Example app in console-subscriber doesn't build

[hardliner66]

The app example in console-subscriber fails because it's trying to use task::Builder which is non existent.

[hawkw]

tokio::task::Builder is an unstable tokio API. This means you need to build with the environment variable RUSTFLAGS="--cfg tokio_unstable".

In general, the console relies on unstable features in Tokio (the tracing support that powers the console is also unstable). So, to use the console, you will need to enable --cfg tokio_unstable. See here for details.

There's a .cargo/config file in this repository that should automatically enable this flag when building inside the console repo (such as building the examples). I'm surprised that didn't work for you --- did you move the example app to another directory before trying to build it?

[iulianR]

I also hit this problem just now. While looking for the solution I came across this other issue: rust-lang/cargo#5376 (comment). In my case, I have this in my ~/.cargo/config.toml:

[target.x86_64-unknown-linux-gnu]
linker = "/usr/bin/clang"
rustflags = ["-Clink-arg=-fuse-ld=lld"]

Commenting the rustflags in there solves the problem.

[hawkw]

Oh, that makes sense; the working directory's .cargo/config rustflags setting isn't combined with the global .cargo/config's. That seems mildly surprising...

[hardliner66]

I have the same settings set in my ~/.cargo/config.

Currently it seems that the more specific [target.x86_64-unknown-linux-gnu] in ~/.cargo/config overrides the more generic [build] in the current project. If you change the local .cargo/config to [target.x86_64-unknown-linux-gnu] instead of [build] it properly combines with the settings from ~/.cargo/config.

So in order for it to work properly for all targets you can set rustflags for each triple where you or a teammate uses a custom rustflags setting.

e.g.:

[build]
rustflags = ["--cfg", "tokio_unstable"]

[target.x86_64-unknown-linux-gnu]
rustflags = ["--cfg", "tokio_unstable"]

This isn't ideal, but can be worked around. Depending on your use case, it might make sense to just add the tokio settings to the global config file instead and enable it everywhere.

[hawkw]

@hardliner66 oh, that's interesting! Perhaps we should add [target.<TARGET>] settings to the .cargo/config in this repo so that the examples works. We should probably do this for all common targets, so that it also works if, for example, people are building on MacOS and have per-target rustflags overrides...

[hardliner66]

It should at least be documented as a gotcha, but having a copy-paste ready example for the most common targets sounds reasonable.

[hawkw]

The documentation has been updated to warn about this, so I'm going to close this issue now.