Cargo: Build uses wrong features when having same crate as dependency and build dependency

[Dirbaio]

Problem
When having log as both a dependency and a transitive build-dependency, cargo seems to compile the dependency with the wrong features.

Steps

1. Install the larget: rustup target add thumbv7em-none-eabihf

1. put this in Cargo.toml

[package]
name = "testlib"
version = "0.1.0"
authors = ["Dario Nieuwenhuis <[email protected]>"]
edition = "2018"

[dependencies]
log = { version = "0.4.8", default-features = false }

[build-dependencies]
bindgen = "0.54.1"

1. Put this in src/lib.rs

#![no_std]

1. run cargo build --target thumbv7em-none-eabihf --verbose

       Fresh cfg-if v0.1.10
   Compiling log v0.4.8
     Running `rustc --crate-name log /home/dirbaio/.cargo/registry/src/github.com-1ecc6299db9ec823/log-0.4.8/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -Cembed-bitcode=no -C debuginfo=2 --cfg 'feature="std"' -C metadata=a51f589eb4222210 -C extra-filename=-a51f589eb4222210 --out-dir /home/dirbaio/akiles/testlib/target/thumbv7em-none-eabihf/debug/deps --target thumbv7em-none-eabihf -L dependency=/home/dirbaio/akiles/testlib/target/thumbv7em-none-eabihf/debug/deps -L dependency=/home/dirbaio/akiles/testlib/target/debug/deps --extern cfg_if=/home/dirbaio/akiles/testlib/target/thumbv7em-none-eabihf/debug/deps/libcfg_if-39845f5cb495a51a.rmeta --cap-lints allow --cfg atomic_cas`
error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv7em-none-eabihf` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: could not compile `log`.

Caused by:
  process didn't exit successfully: `rustc --crate-name log /home/dirbaio/.cargo/registry/src/github.com-1ecc6299db9ec823/log-0.4.8/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -Cembed-bitcode=no -C debuginfo=2 --cfg 'feature="std"' -C metadata=a51f589eb4222210 -C extra-filename=-a51f589eb4222210 --out-dir /home/dirbaio/akiles/testlib/target/thumbv7em-none-eabihf/debug/deps --target thumbv7em-none-eabihf -L dependency=/home/dirbaio/akiles/testlib/target/thumbv7em-none-eabihf/debug/deps -L dependency=/home/dirbaio/akiles/testlib/target/debug/deps --extern cfg_if=/home/dirbaio/akiles/testlib/target/thumbv7em-none-eabihf/debug/deps/libcfg_if-39845f5cb495a51a.rmeta --cap-lints allow --cfg atomic_cas` (exit code: 1)

As you can see, cargo is trying to build log with --target thumbv7em-none-eabihf and --cfg 'feature="std"', which is impossible.

If you remove either the log dependency or the bindgen build-dependency, then there's no errors. It only happens when both are there. The features for the log crate are somehow mixed up between build dependencies and runtime dependencies.

Notes

[dirbaio@mars testlib]$ cargo version
cargo 1.46.0-nightly (fede83ccf 2020-07-02)
[dirbaio@mars testlib]$ rustc --version
rustc 1.46.0-nightly (8ac1525e0 2020-07-07)
[dirbaio@mars testlib]$ rustup show
Default host: x86_64-unknown-linux-gnu
rustup home:  /home/dirbaio/.rustup

installed toolchains
--------------------

nightly-x86_64-unknown-linux-gnu (default)

installed targets for active toolchain
--------------------------------------

thumbv7em-none-eabi
thumbv7em-none-eabihf
x86_64-unknown-linux-gnu

active toolchain
----------------

nightly-x86_64-unknown-linux-gnu (default)
rustc 1.46.0-nightly (8ac1525e0 2020-07-07)

[ehuss]

You can use -Zfeatures=host_dep to decouple the features. More details in the documentation: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#features
Closing as duplicate of #7915.