Represent lifetimes as two joint tokens in proc macros

src/libsyntax/parse/lexer/mod.rs

@@ -1773,10 +1773,7 @@ fn ident_continue(c: Option<char>) -> bool {
 // The string is a valid identifier or a lifetime identifier.
 pub fn is_valid_ident(s: &str) -> bool {
     let mut chars = s.chars();
-    match chars.next() {
-        Some('\'') => ident_start(chars.next()) && chars.all(|ch| ident_continue(Some(ch))),
-        ch => ident_start(ch) && chars.all(|ch| ident_continue(Some(ch)))
-    }
+    ident_start(chars.next()) && chars.all(|ch| ident_continue(Some(ch)))
 }
 
 #[cfg(test)]