CODEWITHSUNDEEP
rust
Greg Melton
Greg Melton

Reputation: 91

Why does this work with #[cfg(tests)] but not without?

Recently, I've been playing with Rust and gRPC using the Tonic libraries. I started looking at how to create a custom Codec and I'm scratching my head over this...

Starting with this chunk of code, I copied the MockEncoder & MockDecoder and added all the same imports used here in the test module: https://github.com/hyperium/tonic/blob/master/tonic/src/codec/prost.rs#L133-L158

Then I got stuck on this error:

no method named `bytes` found for mutable reference `&mut tonic::codec::DecodeBuf<'_>` in the current scope

method not found in `&mut tonic::codec::DecodeBuf<'_>`rustc(E0599)
codec.rs(55, 37): method not found in `&mut tonic::codec::DecodeBuf<'_>`

The error is complaining about let out = Vec::from(buf.bytes()); because DecodeBuf doesn't implement a bytes method.

Now, for some reason, if I wrap this code I copied in a module with #[cfg(tests)] (similar to how this originally appeared in Tonic) this error goes away. I can compile and run tests without any errors.

Curious, what is #[cfg(tests)] doing that makes buf.bytes() compile and is there something I can import in order to move MockDecoder outside of this test config?

Upvotes: 0

Views: 332

Answers (1)

bk2204
bk2204

Reputation: 76529

The option is #[cfg(test)] (singular), not #[cfg(tests)] (plural). This is probably not failing because it's not being compiled or run at all, since the option is never set.

Upvotes: 2

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