Treat `Function` literals uniformly, expecting SAM or FunctionN.

They both compile to INDY/MetaLambdaFactory, except when they
occur in a constructor call. (TODO: can we lift the ctor arg
expression to a method and avoid statically synthesizing
anonymous subclass altogether?)

Typers:
  - no longer synthesize SAMs -- *adapt* a Function literal
    to the expected (SAM/FunctionN) type
  - Deal with polymorphic/existential sams (relevant tests:
    pos/t8310, pos/t5099.scala, pos/t4869.scala) We know where
    to find the result type, as all Function nodes have a
    FunctionN-shaped type during erasure. (Including function
    literals targeting a SAM type -- the sam type is tracked as
    the *expected* type.)

    Lift restriction on sam types being class types. It's enough
    that they dealias to one, like regular instance creation
    expressions.

Contexts:
  - No longer need encl method hack for return in sam.

Erasure:
  - erasure preserves SAM type for function nodes
  - Normalize sam to erased function type during erasure,
    otherwise we may box the function body from `$anonfun(args)`
    to `{$anonfun(args); ()}` because the expected type for the
    body is now `Object`, and thus `Unit` does not conform.

Delambdafy:
  - must set static flag before calling createBoxingBridgeMethod
  - Refactored `createBoxingBridgeMethod` to wrap my head around
    boxing, reworked it to generalize from FunctionN's boxing
    needs to arbitrary LMF targets.

Other refactorings: ThisReferringMethodsTraverser, TreeGen.

5 files changed, 9 insertions, 10 deletions

diff --git a/test/files/neg/sammy_restrictions.check b/test/files/neg/sammy_restrictions.check
index 8cc49f9aa9..0276f3a067 100644
--- a/test/files/neg/sammy_restrictions.check
+++ b/test/files/neg/sammy_restrictions.check
@@ -8,9 +8,6 @@ sammy_restrictions.scala:32: error: type mismatch;
  required: TwoAbstract
   ((x: Int) => 0): TwoAbstract
             ^
-sammy_restrictions.scala:34: error: class type required but DerivedOneAbstract with OneAbstract found
-  ((x: Int) => 0): NonClassType                 // "class type required". I think we should avoid SAM translation here.
-            ^
 sammy_restrictions.scala:35: error: type mismatch;
  found   : Int => Int
  required: NoEmptyConstructor
@@ -46,4 +43,4 @@ sammy_restrictions.scala:44: error: type mismatch;
  required: PolyMethod
   ((x: Int) => 0): PolyMethod
             ^
-10 errors found
+9 errors found
diff --git a/test/files/neg/sammy_restrictions.scala b/test/files/neg/sammy_restrictions.scala
index d003cfaf36..101342ad0b 100644
--- a/test/files/neg/sammy_restrictions.scala
+++ b/test/files/neg/sammy_restrictions.scala
@@ -31,7 +31,7 @@ object Test {
   (() => 0)      : NoAbstract
   ((x: Int) => 0): TwoAbstract
   ((x: Int) => 0): DerivedOneAbstract           // okay
-  ((x: Int) => 0): NonClassType                 // "class type required". I think we should avoid SAM translation here.
+  ((x: Int) => 0): NonClassType                 // okay -- we also allow type aliases in instantiation expressions, if they resolve to a class type
   ((x: Int) => 0): NoEmptyConstructor
   ((x: Int) => 0): OneEmptyConstructor          // okay
   ((x: Int) => 0): OneEmptySecondaryConstructor // derived class must have an empty *primary* to call.
diff --git a/test/files/pos/sammy_implicit.scala b/test/files/pos/sammy_implicit.scala
index c9c2519bab..e4b82df4cc 100644
--- a/test/files/pos/sammy_implicit.scala
+++ b/test/files/pos/sammy_implicit.scala
@@ -6,5 +6,5 @@ abstract class SamImplicitConvert {
 
   implicit def conv(xs: Array[Int]): Lst[Int]
 
-  val encoded = flatMap (_.getBytes)
+  def encoded = flatMap (_.getBytes)
 }
diff --git a/test/files/pos/sammy_poly.scala b/test/files/pos/sammy_poly.scala
index c629be7166..75ee36f654 100644
--- a/test/files/pos/sammy_poly.scala
+++ b/test/files/pos/sammy_poly.scala
@@ -1,7 +1,8 @@
 // test synthesizeSAMFunction where the sam type is not fully defined
 class T {
   trait F[T, U] { def apply(x: T): U }
+//  type F[T, U] = T => U
   // NOTE: the f(x) desugaring for now assumes the single abstract method is called 'apply'
   def app[T, U](x: T)(f: F[T, U]): U = f(x)
   app(1)(x => List(x))
-}
\ No newline at end of file
+}
diff --git a/test/files/run/indylambda-boxing/test.scala b/test/files/run/indylambda-boxing/test.scala
index cc0a460640..82f8d2f497 100644
--- a/test/files/run/indylambda-boxing/test.scala
+++ b/test/files/run/indylambda-boxing/test.scala
@@ -2,15 +2,16 @@ class Capture
 class Test {
   def test1 = (i: Int) => ""
   def test2 = (i: VC) => i
-  def test3 = (i: Int) => i
+  def test3 = (i: Int) => i // not adapted, specialized
 
-  def test4 = {val c = new Capture; (i: Int) => {(c, Test.this.toString); 42} }
+  def test4 = {val c = new Capture; (i: Int) => {(c, Test.this.toString); 42} } // not adapted, specialized
   def test5 = {val c = new Capture; (i: VC) => (c, Test.this.toString) }
   def test6 = {val c = new Capture; (i: Int) => (c, Test.this.toString) }
 
   def test7 = {val vc = new Capture; (i: Int) => vc }
-  def test8 = {val c = 42; (s: String) => (s, c)}
+  def test8 = {val c = 42; (s: String) => (s, c)} // not adapted
   def test9 = {val c = 42; (s: String) => ()}
+  def test10 = {(s: List[String]) => ()}
 }
 
 object Test {