cargo build --features nice

_posts/2023-05-26-ensuring-features-for-cargo.md

@@ -0,0 +1,36 @@
+---
+layout: post
+title: "Requiring non-default features to be set in Rust"
+tags:
+- rust
+---
+
+I found myself refactoring a Rust crate in which I had two non-default features
+but _at least one_ would need to be set in order for `cargo build` to function.
+Cargo allows a `default` feature set, or allows different targets to have
+[required-features](https://doc.rust-lang.org/cargo/reference/cargo-targets.html#the-required-features-field)
+defined. My use-case is different unfortunately, I wanted slightly different
+semantics to support _either_ `s3` or `azure` features. I stopped by `##rust`
+on [libera.chat](https://libera.chat) and as usually happens, got a nudge in
+the right direction: `build.rs`:
+
+
+By adding the following to `build.rs` I was able to forcefully halt the build
+operation before it even really got started.
+
+
+```rust
+#[cfg(not(any(feature = "s3", feature = "azure")))]
+compile_error!(
+    "Either the \"s3\" or the \"azure\" feature must be enabled to compile"
+);
+fn main() {}
+```
+
+
+
+Using the `compile_error!` macro in `build.rs` ensures that users will _only_
+see the following compilation error message, rather than a long list of other
+errors which may come from missing feature definitions.
+
+Quick and easy trick to get required non-default features enabled!