Merge pull request #4403 from gourlaysama/wip/t9239-generic-signature

SI-9239 fix java generic signature when traits extend classes

3 files changed, 24 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Erasure.scala b/src/compiler/scala/tools/nsc/transform/Erasure.scala
index facce9062b..9fdc3a9d72 100644
--- a/src/compiler/scala/tools/nsc/transform/Erasure.scala
+++ b/src/compiler/scala/tools/nsc/transform/Erasure.scala
@@ -188,14 +188,16 @@ abstract class Erasure extends AddInterfaces
   /* Drop redundant types (ones which are implemented by some other parent) from the immediate parents.
    * This is important on Android because there is otherwise an interface explosion.
    */
-  def minimizeParents(parents: List[Type]): List[Type] = {
-    var rest   = parents
-    var leaves = collection.mutable.ListBuffer.empty[Type]
+  def minimizeParents(parents: List[Type]): List[Type] = if (parents.isEmpty) parents else {
+    def isInterfaceOrTrait(sym: Symbol) = sym.isInterface || sym.isTrait
+
+    var rest   = parents.tail
+    var leaves = collection.mutable.ListBuffer.empty[Type] += parents.head
     while(rest.nonEmpty) {
       val candidate = rest.head
       val nonLeaf = leaves exists { t => t.typeSymbol isSubClass candidate.typeSymbol }
       if(!nonLeaf) {
-        leaves = leaves filterNot { t => candidate.typeSymbol isSubClass t.typeSymbol }
+        leaves = leaves filterNot { t => isInterfaceOrTrait(t.typeSymbol) && (candidate.typeSymbol isSubClass t.typeSymbol) }
         leaves += candidate
       }
       rest = rest.tail
diff --git a/test/files/pos/t9239/Declaration.scala b/test/files/pos/t9239/Declaration.scala
new file mode 100644
index 0000000000..452dcc1e77
--- /dev/null
+++ b/test/files/pos/t9239/Declaration.scala
@@ -0,0 +1,3 @@
+class Foo[A]
+trait Bar[A] extends Foo[A]
+class Baz[A] extends Bar[A]
diff --git a/test/files/pos/t9239/Usage.java b/test/files/pos/t9239/Usage.java
new file mode 100644
index 0000000000..d1e3fb0c3e
--- /dev/null
+++ b/test/files/pos/t9239/Usage.java
@@ -0,0 +1,15 @@
+/**
+ * Used to fail with:
+ *
+ * Usage.java:5: error: incompatible types: Baz<String> cannot be converted to Foo<String>
+ * 	  foo(f);
+ *            ^
+ */
+public class Usage {
+  public Usage() {
+	  Baz<String> f = null;
+	  foo(f);
+  }
+
+  public void foo(Foo<String> f) { };
+}