List of default/all available extensions about rust-overlay HOT 2 CLOSED

What are the default extensions that come with rust-bin?

pkgs.rust-bin.nightly.latest.rust is an aggregated "component" provided by upstream. What components it has also depends on upstream.
But it usually has cargo, rustc, rustdoc, miri, rls, rust-analyzer, rustfmt, clippy and almost all binaries which seems enough for common users. (But rust-src is not contained by default)

How can I see which extensions are available for my platform/targets?

Currently, no, except typing an non-existent component to get the error message like what you do.
We may add a more convenient way to do that in the future.

Is that expected on macOS or is there something I'm doing wrong here?

You did nothing wrong. It's simply because rust nightly 2021-02-06 actually does NOT have rustfmt built. Note that nightly releases don't always have all common components built (successfully) due to rustc internal changes.

You can check this site for avilability of components in each nightly releases, and pick an older release which contains all components you need.
https://rust-lang.github.io/rustup-components-history/

from rust-overlay.

Thank you so much for the thorough response!

from rust-overlay.