[Feature Request] Move ephemeral server behind feature flag

[h7kanna]

Is your feature request related to a problem? Please describe.

As ephemeral_server is only used for testing, Can it be moved into a separate crate to reduce deps in the core and optimize compilation time for user code for using client and worker?

Describe the solution you'd like

Additional context

I am trying to optimize compilation time for worker code, and zip dependency of ephemeral_server is big contributor

[cretz]

As ephemeral_server is only used for testing

It's not only used for testing. It's used by all official users of the core crate today in non-testing code. All SDKs that use core use this.

Having said that, if we think our official Rust SDK is going to put this server behind a feature flag anyways, I don't mind. Would like it to be a default on feature though. Would also support a different dependency/approach to unzip files if the dependency is that burdensome.

[h7kanna]

Oh, I am not aware that it is used in non-test code in other SDKs. I only looked at its usage in tests.
Ya, it being behind the default feature should work.

[h7kanna]

@cretz , I created PR to add the feature and made it default.

[cretz]

Oh, I am not aware that it is used in non-test code in other SDKs

https://typescript.temporal.io/api/classes/testing.TestWorkflowEnvironment, https://python.temporal.io/temporalio.testing.WorkflowEnvironment.html, and https://dotnet.temporal.io/api/Temporalio.Testing.WorkflowEnvironment.html are all powered by it.

Thanks for the PR! Will let @Sushisource review.

[h7kanna]

Seems like the change to add as 'default' does not work because of the missing cargo feature in stable Rust 😔

rust-lang/cargo#8366
rust-lang/cargo#5015

cargo tree --package=temporal-sdk-core --no-default-features --edges normal -Zpackage-features
error: the `-Z` flag is only accepted on the nightly channel of Cargo, but this is the `stable` channel
See https://doc.rust-lang.org/book/appendix-07-nightly-rust.html for more information about Rust release channels.

[h7kanna]

@cretz @Sushisource

Unfortunately, due to 'feature unification in cargo workspace', we cannot add a feature and add it in default and also can ignore the feature with 'no-default-feature' or 'default-feature = false' in a user crate.

I also created another PR #561 without default, But as mentioned above this will need changes to existing SDK code 😔.

Anyways, I am just putting it here if you want to consider this in the future as it is contributing significant time to compilation in Rust-based worker code.

[cretz]

This is quite a bit to just avoid the zip dependency. I wonder if there's another way we can tackle that dependency need.