Conditional compilation based on imports (not an issue)

[DevinR528]

I saw you had mentioned something about extending realia to also conditionally compile based on crates. Today I saw this crate https://crates.io/crates/proc-macro-crate which at least accesses the Cargo.toml file? Just thought it might be helpful 🤷.

Edit: Ahh "downstream" dependencies, so this is the wrong way sorry nvm.

[mtkennerly]

Actually, that just gave me an idea. My previous attempts focused on using a build.rs to generate static crate info, but I see that proc-macro-crate checks std::env::var("CARGO_MANIFEST_DIR") in the proc macro itself. I checked, and that gives me the downstream crate's manifest dir, not Realia's, which I should then be able to pass to the cargo metadata command. That might just work!

[mtkennerly]

Success :D I just published v0.2.0, which includes these new attributes:

• #[realia::dep("your-crate", "a-dependency")]
• #[realia::dep("your-crate", "a-dependency", "1.2.3")]
• #[realia::dep_since("your-crate", "a-dependency", "1.2.3")]
• #[realia::dep_before("your-crate", "a-dependencyo", "1.2.3")]
• #[realia::dep_from_registry("your-crate", "a-dependency")]

The only caveats are:

• You have to specify your crate's name, since the implementation relies on CARGO_MANIFEST_DIR. Otherwise, you'd get different results for cargo build in your project vs a downstream project.
• I don't know how to reliably detect which features are enabled, so optional dependencies are ignored for now. When I'm assembling the arguments for cargo metadata, I only get to see how rustc was invoked, not how Cargo was invoked.

[DevinR528]

Nice!! Glad it worked out.