Build fails when -Zallow-features doesn't include backtrace

[bjorn3]

-Zallow-features makes it possible to restrict which unstable features are used. Anyhow uses the backtrace feature if it detects it to be available. This check uses CARGO_ENCODED_RUSTFLAGS which contains the rustflags required for compiling for the host. When using RUSTFLAGS="-Zallow-features=" cargo build --target x86_64-unknown-linux-gnu, CARGO_ENCODED_RUSTFLAGS doesn't contain -Zallow-features=, so anyhow thinks the backtrace feature is available, however when compiling anyhow for the target -Zallow-features= is passed to rustc and thus the compilation fails.

[vi]

Implemented a pull request with additional negative Cargo feature to turn off all backtracing: #256.

[dtolnay]

I was not able to reproduce this. Would you be able to provide a complete Cargo.toml and cargo/rustc version that reproduces this issue?

[bjorn3]

I can't reproduce this anymore either.