From 76f033f8c70f4cdb8f8382de97de5656bea91c53 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hu=C3=A1ng=20J=C3=B9nli=C3=A0ng?= <jlhwung@gmail.com>
Date: Wed, 5 Aug 2020 20:21:35 -0400
Subject: [PATCH] simplify isLookaheadRelational method (#11922)

* refactor: move isLookaheadRelational to flow plugins

* refactor: simplify isLookaheadRelational to isLookaheadToken_lt
---
 packages/babel-parser/src/parser/util.js  | 13 -------------
 packages/babel-parser/src/plugins/flow.js | 14 +++++++++++++-
 2 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/packages/babel-parser/src/parser/util.js b/packages/babel-parser/src/parser/util.js
index d6aa742df695..8b47a85be631 100644
--- a/packages/babel-parser/src/parser/util.js
+++ b/packages/babel-parser/src/parser/util.js
@@ -6,7 +6,6 @@ import State from "../tokenizer/state";
 import type { Node } from "../types";
 import { lineBreak } from "../util/whitespace";
 import { isIdentifierChar } from "../util/identifier";
-import * as charCodes from "charcodes";
 import { Errors } from "./error";
 
 type TryParse<Node, Error, Thrown, Aborted, FailState> = {
@@ -35,18 +34,6 @@ export default class UtilParser extends Tokenizer {
     return this.match(tt.relational) && this.state.value === op;
   }
 
-  isLookaheadRelational(op: "<" | ">"): boolean {
-    const next = this.nextTokenStart();
-    if (this.input.charAt(next) === op) {
-      if (next + 1 === this.input.length) {
-        return true;
-      }
-      const afterNext = this.input.charCodeAt(next + 1);
-      return afterNext !== op.charCodeAt(0) && afterNext !== charCodes.equalsTo;
-    }
-    return false;
-  }
-
   // TODO
 
   expectRelational(op: "<" | ">"): void {
diff --git a/packages/babel-parser/src/plugins/flow.js b/packages/babel-parser/src/plugins/flow.js
index b532ce04f47e..1887cfa68a60 100644
--- a/packages/babel-parser/src/plugins/flow.js
+++ b/packages/babel-parser/src/plugins/flow.js
@@ -2873,7 +2873,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       noCalls: ?boolean,
       subscriptState: N.ParseSubscriptState,
     ): N.Expression {
-      if (this.match(tt.questionDot) && this.isLookaheadRelational("<")) {
+      if (this.match(tt.questionDot) && this.isLookaheadToken_lt()) {
         subscriptState.optionalChainMember = true;
         if (noCalls) {
           subscriptState.stop = true;
@@ -3475,4 +3475,16 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         super.updateContext(prevType);
       }
     }
+
+    // check if the next token is a tt.relation("<")
+    isLookaheadToken_lt(): boolean {
+      const next = this.nextTokenStart();
+      if (this.input.charCodeAt(next) === charCodes.lessThan) {
+        const afterNext = this.input.charCodeAt(next + 1);
+        return (
+          afterNext !== charCodes.lessThan && afterNext !== charCodes.equalsTo
+        );
+      }
+      return false;
+    }
   };