SI-7899 Don't infer by-name types during, e.g. eta-expansion

Given:

    def id[A](a: A): A = a
    def foo(f: (=> Int) => Int) = ()
    foo(id)

We eta-expanded `id` and inferred `A` to be `=> Int` to satisfy the
expected type set forth by the formal parameter `f`.

We really shouldn't go about inferring types that we can't *write*.
Our attempt to do so led promptly into a `ClassCastException` in the
enclosed test.

This commit:

  - drops by-name-ness during `inferExprInstance`
  - tests that this results in a type error for the reported bug
    (neg/t7899)
  - tests that a method with a by-name parameter can still be
    eta expanded to match function with a corresponding by-name
    parameter (run/t7899)
  - discovers the same latent CCE in pos/t7584
     - now that would be a type error
     - so we compensate by using placeholder functions rather than
       eta-expansion.
     - and move that that test to `run` for good measure.

1 files changed, 0 insertions, 11 deletions

diff --git a/test/files/pos/t7584.scala b/test/files/pos/t7584.scala
deleted file mode 100644
index 52d127ecb9..0000000000
--- a/test/files/pos/t7584.scala
+++ /dev/null
@@ -1,11 +0,0 @@
-object Test {
-  def fold[A, B](f: (A, => B) => B) = ???
-  def f[A, B](x: A, y: B): B = ???
-  def bip[A, B] = fold[A, B]((x, y) => f(x, y))
-  def bop[A, B] = fold[A, B](f)
-
-  // these work:
-  fold[Int, Int]((x, y) => f(x, y))
-  fold[Int, Int](f)
-}
-