Enable env communication

[pvdrz]

related issue: #800. r? @RalfJung

[RalfJung]

Please also add a corresponding bool to Evaluator and initialize it with this boolean, so that the flag is available during execution.

[pvdrz]

Should I still keep the field in Evaluator? I could populate the hashmap with the env variables without having to store the communicate boolean.

[RalfJung]

Would you like to add this to the README as well?

Should I still keep the field in Evaluator?

Yes. Future extensions of this system might need it at run-time.
This PR is more generally useful than just the env var PR it paves the ground for. :)

[pvdrz]

I decided to keep going. I'm adding some comments in certain parts where I'd like to have some feedback because I'm not feeling too sure about them.

[RalfJung]

I decided to keep going.

I asked you to keep it separate to make review easier. :/ I would have landed the other thing this morning. You could have kept going locally without updating this PR. Just have mutliple branches and then when the nits are done here rebase your other branch.

But I don't have time for a bigger review right now. Maybe on the weekend.

[pvdrz]

I decided to keep going.

I asked you to keep it separate to make review easier. :/ I would have landed the other thing this morning. You could have kept going locally without updating this PR. Just have mutliple branches and then when the nits are done here rebase your other branch.

But I don't have time for a bigger review right now. Maybe on the weekend.

Sorry :/ I did not think about it. Anyway we have no rush here I guess.

[pvdrz]

I believe we're ready to go

[RalfJung]

Thanks for your patience!

@bors r+

[bors]

📌 Commit 451a09a has been approved by RalfJung

[bors]

⌛ Testing commit 451a09a with merge 1f504ea...

[pvdrz]

I am going to start migrating the env related code in shims::foreign_items to shims::env::EnvVars when this is merged!

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: RalfJung
Pushing 1f504ea to master...

[RalfJung]

Uh, this is odd:

warning: field is never used: `communicate`
  --> src/machine.rs:97:5
   |
97 |     pub(crate) communicate: bool,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

[RalfJung]

Ah, I entirely forgot that the machine has this flag. So can you remove this parameter, and use ecx.machine.communicate instead?

[RalfJung]

Since you are probably asleep, I'll do this as part of #909.