[BUG] parsing a string containing escaped double quotes during polymorphic deserialization

[OnceEnchanted]

Problem Description

• Parsing a string containing escaped double quotes throws exception during polymorphic deserialization if the string comes before a field defining the object's type.

Environment Information

• JDK: Eclipse Temurin 25.0.1
• Version Information: Fastjson2 2.0.61

Reproduction Steps

Example code:

@JSONType(typeKey = "objectType")
sealed interface Animal {
    @JSONType(typeName = "cat")
    record Cat(String field) implements Animal {
    }
}

String json = "{\"field\": \"some\\\"text\", \"objectType\": \"cat\"}";
// Actual JSON to parse: {"field": "some\"text", "objectType": "cat"}
JSON.parseObject(json, Animal.class); // throws com.alibaba.fastjson2.JSONException

Output:

com.alibaba.fastjson2.JSONException: illegal fieldName input116, offset 18, character t, line 1, column 18, fastjson-version 2.0.61 {"field": "some\"text", "objectType": "cat"}

	at com.alibaba.fastjson2.JSONReader.readFieldNameHashCodeError(JSONReader.java:6885)
	at com.alibaba.fastjson2.JSONReaderASCII.readFieldNameHashCode(JSONReaderASCII.java:129)
	at com.alibaba.fastjson2.reader.ObjectReaderNoneDefaultConstructor.readObject(ObjectReaderNoneDefaultConstructor.java:310)
	at com.alibaba.fastjson2.reader.ORG_1_1_Cat.readObject(Unknown Source)
	at com.alibaba.fastjson2.reader.ObjectReaderSeeAlso.readObject(ObjectReaderSeeAlso.java:312)
	at com.alibaba.fastjson2.JSON.parseObject(JSON.java:992)

Expected Correct Result

String in the field must be deserialized correctly as: some"text