Also reduce term projections

[odersky]

We already reduce R { type A = T } # A to T in most situations when we create types. We now also reduce R { val x: S } # x to S if S is a singleton type.

This will simplify types as we go to more term-dependent typing. As a concrete benefit, it will avoid several test-pickling failures due to pickling differences when using dependent types.

[odersky]

test performance please

[odersky]

@mbovel Performance tests seem to be inoperational

[odersky]

I am afraid this PR needs a performance test to be mergeable.

[mbovel]

test performance please

[dottybot]

performance test scheduled: 1 job(s) in queue, 0 running.

[dottybot]

Performance test finished successfully:

Visit https://dotty-bench.epfl.ch/19389/ to see the changes.

Benchmarks is based on merging with main (bfabc31)

[odersky]

test performance please

[dottybot]

performance test scheduled: 1 job(s) in queue, 0 running.

[dottybot]

Performance test finished successfully:

Visit https://dotty-bench.epfl.ch/19389/ to see the changes.

Benchmarks is based on merging with main (bfabc31)

[odersky]

Looks like it does not affect performance, so I think we should adopt this, since it can make dependent types smaller.

[mbovel]

Is there any way we could write a test for this?

This works:

type T
type T1 = { type A = T } # A
def test = summon[T1 =:= T]

But I can't do:

type S <: Singleton
type S1 = { val x: S } # x
def test = summon[S1 =:= S]

-- [E007] Type Mismatch Error: tests/pos/projection-term-singleton.scala:2:10 --
2 |type S1 = { val x: S } # x
  |          ^^^^^^^^^^^^
  |          Found:    Object{val x: S}
  |          Required: ?{ x: ? }

I guess this is because in R # x, the typer expects R to have a type member named x, not a term member?

I also tried:

import scala.reflect.Selectable.reflectiveSelectable
type S <: Singleton
def test =
  def foo: { val x: S } = ???
  val x: S  = foo.x

and

import scala.reflect.Selectable.reflectiveSelectable
def getX[S, R <: {val x: S}](r: R) = r.x

but both already pass before your PR.