build-dependencies should not share the same feature space with target dependencies

[kvinwang]

Problem
The bindgen crate turns on the feature log/std. When I use bindgen as a build-dependency in a no_std crate which using the log crate, the log/std is turned on unexpectly.

Steps

cargo new --lib foo
cd foo
cat >> Cargo.toml <<EOF
[dependencies.log]
default-features = false
version = "0.4"

[build-dependencies]
bindgen = "0.49"
EOF
cargo +nightly check -Z build-std=core,alloc --target=x86_64-linux-kernel

output:

error[E0463]: can't find crate for `std`
  |
  = note: the `x86_64-linux-kernel` 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`.

Changing then version of log to = 0.3.8 makes the cargo check happy.

Possible Solution(s)

Notes

Output of cargo version:
cargo 1.44.0-nightly (7019b3e 2020-03-17)

[Eh2406]

This is a well known issue, these days there is an experimental fix at #7916. Please leave the report there or on one of the other open issues.