[parser] Disallow numeric separator in unicode scape sequences

packages/babel-parser/src/tokenizer/index.js

@@ -897,6 +897,19 @@ export default class Tokenizer extends LocationParser {
 
     let total = 0;
 
+    // Called from readHexChar
+    if (radix === 16) {
+      const unicode = this.input.slice(this.state.pos, this.state.pos + len);
+
+      if (unicode.includes("_")) {
+        const numSeparatorPos = this.input.indexOf("_");
+        this.raise(
+          numSeparatorPos,
+          "Numeric separators are not allowed inside unicode escape sequences",
+        );
+      }
+    }
+
     for (let i = 0, e = len == null ? Infinity : len; i < e; ++i) {
       const code = this.input.charCodeAt(this.state.pos);
       let val;

packages/babel-parser/test/fixtures/experimental/numeric-separator/invalid-hex/input.js

@@ -0,0 +1 @@
+"\x1_2"

packages/babel-parser/test/fixtures/experimental/numeric-separator/invalid-hex/options.json

@@ -0,0 +1 @@
+{ "throws": "Numeric separators are not allowed inside unicode escape sequences (1:4)" }

packages/babel-parser/test/fixtures/experimental/numeric-separator/invalid-unicode-2/input.js

@@ -0,0 +1 @@
+"\u12_34"

packages/babel-parser/test/fixtures/experimental/numeric-separator/invalid-unicode-2/options.json

@@ -0,0 +1 @@
+{ "throws": "Numeric separators are not allowed inside unicode escape sequences (1:5)" }

packages/babel-parser/test/fixtures/experimental/numeric-separator/invalid-unicode/input.js

@@ -0,0 +1 @@
+"\u{1F_639}"

packages/babel-parser/test/fixtures/experimental/numeric-separator/invalid-unicode/options.json

@@ -0,0 +1 @@
+{ "throws": "Numeric separators are not allowed inside unicode escape sequences (1:6)" }