add regression test for export class incremental compilation

Author: bishabosha

sbt-dotty/sbt-test/source-dependencies/export-clauses/A.scala

@@ -0,0 +1,7 @@
+class A(val c: C) {
+  export c._
+}
+
+object A {
+  def create: A = new A(new C())
+}

sbt-dotty/sbt-test/source-dependencies/export-clauses/B.scala

@@ -0,0 +1,3 @@
+class B {
+  val x: Int = 23
+}

sbt-dotty/sbt-test/source-dependencies/export-clauses/C.scala

@@ -0,0 +1 @@
+class C extends B

sbt-dotty/sbt-test/source-dependencies/export-clauses/D.scala

@@ -0,0 +1,3 @@
+object D {
+  val foo: Int = A.create.x
+}

sbt-dotty/sbt-test/source-dependencies/export-clauses/changes/B1.scala

@@ -0,0 +1,3 @@
+class B {
+  val x: String = "x"
+}

sbt-dotty/sbt-test/source-dependencies/export-clauses/project/DottyInjectedPlugin.scala

@@ -0,0 +1,12 @@
+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"),
+    scalacOptions += "-source:3.0-migration"
+  )
+}

sbt-dotty/sbt-test/source-dependencies/export-clauses/project/plugins.sbt

@@ -0,0 +1 @@
+addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % sys.props("plugin.version"))

sbt-dotty/sbt-test/source-dependencies/export-clauses/test

@@ -0,0 +1,4 @@
+> compile
+$ copy-file changes/B1.scala B.scala
+# Compilation of D.scala should fail because the signature of B.x changed
+-> compile