Merge pull request #2739 from retronym/ticket/7668

SI-7668 Better return type inheritance for dep. method types

2 files changed, 15 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index e8a1e8e85a..cac6bd2ef2 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -1085,6 +1085,9 @@ trait Namers extends MethodSynthesis {
             overriddenTp = overriddenTp.resultType
           }
 
+          // SI-7668 Substitute parameters from the parent method with those of the overriding method.
+          overriddenTp = overriddenTp.substSym(overridden.paramss.flatten, vparamss.flatten.map(_.symbol))
+
           overriddenTp match {
             case NullaryMethodType(rtpe) => overriddenTp = rtpe
             case MethodType(List(), rtpe) => overriddenTp = rtpe
diff --git a/test/files/pos/t7668.scala b/test/files/pos/t7668.scala
new file mode 100644
index 0000000000..222a13d039
--- /dev/null
+++ b/test/files/pos/t7668.scala
@@ -0,0 +1,12 @@
+trait Space {
+  type T
+  val x: T
+}
+
+trait Extractor {
+  def extract(s: Space): s.T
+}
+
+class Sub extends Extractor {
+  def extract(s: Space) = s.x
+}