Dependency fails with "the feature doc_cfg has already been declared"

[pka]

Crate name: geozero
Build failure link: https://docs.rs/crate/geozero/0.7.2/builds/355163

Additional details:
geozero has the following Cargo.toml entry:

[package.metadata.docs.rs]
all-features = true
rustc-args = ["--cfg", "docsrs"] 

cfg(docsrs) is required for a doc.rs build of the dependency gdal: https://github.com/georust/gdal/blob/master/build.rs#L3

The failing tokio-stream crate does in fact set a feature twice based on docsrs: https://github.com/tokio-rs/tokio/blob/master/tokio-stream/src/lib.rs#L17-L23

But a local doc build is successful!

[jyn514]

This should be reported upstream to Tokio, we can't fix it on our end.

But a local doc build is successful!

Local builds don't pass --cfg docsrs by default.

[Nemo157]

There is a bug somewhere here since tokio-stream successfully built its docs, and it appears to activate the cfg for its build. Maybe rustdoc allows duplicate features, while rustc doesn't?

[pka]

This should be reported upstream to Tokio, we can't fix it on our end.

PR: tokio-rs/tokio#3561

But a local doc build is successful!

Local builds don't pass --cfg docsrs by default.

I tried to imitate docs.rs build with
cargo +nightly doc --all-features --config 'build.rustflags=["--cfg", "docsrs"]' -Z unstable-options

Am I missing something?

[Nemo157]

I've opened rust-lang/rust#82588 for the rustdoc bug that allowed tokio-stream's docs to succeed.

Using cargo +nightly doc --all-features --config 'build.rustflags=["--cfg", "docsrs"]' -Z unstable-options on a crate that depends on tokio-stream I get the build failure, but at least on my machine I had to override CARGO_HOME for it to avoid loading my ~/.cargo/config, which sets target.x86_64-unknown-linux-gnu.rustflags overriding the build.rustflags config.

[pka]

So nothing else to be done here, I think. Thanks @jyn514 and @Nemo157 for looking into it!