Fix #4166: Add regression test

Author: nicolasstucki

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -58,6 +58,7 @@ class CompilationTests extends ParallelTesting {
     compileFile("tests/pos-special/i3323.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("tests/pos-special/i3323b.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("tests/pos-special/i3589-b.scala", defaultOptions.and("-Xfatal-warnings")) +
+    compileFile("tests/pos-special/i4166.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("tests/pos-special/completeFromSource/Test.scala", defaultOptions.and("-sourcepath", "tests/pos-special")) +
     compileFile("tests/pos-special/completeFromSource/Test2.scala", defaultOptions.and("-sourcepath", "tests/pos-special")) +
     compileFile("tests/pos-special/completeFromSource/Test3.scala", defaultOptions.and("-sourcepath", "tests/pos-special", "-scansource")) +

tests/pos-special/i4166.scala

@@ -0,0 +1,7 @@
+package foo {
+  class Hello
+}
+
+package bar {
+  class Hello
+}