docs: Document why json_dumps requires sorted keys for cache hashing #20657
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Add comprehensive docstring to json_dumps() explaining that key sorting is critical for deterministic JSON output, which is used to compute cache hashes in incremental type checking. Without sorted keys, dictionaries with the same content but different key insertion order would produce different hashes, causing incorrect cache invalidation. This addresses the TODO comment and clarifies the relationship between JSON serialization and the caching system.
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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Summary
This PR adds comprehensive documentation to
json_dumps()explaining why key sorting is critical for deterministic JSON output.Motivation
The function had a TODO comment asking to document why key sorting is necessary. This is important because:
hash_digest/hash_digest_bytesinbuild.py)testIncrementalInternalScrambletest specifically validates this behaviorChanges
Testing
No functional changes - this is documentation only. Existing tests should continue to pass.