MACOSX_DEPLOYMENT_TARGET causing spurious rebuilds due to objc-sys

[emilk]

Running maturin develop will set the MACOSX_DEPLOYMENT_TARGET environment variable. The objc-sys crate has a build.rs file that rebuilds if MACOSX_DEPLOYMENT_TARGET changes.

The problem comes from me then running a normal cargo build, which doesn't set MACOSX_DEPLOYMENT_TARGET. Now objc-sys and all its dependencies (a lot of them, including winit) will rebuild. When I type maturing develop again, everything rebuilds yet again.

One solution is to set MACOSX_DEPLOYMENT_TARGET=11.0 globally in my ~/.zshrc, but I'd like for a more solid solution that works for any contributor to my repository.

I initially though that adding MACOSX_DEPLOYMENT_TARGET="11.0" under [env] in .cargo/config.toml would solve it, but those env-vars seems to only be visible to build.rs files inside my repository, and hence not by objc-sys/build.rs.

So now I'm wondering - can we have an option so that Maturin does NOT set MACOSX_DEPLOYMENT_TARGET, at least not when running maturin develop? What would be the effect of not setting it?

[messense]

It should be fine to not set MACOSX_DEPLOYMENT_TARGET for maturin develop, but for distribution (maturin build) we need to set it, otherwise the wheel built on newer macOS version may not work on older macOS versions.