ariesdevil opened a new pull request, #3094:
URL: https://github.com/apache/fory/pull/3094

   
   
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   ## Why?
   
   When computing struct version hash (fingerprint) for cross-language 
compatibility, Java and C++ treat enum fields as `nullable=true` by default 
(since Java enums are reference types that can be null). However, Rust's 
proc-macro cannot determine at compile time whether a field type is an enum, 
causing fingerprint mismatch between Rust and Java/C++.
   
   For example, a struct like:
   ```rust
   struct Message {
       state: MyEnum,  // Java: nullable=true, Rust (before): nullable=false
       name: String,
   }
   ```
   Would produce different version hashes in Rust vs Java/C++, breaking 
cross-language schema compatibility.
   
   ## What does this PR do?
   
   This PR aligns Rust's struct fingerprint computation with Java/C++ behavior:
   
   1. **Add runtime enum detection for fingerprint computation**
      - Create `gen_struct_version_hash_ts()` that generates code to compute 
fingerprint at runtime
      - For user-defined types (TypeId::UNKNOWN at macro time), call 
`fory_static_type_id()` to detect enums
      - For known primitive types, use compile-time constants to avoid 
unnecessary trait bounds
   
   2. **Add helper function `is_enum_type_id()`**
      - Checks if TypeId is ENUM, NAMED_ENUM, or UNION (Union-compatible Rust 
enums)
   
   3. **Fix Union-compatible enum handling**
      - Add `xlang` parameter to `fory_actual_type_id()` for proper TypeId 
selection
      - Fix enum variant meta registration to handle Union-compatible enums
      - Fix `field_need_write_type_info()` to handle UNION TypeId
   
   Now Rust computes the same fingerprint as Java/C++.
   
   ## Related issues
   
   <!--
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   - #xxxx0
   - #xxxx1
   - Fixes #xxxx2
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   ## Does this PR introduce any user-facing change?
   
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   - [ ] Does this PR introduce any public API change?
   - [x] Does this PR introduce any binary protocol compatibility change?
   **Note**: This changes the struct version hash computation for structs 
containing enum fields. The new hash will match Java/C++, but may differ from 
previous Rust versions. This is intentional for cross-language compatibility.
   
   ## Benchmark
   
   
   ## Others
   It's really hard to determine this bug :sob:...
   
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