Add REPL test

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

@@ -462,10 +462,36 @@ class ReplCompilerTests extends ReplTest:
     .andThen:
       run("0") // check for crash
       val last = lines()
-      println(last)
       assertTrue(last(0), last(0) == ("Options incompatible with repl will be ignored: -Ybest-effort, -Ywith-best-effort-tasty"))
       assertTrue(last(1), last(1) == ("val res0: Int = 0"))
 
+  @Test def `i9879`: Unit = initially:
+    run {
+      """|opaque type A = Int; def getA: A = 0
+         |object Wrapper { opaque type A = Int; def getA: A = 1 }
+         |val x = getA
+         |val y = Wrapper.getA""".stripMargin
+    }
+    val expected = List(
+      "def getA: A",
+      "// defined object Wrapper",
+      "val x: A = 0",
+      "val y: Wrapper.A = 1"
+    )
+    assertEquals(expected, lines())
+
+  @Test def `i9879b`: Unit = initially:
+    run {
+      """|def test =
+         |  type A = Int
+         |  opaque type B = String
+         |  object Wrapper { opaque type C = Int }
+         |  ()""".stripMargin
+    }
+    val all = lines()
+    assertEquals(6, all.length)
+    assertTrue(all.head.startsWith("-- [E103] Syntax Error"))
+    assertTrue(all.exists(_.trim().startsWith("|  Illegal start of statement: this modifier is not allowed here")))
 
 object ReplCompilerTests: