add -Xfuture option. fix procedure syntax warnings

[xuwei-k]

No description provided.

[ashawley]

Thanks for doing this, Kenji.

Your commit message says "add -Xfuture option." Did you forget to include a file? Maybe build.sbt?

[xuwei-k]

Did you forget to include a file? Maybe build.sbt?

Oops. fixed

[ashawley]

Hey @SethTisue, is -Xfuture something we can consider enabling or does it cause a time warp in either the community build universe or compiler bootstrap? I'm thinking of a scenario where a new -Xfuture compiler error could keep the bootstrap process from working. Maybe you could think of other scenarios.

[SethTisue]

I would not suggest using -Xfuture except possibly as an alternate additional testing path — not by default. It isn't something you want enabled in a release build. (Not because of bootstrapping in particular, just general concerns about quality. You want to use the best-tested version of the compiler for doing release builds of core libraries.)

-Xfuture may go away anyway in 2.13: scala/scala-dev#471

[ashawley]

Ok, so -Xfuture is going away in the future. Good to know. That's not a scenario I had considered.

[ashawley]

I'll merge, but undo -Xfuture and add a note per Seth's comments.