1 files changed, 101 insertions, 0 deletions
diff --git a/third_party/rust/syn/src/ident.rs b/third_party/rust/syn/src/ident.rs
new file mode 100644
index 0000000000..8e3d8bda97
--- /dev/null
+++ b/third_party/rust/syn/src/ident.rs
@@ -0,0 +1,101 @@
+#[cfg(feature = "parsing")]
+use crate::buffer::Cursor;
+#[cfg(feature = "parsing")]
+use crate::lookahead;
+#[cfg(feature = "parsing")]
+use crate::parse::{Parse, ParseStream, Result};
+#[cfg(feature = "parsing")]
+use crate::token::Token;
+
+pub use proc_macro2::Ident;
+
+#[cfg(feature = "parsing")]
+#[doc(hidden)]
+#[allow(non_snake_case)]
+pub fn Ident(marker: lookahead::TokenMarker) -> Ident {
+    match marker {}
+}
+
+#[cfg(feature = "parsing")]
+fn accept_as_ident(ident: &Ident) -> bool {
+    match ident.to_string().as_str() {
+        "_" |
+        // Based on https://doc.rust-lang.org/grammar.html#keywords
+        // and https://github.com/rust-lang/rfcs/blob/master/text/2421-unreservations-2018.md
+        // and https://github.com/rust-lang/rfcs/blob/master/text/2420-unreserve-proc.md
+        "abstract" | "as" | "become" | "box" | "break" | "const" | "continue" |
+        "crate" | "do" | "else" | "enum" | "extern" | "false" | "final" | "fn" |
+        "for" | "if" | "impl" | "in" | "let" | "loop" | "macro" | "match" |
+        "mod" | "move" | "mut" | "override" | "priv" | "pub" | "ref" |
+        "return" | "Self" | "self" | "static" | "struct" | "super" | "trait" |
+        "true" | "type" | "typeof" | "unsafe" | "unsized" | "use" | "virtual" |
+        "where" | "while" | "yield" => false,
+        _ => true,
+    }
+}
+
+#[cfg(feature = "parsing")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+impl Parse for Ident {
+    fn parse(input: ParseStream) -> Result<Self> {
+        input.step(|cursor| {
+            if let Some((ident, rest)) = cursor.ident() {
+                if accept_as_ident(&ident) {
+                    return Ok((ident, rest));
+                }
+            }
+            Err(cursor.error("expected identifier"))
+        })
+    }
+}
+
+#[cfg(feature = "parsing")]
+impl Token for Ident {
+    fn peek(cursor: Cursor) -> bool {
+        if let Some((ident, _rest)) = cursor.ident() {
+            accept_as_ident(&ident)
+        } else {
+            false
+        }
+    }
+
+    fn display() -> &'static str {
+        "identifier"
+    }
+}
+
+macro_rules! ident_from_token {
+    ($token:ident) => {
+        impl From<Token![$token]> for Ident {
+            fn from(token: Token![$token]) -> Ident {
+                Ident::new(stringify!($token), token.span)
+            }
+        }
+    };
+}
+
+ident_from_token!(self);
+ident_from_token!(Self);
+ident_from_token!(super);
+ident_from_token!(crate);
+ident_from_token!(extern);
+
+impl From<Token![_]> for Ident {
+    fn from(token: Token![_]) -> Ident {
+        Ident::new("_", token.span)
+    }
+}
+
+pub fn xid_ok(symbol: &str) -> bool {
+    let mut chars = symbol.chars();
+    let first = chars.next().unwrap();
+    if !(first == '_' || unicode_ident::is_xid_start(first)) {
+        return false;
+    }
+    for ch in chars {
+        if !unicode_ident::is_xid_continue(ch) {
+            return false;
+        }
+    }
+    true
+}