Building docs for tokio panics

[davidpdrsn]

Problem
Building the docs for tokio in the root of the workspace panics.

❯ RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features
thread 'main' panicked at 'no entry found for key', src/tools/cargo/src/cargo/ops/cargo_compile.rs:1638:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

It works if run from a subdirectory:

~/dev/tokio
❯ cd tokio

~/dev/tokio/tokio
❯ RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features
    Finished dev [unoptimized + debuginfo] target(s) in 0.12s

Steps

1. git clone https://github.com/tokio-rs/tokio
2. cd tokio
3. RUSTDOCFLAGS="--cfg docsrs" cargo +nightly doc --all-features

Notes

Output of cargo version:

❯ cargo +nightly version
cargo 1.52.0-nightly (32da9eaa5 2021-03-13)

Tested on macOS 10.15.7.