Cargo Doc Collision

This repository is a minimal example demonstration of cargo doc erroneously emitting the following error:

error: document output filename collision
The lib `child-a-macros` in package `child-a-macros v0.1.0 (/home/dricross/git/cargo-doc-collision-minimal/crates/child-a/macros)` has the same name as the lib `child-a-macros` in package `child-a-macros v0.1.0 (/home/dricross/git/cargo-doc-collision-minimal/crates/child-a/macros)`.
Only one may be documented at once since they output to the same path.
Consider documenting only one, renaming one, or marking one with `doc = false` in Cargo.toml.

This is a demonstration monorepo which contains a proc-macro crate. Key configurations that appear to cause this issue:

• Virtual workspace containing a crate containing a proc-macro crate.
• Target specified in workspace configuration file.
• Any level of optimizations enabled.
• Certain compiler verions used, starting at least as early as nightly-2021-10-14.

Notes

• Removing the [build] section and running cargo doc --target x86_64-unknown-linux-gnu will succeed.
• Changing opt-level in dev profile to 0 will cause cargo doc to succeed. cargo doc --release will continue to fail.
  • Any non-zero opt-level will fail.
• rustc version nightly-2021-10-14 is the first to display this behavior for x86_64-unknown-linux-gnu and armv7r-none-eabihf targets. Prior nightly rustc versions will display this behavior for x86_64-apple-darwin.