fix(tonic-build,tonic) Add back TLS handling in generated Client::connect code

[mkatychev]

Motivation

The recent breaking change in #1731 removed the ability for generated client functions to connect to HTTPS endpoints through strings alone.
For example the doctest below would fail in 0.12.x tonic-build connection code:

tonic/tonic/src/transport/channel/endpoint.rs

Lines 79 to 82 in 03913b9

	/// ```
	/// # use tonic::transport::Endpoint;
	/// Endpoint::from_static("https://example.com");
	/// ```

Solution

This PR introduces a best attempt at picking up tls feature flags in Endpoint::new to allow successfully connecting to strings that contain https:// once more

[mkatychev]

@tottoto @djc Let me know if there is a better approach to handle generated clients. 0.12 ::connect does not work with TLS anymore.

[mkatychev]

Though this fix is in tonic, as mentioned in

tonic/tonic/src/transport/channel/endpoint.rs

Lines 43 to 44 in decbf61

	// FIXME: determine if we want to expose this or not. This is really
	// just used in codegen for a shortcut.

Endpoint::new is mainly used in generated code through tonic-build.

[djc]

Seems a little ugly but probably still better to fix the regression for now.

[tottoto]

Personally, I do not like this kind of implicit configuration and would prefer that users explicitly configure TLS. It seems better to update the documentation instead.

[djc]

Personally, I do not like this kind of implicit configuration and would prefer that users explicitly configure TLS. It seems better to update the documentation instead.

I'm sympathetic to this but I think regressing user's code in an upgrade is worse, and I don't think adding documentation is enough. We could improve this via the type system instead.

[mkatychev]

@tottoto I would be happy to hear of alternatives, #1731 for better or worse took a lot of convenience out of a TLS approach that "just works".
Long term, From<Uri> for Endpoint should be where a TLS config decision is made, this should enable getting rid of Endpoint::new entirely.
A Uri's scheme should determine whether TLS is enabled if some feature flag like auto_tls is enabled. It's fine to be explicit about configuring TLS but I would rather not do it on each connection and a non-default feature flag seems explicit enough.

[tottoto]

It's fine to be explicit about configuring TLS but I would rather not do it on each connection and a non-default feature flag seems explicit enough.

You can define your own constructor such as function to construct connection with your config.

[mkatychev]

It's fine to be explicit about configuring TLS but I would rather not do it on each connection and a non-default feature flag seems explicit enough.

You can define your own constructor such as function to construct connection with your config.

That is not the case for generated code.