add transitivity test

Author: bishabosha

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

@@ -52,6 +52,7 @@ class CompilationTests {
       compileFile("tests/pos-special/notNull.scala", defaultOptions.and("-Yexplicit-nulls")),
       compileDir("tests/pos-special/adhoc-extension", defaultOptions.and("-source", "3.1", "-feature", "-Xfatal-warnings")),
       compileFile("tests/pos-special/i7575.scala", defaultOptions.andLanguageFeature("dynamics")),
+      compileFile("tests/pos-special/i10511-transitivity.scala", defaultOptions), // avoid pickling test
       compileFile("tests/pos-special/kind-projector.scala", defaultOptions.and("-Ykind-projector")),
       compileFile("tests/run/i5606.scala", defaultOptions.and("-Yretain-trees")),
       compileFile("tests/pos-custom-args/i5498-postfixOps.scala", defaultOptions withoutLanguageFeature "postfixOps"),

tests/pos-special/i10511-transitivity.scala

@@ -0,0 +1,20 @@
+enum Bool {
+  case True
+  case False
+}
+
+import Bool._
+
+type Not[B <: Bool] = B match {
+  case True.type => False.type
+  case False.type => True.type
+}
+
+val t: True.type = True
+val f: False.type = False
+
+val t1: Not[f.type] = t // transitivity
+val f1: Not[t.type] = f // transitivity
+
+val t2: Not[f1.type] = t1 // transitivity x2
+val f2: Not[t1.type] = f1 // transitivity x2