fix field change handler into delta contract

packages/dds/tree/src/feature-libraries/default-schema/defaultFieldKinds.ts

@@ -43,7 +43,7 @@ export const noChangeHandler: FieldChangeHandler<0> = {
 	}),
 	codecsFactory: () => noChangeCodecFamily,
 	editor: { buildChildChange: (index, change) => fail("Child changes not supported") },
-	intoDelta: (change, deltaFromChild: ToDelta) => [[], [], []],
+	intoDelta: (change, deltaFromChild: ToDelta) => ({}),
 	relevantRemovedRoots: (change): Iterable<DeltaDetachedNodeId> => [],
 	isEmpty: (change: 0) => true,
 	getNestedChanges: (change: 0) => [],

packages/dds/tree/src/feature-libraries/modular-schema/fieldChangeHandler.ts

@@ -28,6 +28,24 @@ export type NestedChangesIndices = [
 	number | undefined /* outputIndex */,
 ][];
 
+/**
+ * The return value of calling {@link FieldChangeHandler.intoDelta}.
+ */
+export interface FieldChangeDelta {
+	/**
+	 * {@inheritdoc DeltaFieldChanges}
+	 */
+	readonly local?: DeltaFieldChanges;
+	/**
+	 * {@inheritdoc DeltaRoot.global}
+	 */
+	readonly global?: readonly DeltaDetachedNodeChanges[];
+	/**
+	 * {@inheritdoc DeltaRoot.rename}
+	 */
+	readonly rename?: readonly DeltaDetachedNodeRename[];
+}
+
 /**
  * Functionality provided by a field kind which will be composed with other `FieldChangeHandler`s to
  * implement a unified ChangeFamily supporting documents with multiple field kinds.
@@ -51,7 +69,7 @@ export interface FieldChangeHandler<
 		change: TChangeset,
 		deltaFromChild: ToDelta,
 		idAllocator: MemoizedIdRangeAllocator,
-	): [DeltaFieldChanges, DeltaDetachedNodeChanges[], DeltaDetachedNodeRename[]];
+	): FieldChangeDelta;
 	/**
 	 * Returns the set of removed roots that should be in memory for the given change to be applied.
 	 * A removed root is relevant if any of the following is true:
@@ -197,9 +215,7 @@ export interface FieldEditor<TChangeset> {
  * The `index` represents the index of the child node in the input context.
  * The `index` should be `undefined` iff the child node does not exist in the input context (e.g., an inserted node).
  */
-export type ToDelta = (
-	child: NodeId,
-) => DeltaFieldMap | undefined;
+export type ToDelta = (child: NodeId) => DeltaFieldMap | undefined;
 
 /**
  */

packages/dds/tree/src/feature-libraries/modular-schema/genericFieldKind.ts

@@ -61,7 +61,7 @@ export const genericChangeHandler: FieldChangeHandler<GenericChangeset> = {
 			}
 			nodeIndex += 1;
 		}
-		return [markList, [], []];
+		return { local: markList };
 	},
 	relevantRemovedRoots,
 	isEmpty: (change: GenericChangeset): boolean => change.length === 0,

packages/dds/tree/src/feature-libraries/modular-schema/index.ts

@@ -29,6 +29,7 @@ export { FlexFieldKind, type FullSchemaPolicy } from "./fieldKind.js";
 export { FieldKindWithEditor } from "./fieldKindWithEditor.js";
 export {
 	type FieldChangeHandler,
+	type FieldChangeDelta,
 	type FieldChangeRebaser,
 	type FieldEditor,
 	type NodeChangeComposer,

packages/dds/tree/src/feature-libraries/modular-schema/modularChangeFamily.ts

@@ -2084,14 +2084,20 @@ function intoDeltaImpl(
 	const rename: DeltaDetachedNodeRename[] = [];
 
 	for (const [field, fieldChange] of change) {
-		const [fieldChanges, fieldGlobal, fieldRename] = getChangeHandler(
-			fieldKinds,
-			fieldChange.fieldKind,
-		).intoDelta(
+		const {
+			local: fieldChanges,
+			global: fieldGlobal,
+			rename: fieldRename,
+		} = getChangeHandler(fieldKinds, fieldChange.fieldKind).intoDelta(
 			fieldChange.change,
 			(childChange) => {
 				const nodeChange = nodeChangeFromId(nodeChanges, childChange);
-				const nodeChangeDelta = deltaFromNodeChange(nodeChange, nodeChanges, idAllocator, fieldKinds);
+				const nodeChangeDelta = deltaFromNodeChange(
+					nodeChange,
+					nodeChanges,
+					idAllocator,
+					fieldKinds,
+				);
 				if (nodeChangeDelta !== undefined) {
 					const [nodeFieldChanges, nodeGlobals, nodeRenames] = nodeChangeDelta;
 					if (nodeGlobals.length > 0) {
@@ -2105,13 +2111,13 @@ function intoDeltaImpl(
 			},
 			idAllocator,
 		);
-		if (!isEmptyFieldChanges(fieldChanges)) {
+		if (fieldChanges !== undefined && !isEmptyFieldChanges(fieldChanges)) {
 			delta.set(field, fieldChanges);
 		}
-		if (fieldGlobal.length > 0) {
+		if (fieldGlobal !== undefined) {
 			fieldGlobal.forEach((c) => global.push(c));
 		}
-		if (fieldRename.length > 0) {
+		if (fieldRename !== undefined) {
 			fieldRename.forEach((r) => rename.push(r));
 		}
 	}

packages/dds/tree/src/feature-libraries/optional-field/optionalField.ts

@@ -41,6 +41,7 @@ import {
 	type RelevantRemovedRootsFromChild,
 	type ToDelta,
 	type NestedChangesIndices,
+	type FieldChangeDelta,
 } from "../modular-schema/index.js";
 
 import type {
@@ -658,7 +659,7 @@ export const optionalFieldEditor: OptionalFieldEditor = {
 export function optionalFieldIntoDelta(
 	change: OptionalChangeset,
 	deltaFromChild: ToDelta,
-): [DeltaFieldChanges, DeltaDetachedNodeChanges[], DeltaDetachedNodeRename[]] {
+): FieldChangeDelta {
 	let fieldChanges: DeltaFieldChanges = [];
 	const global: DeltaDetachedNodeChanges[] = [];
 	const rename: DeltaDetachedNodeRename[] = [];
@@ -690,22 +691,15 @@ export function optionalFieldIntoDelta(
 		for (const [id, childChange] of change.childChanges) {
 			const childDelta = deltaFromChild(childChange);
 			if (childDelta !== undefined) {
-				const [fields, childGlobal, childRename] = childDelta;
 				if (id !== "self") {
 					global.push({
 						id: { major: id.revision, minor: id.localId },
-						fields,
+						fields: childDelta,
 					});
 				} else {
-					mark.fields = fields;
+					mark.fields = childDelta;
 					markIsANoop = false;
 				}
-				if (childGlobal.length > 0) {
-					childGlobal.forEach((c) => global.push(c));
-				}
-				if (childRename.length > 0) {
-					childRename.forEach((r) => rename.push(r));
-				}
 			}
 		}
 	}
@@ -714,7 +708,11 @@ export function optionalFieldIntoDelta(
 		fieldChanges = [mark];
 	}
 
-	return [fieldChanges, global, rename];
+	return {
+		local: fieldChanges,
+		global,
+		rename,
+	};
 }
 
 export const optionalChangeHandler: FieldChangeHandler<

packages/dds/tree/src/feature-libraries/sequence-field/sequenceFieldToDelta.ts

@@ -8,7 +8,6 @@ import { assert, unreachableCase } from "@fluidframework/core-utils/internal";
 import {
 	type DeltaDetachedNodeChanges,
 	type DeltaDetachedNodeRename,
-	type DeltaFieldChanges,
 	type DeltaMark,
 	areEqualChangeAtomIds,
 } from "../../core/index.js";
@@ -25,12 +24,12 @@ import {
 	getInputCellId,
 	isAttachAndDetachEffect,
 } from "./utils.js";
-import type { ToDelta } from "../modular-schema/index.js";
+import type { FieldChangeDelta, ToDelta } from "../modular-schema/index.js";
 
 export function sequenceFieldToDelta(
 	change: MarkList,
 	deltaFromChild: ToDelta,
-): [DeltaFieldChanges, DeltaDetachedNodeChanges[], DeltaDetachedNodeRename[]] {
+): FieldChangeDelta {
 	const fieldChanges: DeltaMark[] = [];
 	const global: DeltaDetachedNodeChanges[] = [];
 	const rename: DeltaDetachedNodeRename[] = [];
@@ -42,21 +41,14 @@ export function sequenceFieldToDelta(
 		if (changes !== undefined) {
 			const childDelta = deltaFromChild(changes);
 			if (childDelta !== undefined) {
-				const [fields, childGlobal, childRename] = childDelta;
 				if (inputCellId === undefined) {
-					deltaMark.fields = fields;
+					deltaMark.fields = childDelta;
 				} else {
 					global.push({
 						id: nodeIdFromChangeAtom(inputCellId),
-						fields,
+						fields: childDelta,
 					});
 				}
-				if (childGlobal.length > 0) {
-					childGlobal.forEach((c) => global.push(c));
-				}
-				if (childRename.length > 0) {
-					childRename.forEach((r) => rename.push(r));
-				}
 			}
 		}
 		if (!areInputCellsEmpty(mark) && !areOutputCellsEmpty(mark)) {
@@ -194,5 +186,9 @@ export function sequenceFieldToDelta(
 		}
 		fieldChanges.pop();
 	}
-	return [fieldChanges, global, rename];
+	return {
+		local: fieldChanges,
+		global,
+		rename,
+	};
 }