[PR] Improve coder inference in WithKeys to reduce mismatch risks [beam]

Tue, 28 Apr 2026 09:18:53 -0700 


Subramanya-Veeregowda opened a new pull request, #38303:
URL: https://github.com/apache/beam/pull/38303

   This PR improves coder inference logic in WithKeys to reduce the risk of 
mismatches between inferred key coders and actual input types.
   
   Currently, when keyType is null, the coder is inferred using:
   coderRegistry.getOutputCoder(fn, in.getCoder())
   
   This relies on function-based inference, which may not always accurately 
reflect the actual runtime types.
   
   - Prefer using input coder context when available
   - Add safer fallback handling for coder inference
   - Preserve existing behavior when inference fails
   
   - Added/updated test to verify coder is correctly inferred
   - Verified pipeline execution completes successfully
   
   This change improves robustness of coder inference without altering existing 
APIs or breaking backward compatibility.
   
   Fixes #18571
   
   ------------------------
   
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