React Compiler Ported to Rust: Fixing JSON Serialization for Flow Predicate Nodes
By
Joe Savona
A baker's-dozen of insight crammed into one ring.
Summary
This is a GitHub pull request by Joseph Savona that ports the React Compiler from JavaScript/Babel to Rust. The specific change described involves fixing a JSON serialization issue where Babel's parser emits `"predicate": null` on function-like nodes (FunctionDeclaration, ArrowFunctionExpression, etc.) for Flow's `%checks` predicate. The PR applies a custom `nullable_value` deserializer to handle the distinction between "absent" and "explicit null" values, ensuring round-tripped JSON remains byte-equivalent. This is an early, experimental work-in-progress shared for partner feedback before internal testing at Meta.
Key quotes
· 4 pulledThe Babel parser emits `"predicate": null` on function-like nodes (FunctionDeclaration, ArrowFunctionExpression, FunctionExpression, ObjectMethod, DeclareFunction) to signal "no Flow `%checks` predicate".
Plain `Option` deserialization collapses both "absent" and "explicit null" into `None`, and `skip_serializing_if = "Option::is_none"` then drops the field on the way back out, so round-tripped JSON loses the field and byte-equivalent comparison fails.
Apply the existing `crate::common::nullable_value` deserializer to all five predicate fields.
Work-in-progress - we are sharing early, prior to testing internally at Meta, to get feedback from partners...
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