From 99079228d8b0cf15bd892c18cb040e79a3c0480a Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Tue, 3 May 2022 16:08:16 +0200
Subject: [PATCH] Eta expand CTFs in super accessors if needed

Fixes #14999
---
 .../dotty/tools/dotc/transform/ResolveSuper.scala   | 11 ++++++-----
 tests/pos/i14999.scala                              | 13 +++++++++++++
 2 files changed, 19 insertions(+), 5 deletions(-)
 create mode 100644 tests/pos/i14999.scala

diff --git a/compiler/src/dotty/tools/dotc/transform/ResolveSuper.scala b/compiler/src/dotty/tools/dotc/transform/ResolveSuper.scala
index 621935df6bb8..dd109ce153eb 100644
--- a/compiler/src/dotty/tools/dotc/transform/ResolveSuper.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ResolveSuper.scala
@@ -48,11 +48,12 @@ class ResolveSuper extends MiniPhase with IdentityDenotTransformer { thisPhase =
     import ops._
 
     def superAccessors(mixin: ClassSymbol): List[Tree] =
-      for (superAcc <- mixin.info.decls.filter(_.isSuperAccessor))
-        yield {
-          util.Stats.record("super accessors")
-          DefDef(mkForwarderSym(superAcc.asTerm), forwarderRhsFn(rebindSuper(cls, superAcc)))
-      }
+      for superAcc <- mixin.info.decls.filter(_.isSuperAccessor)
+      yield
+        util.Stats.record("super accessors")
+        val fwd = mkForwarderSym(superAcc.asTerm)
+        DefDef(fwd, forwarderRhsFn(rebindSuper(cls, superAcc))
+          .andThen(_.etaExpandCFT(using ctx.withOwner(fwd))))
 
     val overrides = mixins.flatMap(superAccessors)
 
diff --git a/tests/pos/i14999.scala b/tests/pos/i14999.scala
new file mode 100644
index 000000000000..1b32361e5e52
--- /dev/null
+++ b/tests/pos/i14999.scala
@@ -0,0 +1,13 @@
+trait Foo:
+   def foo: String ?=> Int =
+     summon[String].length
+
+trait Bar extends Foo:
+   override def foo =
+      super.foo
+
+class Baz extends Bar
+
+@main def Test =
+  given String = "hello"
+  assert(Baz().foo == 5)