1 files changed, 35 insertions, 0 deletions
diff --git a/third_party/rust/rustversion/src/attr.rs b/third_party/rust/rustversion/src/attr.rs
new file mode 100644
index 0000000000..6023d1eaf1
--- /dev/null
+++ b/third_party/rust/rustversion/src/attr.rs
@@ -0,0 +1,35 @@
+use crate::error::{Error, Result};
+use crate::expr::{self, Expr};
+use crate::{iter, token};
+use proc_macro::{Span, TokenStream};
+
+pub struct Args {
+    pub condition: Expr,
+    pub then: Then,
+}
+
+pub enum Then {
+    Const(Span),
+    Attribute(TokenStream),
+}
+
+pub fn parse(input: TokenStream) -> Result<Args> {
+    let ref mut input = iter::new(input);
+    let condition = expr::parse(input)?;
+
+    token::parse_punct(input, ',')?;
+    if input.peek().is_none() {
+        return Err(Error::new(Span::call_site(), "expected one or more attrs"));
+    }
+
+    let const_span = token::parse_optional_keyword(input, "const");
+    let then = if let Some(const_span) = const_span {
+        token::parse_optional_punct(input, ',');
+        token::parse_end(input)?;
+        Then::Const(const_span)
+    } else {
+        Then::Attribute(input.collect())
+    };
+
+    Ok(Args { condition, then })
+}