cargo rustdoc does not pass extra arguments when documenting a binary

[jyn514]

Problem
cargo rustdoc does not pass any arguments to the rustdoc binary when documenting a binary instead of a library.

Steps

$ cargo new bin
     Created binary (application) `bin` package
$ cd bin
$ cargo rustdoc -v --bin bin -- --this-flag-is-invalid
Documenting bin v0.1.0 (/home/joshua/src/bin)
     Running `rustdoc --edition=2018 --crate-type bin --crate-name bin src/main.rs -o /home/joshua/.local/lib/cargo/target/doc --error-format=json --json=diagnostic-rendered-ansi --document-private-items -L dependency=/home/joshua/.local/lib/cargo/target/debug/deps`
    Finished dev [unoptimized + debuginfo] target(s) in 0.46s

Possible Solution(s)

Notes

Output of cargo version: cargo 1.46.0-nightly (c26576f9a 2020-06-23) (but this also happens on 1.44.1 stable)

[jyn514]

Relevant code:

cargo/src/cargo/ops/cargo_compile.rs

Line 472 in d267fac

if rustdoc_document_private_items || unit.target.is_bin() {

[jyn514]

I'm interested in working on this.