print null result of replStringOf as null

[Cherry-picked 390d956][modified]

Author: WojciechMazur

compiler/src/dotty/tools/repl/Rendering.scala

@@ -99,9 +99,7 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None):
     val maxPrintElements = ctx.settings.VreplMaxPrintElements.valueIn(ctx.settingsState)
     val maxPrintCharacters = ctx.settings.VreplMaxPrintCharacters.valueIn(ctx.settingsState)
     // stringOf returns null if value.toString returns null. Show some text as a fallback.
-    def toIdentityString(value: Object): String =
-      s"${value.getClass.getName}@${System.identityHashCode(value).toHexString}"
-    def fallback = s"""${toIdentityString(value)} // return value of "${sym.name}.toString" is null"""
+    def fallback = s"""null // result of "${sym.name}.toString" is null"""
     if value == null then "null" else
       myReplStringOf(value, maxPrintElements, maxPrintCharacters) match
         case null => fallback

compiler/test/dotty/tools/repl/ReplCompilerTests.scala

@@ -352,18 +352,17 @@ class ReplCompilerTests extends ReplTest:
       run("val tpolecat = new Object { override def toString(): String = null }")
     .andThen:
       val last = lines().last
-      assertTrue(last, last.startsWith("val tpolecat: Object = anon"))
-      assertTrue(last, last.endsWith("""// return value of "tpolecat.toString" is null"""))
+      assertTrue(last, last.startsWith("val tpolecat: Object = null"))
+      assertTrue(last, last.endsWith("""// result of "tpolecat.toString" is null"""))
 
   @Test def `i17333 print toplevel object with null toString`: Unit =
     initially:
       run("object tpolecat { override def toString(): String = null }")
-      .andThen:
-        run("tpolecat")
-        val last = lines().last
-        assertTrue(last, last.startsWith("val res0: tpolecat.type = tpolecat"))
-        assertTrue(last, last.endsWith("""// return value of "res0.toString" is null"""))
-end ReplCompilerTests
+    .andThen:
+      run("tpolecat")
+      val last = lines().last
+      assertTrue(last, last.startsWith("val res0: tpolecat.type = null"))
+      assertTrue(last, last.endsWith("""// result of "res0.toString" is null"""))
 
 object ReplCompilerTests: