From 0d89ab1fe4adfe7165a2e3812d76dbb586c79798 Mon Sep 17 00:00:00 2001
From: Adriaan Moors <adriaan.moors@typesafe.com>
Date: Thu, 4 Feb 2016 15:26:57 -0800
Subject: SI-9449 sam expansion for explicitly eta-expanded method

---
 src/compiler/scala/tools/nsc/typechecker/Typers.scala | 12 ++++++++++--
 test/files/pos/t9449.scala                            | 19 +++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 test/files/pos/t9449.scala

diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 383953f27e..5a62c32d2e 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2908,6 +2908,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
        *   (a => a): MyFun
        *
        * Note that the arity of the sam must correspond to the arity of the function.
+       * TODO: handle vararg sams?
        */
       val ptNorm =
         if (sam.exists && sameLength(sam.info.params, fun.vparams)) samToFunctionType(pt, sam)
@@ -4407,6 +4408,13 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
         tp
       }
 
+      def expectingFunctionMatchingFormals(formals: List[Symbol]) =
+        isFunctionType(pt) || {
+          val sam = samOf(pt)
+          // TODO: handle vararg sam here and in typedFunction
+          sam.exists && sameLength(sam.info.params, formals)
+        }
+
       def typedEta(expr1: Tree): Tree = expr1.tpe match {
         case TypeRef(_, ByNameParamClass, _) =>
           val expr2 = Function(List(), expr1) setPos expr1.pos
@@ -4417,10 +4425,10 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           new ChangeOwnerTraverser(context.owner, expr2.symbol).traverse(expr2)
           typed1(expr2, mode, pt)
         case PolyType(_, MethodType(formals, _)) =>
-          if (isFunctionType(pt)) expr1
+          if (expectingFunctionMatchingFormals(formals)) expr1
           else adapt(expr1, mode, functionTypeWildcard(expr1, formals.length))
         case MethodType(formals, _) =>
-          if (isFunctionType(pt)) expr1
+          if (expectingFunctionMatchingFormals(formals)) expr1
           else adapt(expr1, mode, functionTypeWildcard(expr1, formals.length))
         case ErrorType =>
           expr1
diff --git a/test/files/pos/t9449.scala b/test/files/pos/t9449.scala
new file mode 100644
index 0000000000..06653cca83
--- /dev/null
+++ b/test/files/pos/t9449.scala
@@ -0,0 +1,19 @@
+trait II {
+  def apply(x: Int): Int
+}
+
+object Test {
+  def ii(x: Int): Int = x
+  def test = {
+    val ii1: II = x => ii(x) // works
+    val ii2: II = ii         // works (adapting `ii` to `II`)
+    val ii3: II = ii _       // fails -- should work
+                             // typedTyped({ii : (() => <empty>)})
+                             //    typedEta(ii, pt = II)
+                             //       adapt(ii, pt = (? => ?))
+                             //          instantiatedToMethodType(ii, pt = (? => ?))
+    // val ii3: II = ii _ // error:
+    // found   : Int => Int
+    // required: II
+  }
+}
\ No newline at end of file
-- 
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