Compiler crash on function-return style currying

[Checkroth]

Mock testing in Specs2, came across a compiler crash that is easily reproducible.

Mock testing works on curried functions in this style:
def func(arg1: A)(arg2: A): A

But it blows up when using the function return style:
def func(arg1: A): A => A

I have reproduced it in a very simple test, using the exact format my actual code contained:

trait IntFunctions {
    def cf(i: Int): Int => Int
  }

  class Implemented extends IntFunctions {
    override def cf(i: Int) = i2 => {
      i + i2
    }
  }

  "Test for github" >> new MockContext {
    val additionFunc = mock[IntFunctions]

    (additionFunc.cf(_: Int)(_: Int)).expects(*, *)

    val firstStep = additionFunc.cf(1)
    firstStep(2)
  }

Changing the final bit of the test to additionFunc.cf(1)(2) results in the exact same issue.

Here is the compiler crash (snippet):

[error] 
[error]   last tree to typer: This(<$anon: org#15.scalamock#12204.specs2#13246.MockContext#13286>)
[error]        tree position: line 26 of test.scala
[error]             tree tpe: test#8865.anon$1#90473
[error]               symbol: final <$anon: org#15.scalamock#12204.specs2#13246.MockContext#13286> in package tests#8865
[error]    symbol definition: final class anon$1#90473 extends org#15.scalamock#12204.specs2#13246.MockContext#13286 (a ClassSymbol)
[error]       symbol package: tests
[error]        symbol owners: <$anon: org#15.scalamock#12204.specs2#13246.MockContext#13286>
[error]            call site: <$anon: Function0#2089> in package tests#8865 in package tests#8864
[error] 
[error] == Source file context for tree position ==
[error] 
[error]     23   }
[error]     24 
[error]     25   "Test for github" >> new MockContext {
[error]     26     val additionFunc = mock[IntFunctions]
[error]     27 
[error]     28     (additionFunc.cf(_: Int)(_: Int)).expects(*, *)
[error]     29 
[error] Total time: 3 s, completed Aug 8, 2016 4:59:38 PM

But if I change the implementation to what we see in the documentation:

trait IntFunctions {
    def cf(i: Int)(i2: Int) : Int
  }

  class Implemented extends IntFunctions {
    override def cf(i: Int)(i2: Int) = {
      i + i2
    }
  }

  "Test for github" >> new MockContext {
    val additionFunc = mock[IntFunctions]

    (additionFunc.cf(_: Int)(_: Int)).expects(*, *)

    val firstStep = additionFunc.cf(1) _
    firstStep(2)
  }

Then we get a successful test case
[success] Total time: 7 s, completed Aug 8, 2016 5:15:02 PM

[Checkroth]

Corresponding PR adding a test for this case:

#151

[barkhorn]

able to reproduce this on 3.4.2, but I feel I lack the knowledge of macros to fix this at the moment.

this test compiles and succeeds:

    val additionFunc = mock[IntFunctions]
    val curried = mock[Int => Int]

    (additionFunc.cf(_: Int)).expects(*).returning(curried)
    (curried.apply _).expects(*).returning(5)

    val firstStep = additionFunc.cf(1)
    val r = firstStep(2)
    r === 5

leaving this in triage for now until I understand it better or someone else wants to submit a PR