When parsing workspace.members, the result of glob matching doesn't filter directories. It will gladly append Cargo.toml to file paths like README.md:

Assumes a manifest being parsed contains:

[workspace]
members = [
    "examples/*",
    "tests/*",
]

... and these directories contain a README.md or other files as direct children. An example repo in the wild where this is done:

• egui:
  • https://github.com/emilk/egui/blob/4e101d25cde5a396804ece4a916970e2390fb434/Cargo.toml#L17-L18
  • https://github.com/emilk/egui/blob/4e101d25cde5a396804ece4a916970e2390fb434/examples/README.md
  • https://github.com/emilk/egui/blob/4e101d25cde5a396804ece4a916970e2390fb434/tests/README.md

This kind of setup causes Subcommand::new() to return an error here:

The glob result needs to be filtered to match directories. Checking manifest_dir.is_dir() is a good start, but symlinks also need to be followed.