Use required-features in Cargo.toml

[adamcrume]

The expressions example only makes sense with the tensorflow_unstable feature enabled. It currently compiles to a no-op if the feature isn't present, but even better would be to use the new required-features field.

http://doc.crates.io/manifest.html#the-required-features-field-optional

[adamcrume]

Note: The required-features field doesn't appear to be present in cargo 0.16.0-nightly, which is used in the current stable release of rust.

[sanmai-NL]

I've tried to check whether the field is supported with current stable Rust & Cargo, but I haven't managed to find a procedure to do so. Best way is that you list the steps you took so others can carry those out again later (and list also the exact versions of things you check against, e.g. stable Rust version).

[adamcrume]

I tried adding

[[example]]
name = "expressions"
required-features = ["tensorflow_unstable"]

to Cargo.toml.

Running cargo run --example expressions against nightly (rustc 1.19.0-nightly (75b056812 2017-05-15) and cargo 0.20.0-nightly (13d92c64d 2017-05-12)) correctly prints

error: target `expressions` requires the features: `tensorflow_unstable`
Consider enabling them by passing e.g. `--features="tensorflow_unstable"`

but running against stable (rustc 1.16.0 (30cf806ef 2017-03-10) and cargo-0.17.0-nightly (f9e5481 2017-03-03)) prints

warning: unused manifest key: example.required-features

I'm using multirust, and for some reason it's using 1.16 for the stable channel, when it should be using 1.17.

[Enet4]

I'm using multirust, and for some reason it's using 1.16 for the stable channel, when it should be using 1.17.

Don't you mean Rustup? Multirust has been obsolete for a while. According to the announcement of version 1.17, required-features is already available in stable, so you might just need to update your toolchains.

[adamcrume]

No, I meant multirust. I didn't realize it had been deprecated. I guess I have to swtich. :/ I have some commits in the works, and this will be fixed in one of them.