WIP: add panicking PartialEq for Delimiter

Author: Kobzol

compiler/rustc_ast/src/token.rs

@@ -99,7 +99,7 @@ impl fmt::Display for MetaVarKind {
 /// Describes how a sequence of token trees is delimited.
 /// Cannot use `proc_macro::Delimiter` directly because this
 /// structure should implement some additional traits.
-#[derive(Copy, Clone, Debug, PartialEq, Encodable, Decodable, HashStable_Generic)]
+#[derive(Copy, Clone, Debug, Encodable, Decodable, HashStable_Generic)]
 pub enum Delimiter {
     /// `( ... )`
     Parenthesis,
@@ -115,6 +115,22 @@ pub enum Delimiter {
     Invisible(InvisibleOrigin),
 }
 
+impl PartialEq for Delimiter {
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (Delimiter::Parenthesis, Delimiter::Parenthesis) => true,
+            (Delimiter::Brace, Delimiter::Brace) => true,
+            (Delimiter::Bracket, Delimiter::Bracket) => true,
+            (Delimiter::Invisible(a), Delimiter::Invisible(b)) if a == b => {
+                panic!(
+                    "Comparing an invisible delimiter using PartialEq results in a different output than before"
+                );
+            }
+            _ => false,
+        }
+    }
+}
+
 impl Delimiter {
     // Should the parser skip these delimiters? Only happens for certain kinds
     // of invisible delimiters. Ideally this function will eventually disappear