add failing test: demo transparent inline can not see forwarders at typer

At typer, when transparent inline methods are expanded, unroll forwarders
are not yet generated.

So if we define forwarders for the first time, in the same compilation
unit that inlines a call to the forwarder, then it will fail.

Perhaps we can detect this and suspend the unit, otherwise it would seem
unreasonable complexity to generate forwarders in typer.

Author: bishabosha

sbt-test/tasty-compat/add-param-unroll2/a_v1/A.scala

@@ -0,0 +1,10 @@
+package a
+
+import scala.annotation.unroll
+
+// new project with a single file, first compile via Zinc
+object A {
+
+  def foo(s: String, x: Int): String = s + x
+
+}

sbt-test/tasty-compat/add-param-unroll2/a_v2/B.scala

@@ -0,0 +1,8 @@
+package b
+
+import a.*
+
+// Add a separate file in the same project as A, second compile via Zinc
+object B {
+  transparent inline def caller = A.foo("abc", 2)
+}

sbt-test/tasty-compat/add-param-unroll2/a_v3/A.scala

@@ -0,0 +1,17 @@
+package a
+import b.*
+
+import scala.annotation.unroll
+
+// modify A.scala and add a parameter to foo, and add C, third compile via Zinc
+object A {
+
+  def foo(s: String, x: Int, @unroll b: Boolean = true): String = s + x + b
+
+}
+
+// C is the same compilation unit as A, and inlines B.caller, so its TASTy will see the forwarder
+// where the associated file came from source
+object C {
+  val res = B.caller
+}

sbt-test/tasty-compat/add-param-unroll2/build.sbt

@@ -0,0 +1,28 @@
+lazy val commonSettings = Seq(
+  scalacOptions += "-experimental",
+)
+
+lazy val printSettings = Seq(
+  scalacOptions += "-Yprint-tasty",
+)
+
+lazy val a_v1 = project.in(file("a_v1"))
+  .settings(commonSettings)
+  .settings(
+    Compile / classDirectory := (ThisBuild / baseDirectory).value / "v2-input"
+  )
+
+lazy val a_v2 = project.in(file("a_v2"))
+  .settings(commonSettings)
+  .settings(printSettings)
+  .settings(
+    Compile / unmanagedClasspath += (ThisBuild / baseDirectory).value / "v2-input",
+    Compile / classDirectory := (ThisBuild / baseDirectory).value / "v3-input"
+  )
+
+lazy val a_v3 = project.in(file("a_v3"))
+  .settings(commonSettings)
+  .settings(
+    Compile / unmanagedClasspath += (ThisBuild / baseDirectory).value / "v3-input",
+    Compile / classDirectory := (ThisBuild / baseDirectory).value / "v3-output"
+  )

sbt-test/tasty-compat/add-param-unroll2/project/DottyInjectedPlugin.scala

@@ -0,0 +1,11 @@
+import sbt._
+import Keys._
+
+object DottyInjectedPlugin extends AutoPlugin {
+  override def requires = plugins.JvmPlugin
+  override def trigger = allRequirements
+
+  override val projectSettings = Seq(
+    scalaVersion := sys.props("plugin.scalaVersion")
+  )
+}

sbt-test/tasty-compat/add-param-unroll2/test

@@ -0,0 +1,8 @@
+# compile library A via Zinc, with an initial file A defining method foo
+> a_v1/compile
+# compile library A via Zinc, for the second time, adding a new file that defines an inline
+# method B.caller, calling A.foo
+> a_v2/compile
+# compile library A via Zinc, for the third time, add a new parameter to A.foo, using @unroll to generate a forwarder
+# in the same file A.scala, define object C that inlines B.caller, it should succeed and resolve the new invisible forwarder
+> a_v3/compile