Update compiler/rustc_parse/src/parser/cfg_select.rs

Co-authored-by: Joe ST <joe@fbstj.net>

Author: folkertdev

compiler/rustc_parse/src/parser/cfg_select.rs

@@ -14,8 +14,11 @@ pub enum CfgSelectRule {
 
 #[derive(Default)]
 pub struct CfgSelectBranches {
+    /// all the conditional branches
     pub reachable: Vec<(MetaItemInner, TokenStream, Span)>,
+    /// the first wildcard `_ => { ... }` branch
     pub wildcard: Option<(Token, TokenStream, Span)>,
+    /// all branches after the first wildcard, including further wildcards
     pub unreachable: Vec<(CfgSelectRule, TokenStream, Span)>,
 }