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Infer function parameter types from partially eta-expanded methods (backport #7316 and #7333) #7340

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merged 5 commits into from
Nov 2, 2018
Merged

Infer function parameter types from partially eta-expanded methods (backport #7316 and #7333) #7340

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210c296
[backport] Factor typedFunction.
adriaanm Oct 5, 2018
9614c3a
[backport] Do less in typedFunction after typer
adriaanm Oct 5, 2018
984502e
[backport] Pull out `argsResProtosFromFun`,
adriaanm Oct 12, 2018
93cd804
[backport] Recover fun param types from (partial) eta-expansion
adriaanm Oct 12, 2018
8dab041
[backport] Review feedback
adriaanm Oct 19, 2018
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[backport] Recover fun param types from (partial) eta-expansion 
Generalize function parameter type inference to allow
any subset (including permutation) of parameters with
unknown types to be inferred from the method they are
applied to.

Before, we required all method arguments to come from
the function's vparams, in order.

Example:

```
scala> def repeat(x: Int, y: String) = y * x
repeat: (x: Int, y: String)String

scala> val sayAaah = repeat(_, "a")
sayAaah: Int => String

scala> val thrice = x => repeat(3, x)
thrice: String => String

scala> val repeatFlip = (x, y) => repeat(y, x)
repeatFlip: (String, Int) => String
```

Backported from 967ab56
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adriaanm committed Oct 15, 2018
commit 93cd804a78516fb27576b616b5260112c10a0db6
6 changes: 6 additions & 0 deletions test/files/pos/eta_partial.scala
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class Test {
def repeat(x: Int, y: String) = y * x
val sayAaah = repeat(_, "a") // partial eta-expansion recovers fun param types from method (place holder syntax)
val thrice = x => repeat(3, x) // partial eta-expansion recovers fun param types from method (explicit version)
val repeatFlip = (x, y) => repeat(y, x) // partial eta-expansion recovers fun param types from method (explicit version, two params)
}