feat: add feature_specific macroHEADv0.1.0master

1 files changed, 88 insertions, 0 deletions

diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..87d933c
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,88 @@
+//! Utility macros for utilizing cargo features.
+
+#![deny(clippy::all)]
+#![deny(clippy::pedantic)]
+#![deny(missing_docs)]
+
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse2, Item, LitStr};
+
+/// Specifies that a item is only available with a specific feature enabled. This will also
+/// document that item is only available with the specified feature enabled by using
+/// the [`doc_cfg`] feature.
+///
+/// All this macro does is to add the following attributes:
+/// ```text
+/// #[cfg(feature = {FEATURE})]
+/// #[cfg_attr(doc_cfg, doc(cfg(feature = {FEATURE})))]
+/// ```
+///
+/// With `{FEATURE}` being replaced with the feature argument.
+///
+/// # Arguments
+/// - The feature. For example: `"parsing"`
+///
+/// # Panics
+/// If not attributed to a item or if arguments is missing.
+///
+/// # Examples
+/// ```
+/// # use feature_macros::feature_specific;
+/// #
+/// #[feature_specific("cool-things")]
+/// pub fn do_some_cool_thing() {
+///     // ...
+/// }
+/// ```
+///
+/// [`doc_cfg`]: https://doc.rust-lang.org/unstable-book/language-features/doc-cfg.html
+#[proc_macro_attribute]
+pub fn feature_specific(args_stream: TokenStream, item_stream: TokenStream) -> TokenStream {
+    create_feature_specific(args_stream.into(), item_stream.into())
+        .unwrap()
+        .into()
+}
+
+fn create_feature_specific(
+    args_stream: proc_macro2::TokenStream,
+    item_stream: proc_macro2::TokenStream,
+) -> Result<proc_macro2::TokenStream, Box<dyn std::error::Error>> {
+    let item = parse2::<Item>(item_stream)?;
+
+    let feature = parse2::<LitStr>(args_stream).unwrap().value();
+
+    Ok(quote! {
+        #[cfg(feature = #feature)]
+        #[cfg_attr(doc_cfg, doc(cfg(feature = #feature)))]
+        #item
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use std::error::Error;
+
+    use super::*;
+
+    #[test]
+    fn create_feature_specific_works() -> Result<(), Box<dyn Error>> {
+        assert_eq!(
+            create_feature_specific(
+                quote! {"extra-stuff"},
+                quote! {
+                    pub mod extra;
+                },
+            )?
+            .to_string(),
+            quote! {
+                #[cfg(feature = "extra-stuff")]
+                #[cfg_attr(doc_cfg, doc(cfg(feature = "extra-stuff")))]
+                pub mod extra;
+            }
+            .to_string()
+        );
+
+        Ok(())
+    }
+}