Uniffi-bindgen not detected in cargo workspace

[Hinton]

Bug Description

Maturin includes support for workspace bundled uniffi-bindgen in

maturin/src/module_writer.rs

Lines 876 to 882 in 09e4f55

	let has_uniffi_bindgen_target = root_pkg
	.map(|pkg| {
	pkg.targets
	.iter()
	.any(|target| target.name == "uniffi-bindgen" && target.is_bin())
	})
	.unwrap_or(false);

However this doesn't seem to work correctly and instead I get the following error message.

💥 maturin failed
  Caused by: Failed to run uniffi-bindgen, did you install it? Try `pip install uniffi-bindgen`
  Caused by: No such file or directory (os error 2)

I can resolve it by adding my target dir to the path, but this "should" be unnecessary with the above logic.

Your maturin version (maturin --version)

1.4.0

Your Python version (python -V)

3.9.6

Your pip version (pip -V)

21.2.4

What bindings you're using

uniffi

Does cargo build work?

• Yes, it works

If on windows, have you checked that you aren't accidentally using unix path (those with the forward slash /)?

• Yes

Steps to Reproduce

1. Checkout https://github.com/Hinton/maturin-repro
2. Run maturin build, note it fails due to unffi-bindgen not being in path.