refactor: make sure the patch logic isn't duplicated

Author: ckipp01

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2941,13 +2941,13 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
  case closure(_, _, _) =>
  case _ =>
  val recovered = typed(qual)(using ctx.fresh.setExploreTyperState())
- report.errorOrMigrationWarning(
- OnlyFunctionsCanBeFollowedByUnderscore(recovered.tpe.widen, tree), tree.srcPos, from = `3.0`
- )
+ val msg = OnlyFunctionsCanBeFollowedByUnderscore(recovered.tpe.widen, tree)
+ report.errorOrMigrationWarning(msg, tree.srcPos, from = `3.0`)
  if (migrateTo3) {
  // Under -rewrite, patch `x _` to `(() => x)`
- patch(Span(tree.span.start), "(() => ")
- patch(Span(qual.span.end, tree.span.end), ")")
+ msg.actions
+ .flatMap(_.patches)
+ .map(actionPatch => patch(actionPatch.srcPos.span, actionPatch.replacement))
  return typed(untpd.Function(Nil, qual), pt)
  }
  }
@@ -3951,10 +3951,17 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
  def adaptNoArgsUnappliedMethod(wtp: MethodType, functionExpected: Boolean, arity: Int): Tree = {
  /** Is reference to this symbol `f` automatically expanded to `f()`? */
  def isAutoApplied(sym: Symbol): Boolean =
+ lazy val msg = MissingEmptyArgumentList(sym.show, tree)
+
  sym.isConstructor
  || sym.matchNullaryLoosely
- || Feature.warnOnMigration(MissingEmptyArgumentList(sym.show, tree), tree.srcPos, version = `3.0`)
- && { patch(tree.span.endPos, "()"); true }
+ || Feature.warnOnMigration(msg, tree.srcPos, version = `3.0`)
+ && { 
+ msg.actions
+ .flatMap(_.patches)
+ .map(actionPatch => patch(actionPatch.srcPos.span, actionPatch.replacement))
+ true
+ }
 
  /** If this is a selection prototype of the form `.apply(...): R`, return the nested
  * function prototype `(...)R`. Otherwise `pt`.