[sammy] use correct type for method to override

Don't naively derive types for the single method's signature
from the provided function's type, as it may be a subtype
of the method's MethodType.

Instead, once the sam class type is fully defined, determine
the sam's info as seen from the class's type, and use those
to generate the correct override.

```
scala> Arrays.stream(Array(1, 2, 3)).map(n => 2 * n + 1).average.ifPresent(println)
5.0

scala> IntStream.range(1, 4).forEach(println)
1
2
3
```

Also, minimal error reporting

Can't figure out how to do it properly, but some reporting
is better than crashing. Right? Test case that illustrates
necessity of the clumsy stop gap `if (block exists (_.isErroneous))`
enclosed as `sammy_error_exist_no_crash`

added TODO for repeated and by-name params

7 files changed, 39 insertions, 24 deletions

diff --git a/test/files/neg/sammy_error_exist_no_crash.check b/test/files/neg/sammy_error_exist_no_crash.check
new file mode 100644
index 0000000000..a0d2237ce0
--- /dev/null
+++ b/test/files/neg/sammy_error_exist_no_crash.check
@@ -0,0 +1,6 @@
+sammy_error_exist_no_crash.scala:5: error: Could not derive subclass of F[? >: String]
+ (with SAM `def method apply(s: String)Int`)
+ based on: ((x$1: String) => x$1.<parseInt: error>).
+  bar(_.parseInt)
+        ^
+one error found
diff --git a/test/files/neg/sammy_error_exist_no_crash.flags b/test/files/neg/sammy_error_exist_no_crash.flags
new file mode 100644
index 0000000000..e1b37447c9
--- /dev/null
+++ b/test/files/neg/sammy_error_exist_no_crash.flags
@@ -0,0 +1 @@
+-Xexperimental
\ No newline at end of file
diff --git a/test/files/neg/sammy_error_exist_no_crash.scala b/test/files/neg/sammy_error_exist_no_crash.scala
new file mode 100644
index 0000000000..da7e47206f
--- /dev/null
+++ b/test/files/neg/sammy_error_exist_no_crash.scala
@@ -0,0 +1,6 @@
+abstract class F[T] { def apply(s: T): Int }
+
+object NeedsNiceError {
+  def bar(x: F[_ >: String]) = ???
+  bar(_.parseInt)
+}
\ No newline at end of file
diff --git a/test/files/neg/sammy_restrictions.scala b/test/files/neg/sammy_restrictions.scala
index 5f1a04cd20..d003cfaf36 100644
--- a/test/files/neg/sammy_restrictions.scala
+++ b/test/files/neg/sammy_restrictions.scala
@@ -1,28 +1,28 @@
-class NoAbstract
+abstract class NoAbstract
 
-class TwoAbstract { def ap(a: Int): Int; def pa(a: Int): Int }
+abstract class TwoAbstract { def ap(a: Int): Int; def pa(a: Int): Int }
 
-class Base // check that the super class constructor isn't considered.
-class NoEmptyConstructor(a: Int) extends Base { def this(a: String) = this(0); def ap(a: Int): Int }
+abstract class Base // check that the super class constructor isn't considered.
+abstract class NoEmptyConstructor(a: Int) extends Base { def this(a: String) = this(0); def ap(a: Int): Int }
 
-class OneEmptyConstructor() { def this(a: Int) = this(); def ap(a: Int): Int }
+abstract class OneEmptyConstructor() { def this(a: Int) = this(); def ap(a: Int): Int }
 
-class OneEmptySecondaryConstructor(a: Int) { def this() = this(0); def ap(a: Int): Int }
+abstract class OneEmptySecondaryConstructor(a: Int) { def this() = this(0); def ap(a: Int): Int }
 
-class MultipleConstructorLists()() { def ap(a: Int): Int }
+abstract class MultipleConstructorLists()() { def ap(a: Int): Int }
 
-class MultipleMethodLists()() { def ap(a: Int)(): Int }
+abstract class MultipleMethodLists()() { def ap(a: Int)(): Int }
 
-class ImplicitConstructorParam()(implicit a: String) { def ap(a: Int): Int }
+abstract class ImplicitConstructorParam()(implicit a: String) { def ap(a: Int): Int }
 
-class ImplicitMethodParam() { def ap(a: Int)(implicit b: String): Int }
+abstract class ImplicitMethodParam() { def ap(a: Int)(implicit b: String): Int }
 
-class PolyClass[T] { def ap(a: T): T }
+abstract class PolyClass[T] { def ap(a: T): T }
 
-class PolyMethod { def ap[T](a: T): T }
+abstract class PolyMethod { def ap[T](a: T): T }
 
-class OneAbstract { def ap(a: Any): Any }
-class DerivedOneAbstract extends OneAbstract
+abstract class OneAbstract { def ap(a: Int): Any }
+abstract class DerivedOneAbstract extends OneAbstract
 
 object Test {
   implicit val s: String = ""
diff --git a/test/files/pos/sammy_exist.scala b/test/files/pos/sammy_exist.scala
index 95c7c7b68e..f05ae20463 100644
--- a/test/files/pos/sammy_exist.scala
+++ b/test/files/pos/sammy_exist.scala
@@ -9,16 +9,9 @@ class S[T](x: T) { def map[R](f: Fun[_ >: T, _ <: R]): R = f(x) }
 
 class Bla { def foo: Bla = this }
 
+// NOTE: inferred types show unmoored skolems, should pack them to display properly as bounded wildcards
 object T {
-  val aBlaSAM = (new S(new Bla)).map(_.foo) // : Bla should be inferred, when running under -Xexperimental [TODO]
+  val aBlaSAM = (new S(new Bla)).map(_.foo)
   val fun: Fun[Bla, Bla] = (x: Bla) => x
-  val aBlaSAMX = (new S(new Bla)).map(fun) // : Bla should be inferred, when running under -Xexperimental [TODO]
+  val aBlaSAMX = (new S(new Bla)).map(fun)
 }
-//
-// // or, maybe by variance-cast?
-// import annotation.unchecked.{uncheckedVariance => uv}
-// type SFun[-A, +B] = Fun[_ >: A, _ <: B @uv]
-//
-// def jf[T, R](f: T => R): SFun[T, R] = (x: T) => f(x): R
-//
-// val aBlaSAM = (new S(new Bla)).map(jf(_.foo)) // : Bla should be inferred [type checks, but existential inferred]
\ No newline at end of file
diff --git a/test/files/pos/sammy_override.flags b/test/files/pos/sammy_override.flags
new file mode 100644
index 0000000000..48fd867160
--- /dev/null
+++ b/test/files/pos/sammy_override.flags
@@ -0,0 +1 @@
+-Xexperimental
diff --git a/test/files/pos/sammy_override.scala b/test/files/pos/sammy_override.scala
new file mode 100644
index 0000000000..a1d0651c39
--- /dev/null
+++ b/test/files/pos/sammy_override.scala
@@ -0,0 +1,8 @@
+trait IntConsumer {
+  def consume(x: Int): Unit
+}
+
+object Test {
+  def anyConsumer(x: Any): Unit = ???
+  val f: IntConsumer = anyConsumer
+}
\ No newline at end of file