fix test, change val name, & change warning point

Author: Medowhill

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -1364,7 +1364,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
    *  Two trials: First, without implicits or SAM conversions enabled. Then,
    *  if the fist finds no eligible candidates, with implicits and SAM conversions enabled.
    */
-  def resolveOverloaded(alts: List[TermRef], pt: Type, pos: Position = NoPosition)(implicit ctx: Context): List[TermRef] = track("resolveOverloaded") {
+  def resolveOverloaded(alts: List[TermRef], pt: Type)(implicit ctx: Context): List[TermRef] = track("resolveOverloaded") {
 
     /** Is `alt` a method or polytype whose result type after the first value parameter
      *  section conforms to the expected type `resultType`? If `resultType`
@@ -1409,9 +1409,9 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
       case _ => chosen
     }
 
-    var found = resolveOverloaded(alts, pt, Nil, pos)(ctx.retractMode(Mode.ImplicitsEnabled))
+    var found = resolveOverloaded(alts, pt, Nil)(ctx.retractMode(Mode.ImplicitsEnabled))
     if (found.isEmpty && ctx.mode.is(Mode.ImplicitsEnabled))
-      found = resolveOverloaded(alts, pt, Nil, pos)
+      found = resolveOverloaded(alts, pt, Nil)
     found match {
       case alt :: Nil => adaptByResult(alt) :: Nil
       case _ => found
@@ -1423,7 +1423,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
    *  called twice from the public `resolveOverloaded` method, once with
    *  implicits and SAM conversions enabled, and once without.
    */
-  private def resolveOverloaded(alts: List[TermRef], pt: Type, targs: List[Type], pos: Position)(implicit ctx: Context): List[TermRef] = track("resolveOverloaded") {
+  private def resolveOverloaded(alts: List[TermRef], pt: Type, targs: List[Type])(implicit ctx: Context): List[TermRef] = track("resolveOverloaded") {
 
     def isDetermined(alts: List[TermRef]) = alts.isEmpty || alts.tail.isEmpty
 

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2268,7 +2268,7 @@ class Typer extends Namer
         val altDenots = ref.denot.alternatives
         typr.println(i"adapt overloaded $ref with alternatives ${altDenots map (_.info)}%, %")
         val alts = altDenots.map(TermRef(ref.prefix, ref.name, _))
-        resolveOverloaded(alts, pt, tree.pos) match {
+        resolveOverloaded(alts, pt) match {
           case alt :: Nil =>
             readaptSimplified(tree.withType(alt))
           case Nil =>
@@ -2480,9 +2480,11 @@ class Typer extends Namer
           !tree.symbol.isConstructor &&
           !tree.symbol.is(InlineMethod) &&
           !ctx.mode.is(Mode.Pattern) &&
-          !(isSyntheticApply(tree) && !isExpandableApply))
+          !(isSyntheticApply(tree) && !isExpandableApply)) {
+        if (!pt.classSymbol.hasAnnotation(defn.FunctionalInterfaceAnnot))
+          ctx.warning(ex"${tree.symbol} is eta-expanded even though $pt does not have the @FunctionalInterface annotation.", tree.pos)
         simplify(typed(etaExpand(tree, wtp, arity), pt), pt, locked)
-      else if (wtp.paramInfos.isEmpty && isAutoApplied(tree.symbol))
+      } else if (wtp.paramInfos.isEmpty && isAutoApplied(tree.symbol))
         readaptSimplified(tpd.Apply(tree, Nil))
       else if (wtp.isImplicitMethod)
         err.typeMismatch(tree, pt)

tests/neg-custom-args/fatal-warnings/i4364.scala

@@ -1,14 +1,9 @@
 object Test {
-  def foo(c: java.util.function.Consumer[String]) = c.accept("")
-
-  def f(x: String): Unit = ()
+  def foo(c: java.util.function.Consumer[Integer]) = c.accept(0)
   def f(x: Int): Unit = ()
 
   def main(args: Array[String]) = {
     foo(f) // Ok: Consumer is @FunctionalInterface
-
-    val oos = new java.io.ObjectOutputStream(f) // error: OutputStream is not @FunctionalInterface
-    oos.write(0)
-    oos.close()
+    new java.io.ObjectOutputStream(f) // error: OutputStream is not @FunctionalInterface
   }
 }