Properly Configuring lettre for Tokio + RustTLS

[DK26]

Hello there,

I am relatively new to Rust and lettre and I am having trouble figuring out how to properly configure lettre to work with Tokio and Rust-TLS.

Basically, I tried to copy different combinations of features to use in cargo, some of which I found within the code examples.
But I seem to get the compile error:

error: Lettre is being built with the `tokio1` and the `native-tls` features, but the `tokio1-native-tls` feature hasn't been turned on.
       If you'd like to use rustls make sure that the `native-tls` hasn't been enabled by mistake (you may need to import lettre without default features)
       If you're building a library which depends on lettre import it without default features and enable just the features you need.

I don't understand why I'm getting this message. I'm trying to opt into rust-tls instead of native-tls.

Some configurations I tried:

lettre = { version = "0.10.0-rc.5", default-features = false, features = ["rustls-tls", "tokio1_rustls", "tokio1-rustls-tls"] }

lettre = { version = "0.10.0-rc.5", default-features = false, features = ["tokio1-rustls-tls"] }

lettre = { version = "0.10.0-rc.5", default-features = false, features = ["builder", "hostname", "smtp-transport", "tokio1", "tokio1-rustls-tls"] }

I saw issue #552 but its solution is for AsyncStd and not Tokio. Once again I failed playing around with the values so I though I'll just ask.

[DK26]

OK..

So one of my Cargo dependencies is another external crate of mine that uses lettre.
I configured that crate's Cargo.toml file with the following:

lettre = { version = "0.10.0-rc.5", default-features = false }

And my current, main Cargo.toml like this:

lettre = { version = "0.10.0-rc.5", default-features = false, features = ["builder", "hostname", "smtp-transport","tokio1", "tokio1-rustls-tls"] }

And it worked.

It appears that native-tls is a default activated feature and it causes a conflict if default-features is not set to false in any of the dependencies.

[DK26]

Is there a possibility to check if default-features is set to true?
Or maybe check if activated feature is within the set of default-features?

We could add a new line to the end of the message:

... If you did not activate the `X` feature, please refer to the `Cargo.toml` file of any other dependency that might be using the `lettre` crate.

And if the X feature is a default feature, we could add:

... Feature `X` might be activated by default in one of the dependencies. If this is not desired, please refer to their `Cargo.toml` file and try to disable the default features with `default-features = false`. Do notice that as a result you may be required to add some features manually.

[DK26]

I just realized that this is what the original message was trying to convey me. Stupid me 😁

[DK26]

And it worked.
It appears that native-tls is a default activated feature and it causes a conflict if default-features is not set to false in any of the dependencies.

That's correct. If you think there's something we could do to make the message clearer here is where we generate it https://github.com/lettre/lettre/blob/master/src/lib.rs#L120

How about the next two:

Lettre is being built with the `tokio1` and the `native-tls` features, but the `tokio1-native-tls` feature hasn't been turned on.
If you were trying to opt into `rust-tls` and did not activate `native-tls`, disable the default-features of lettre in `Cargo.toml` and manually add the required features.
Make sure to apply the same to any of your crate dependencies that use the `lettre` crate.

and

Lettre is being built with the `tokio1` and the `rustls-tls` features, but the `tokio1-rustls-tls` feature hasn't been turned on.
If you'd like to use `native-tls` make sure that the `rustls-tls` hasn't been enabled by mistake.
Make sure to apply the same to any of your crate dependencies that use the `lettre` crate.

[paolobarbolini]

Sounds perfect. I'll send a PR later in the day

[DK26]

Hope it's OK with you, I have had some time so I already sent full PR ;-)