1 files changed, 33 insertions, 0 deletions
diff --git a/src/libsyntax/token.rs b/src/libsyntax/token.rs
index 862934300e0..6eeee498815 100644
--- a/src/libsyntax/token.rs
+++ b/src/libsyntax/token.rs
@@ -270,6 +270,39 @@ impl TokenKind {
         Literal(Lit::new(kind, symbol, suffix))
     }
 
+    // An approximation to proc-macro-style single-character operators used by rustc parser.
+    // If the operator token can be broken into two tokens, the first of which is single-character,
+    // then this function performs that operation, otherwise it returns `None`.
+    pub fn break_two_token_op(&self) -> Option<(TokenKind, TokenKind)> {
+        Some(match *self {
+            Le => (Lt, Eq),
+            EqEq => (Eq, Eq),
+            Ne => (Not, Eq),
+            Ge => (Gt, Eq),
+            AndAnd => (BinOp(And), BinOp(And)),
+            OrOr => (BinOp(Or), BinOp(Or)),
+            BinOp(Shl) => (Lt, Lt),
+            BinOp(Shr) => (Gt, Gt),
+            BinOpEq(Plus) => (BinOp(Plus), Eq),
+            BinOpEq(Minus) => (BinOp(Minus), Eq),
+            BinOpEq(Star) => (BinOp(Star), Eq),
+            BinOpEq(Slash) => (BinOp(Slash), Eq),
+            BinOpEq(Percent) => (BinOp(Percent), Eq),
+            BinOpEq(Caret) => (BinOp(Caret), Eq),
+            BinOpEq(And) => (BinOp(And), Eq),
+            BinOpEq(Or) => (BinOp(Or), Eq),
+            BinOpEq(Shl) => (Lt, Le),
+            BinOpEq(Shr) => (Gt, Ge),
+            DotDot => (Dot, Dot),
+            DotDotDot => (Dot, DotDot),
+            ModSep => (Colon, Colon),
+            RArrow => (BinOp(Minus), Gt),
+            LArrow => (Lt, BinOp(Minus)),
+            FatArrow => (Eq, Gt),
+            _ => return None,
+        })
+    }
+
     /// Returns tokens that are likely to be typed accidentally instead of the current token.
     /// Enables better error recovery when the wrong token is found.
     pub fn similar_tokens(&self) -> Option<Vec<TokenKind>> {