1 files changed, 46 insertions, 0 deletions
diff --git a/third_party/rust/const_fn/src/utils.rs b/third_party/rust/const_fn/src/utils.rs
new file mode 100644
index 0000000000..e557ea57e0
--- /dev/null
+++ b/third_party/rust/const_fn/src/utils.rs
@@ -0,0 +1,46 @@
+use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree};
+use std::iter::FromIterator;
+
+use crate::Result;
+
+macro_rules! error {
+    ($span:expr, $msg:expr) => {{
+        crate::error::Error::new($span, $msg)
+    }};
+    ($span:expr, $($tt:tt)*) => {
+        error!($span, format!($($tt)*))
+    };
+}
+
+pub(crate) fn tt_span(tt: Option<&TokenTree>) -> Span {
+    tt.map_or_else(Span::call_site, TokenTree::span)
+}
+
+pub(crate) fn parse_as_empty(mut tokens: impl Iterator<Item = TokenTree>) -> Result<()> {
+    match tokens.next() {
+        Some(tt) => Err(error!(tt.span(), "unexpected token: {}", tt)),
+        None => Ok(()),
+    }
+}
+
+// (`#[cfg(<tokens>)]`, `#[cfg(not(<tokens>))]`)
+pub(crate) fn cfg_attrs(tokens: TokenStream) -> (TokenStream, TokenStream) {
+    let f = |tokens| {
+        let tokens = TokenStream::from_iter(vec![
+            TokenTree::Ident(Ident::new("cfg", Span::call_site())),
+            TokenTree::Group(Group::new(Delimiter::Parenthesis, tokens)),
+        ]);
+        TokenStream::from_iter(vec![
+            TokenTree::Punct(Punct::new('#', Spacing::Alone)),
+            TokenTree::Group(Group::new(Delimiter::Bracket, tokens)),
+        ])
+    };
+
+    let cfg_not = TokenTree::Group(Group::new(Delimiter::Parenthesis, tokens.clone()));
+    let cfg_not = TokenStream::from_iter(vec![
+        TokenTree::Ident(Ident::new("not", Span::call_site())),
+        cfg_not,
+    ]);
+
+    (f(tokens), f(cfg_not))
+}