean = myEnrichedErrorMessage
-
-  def enrichErrorMessage(errorMessage: String)(using Context): String =
-    if enrichedErrorMessage then errorMessage
-    else
-      myEnrichedErrorMessage = true
-      report.enrichErrorMessage(errorMessage)
-
   def compile(files: List[AbstractFile]): Unit =
     try compileSources(files.map(runContext.getSource(_)))
-    catch case NonFatal(ex) if !enrichedErrorMessage =>
+    catch case NonFatal(ex) if !this.enrichedErrorMessage =>
       val files1 = if units.isEmpty then files else units.map(_.source.file)
-      report.echo(enrichErrorMessage(s"exception occurred while compiling ${files1.map(_.path)}"))
+      report.echo(this.enrichErrorMessage(s"exception occurred while compiling ${files1.map(_.path)}"))
       throw ex
 
   /** TODO: There's a fundamental design problem here: We assemble phases using `fusePhases`
@@ -408,9 +400,13 @@ class Run(comp: Compiler, ictx: Context) extends ImplicitRunInfo with Constraint
 
 object Run {
   extension (run: Run | Null)
-    def enrichedErrorMessage: Boolean = if run == null then false else run.enrichedErrorMessage
+    def enrichedErrorMessage: Boolean = if run == null then false else run.myEnrichedErrorMessage
     def enrichErrorMessage(errorMessage: String)(using Context): String =
-      if run == null
-      then report.enrichErrorMessage(errorMessage)
-      else run.enrichErrorMessage(errorMessage)
+      if run == null then
+        report.enrichErrorMessage(errorMessage)
+      else if !run.enrichedErrorMessage then
+        run.myEnrichedErrorMessage = true
+        report.enrichErrorMessage(errorMessage)
+      else
+        errorMessage
 }