Use symbol.showDcl, add sentence on explicitly passing arg

Author: ysthakur

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -2746,7 +2746,9 @@ class MissingImplicitArgument(
           i"\n\nNote: ${s.ref.symbol.showLocated} was not considered because it was not imported with `import given`."
         def noChainConversionsNote(s: Iterable[TermRef]): Option[String] =
           Option.when(s.nonEmpty)(
-              i"\n\nNote: Chaining implicit conversions is no longer allowed in Scala. The following conversions were ignored:${s.map(g => "\n  - " + g.symbol.showLocated).mkString}"
+              i"\n\nNote: Chaining implicit conversions is no longer allowed in Scala. " +
+              i"The following conversions were ignored:${s.map(g => s"\n  - ${g.symbol.showDcl}").mkString}" +
+              i"\nIf there is an implicit `Conversion[A, ${pt.show}]` and an implicit `A` in scope, you need to explicitly pass the argument, e.g. `(using summon[A])`"
           )
         super.msgPostscript
         ++ ignoredInstanceNormalImport.map(hiddenImplicitNote)

tests/neg/i16453.check

@@ -1,7 +1,8 @@
 -- [E172] Type Error: tests/neg/i16453.scala:10:43 ---------------------------------------------------------------------
 10 |  val fails = summon[String => Option[Int]] // error
    |                                           ^
-   |     No given instance of type String => Option[Int] was found for parameter x of method summon in object Predef
+   |No given instance of type String => Option[Int] was found for parameter x of method summon in object Predef
    |
-   |     Note: Chaining implicit conversions is no longer allowed in Scala. The following conversions were ignored:
-   |       - given instance given_Conversion_Function_Function
+   |Note: Chaining implicit conversions is no longer allowed in Scala. The following conversions were ignored:
+   |  - final given def given_Conversion_Function_Function[T]: Conversion[String => T, String => Option[T]]
+   |If there is an implicit `Conversion[A, String => Option[Int]]` and an implicit `A` in scope, you need to explicitly pass the argument, e.g. `(using summon[A])`