Re: [PR] AVRO-3527: Generated equals() and hashCode() for SpecificRecords [avro]

["benoitcanton (via GitHub)" <gi...@apache.org>]

benoitcanton commented on PR #1708:
URL: https://github.com/apache/avro/pull/1708#issuecomment-3523836333

   Hi @steven-aerts @RyanSkraba 
   
   This PR introduced a bug in the Avro tools 1.12.1 when a schema includes a field with name `result`. 
   
   In the following example, the schema contains two fields:
   - A field `result` of type `["null", "string"]` 
   - A field `anotherField` of type` enum
   
   The `hashCode` method generated based on the `record.vm` template will be as follow:
   
   ```java
     @Override
     public int hashCode() {
       int result = 1;
       result = 31 * result + (eventHeader == null ? 0 : eventHeader.hashCode());
       result = 31 * result + (result == null ? 0 : result.hashCode());
       result = 31 * result + (anotherField == null ? 0 : ((java.lang.Enum) anotherField).ordinal());
       return result;
     }
   ```
   
   Now since the schema has a field `result` of type `["null", "string"]` and the generated `hashCode` method declares a `result` of type `int`. The `result.hashCode()` will fail since the local `result` takes precedence.
   
   Trying to compile a project using the generated java class throws:
   
   ```
   Compiling with JDK Java compiler API.
   ..../MyEvent.java:1744: error: bad operand types for binary operator '=='
       result = 31 * result + (result == null ? 0 : result.hashCode());
                                      ^
     first type:  int
     second type: <null>
   ..../MyEvent.java:1744: error: int cannot be dereferenced
       result = 31 * result + (result == null ? 0 : result.hashCode());
                                                          ^
   2 errors
   > Task :compileJava FAILED
   ```
   
   For the sake of validating my findings, I have updated my schema and renamed my field `result` to `res` and sure enough that "fixed" the issue. Obviously, this is not a solution.
   
   One workaround would be to use custom Velocity templates, to rename `int result = 1` to `int result2 = 1` (just an example) but that is unpractical to maintain.
   
   @steven-aerts @RyanSkraba  It would be great if we could rename the `result` in the `record.vm` template to be something less common.
   
   If this Github thread is not the right place to report this bug, please let me know where to report it. Thanks!


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