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@@ -50,79 +50,127 @@ function enumerableStringKeys(value: object): string[] | undefined {
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return keys as string[]
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}
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-/**
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- * Validate and detach lossless JSON in one read per property, so a stateful
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- * getter cannot change between validation and copying. Accepts ordinary arrays,
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- * plain or null-prototype objects, and JSON scalars; rejects sparse, cyclic,
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- * exotic, negative-zero, and non-finite values. Getter throws propagate.
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- *
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- * @param value - the candidate value to validate and detach.
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- * @returns the detached snapshot, or `undefined` when the value is not
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- * losslessly JSON-serializable.
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- */
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-export function snapshotJsonValue<T>(value: T): T | undefined {
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+type SnapshotDestination =
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+ | { kind: 'root' }
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+ | { kind: 'array'; target: JsonValue[]; index: number }
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+ | { kind: 'object'; target: { [key: string]: JsonValue }; key: string }
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+
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+type JsonWalkTask =
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+ | { kind: 'visit'; value: unknown; destination?: SnapshotDestination }
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+ | { kind: 'array-item'; source: unknown[]; index: number; target?: JsonValue[] }
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+ | { kind: 'object-property'; source: Record<string, unknown>; key: string; target?: { [key: string]: JsonValue } }
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+ | { kind: 'leave'; source: object }
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+
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+/** Validate lossless JSON iteratively, optionally materializing a detached snapshot. */
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+function walkJsonValue(value: unknown, detach: boolean): JsonValue | true | undefined {
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const ancestors = new Set<object>()
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+ let root: JsonValue | undefined
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+ const assign = (destination: SnapshotDestination | undefined, item: JsonValue): void => {
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+ if (destination === undefined) return
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+ if (destination.kind === 'root') {
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+ root = item
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+ } else if (destination.kind === 'array') {
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+ destination.target[destination.index] = item
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+ } else {
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+ Object.defineProperty(destination.target, destination.key, {
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+ value: item,
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+ enumerable: true,
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+ configurable: true,
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+ writable: true,
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+ })
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+ }
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+ }
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- const visit = (current: unknown): JsonValue | undefined => {
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- if (current === null) return null
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- switch (typeof current) {
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- case 'boolean':
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- case 'string':
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- return current
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- case 'number':
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- return Number.isFinite(current) && !Object.is(current, -0) ? current : undefined
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- case 'bigint':
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- case 'function':
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- case 'symbol':
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- case 'undefined':
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- return undefined
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- case 'object':
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- break
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+ const tasks: JsonWalkTask[] = [{
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+ kind: 'visit',
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+ value,
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+ ...(detach ? { destination: { kind: 'root' } as const } : {}),
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+ }]
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+ for (let task = tasks.pop(); task !== undefined; task = tasks.pop()) {
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+ if (task.kind === 'leave') {
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+ ancestors.delete(task.source)
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+ continue
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+ }
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+ if (task.kind === 'array-item') {
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+ if (!Object.prototype.hasOwnProperty.call(task.source, task.index)) return undefined
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+ tasks.push({
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+ kind: 'visit',
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+ value: task.source[task.index],
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+ ...(task.target === undefined ? {} : { destination: { kind: 'array', target: task.target, index: task.index } as const }),
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+ })
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+ continue
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+ }
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+ if (task.kind === 'object-property') {
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+ tasks.push({
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+ kind: 'visit',
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+ value: task.source[task.key],
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+ ...(task.target === undefined ? {} : { destination: { kind: 'object', target: task.target, key: task.key } as const }),
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+ })
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+ continue
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}
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+ const current = task.value
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+ if (current === null) {
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+ assign(task.destination, null)
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+ continue
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+ }
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+ if (typeof current === 'boolean' || typeof current === 'string') {
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+ assign(task.destination, current)
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+ continue
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+ }
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+ if (typeof current === 'number') {
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+ if (!Number.isFinite(current) || Object.is(current, -0)) return undefined
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+ assign(task.destination, current)
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+ continue
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+ }
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+ if (typeof current !== 'object') return undefined
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if (ancestors.has(current)) return undefined
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- ancestors.add(current)
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- try {
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- if (Array.isArray(current)) {
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- if (!hasPlainArrayPrototype(current)) return undefined
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- const length = current.length
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- // Every ordinary array owns `length`; dense indexed elements account
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- // for the remaining keys. Anything else would be lost by JSON and by
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- // structured clone, including symbols and non-enumerable properties.
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- if (Reflect.ownKeys(current).length !== length + 1) return undefined
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- const snapshot: JsonValue[] = []
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- for (let index = 0; index < length; index++) {
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- if (!Object.prototype.hasOwnProperty.call(current, index)) return undefined
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- const item = visit(current[index])
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- if (item === undefined) return undefined
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- snapshot.push(item)
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- }
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- return snapshot
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- }
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- if (!hasPlainObjectPrototype(current)) return undefined
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- const keys = enumerableStringKeys(current)
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- if (keys === undefined) return undefined
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- const snapshot: { [key: string]: JsonValue } = {}
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- for (const key of keys) {
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- const item = visit((current as Record<string, unknown>)[key])
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- if (item === undefined) return undefined
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- // Define the key as data so a JSON field literally named "__proto__"
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- // cannot mutate the snapshot's prototype through ordinary assignment.
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- Object.defineProperty(snapshot, key, {
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- value: item,
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- enumerable: true,
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- configurable: true,
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- writable: true,
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- })
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+ if (Array.isArray(current)) {
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+ if (!hasPlainArrayPrototype(current)) return undefined
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+ const length = current.length
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+ if (Reflect.ownKeys(current).length !== length + 1) return undefined
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+ const target = detach ? [] as JsonValue[] : undefined
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+ if (target !== undefined) assign(task.destination, target)
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+ ancestors.add(current)
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+ tasks.push({ kind: 'leave', source: current })
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+ for (let index = length - 1; index >= 0; index--) {
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+ tasks.push({ kind: 'array-item', source: current, index, ...(target === undefined ? {} : { target }) })
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}
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- return snapshot
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- } finally {
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- ancestors.delete(current)
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+ continue
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+ }
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+
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+ if (!hasPlainObjectPrototype(current)) return undefined
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+ const keys = enumerableStringKeys(current)
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+ if (keys === undefined) return undefined
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+ const target = detach ? {} as { [key: string]: JsonValue } : undefined
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+ if (target !== undefined) assign(task.destination, target)
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+ ancestors.add(current)
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+ tasks.push({ kind: 'leave', source: current })
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+ for (let index = keys.length - 1; index >= 0; index--) {
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+ const key = keys[index]
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+ /* v8 ignore next -- the loop is bounded by the captured key count. */
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+ if (key === undefined) return undefined
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+ tasks.push({ kind: 'object-property', source: current as Record<string, unknown>, key, ...(target === undefined ? {} : { target }) })
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}
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}
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+ return detach ? root : true
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+}
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- return visit(value) as T | undefined
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+/**
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+ * Validate and detach lossless JSON in one read per property, so a stateful
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+ * getter cannot change between validation and copying. Traversal is iterative,
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+ * so valid nesting is bounded by available memory rather than the JavaScript
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+ * call stack. Accepts ordinary arrays, plain or null-prototype objects, and JSON
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+ * scalars; rejects sparse, cyclic, exotic, negative-zero, and non-finite values.
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+ * Getter throws propagate.
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+ *
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+ * @param value - the candidate value to validate and detach.
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+ * @returns the detached snapshot, or `undefined` when the value is not
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+ * losslessly JSON-serializable.
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+ */
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+export function snapshotJsonValue<T>(value: T): T | undefined {
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+ return walkJsonValue(value, true) as T | undefined
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}
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/**
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@@ -130,46 +178,8 @@ export function snapshotJsonValue<T>(value: T): T | undefined {
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* detaching it. Only own enumerable string properties participate; `toJSON`
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* is ignored and getters run, so persistence boundaries use the snapshotter.
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* @param value - the candidate event data to test.
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- * @param seen - current recursion path; callers omit it.
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* @returns whether `value` survives JSON round-trip losslessly.
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*/
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-export function isJsonValue(value: unknown, seen: Set<object> = new Set()): boolean {
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- if (value === null) return true
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- switch (typeof value) {
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- case 'boolean':
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- case 'string':
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- return true
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- case 'number':
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- return Number.isFinite(value) && !Object.is(value, -0)
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- case 'bigint':
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- case 'function':
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- case 'symbol':
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- case 'undefined':
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- return false
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- case 'object':
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- break // handled below
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- }
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- // object
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- if (seen.has(value)) return false // circular
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- seen.add(value)
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- try {
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- if (Array.isArray(value)) {
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- if (!hasPlainArrayPrototype(value)) return false
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- if (Reflect.ownKeys(value).length !== value.length + 1) return false
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- // Reject sparse arrays: a hole is skipped by `every`/`forEach` but
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- // JSON.stringify writes it as `null`, so `[1, , 3]` would round-trip
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- // lossily. Require every index 0..length-1 to be an OWN property.
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- for (let i = 0; i < value.length; i++) {
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- if (!Object.prototype.hasOwnProperty.call(value, i)) return false
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- if (!isJsonValue(value[i], seen)) return false
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- }
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- return true
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- }
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- // Plain object only (reject Map/Set/Date/class instances).
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- if (!hasPlainObjectPrototype(value)) return false
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- const keys = enumerableStringKeys(value)
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- return keys !== undefined && keys.every(key => isJsonValue((value as Record<string, unknown>)[key], seen))
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- } finally {
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- seen.delete(value)
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- }
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+export function isJsonValue(value: unknown): boolean {
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+ return walkJsonValue(value, false) === true
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}
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Tianyi Cui