Unable to control --debug / --release via PEP517 backend

[mgorny]

Unless I'm mistaken, there is no way to pass --debug / --release argument to build_rust when building via the PEP517 backend.

[davidhewitt]

I think you're correct. Unless things have changed, I don't think PEP517 gives a mechanism to pass arguments to the build backend in general.

This was solved in maturin with MATURIN_PEP517_ARGS env var. See PyO3/maturin#786

I'd accept a PR to achieve a similar control via env var here, though the design might be a bit different.

[mgorny]

I think you're correct. Unless things have changed, I don't think PEP517 gives a mechanism to pass arguments to the build backend in general.

Actually, PEP517 provides a config_settings dict that can be used to pass options to the backend. However, I don't think that setuptools provides a way for plugins to utilize it.

That said, I'm not really sure because the code is very complex and unreadable to me, and it's undocumented.

[davidhewitt]

Hmm, reading around a little, I think we can try to support something like

python -m build -C--build-option=--rust-debug

Looks like all PEP517 arguments to setuptools builds must go under the --build-option and --global-option namespaces like this.

[mgorny]

Thinking about it, I'd prefer environment variable approach — if only because it means we can set it globally and not have to worry whether the package in question uses setuptools-rust or not.

[davidhewitt]

Since 1.8.0 we now have SETUPTOOLS_RUST_CARGO_PROFILE, which should meet this need.

Note that for --debug, the profile is called dev, i.e. SETUPTOOLS_RUST_CARGO_PROFILE=dev. (This was a choice made by cargo for a reason which I am not privy to.)

[mgorny]

Thanks! FWICS, maturin uses dev also, so that's consistent.

[davidhewitt]

Yes I think maturin also inherited this from cargo.