Fixes #12039 (#12066)

src/js_lexer/identifier.zig

@@ -48,6 +48,7 @@ pub const JumpTable = struct {
             // explicitly tell LLVM's optimizer about values we know will not be in the range of this switch statement
             0xaa...0xffd7 => isIdentifierPartSlow16(@as(u16, @intCast(codepoint))),
             (0xffd7 + 1)...0xe01ef => isIdentifierPartSlow32(codepoint),
+
             else => false,
         };
     }
@@ -108,6 +109,8 @@ pub const JumpTable = struct {
             'A'...'Z', 'a'...'z', '0'...'9', '$', '_' => true,
             else => if (codepoint < 128)
                 return false
+            else if (codepoint == 0x200C or codepoint == 0x200D)
+                return true
             else
                 return isIdentifierPartSlow(codepoint),
         };

src/js_parser.zig

@@ -12919,6 +12919,13 @@ fn NewParser_(
                         }
                     }
 
+                    // Handle invalid identifiers in property names
+                    // https://github.com/oven-sh/bun/issues/12039
+                    if (p.lexer.token == .t_syntax_error) {
+                        p.log.addRangeErrorFmt(p.source, name_range, p.allocator, "Unexpected {}", .{bun.fmt.quote(name)}) catch bun.outOfMemory();
+                        return error.SyntaxError;
+                    }
+
                     key = p.newExpr(E.String{ .data = name }, name_range.loc);
 
                     // Parse a shorthand property

test/regression/issue/012039.test.ts

@@ -0,0 +1,29 @@
+import { test, expect } from "bun:test";
+
+// Previously, this would crash due to the invalid property name
+test("#12039 ZWJ", async () => {
+  const code = /*js*/ `
+export default class {
+  W‍;
+}
+`;
+  expect(() => new Bun.Transpiler().transformSync(code)).not.toThrow();
+});
+
+test("#12039 ZWNJ", async () => {
+  const code = /*js*/ `
+export default class {
+  W${String.fromCodePoint(0x200d)};
+}
+`;
+  expect(() => new Bun.Transpiler().transformSync(code)).not.toThrow();
+});
+
+test("#12039 invalid property name for identifier", async () => {
+  const code = /*js*/ `
+export default class {
+  W${String.fromCodePoint(129)};
+}
+`;
+  expect(() => new Bun.Transpiler().transformSync(code)).toThrow(`Unexpected "W`);
+});