1 files changed, 35 insertions, 0 deletions
diff --git a/rustversion/src/attr.rs b/rustversion/src/attr.rs
new file mode 100644
index 0000000..591b2c0
--- /dev/null
+++ b/rustversion/src/attr.rs
@@ -0,0 +1,35 @@
+use crate::expr::Expr;
+use proc_macro2::TokenStream;
+use syn::parse::{Parse, ParseStream, Result};
+use syn::Token;
+
+pub struct Args {
+    pub condition: Expr,
+    pub then: Then,
+}
+
+pub enum Then {
+    Const(Token![const]),
+    Attribute(TokenStream),
+}
+
+impl Parse for Args {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let condition: Expr = input.parse()?;
+
+        input.parse::<Token![,]>()?;
+        if input.is_empty() {
+            return Err(input.error("expected one or more attrs"));
+        }
+
+        let const_token: Option<Token![const]> = input.parse()?;
+        let then = if let Some(const_token) = const_token {
+            input.parse::<Option<Token![,]>>()?;
+            Then::Const(const_token)
+        } else {
+            input.parse().map(Then::Attribute)?
+        };
+
+        Ok(Args { condition, then })
+    }
+}