1 files changed, 72 insertions, 0 deletions
diff --git a/third_party/rust/rustversion/src/expand.rs b/third_party/rust/rustversion/src/expand.rs
new file mode 100644
index 0000000000..813ba85d7d
--- /dev/null
+++ b/third_party/rust/rustversion/src/expand.rs
@@ -0,0 +1,72 @@
+use crate::attr::{self, Then};
+use crate::error::{Error, Result};
+use crate::{constfn, expr, iter, token};
+use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};
+use std::iter::FromIterator;
+
+pub fn cfg(introducer: &str, args: TokenStream, input: TokenStream) -> TokenStream {
+    try_cfg(introducer, args, input).unwrap_or_else(Error::into_compile_error)
+}
+
+fn try_cfg(introducer: &str, args: TokenStream, input: TokenStream) -> Result<TokenStream> {
+    let introducer = Ident::new(introducer, Span::call_site());
+
+    let mut full_args = TokenStream::from(TokenTree::Ident(introducer));
+    if !args.is_empty() {
+        full_args.extend(std::iter::once(TokenTree::Group(Group::new(
+            Delimiter::Parenthesis,
+            args,
+        ))));
+    }
+
+    let ref mut full_args = iter::new(full_args);
+    let expr = expr::parse(full_args)?;
+    token::parse_end(full_args)?;
+
+    if expr.eval(crate::RUSTVERSION) {
+        Ok(input)
+    } else {
+        Ok(TokenStream::new())
+    }
+}
+
+pub fn try_attr(args: attr::Args, input: TokenStream) -> Result<TokenStream> {
+    if !args.condition.eval(crate::RUSTVERSION) {
+        return Ok(input);
+    }
+
+    match args.then {
+        Then::Const(const_token) => constfn::insert_const(input, const_token),
+        Then::Attribute(then) => {
+            // #[cfg_attr(all(), #then)]
+            Ok(TokenStream::from_iter(
+                vec![
+                    TokenTree::Punct(Punct::new('#', Spacing::Alone)),
+                    TokenTree::Group(Group::new(
+                        Delimiter::Bracket,
+                        TokenStream::from_iter(vec![
+                            TokenTree::Ident(Ident::new("cfg_attr", Span::call_site())),
+                            TokenTree::Group(Group::new(
+                                Delimiter::Parenthesis,
+                                TokenStream::from_iter(
+                                    vec![
+                                        TokenTree::Ident(Ident::new("all", Span::call_site())),
+                                        TokenTree::Group(Group::new(
+                                            Delimiter::Parenthesis,
+                                            TokenStream::new(),
+                                        )),
+                                        TokenTree::Punct(Punct::new(',', Spacing::Alone)),
+                                    ]
+                                    .into_iter()
+                                    .chain(then),
+                                ),
+                            )),
+                        ]),
+                    )),
+                ]
+                .into_iter()
+                .chain(input),
+            ))
+        }
+    }
+}