(tree) Add constraint to the output context of a change

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

@@ -160,8 +160,17 @@ export interface IDefaultEditBuilder {
 		destinationIndex: number,
 	): void;
 
-	// TODO: document
-	addNodeExistsConstraint(path: UpPath): void;
+	/**
+	 * Add a constraint that the node at the given path must exist.
+	 * @param path - The path to the node that must exist.
+	 */
+	addInputNodeExistsConstraint(path: UpPath): void;
+
+	/**
+	 * Add a constraint that the node at the given path must exist when undoing a change.
+	 * @param path - The path to the node that must exist when undoing a change.
+	 */
+	addUndoNodeExistsConstraint(path: UpPath): void;
 }
 
 /**
@@ -187,8 +196,12 @@ export class DefaultEditBuilder implements ChangeFamilyEditor, IDefaultEditBuild
 		this.modularBuilder.exitTransaction();
 	}
 
-	public addNodeExistsConstraint(path: UpPath): void {
-		this.modularBuilder.addNodeExistsConstraint(path, this.mintRevisionTag());
+	public addInputNodeExistsConstraint(path: UpPath): void {
+		this.modularBuilder.addInputNodeExistsConstraint(path, this.mintRevisionTag());
+	}
+
+	public addUndoNodeExistsConstraint(path: UpPath): void {
+		this.modularBuilder.addOutputNodeExistsConstraint(path, this.mintRevisionTag());
 	}
 
 	public valueField(field: FieldUpPath): ValueFieldEditBuilder<ITreeCursorSynchronous> {

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

@@ -20,6 +20,12 @@ import type { CrossFieldManager } from "./crossFieldQueries.js";
 import type { CrossFieldKeyRange, NodeId } from "./modularChangeTypes.js";
 import type { EncodedNodeChangeset } from "./modularChangeFormat.js";
 
+export type NestedChangesIndices = [
+	NodeId,
+	number | undefined /* inputIndex */,
+	number | undefined /* outputIndex */,
+][];
+
 /**
  * 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.
@@ -75,13 +81,16 @@ export interface FieldChangeHandler<
 	 * @param change - The field change to get the child changes from.
 	 *
 	 * @returns The set of `NodeId`s that correspond to nested changes in the given `change`.
-	 * Each `NodeId` is associated with the index of the node in the field in the input context of the changeset
-	 * (or `undefined` if the node is not attached in the input context).
+	 * Each `NodeId` is associated with the following:
+	 * - index of the node in the field in the input context of the changeset (or `undefined` if the node is not
+	 * attached in the input context).
+	 * - index of the node in the field in the output context of the changeset (or `undefined` if the node is not
+	 * attached in the output context).
 	 * For all returned entries where the index is defined,
 	 * the indices are are ordered from smallest to largest (with no duplicates).
 	 * The returned array is owned by the caller.
 	 */
-	getNestedChanges(change: TChangeset): [NodeId, number | undefined][];
+	getNestedChanges(change: TChangeset): NestedChangesIndices;
 
 	/**
 	 * @returns A list of all cross-field keys contained in the change.

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

@@ -17,6 +17,7 @@ import { assert } from "@fluidframework/core-utils/internal";
 import type { CrossFieldManager } from "./crossFieldQueries.js";
 import type {
 	FieldChangeHandler,
+	NestedChangesIndices,
 	NodeChangeComposer,
 	NodeChangePruner,
 	NodeChangeRebaser,
@@ -82,8 +83,9 @@ function compose(
 	return composed;
 }
 
-function getNestedChanges(change: GenericChangeset): [NodeId, number | undefined][] {
-	return change.toArray().map(([index, nodeChange]) => [nodeChange, index]);
+function getNestedChanges(change: GenericChangeset): NestedChangesIndices {
+	// For generic changeset, the indices in the input and output contexts are the same.
+	return change.toArray().map(([index, nodeChange]) => [nodeChange, index, index]);
 }
 
 function rebaseGenericChange(

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

@@ -41,6 +41,7 @@ export {
 	type ToDelta,
 	NodeAttachState,
 	type FieldChangeEncodingContext,
+	type NestedChangesIndices,
 } from "./fieldChangeHandler.js";
 export type {
 	CrossFieldKeyRange,

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

@@ -213,14 +213,18 @@ function makeModularChangeCodec(
 		context: FieldChangeEncodingContext,
 	): EncodedNodeChangeset {
 		const encodedChange: EncodedNodeChangeset = {};
-		const { fieldChanges, nodeExistsConstraint } = change;
+		const { fieldChanges, inputNodeExistsConstraint, outputNodeExistsConstraint } = change;
 
 		if (fieldChanges !== undefined) {
 			encodedChange.fieldChanges = encodeFieldChangesForJsonI(fieldChanges, context);
 		}
 
-		if (nodeExistsConstraint !== undefined) {
-			encodedChange.nodeExistsConstraint = nodeExistsConstraint;
+		if (inputNodeExistsConstraint !== undefined) {
+			encodedChange.inputNodeExistsConstraint = inputNodeExistsConstraint;
+		}
+
+		if (outputNodeExistsConstraint !== undefined) {
+			encodedChange.outputNodeExistsConstraint = outputNodeExistsConstraint;
 		}
 
 		return encodedChange;
@@ -299,7 +303,8 @@ function makeModularChangeCodec(
 		idAllocator: IdAllocator,
 	): NodeChangeset {
 		const decodedChange: NodeChangeset = {};
-		const { fieldChanges, nodeExistsConstraint } = encodedChange;
+		const { fieldChanges, inputNodeExistsConstraint, outputNodeExistsConstraint } =
+			encodedChange;
 
 		if (fieldChanges !== undefined) {
 			decodedChange.fieldChanges = decodeFieldChangesFromJson(
@@ -311,8 +316,12 @@ function makeModularChangeCodec(
 			);
 		}
 
-		if (nodeExistsConstraint !== undefined) {
-			decodedChange.nodeExistsConstraint = nodeExistsConstraint;
+		if (inputNodeExistsConstraint !== undefined) {
+			decodedChange.inputNodeExistsConstraint = inputNodeExistsConstraint;
+		}
+
+		if (outputNodeExistsConstraint !== undefined) {
+			decodedChange.outputNodeExistsConstraint = outputNodeExistsConstraint;
 		}
 
 		return decodedChange;
@@ -476,7 +485,7 @@ function makeModularChangeCodec(
 				changes: encodeFieldChangesForJson(change.fieldChanges, context, change.nodeChanges),
 				builds: encodeDetachedNodes(change.builds, context),
 				refreshers: encodeDetachedNodes(change.refreshers, context),
-				violations: change.constraintViolationCount,
+				violations: change.inputConstraintViolationCount,
 			};
 		},
 
@@ -505,7 +514,7 @@ function makeModularChangeCodec(
 			}
 
 			if (encodedChange.violations !== undefined) {
-				decoded.constraintViolationCount = encodedChange.violations;
+				decoded.inputConstraintViolationCount = encodedChange.violations;
 			}
 
 			const decodedRevInfos = decodeRevisionInfos(encodedChange.revisions, context);