Define a struct once as an asset and reuse its shape (#253)

A struct used to declare its fields wherever it stood. The same shape
in two variables meant typing it twice, and Pack/Expand copied it once
without staying in sync. A Struct asset now holds the shape in one
place, and every struct that picks it as its type follows it.

- New asset type "Struct" (not placeable, group Structs, own icon).
  The inspector shows its fields with name, kind and default value,
  and "Open" shows them in the variables tab.
- Struct variables and struct fields get a Type row: own fields, any
  Struct asset, or "Make struct type". With a type the fields come
  from the asset and cannot be added, renamed or removed there. The
  values stay per variable, overrides on placed objects still work.
- Pack and Expand get the setting Type. With a type their ports are
  the fields of the asset and read-only in the inspector.
- A change to the asset reaches every typed place in one undo step
  (syncStructTypes). A new field arrives with its default. A removed
  field goes along with its port, edge and typed value. A renamed
  field keeps its value in variables, overrides and on ports with
  edges, also through nested types.
- Undo for these edits records plain assignments (Recorder), because
  the reach of a change is not known in advance.
- Cycles such as Loot in Loot, also through another type, are refused
  and not offered in the picker.
- Deleting the asset names how many places use it. Afterwards each
  place keeps its fields as its own.
- Loading reshapes a stale copy in a project file to its type.
- "Make struct type" creates an asset from an existing struct and
  links the place to it.

Differs from the plan:

- A changed default value applies to new fields and newly typed
  places only. Existing values stay.
- Removing a single field shows no warning. Undo brings it back.

Typed lists are left for #254. Lists stay dynamic for now.

Found by e2e: after deleting or renaming the type the inspector did
not rebuild and kept showing the old name. Fixed, the check was red
before.

Tests:
- ./check.sh: 182 files, 2661 tests, CHECK EXIT 0
- GM_STEPS=1,4,21,22,54: ALL PASSED, 176 checks
- 14 unit tests in tests/core/struct-types.test.ts
- New e2e module 54 with 14 checks, real mouse. Module 04 counts
  23 asset types.
- Counter-probes: without the rename pass 4 unit tests fail, without
  reshaping values 8, without the cycle rule 1. In the browser,
  without spreading changes and with + Field despite a type, 3
  checks fail.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -43,7 +43,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1486 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1500 checks (GM_STEPS=20 for one step)
                                                    #   every tool signs in first – see the Accounts page
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs
@@ -64,6 +64,7 @@ CI. Details, the GPU requirement and the detached runner are in
 | [Scenes](https://git.nockal.com/meleki/game-maker/wiki/Scenes) | The edited scene, the start scene, and switching scenes from a graph |
 | [Scene editing](https://git.nockal.com/meleki/game-maker/wiki/Scene-editing) | Placing, z-order, hierarchy, the editor offset |
 | [Behaviors](https://git.nockal.com/meleki/game-maker/wiki/Behaviors) | Node graphs: variables, the node set, structs and lists, loops, nesting, editing |
+| [Structs](https://git.nockal.com/meleki/game-maker/wiki/Structs) | Struct assets: a named shape that struct variables, fields and `Pack`/`Expand` follow |
 | [Colliders](https://git.nockal.com/meleki/game-maker/wiki/Colliders) | Shapes (box, circle, capsule, polygon), collision events, blocking movement, one-way colliders and raycasts |
 | [Physics](https://git.nockal.com/meleki/game-maker/wiki/Physics) | Rigidbodies, the collider material, gravity, the fixed step |
 | [Textures](https://git.nockal.com/meleki/game-maker/wiki/Textures) | Images, frames, nine-slice, the filter, upload limits |

src/core/commands/assetCommands.ts

@@ -49,6 +49,8 @@ export function buildAsset(type: AssetType, name: string, id = newId()): Asset {
       return { ...base, type: 'behavior', variables: [], graph: createEmptyGraph() };
     case 'variables':
       return { ...base, type: 'variables', variables: [] };
+    case 'struct':
+      return { ...base, type: 'struct', variables: [] };
     case 'collider':
       return { ...base, type: 'collider' };
     case 'rigidbody':

src/core/commands/naming.ts

@@ -1,4 +1,4 @@
-import type { BehaviorAsset, VariablesAsset } from '../model/Asset';
+import type { VariableOwnerAsset } from '../model/Asset';
 import type { Project } from '../model/Project';
 
 function firstFree(taken: ReadonlySet<string>, candidate: (i: number) => string, from: number): string {
@@ -28,7 +28,7 @@ export function nextNumberedName(taken: readonly string[], base: string): string
 }
 
 /** "var1", "var2", … – the first variable name not yet used by the behavior. */
-export function nextVariableName(asset: BehaviorAsset | VariablesAsset, base = 'var'): string {
+export function nextVariableName(asset: VariableOwnerAsset, base = 'var'): string {
   return firstFree(new Set(asset.variables.map((v) => v.key)), (i) => `${base}${i}`, 1);
 }
 

src/core/commands/require.ts

@@ -9,7 +9,7 @@ import type {
   StateMachineAsset,
   TilemapAsset,
   TilemapLayer,
-  VariablesAsset,
+  VariableOwnerAsset,
   VectorArtAsset,
   VectorShape,
 } from '../model/Asset';
@@ -84,10 +84,13 @@ export function requireBehavior(project: Project, assetId: string): BehaviorAsse
   return asset;
 }
 
-/** An asset that declares variables: a behavior, or a Variables asset shared by the whole run. */
+/**
-export function requireVariableOwner(project: Project, assetId: string): BehaviorAsset | VariablesAsset {
+ * An asset that declares variables: a behavior, a Variables asset shared by the whole run, or a
+ * Struct asset, whose fields are declared the same way (#253).
+ */
+export function requireVariableOwner(project: Project, assetId: string): VariableOwnerAsset {
   const asset = findAsset(project, assetId);
-  if (asset?.type !== 'behavior' && asset?.type !== 'variables')
+  if (asset?.type !== 'behavior' && asset?.type !== 'variables' && asset?.type !== 'struct')
     throw new CommandError(`Variable owner ${assetId} not found`);
   return asset;
 }

src/core/commands/structTypeCommands.ts

@@ -0,0 +1,178 @@
+/**
+ * Struct assets as types (#253). An edit of a Struct asset reaches every place using the type, so
+ * those writes are recorded as they happen (`Recorder`) and undone in one go with the edit itself.
+ */
+import { newId } from '../ids';
+import type { GraphNode } from '../graph/Graph';
+import { STRUCT_TYPE_PARAM } from '../graph/nested';
+import type { StructAsset } from '../model/Asset';
+import { nextAssetName } from './naming';
+import { isStruct, type PropertyValue } from '../model/Properties';
+import type { Project } from '../model/Project';
+import {
+  containsType,
+  type FieldRename,
+  isTypedNode,
+  setStructType,
+  structAssetOf,
+  structAt,
+  syncStructTypes,
+} from '../model/structTypes';
+import {
+  coerceValue,
+  type PropertyDef,
+  type StructDef,
+  type StructFieldDef,
+  variableDef,
+} from '../properties/PropertySchema';
+import { valueAt } from '../properties/valuePath';
+import { removeById } from '../util/list';
+import { Recorder } from '../util/recorder';
+import { type Command, CommandError } from './Command';
+import { requireNode, requireVariableOwner } from './require';
+
+/**
+ * Runs an edit of a Struct asset's fields and then carries it to every place of that type. A
+ * `rename` moves the values over first; without it a renamed field would be dropped and added back
+ * at its default.
+ */
+export class WithStructTypes implements Command {
+  readonly label: string;
+  private rec = new Recorder();
+
+  constructor(
+    private readonly inner: Command,
+    private readonly rename?: FieldRename,
+  ) {
+    this.label = inner.label;
+  }
+
+  execute(project: Project): void {
+    this.inner.execute(project);
+    this.rec = new Recorder();
+    syncStructTypes(project, this.rec, this.rename);
+  }
+
+  undo(project: Project): void {
+    this.rec.revert();
+    this.inner.undo(project);
+  }
+}
+
+/** What takes on a type: a struct variable or a struct field inside one, or a `Pack`/`Expand` node. */
+export type StructTypeTarget =
+  | { kind: 'variable'; ownerId: string; key: string; path: readonly string[] }
+  | { kind: 'node'; assetId: string; nodeId: string };
+
+function requireStructVariable(project: Project, ownerId: string, key: string): StructDef {
+  const def = requireVariableOwner(project, ownerId).variables.find((v) => v.key === key);
+  if (def?.kind !== 'struct') throw new CommandError(`Variable "${key}" is no struct`);
+  return def;
+}
+
+function requireTypedNode(project: Project, assetId: string, nodeId: string): GraphNode {
+  const node = requireNode(project, assetId, nodeId);
+  if (!isTypedNode(node)) throw new CommandError('Only Pack and Expand follow a struct type');
+  return node;
+}
+
+/**
+ * Gives a place a type, or with `''` its own fields back – the ones it had from the type, so
+ * nothing is lost either way. Inside a Struct asset a type holding that asset is refused.
+ */
+export class SetStructTypeCommand implements Command {
+  readonly label: string;
+  private rec = new Recorder();
+
+  constructor(
+    private readonly target: StructTypeTarget,
+    private readonly typeId: string,
+  ) {
+    this.label = typeId ? 'Set struct type' : 'Use own fields';
+  }
+
+  execute(project: Project): void {
+    const type = this.typeId ? structAssetOf(project, this.typeId) : undefined;
+    if (this.typeId && !type) throw new CommandError('That struct is gone');
+    this.rec = new Recorder();
+    const target = this.target;
+    if (target.kind === 'node') {
+      const node = requireTypedNode(project, target.assetId, target.nodeId);
+      if (this.typeId) this.rec.set(node.params, STRUCT_TYPE_PARAM, this.typeId);
+      else this.rec.delete(node.params, STRUCT_TYPE_PARAM);
+    } else {
+      const owner = requireVariableOwner(project, target.ownerId);
+      const def = requireStructVariable(project, target.ownerId, target.key);
+      if (!structAt(def, target.path))
+        throw new CommandError(`Field "${target.path.join('.')}" is no struct`);
+      if (type && owner.type === 'struct' && containsType(project, type.id, owner.id))
+        throw new CommandError(`${type.name} holds ${owner.name}, so it cannot be a field of it`);
+      setStructType(def, target.path, this.typeId, this.rec);
+    }
+    syncStructTypes(project, this.rec);
+  }
+
+  undo(): void {
+    this.rec.revert();
+  }
+}
+
+/** A struct field as a declared variable of a Struct asset, its default taken from `value`. */
+function variableOfField(field: StructFieldDef, value: PropertyValue | undefined): PropertyDef {
+  const def = variableDef(
+    field.key,
+    field.kind,
+    undefined,
+    field.kind === 'struct' ? field.fields : undefined,
+  );
+  if (value !== undefined) def.default = coerceValue(def, value);
+  if (def.kind === 'struct' && field.kind === 'struct' && field.structType) def.structType = field.structType;
+  return def;
+}
+
+/**
+ * Turns the fields a struct holds by itself into a Struct asset, and types the struct with it. The
+ * value it holds now becomes the asset's defaults, so the place reads exactly as before.
+ */
+export class MakeStructTypeCommand implements Command {
+  readonly label = 'Make struct type';
+  private asset?: StructAsset;
+  private rec = new Recorder();
+
+  constructor(
+    private readonly ownerId: string,
+    private readonly key: string,
+    private readonly path: readonly string[],
+  ) {}
+
+  /** The asset made, once the command ran – for the caller to select it. */
+  get assetId(): string {
+    return this.asset?.id ?? '';
+  }
+
+  execute(project: Project): void {
+    const owner = requireVariableOwner(project, this.ownerId);
+    const def = requireStructVariable(project, this.ownerId, this.key);
+    const at = structAt(def, this.path);
+    if (!at) throw new CommandError(`Field "${this.path.join('.')}" is no struct`);
+    if (at.structType && structAssetOf(project, at.structType))
+      throw new CommandError('This struct has a type already');
+    if (!this.asset) {
+      const value = valueAt(owner.props[def.key] ?? def.default, this.path);
+      const fields = isStruct(value) ? value : {};
+      const variables = at.fields.map((f) => variableOfField(f, fields[f.key]));
+      const props = Object.fromEntries(variables.map((v) => [v.key, v.default]));
+      const name = nextAssetName(project, this.path.at(-1) ?? this.key);
+      this.asset = { id: newId(), type: 'struct', name, props, variables };
+    }
+    project.assets.push(this.asset);
+    this.rec = new Recorder();
+    setStructType(def, this.path, this.asset.id, this.rec);
+    syncStructTypes(project, this.rec);
+  }
+
+  undo(project: Project): void {
+    this.rec.revert();
+    if (this.asset) project.assets = removeById(project.assets, this.asset.id);
+  }
+}

src/core/commands/variableCommands.ts

@@ -5,7 +5,7 @@ import {
   type PropertyValue,
   type StructValue,
 } from '../model/Properties';
-import { isKeptVariable, setKeptVariable } from '../model/Asset';
+import { isKeptVariable, setKeptVariable, type VariableOwnerAsset } from '../model/Asset';
 import { overrideSites } from '../model/instance';
 import type { Project } from '../model/Project';
 import type { VariableKind } from '../properties/kinds';
@@ -42,7 +42,7 @@ export class AddVariableCommand implements Command {
 
   execute(project: Project): void {
     const asset = requireVariableOwner(project, this.assetId);
-    if (!isValidVariableName(this.def.key)) throw new CommandError(INVALID_NAME);
+    if (!isValidName(asset, this.def.key)) throw new CommandError(INVALID_NAME);
     if (asset.variables.some((v) => v.key === this.def.key))
       throw new CommandError(`Variable "${this.def.key}" already exists`);
     asset.variables.push(this.def);
@@ -139,7 +139,7 @@ export class RenameVariableCommand extends RenameCommand {
   protected rename(project: Project, from: string, to: string): void {
     const asset = requireVariableOwner(project, this.assetId);
     if (from === to) return;
-    if (!isValidVariableName(to)) throw new CommandError(INVALID_NAME);
+    if (!isValidName(asset, to)) throw new CommandError(INVALID_NAME);
     const def = asset.variables.find((v) => v.key === from);
     if (!def) throw new CommandError(`Variable "${from}" not found`);
     if (asset.variables.some((v) => v.key === to)) throw new CommandError(`Variable "${to}" already exists`);
@@ -187,6 +187,14 @@ export class SetVariableKeptCommand implements Command {
   }
 }
 
+/**
+ * A struct's fields are no properties of anything placed, so the reserved property names are free
+ * there – as they are for a struct field.
+ */
+function isValidName(asset: VariableOwnerAsset, name: string): boolean {
+  return asset.type === 'struct' ? isValidFieldName(name) : isValidVariableName(name);
+}
+
 const INVALID_NAME = 'Variable names must start with a letter and contain only letters, digits or _';
 const INVALID_FIELD = 'Field names must start with a letter and contain only letters, digits or _';
 

src/core/graph/nested.ts

@@ -35,6 +35,17 @@ export const VARIABLES_SETTING: PropertyDef = {
   assetTypes: ['variables'],
 };
 
+export const STRUCT_TYPE_PARAM = 'structType';
+
+/** The Struct asset whose fields a `Pack` or `Expand` takes as its ports (#253); empty is by hand. */
+export const STRUCT_TYPE_SETTING: PropertyDef = {
+  key: STRUCT_TYPE_PARAM,
+  label: 'Type',
+  kind: 'asset',
+  default: '',
+  assetTypes: ['struct'],
+};
+
 export function variablesSourceOf(params: PropertyBag): string {
   return textOf(params[VARIABLES_PARAM] ?? '');
 }

src/core/graph/nodes/data/ExpandStruct.ts

@@ -1,5 +1,6 @@
 import type { NodeDef } from '../../NodeRegistry';
 import { asStruct, unplaced, type Value } from '../../values';
+import { STRUCT_TYPE_SETTING } from '../../nested';
 import { struct } from '../shared';
 
 /**
@@ -16,7 +17,7 @@ export const ExpandStruct: NodeDef = {
     'reads as empty.',
   inputs: [struct('value')],
   outputs: [],
-  params: [],
+  params: [STRUCT_TYPE_SETTING],
   declaresPorts: 'outputs',
   // A declared output the struct has no field for is simply absent from the cache, and reads as empty.
   run: (_ctx, inputs) => {

src/core/graph/nodes/data/PackStruct.ts

@@ -1,6 +1,7 @@
 import type { FieldValue } from '../../../model/Properties';
 import type { NodeDef } from '../../NodeRegistry';
 import { asField } from '../../values';
+import { STRUCT_TYPE_SETTING } from '../../nested';
 import { struct } from '../shared';
 
 /**
@@ -14,7 +15,7 @@ export const PackStruct: NodeDef = {
   description: 'Bundles named values into one struct, one input per field.',
   inputs: [],
   outputs: [struct('value')],
-  params: [],
+  params: [STRUCT_TYPE_SETTING],
   declaresPorts: 'inputs',
   run: (_ctx, inputs) => {
     const fields: Record<string, FieldValue> = {};

src/core/model/Asset.ts

@@ -77,6 +77,16 @@ export interface VariablesAsset extends AssetBase {
   scope?: Scope;
 }
 
+/**
+ * A named shape for structs (#253). Its fields are declared as a Variables asset declares its
+ * variables, so the same rows and commands edit them, and `props` holds their defaults. A struct
+ * variable or field naming it in `structType` takes on these fields (see `model/structTypes.ts`).
+ */
+export interface StructAsset extends AssetBase {
+  type: 'struct';
+  variables: PropertyDef[];
+}
+
 /** Placed as a child of the object it belongs to; its position is the offset from that body. */
 export interface ColliderAsset extends AssetBase {
   type: 'collider';
@@ -458,6 +468,7 @@ export type Asset =
   | SceneAsset
   | BehaviorAsset
   | VariablesAsset
+  | StructAsset
   | ColliderAsset
   | RigidbodyAsset
   | ContainerAsset
@@ -475,6 +486,13 @@ export type Asset =
   | SoundAsset
   | ParticlesAsset;
 
+/** The assets whose `variables` are declared by the user – see `requireVariableOwner`. */
+export type VariableOwnerAsset = BehaviorAsset | VariablesAsset | StructAsset;
+
+export function isVariableOwner(asset: Asset | undefined): asset is VariableOwnerAsset {
+  return asset?.type === 'behavior' || asset?.type === 'variables' || asset?.type === 'struct';
+}
+
 /** The assets edited as a node graph – what the graph canvas and the graph commands work on. */
 export type GraphAsset = BehaviorAsset | StateMachineAsset | ShaderAsset | ParticlesAsset;
 

src/core/model/AssetTypes.ts

@@ -5,6 +5,7 @@ export const ASSET_TYPES = [
   'text',
   'behavior',
   'variables',
+  'struct',
   'collider',
   'rigidbody',
   'container',
@@ -32,6 +33,7 @@ export const ASSET_TYPE_LABELS: Record<AssetType, string> = {
   text: 'Text',
   behavior: 'Behavior',
   variables: 'Variables',
+  struct: 'Struct',
   collider: 'Collider',
   rigidbody: 'Rigidbody',
   container: 'Container',
@@ -57,6 +59,7 @@ export const ASSET_TYPE_LABELS: Record<AssetType, string> = {
  * sound is nowhere on screen at all – a graph plays it, so there is nothing to place. A tile is
  * what a tilemap draws with, so it is placed no more directly than a texture is – what is placed
  * is the tilemap. A curve is the way a key or a `Lerp` blends, picked by id like a state machine.
+ * A struct is a shape that variables and fields take on (#253), nothing that exists on its own.
  */
 export type PlaceableAssetType = Exclude<
   AssetType,
@@ -73,6 +76,7 @@ export type PlaceableAssetType = Exclude<
   | 'font'
   | 'sound'
   | 'variables'
+  | 'struct'
 >;
 
 const NOT_PLACEABLE: ReadonlySet<AssetType> = new Set([
@@ -89,6 +93,7 @@ const NOT_PLACEABLE: ReadonlySet<AssetType> = new Set([
   'font',
   'sound',
   'variables',
+  'struct',
 ]);
 
 export function isPlaceableType(type: AssetType): type is PlaceableAssetType {

src/core/model/structTypes.ts

@@ -0,0 +1,374 @@
+/**
+ * Struct assets as types (#253). A struct variable or field naming one in `structType` keeps a copy
+ * of its fields, so everything reading `fields` works as it did; `syncStructTypes` brings every such
+ * copy – and every value and `Pack`/`Expand` port hanging on it – back in line after the asset
+ * changed. A type that is gone leaves the copy as it was: the place keeps its last fields as its own.
+ */
+import type { DeclaredPort, Graph, GraphNode } from '../graph/Graph';
+import { fixedPortKeys, isValidPortName, STRUCT_TYPE_PARAM } from '../graph/nested';
+import { nodeDef } from '../graph/NodeRegistry';
+import { isKindWith } from '../properties/kinds';
+import {
+  coerceFieldValue,
+  emptyFieldValue,
+  type PropertyDef,
+  type StructDef,
+  type StructFieldDef,
+  structOf,
+} from '../properties/PropertySchema';
+import { valueAt, withValueAt } from '../properties/valuePath';
+import type { Recorder } from '../util/recorder';
+import { isGraphAsset, isVariableOwner, type StructAsset, type VariableOwnerAsset } from './Asset';
+import { overrideSites } from './instance';
+import { type FieldValue, isStruct, type PropertyValue, type StructValue, tagOf, textOf } from './Properties';
+import { findAssetOf, type Project } from './Project';
+
+export const PACK_STRUCT = 'PackStruct';
+export const EXPAND_STRUCT = 'ExpandStruct';
+
+/** Deeper than this only a cycle written by hand can go; it is cut there. */
+const MAX_DEPTH = 32;
+
+export function structAssetOf(project: Project, id: string | undefined): StructAsset | undefined {
+  return id ? findAssetOf(project, id, 'struct') : undefined;
+}
+
+export function isTypedNode(node: GraphNode): boolean {
+  return node.type === PACK_STRUCT || node.type === EXPAND_STRUCT;
+}
+
+export function nodeStructType(node: GraphNode): string {
+  return isTypedNode(node) ? textOf(node.params[STRUCT_TYPE_PARAM] ?? '') : '';
+}
+
+/** A declared variable as the struct field it becomes in every value of the type. */
+export function fieldOfVariable(def: PropertyDef): StructFieldDef | undefined {
+  if (def.kind === 'struct')
+    return {
+      key: def.key,
+      kind: 'struct',
+      fields: def.fields,
+      ...(def.structType ? { structType: def.structType } : {}),
+    };
+  if (def.kind === 'list') return { key: def.key, kind: 'list' };
+  return isKindWith('field', def.kind) ? { key: def.key, kind: def.kind } : undefined;
+}
+
+export function typeFields(asset: StructAsset): StructFieldDef[] {
+  return asset.variables.flatMap((def) => fieldOfVariable(def) ?? []);
+}
+
+/** A new value of the type: every field at the default the asset declares for it. */
+export function typeDefault(asset: StructAsset): StructValue {
+  return structOf(typeFields(asset), asset.props);
+}
+
+/** The Struct assets named anywhere inside these fields; a typed field is not looked into. */
+function typesIn(fields: readonly StructFieldDef[]): string[] {
+  return fields.flatMap((f) =>
+    f.kind !== 'struct' ? [] : f.structType ? [f.structType] : typesIn(f.fields),
+  );
+}
+
+/**
+ * Whether a value of type `from` holds one of type `target` anywhere inside, or is one. Such a
+ * type cannot be a field of `target`: its default would never end.
+ */
+export function containsType(project: Project, from: string, target: string, depth = 0): boolean {
+  if (from === target) return true;
+  const asset = structAssetOf(project, from);
+  if (!asset || depth > MAX_DEPTH) return false;
+  return typesIn(typeFields(asset)).some((id) => containsType(project, id, target, depth + 1));
+}
+
+/** Where values of type `target` sit inside a value of type `from`: `[]` when it is one itself. */
+function typePaths(project: Project, from: string, target: string, depth = 0): string[][] {
+  if (from === target) return [[]];
+  const asset = structAssetOf(project, from);
+  if (!asset || depth > MAX_DEPTH) return [];
+  return pathsIn(project, typeFields(asset), target, depth + 1);
+}
+
+function pathsIn(
+  project: Project,
+  fields: readonly StructFieldDef[],
+  target: string,
+  depth: number,
+): string[][] {
+  if (depth > MAX_DEPTH) return [];
+  const paths: string[][] = [];
+  for (const f of fields) {
+    if (f.kind !== 'struct') continue;
+    const inner = f.structType
+      ? typePaths(project, f.structType, target, depth + 1)
+      : pathsIn(project, f.fields, target, depth + 1);
+    for (const path of inner) paths.push([f.key, ...path]);
+  }
+  return paths;
+}
+
+/**
+ * A place that takes on a type: the struct at `path` inside the variable `def` of `owner`. Below it
+ * nothing is a place of its own – the type's fields say what is there.
+ */
+export interface TypedSite {
+  owner: VariableOwnerAsset;
+  def: StructDef;
+  path: string[];
+  structType: string;
+}
+
+export function typedSites(project: Project): TypedSite[] {
+  const sites: TypedSite[] = [];
+  const visit = (
+    owner: VariableOwnerAsset,
+    def: StructDef,
+    at: { structType?: string; fields: readonly StructFieldDef[] },
+    path: string[],
+  ): void => {
+    if (at.structType) {
+      sites.push({ owner, def, path, structType: at.structType });
+      return;
+    }
+    for (const f of at.fields) if (f.kind === 'struct') visit(owner, def, f, [...path, f.key]);
+  };
+  for (const asset of project.assets)
+    if (isVariableOwner(asset))
+      for (const def of asset.variables) if (def.kind === 'struct') visit(asset, def, def, []);
+  return sites;
+}
+
+/** Everywhere the value of a variable is kept: its declared default, the owner's, the overrides. */
+interface Holder {
+  read(): PropertyValue | undefined;
+  write(value: PropertyValue): void;
+}
+
+function holdersOf(project: Project, site: TypedSite, rec: Recorder): Holder[] {
+  const { owner, def } = site;
+  const holders: Holder[] = [
+    { read: () => def.default, write: (value) => rec.set(def, 'default', value as StructValue) },
+  ];
+  if (owner.props[def.key] !== undefined)
+    holders.push({
+      read: () => owner.props[def.key],
+      write: (value) => rec.set(owner.props, def.key, value),
+    });
+  for (const { bag } of overrideSites(project, (id) => id === owner.id))
+    if (bag[def.key] !== undefined)
+      holders.push({ read: () => bag[def.key], write: (value) => rec.set(bag, def.key, value) });
+  return holders;
+}
+
+/**
+ * `value` in the shape of `fields`: what it has keeps its value (brought to the field's kind), what
+ * it lacks takes the type's default, and what the type does not declare falls away.
+ */
+export function shapedStruct(
+  project: Project,
+  fields: readonly StructFieldDef[],
+  value: PropertyValue | undefined,
+  defaults: StructValue,
+  depth = 0,
+): StructValue {
+  const source = isStruct(value) && tagOf(value) === undefined ? value : {};
+  const shaped: Record<string, FieldValue> = {};
+  for (const field of fields) {
+    const own = source[field.key];
+    const fallback = defaults[field.key];
+    const inner = field.kind === 'struct' ? structAssetOf(project, field.structType) : undefined;
+    if (inner && field.kind === 'struct' && depth < MAX_DEPTH) {
+      const innerDefaults = isStruct(fallback) ? fallback : typeDefault(inner);
+      shaped[field.key] = shapedStruct(project, field.fields, own ?? innerDefaults, innerDefaults, depth + 1);
+    } else if (own !== undefined) shaped[field.key] = coerceFieldValue(own, field);
+    else
+      shaped[field.key] = fallback !== undefined ? coerceFieldValue(fallback, field) : emptyFieldValue(field);
+  }
+  return shaped;
+}
+
+/** The declaration with the fields of the struct at `path` replaced – and nothing else touched. */
+function withFieldsAt(
+  fields: readonly StructFieldDef[],
+  path: readonly string[],
+  change: (field: Extract<StructFieldDef, { kind: 'struct' }>) => StructFieldDef,
+): readonly StructFieldDef[] {
+  const [step, ...rest] = path;
+  return fields.map((f) =>
+    f.key !== step || f.kind !== 'struct'
+      ? f
+      : rest.length === 0
+        ? change(f)
+        : { ...f, fields: withFieldsAt(f.fields, rest, change) },
+  );
+}
+
+/** The struct field at `path` of a variable, or the variable itself for none. */
+export function structAt(
+  def: StructDef,
+  path: readonly string[],
+): { fields: readonly StructFieldDef[]; structType?: string } | undefined {
+  let at: { fields: readonly StructFieldDef[]; structType?: string } = def;
+  for (const step of path) {
+    const next = at.fields.find((f) => f.key === step);
+    if (next?.kind !== 'struct') return undefined;
+    at = next;
+  }
+  return at;
+}
+
+function setFields(
+  def: StructDef,
+  path: readonly string[],
+  fields: readonly StructFieldDef[],
+  rec: Recorder,
+) {
+  if (path.length === 0) rec.set(def, 'fields', fields);
+  else
+    rec.set(
+      def,
+      'fields',
+      withFieldsAt(def.fields, path, (f) => ({ ...f, fields })),
+    );
+}
+
+/** Names the type of the struct at `path`; `''` makes it hold its own fields again. */
+export function setStructType(def: StructDef, path: readonly string[], typeId: string, rec: Recorder): void {
+  if (path.length === 0) {
+    if (typeId) rec.set(def, 'structType', typeId);
+    else rec.delete(def, 'structType');
+    return;
+  }
+  rec.set(
+    def,
+    'fields',
+    withFieldsAt(def.fields, path, ({ structType: _dropped, ...f }) =>
+      typeId ? { ...f, structType: typeId } : f,
+    ),
+  );
+}
+
+/** A field of a Struct asset renamed: `path` leads through the type's value to the struct holding it. */
+export interface FieldRename {
+  structType: string;
+  path: readonly string[];
+  from: string;
+  to: string;
+}
+
+function renamedKey(value: StructValue, from: string, to: string): StructValue {
+  const next: Record<string, FieldValue> = {};
+  for (const [key, item] of Object.entries(value)) next[key === from ? to : key] = item;
+  return next;
+}
+
+/** Carries a renamed field's values over, before the shapes are rebuilt – which would drop them. */
+function applyRename(project: Project, rec: Recorder, rename: FieldRename): void {
+  const { from, to } = rename;
+  for (const site of typedSites(project))
+    for (const inside of typePaths(project, site.structType, rename.structType)) {
+      const path = [...site.path, ...inside, ...rename.path];
+      for (const holder of holdersOf(project, site, rec)) {
+        const value = holder.read();
+        const at = valueAt(value, path);
+        if (!isStruct(at) || !(from in at)) continue;
+        holder.write(withValueAt(value, path, renamedKey(at, from, to)) ?? value!);
+      }
+    }
+  if (rename.path.length > 0) return;
+  for (const { graph, node } of typedNodes(project)) {
+    if (nodeStructType(node) !== rename.structType) continue;
+    const ports = node.ports ?? [];
+    if (!ports.some((p) => p.key === from)) continue;
+    rec.set(
+      node,
+      'ports',
+      ports.map((p) => (p.key === from ? { ...p, key: to } : p)),
+    );
+    for (const edge of graph.edges) {
+      if (edge.to.node === node.id && edge.to.port === from) rec.set(edge.to, 'port', to);
+      if (edge.from.node === node.id && edge.from.port === from) rec.set(edge.from, 'port', to);
+    }
+    const inline = node.params[from];
+    if (inline !== undefined) {
+      rec.set(node.params, to, inline);
+      rec.delete(node.params, from);
+    }
+  }
+}
+
+function typedNodes(project: Project): { graph: Graph; node: GraphNode }[] {
+  return project.assets.flatMap((asset) =>
+    isGraphAsset(asset)
+      ? asset.graph.nodes.filter(isTypedNode).map((node) => ({ graph: asset.graph, node }))
+      : [],
+  );
+}
+
+/** The ports follow the fields; an edge on a port that is gone goes with it, as its typed-in value does. */
+function syncNodePorts(
+  graph: Graph,
+  node: GraphNode,
+  fields: readonly StructFieldDef[],
+  rec: Recorder,
+): void {
+  const def = nodeDef(node.type);
+  if (!def) return;
+  const fixed = new Set(fixedPortKeys(def));
+  const ports: DeclaredPort[] = fields
+    .filter((f) => isValidPortName(f.key) && !fixed.has(f.key))
+    .map((f) => ({ key: f.key, kind: f.kind }));
+  const kept = new Set(ports.map((p) => p.key));
+  const gone = new Set((node.ports ?? []).map((p) => p.key).filter((key) => !kept.has(key)));
+  rec.set(node, 'ports', ports);
+  if (gone.size === 0) return;
+  const inputs = def.declaresPorts === 'inputs';
+  const hangs = (end: { node: string; port: string }) => end.node === node.id && gone.has(end.port);
+  if (graph.edges.some((e) => (inputs ? hangs(e.to) : hangs(e.from))))
+    rec.set(
+      graph,
+      'edges',
+      graph.edges.filter((e) => !(inputs ? hangs(e.to) : hangs(e.from))),
+    );
+  if (inputs) for (const key of gone) rec.delete(node.params, key);
+}
+
+/**
+ * Brings every typed place in line with its Struct asset: the copied fields, every value kept for
+ * it, the ports of typed `Pack`/`Expand` nodes. A type holding another type is only right once that
+ * one is, so the passes repeat until one changes nothing. Every write goes through `rec`, so the
+ * whole reach of an edit is undone in one go.
+ */
+export function syncStructTypes(project: Project, rec: Recorder, rename?: FieldRename): void {
+  if (rename) applyRename(project, rec, rename);
+  const passes = project.assets.filter((a) => a.type === 'struct').length + 2;
+  for (let pass = 0; pass < passes; pass++) {
+    const before = rec.count;
+    for (const site of typedSites(project)) {
+      const type = structAssetOf(project, site.structType);
+      // A struct asset naming a type that holds it is a cycle written by hand: left as it is.
+      if (!type || (site.owner.type === 'struct' && containsType(project, type.id, site.owner.id))) continue;
+      const fields = typeFields(type);
+      setFields(site.def, site.path, fields, rec);
+      const defaults = typeDefault(type);
+      for (const holder of holdersOf(project, site, rec)) {
+        const value = holder.read();
+        const next = shapedStruct(project, fields, valueAt(value, site.path), defaults);
+        holder.write(withValueAt(value, site.path, next) ?? next);
+      }
+    }
+    for (const { graph, node } of typedNodes(project)) {
+      const type = structAssetOf(project, nodeStructType(node));
+      if (type) syncNodePorts(graph, node, typeFields(type), rec);
+    }
+    if (rec.count === before) return;
+  }
+}
+
+/** How many places name the type – what deleting it would cut loose. */
+export function structTypeUsages(project: Project, typeId: string): { places: number; nodes: number } {
+  return {
+    places: typedSites(project).filter((site) => site.structType === typeId).length,
+    nodes: typedNodes(project).filter(({ node }) => nodeStructType(node) === typeId).length,
+  };
+}

src/core/properties/PropertySchema.ts

@@ -168,7 +168,8 @@ export type PropertyDef =
   | { key: string; label: string; kind: 'list'; default: ListValue }
   /**
    * `fields` is the declaration; the value carries exactly those keys, which is what lets a struct
-   * keep its shape while single fields are written (`mergeStruct`).
+   * keep its shape while single fields are written (`mergeStruct`). With a `structType` the fields
+   * are a copy of that Struct asset's (#253), kept in step by `syncStructTypes`.
    */
   | {
       key: string;
@@ -176,6 +177,7 @@ export type PropertyDef =
       kind: 'struct';
       default: StructValue;
       fields: readonly StructFieldDef[];
+      structType?: string;
     }
   /** An object variable holds a live handle during a run, and nothing at rest (`NO_OBJECT`). */
   | ObjectDef;
@@ -205,6 +207,7 @@ export interface StructFieldStructDef {
   key: string;
   kind: 'struct';
   fields: readonly StructFieldDef[];
+  structType?: string;
 }
 
 export type StructFieldDef = PrimitiveFieldDef | ListFieldDef | StructFieldStructDef;
@@ -513,6 +516,7 @@ const ASSET_SCHEMAS: Record<AssetType, PropertySchema> = {
   ],
   // Every row is declared on the asset itself – see `schemaForBag`.
   variables: [],
+  struct: [],
   // The states are the asset's graph (see StateMachineAsset), not a property.
   statemachine: [],
   // The nodes are the asset's graph (see ShaderAsset); its parameters are rows of the sprites wearing it.
@@ -694,7 +698,7 @@ export function schemaForObject(project: Project, asset: Asset, object: SceneObj
 function schemaForBag(project: Project, asset: Asset, bag: PropertyBag): PropertySchema {
   if (asset.type === 'behavior') return [...FULL_SCHEMAS.behavior, ...asset.variables];
   // Nothing but declarations: the starting values live in `props` under the very same keys.
-  if (asset.type === 'variables') return asset.variables;
+  if (asset.type === 'variables' || asset.type === 'struct') return asset.variables;
   if (asset.type === 'sprite') return [...FULL_SCHEMAS.sprite, ...shaderParamRows(project, shaderOf(bag))];
   // Unlike a sprite's shader, a source's graph is its own asset's, so no id has to be looked up.
   if (asset.type === 'particles') {

src/core/properties/deviation.ts

@@ -12,7 +12,7 @@ import { deviatesFromAsset, isModified } from './resolve';
  */
 export function markedAssetSchema(project: Project, asset: Asset): PropertySchema {
   // Declared variables are drawn by the inspector's own section, not as asset rows.
-  return asset.type === 'behavior' || asset.type === 'variables'
+  return asset.type === 'behavior' || asset.type === 'variables' || asset.type === 'struct'
     ? schemaFor(asset.type)
     : schemaForAsset(project, asset);
 }

src/core/store/serialize.ts

@@ -70,6 +70,8 @@ import { newId } from '../ids';
 import { SHAPE_FILL_DEFAULT } from '../model/vectorart';
 import { sanitizedCurve } from '../model/curve';
 import { hasParentCycle } from '../model/walk';
+import { syncStructTypes } from '../model/structTypes';
+import { Recorder } from '../util/recorder';
 import {
   DECLARED_PORT_KINDS,
   FIELD_KINDS,
@@ -114,7 +116,7 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
     if (typeof a.id !== 'string' || !a.id || !isAssetType(a.type)) continue;
     rawProps.set(a.id, asRecord(a.props));
     if (a.type === 'sprite' || a.type === 'particles') wearers.set(a.id, a.type);
-    if (a.type === 'behavior' || a.type === 'variables') {
+    if (a.type === 'behavior' || a.type === 'variables' || a.type === 'struct') {
       const vars = normalizeVariables(a.variables);
       variables.set(a.id, vars);
       // The full schema, not just the common rows: this is what pass 2 coerces `props` against, and
@@ -191,6 +193,8 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
       if (readSharedScope(a.scope) === 'scene') shared.scope = 'scene';
       else if (a.persistent === true) shared.persistent = true;
       assets.push(shared);
+    } else if (type === 'struct') {
+      assets.push({ id, type, name, props, variables: variables.get(id) ?? [] });
     } else if (type === 'statemachine') {
       const machine: StateMachineAsset = {
         id,
@@ -271,6 +275,8 @@ export function deserializeProject(raw: unknown, fallbackId = ''): Project {
     gameScale: gameScaleOf(r),
     sceneVisibility: sceneVisibilityOf(r),
   };
+  // A hand-edited file may have copies that no longer match their Struct asset.
+  syncStructTypes(project, new Recorder());
   return project;
 }
 
@@ -386,6 +392,7 @@ function normalizeVariables(raw: unknown): PropertyDef[] {
     const fields = normalizeStructFields(v.fields);
     const def = variableDef(key, kind, undefined, fields);
     def.default = coerceValue(def, (v.default ?? def.default) as PropertyValue);
+    if (def.kind === 'struct') readStructType(def, v.structType);
     defs.push(def);
   }
   return defs;
@@ -410,10 +417,19 @@ function normalizeStructFields(raw: unknown): StructFieldDef[] {
 function readField(key: string, f: Record<string, unknown>): StructFieldDef | null {
   const isFieldKind = (value: unknown) => (FIELD_KINDS as readonly string[]).includes(String(value));
   if (f.kind === 'list') return { key, kind: 'list' };
-  if (f.kind === 'struct') return { key, kind: 'struct', fields: normalizeStructFields(f.fields) };
+  if (f.kind === 'struct') {
+    const field: StructFieldDef = { key, kind: 'struct', fields: normalizeStructFields(f.fields) };
+    readStructType(field, f.structType);
+    return field;
+  }
   return isFieldKind(f.kind) ? { key, kind: f.kind as FieldKind } : null;
 }
 
+/** A dangling id is kept, as a curve's is: the struct keeps the fields it last had (#253). */
+function readStructType(def: { structType?: string }, raw: unknown): void {
+  if (typeof raw === 'string' && raw !== '') def.structType = raw;
+}
+
 function normalizePorts(raw: unknown, fixed: readonly string[], writable: boolean): DeclaredPort[] {
   const ports: DeclaredPort[] = [];
   const seen = new Set(fixed);

src/core/util/recorder.ts

@@ -0,0 +1,41 @@
+/**
+ * Assignments that can be taken back, last one first. For an edit whose reach is not known in
+ * advance – a Struct asset's change lands wherever its type is used (#253) – so undo does not have
+ * to know either. Only plain properties are written, so everything holding a reference to the
+ * changed objects keeps it.
+ */
+export class Recorder {
+  private readonly steps: (() => void)[] = [];
+
+  /** Writing what is already there is no step at all. */
+  set<T extends object, K extends keyof T & string>(target: T, key: K, value: T[K]): void {
+    const had = Object.hasOwn(target, key);
+    const before = target[key];
+    if (had && same(before, value)) return;
+    target[key] = value;
+    this.steps.push(() => {
+      if (had) target[key] = before;
+      else delete target[key];
+    });
+  }
+
+  delete<T extends object, K extends keyof T & string>(target: T, key: K): void {
+    if (!Object.hasOwn(target, key)) return;
+    const before = target[key];
+    delete target[key];
+    this.steps.push(() => (target[key] = before));
+  }
+
+  /** How many writes are held – a pass that leaves it alone changed nothing. */
+  get count(): number {
+    return this.steps.length;
+  }
+
+  revert(): void {
+    for (let step = this.steps.pop(); step; step = this.steps.pop()) step();
+  }
+}
+
+function same(a: unknown, b: unknown): boolean {
+  return a === b || JSON.stringify(a) === JSON.stringify(b);
+}

src/editor/actions.ts

@@ -16,6 +16,7 @@ import { RemoveNodeCommand } from '../core/commands/graphCommands';
 import { RemoveSceneObjectsCommand } from '../core/commands/sceneObjectCommands';
 import type { AssetType } from '../core/model/AssetTypes';
 import { curveUsages } from '../core/model/curve';
+import { structTypeUsages } from '../core/model/structTypes';
 import { generatesPictures } from '../core/model/generated';
 import { isTemplateContent } from '../core/model/instance';
 import type { Command } from '../core/commands/Command';
@@ -133,11 +134,14 @@ export function confirmDeleteAsset(state: EditorState, assetId: string): void {
   const animations = picture ? animationsUsing(state.project, ids).length : 0;
   const tiles = picture ? tilesUsing(state.project, ids).length : 0;
   const eased = asset.type === 'curve' ? curveUsages(state.project, assetId) : { keys: 0, nodes: 0 };
+  const typed = asset.type === 'struct' ? structTypeUsages(state.project, assetId) : { places: 0, nodes: 0 };
   const detail =
     asset.type === 'scene'
       ? `The scene and its ${asset.objects.length} object(s) are removed.`
       : eased.keys > 0 || eased.nodes > 0
         ? `${eased.keys} animation key(s) and ${eased.nodes} Lerp node(s) use it and blend linearly instead.`
+        : typed.places > 0 || typed.nodes > 0
+          ? `${typed.places} struct(s) and ${typed.nodes} Pack/Expand node(s) use it and keep its fields as their own.`
           : references > 0 || animations > 0 || tiles > 0
             ? wornDetail(references, animations, tiles, asset.type)
             : usages === 0

src/editor/inspector/assetSection.ts

@@ -21,11 +21,18 @@ import {
 import type { Command } from '../../core/commands/Command';
 import {
   type Asset,
-  type BehaviorAsset,
   isKeptVariable,
+  isVariableOwner,
   type StateMachineAsset,
+  type VariableOwnerAsset,
   type VariablesAsset,
 } from '../../core/model/Asset';
+import {
+  MakeStructTypeCommand,
+  SetStructTypeCommand,
+  WithStructTypes,
+} from '../../core/commands/structTypeCommands';
+import { containsType, type FieldRename, structAssetOf } from '../../core/model/structTypes';
 import { findAsset, type Project } from '../../core/model/Project';
 import type { PropertyBag, PropertyValue } from '../../core/model/Properties';
 import { readScope, readSharedScope, type Scope, scopeOf, sharedScopeOf } from '../../core/model/Scope';
@@ -38,7 +45,7 @@ import {
 } from '../../core/properties/PropertySchema';
 import { markedAssetSchema } from '../../core/properties/deviation';
 import { isModified, resolveAssetProps } from '../../core/properties/resolve';
-import { Button, Dropdown, HStack, Label, Menu, Theme } from '../../ui';
+import { Button, Dropdown, HStack, Label, Menu, type MenuEntry, Theme } from '../../ui';
 import { FontPreview } from '../font/FontPreview';
 import { clearSaved, hasSaved } from '../saves';
 import { SoundPreview } from '../sound/SoundPreview';
@@ -47,7 +54,7 @@ import { aspectActions, sizeCommand } from './aspectAction';
 import { actionIf, createFieldRow, type FieldHandlers } from './fieldFactory';
 import { addNameField, addNote, addTitle, type InspectorHost } from './host';
 import { buildShapeListSection, shapeListSignature } from './shapeSection';
-import { buildVariable, kindMenu, type VariableEditing } from './variableRows';
+import { buildVariable, kindMenu, type StructTyping, type VariableEditing } from './variableRows';
 import { listSource, previewingHandlers, structFields } from './previewHandlers';
 import { assetValue } from './valueSpecs';
 
@@ -73,13 +80,27 @@ export function assetSignature(project: Project, assetId: string): string {
   const shapes = asset.type === 'vectorart' ? `|${shapeListSignature(asset)}` : '';
   const values = resolveAssetProps(project, asset);
   const rows = schemaForAsset(project, asset).filter((def) => isRowShown(def, values));
-  return rows.map(defSignature).join(',') + machine + kept + keeps + shapes;
+  // A Type row shows the name of its Struct asset, or "Own fields" once that asset is gone (#253).
+  const types = `|types:${typeNames(project, rows)}`;
+  return rows.map(defSignature).join(',') + machine + kept + keeps + shapes + types;
+}
+
+function typeNames(project: Project, rows: readonly (PropertyDef | StructFieldDef)[]): string {
+  return rows
+    .flatMap((def): string[] =>
+      def.kind === 'struct'
+        ? [structAssetOf(project, def.structType)?.name ?? '', typeNames(project, def.fields)]
+        : [],
+    )
+    .join(',');
 }
 
 export function defSignature(def: PropertyDef | StructFieldDef): string {
   // Only a struct has rows of its own, at any depth; a list's items rebuild themselves (#252).
   const fields = def.kind === 'struct' ? def.fields.map(defSignature).join('+') : '';
-  return `${def.key}:${def.kind}${fields ? `(${fields})` : ''}`;
+  // A type decides which of those rows may be changed, and names itself in a row (#253).
+  const type = def.kind === 'struct' && def.structType ? `@${def.structType}` : '';
+  return `${def.key}:${def.kind}${type}${fields ? `(${fields})` : ''}`;
 }
 
 /** Name, properties (asset values marked when they differ from the default) and, for behaviors, the variables. */
@@ -95,7 +116,7 @@ export function buildAssetSection(host: InspectorHost, assetId: string): void {
   });
 
   buildProps(host, asset, markedAssetSchema(host.state.project, asset));
-  if (asset.type === 'behavior' || asset.type === 'variables') buildVariables(host, asset);
+  if (isVariableOwner(asset)) buildVariables(host, asset);
   if (asset.type === 'variables') {
     buildVariablesScope(host, asset);
     buildPersistence(host, asset);
@@ -196,21 +217,21 @@ function fieldsAt(fields: readonly StructFieldDef[], path: readonly string[]): r
 
 /**
  * Declared variables, each with its declaration editable – plus an "add" menu, and in the inspector
- * the way to the same rows in a Variables tab (#252).
+ * the way to the same rows in a Variables tab (#252). A Struct asset's fields are declared the same
+ * way (#253); every change to them is carried on to the places of that type.
  */
-export function buildVariables(
+export function buildVariables(host: InspectorHost, asset: VariableOwnerAsset, inTab = false): void {
-  host: InspectorHost,
+  const isType = asset.type === 'struct';
-  asset: BehaviorAsset | VariablesAsset,
-  inTab = false,
-): void {
   const header = new HStack({ gap: Theme.gap, align: 'center' });
-  header.add(new Label('VARIABLES', { style: 'title' }), 1);
+  header.add(new Label(isType ? 'FIELDS' : 'VARIABLES', { style: 'title' }), 1);
-  const add = new Dropdown('+ Variable', { variant: 'ghost' });
+  const add = new Dropdown(isType ? '+ Field' : '+ Variable', { variant: 'ghost' });
+  const run = (command: Command, rename?: FieldRename): void =>
+    void host.state.execute(isType ? new WithStructTypes(command, rename) : command);
   add.onClick = () => {
     const items = kindMenu(VARIABLE_KINDS, (kind) => {
       const current = findAsset(host.state.project, asset.id);
-      if (current?.type === 'behavior' || current?.type === 'variables')
+      if (isVariableOwner(current))
-        host.state.execute(new AddVariableCommand(asset.id, nextVariableName(current), kind));
+        run(new AddVariableCommand(asset.id, nextVariableName(current, isType ? 'field' : 'var'), kind));
     });
     new Menu(items).openBelow(add);
   };
@@ -218,15 +239,19 @@ export function buildVariables(
   if (!inTab) header.add(openVariablesButton(host, { kind: 'asset', assetId: asset.id }));
   host.body.add(header);
 
-  if (asset.variables.length === 0) addNote(host, 'No variables yet.');
+  if (asset.variables.length === 0) addNote(host, isType ? 'No fields yet.' : 'No variables yet.');
   const values = shownValues(host, asset);
-  const run = (command: Command): void => void host.state.execute(command);
+  const renamed = (path: readonly string[], from: string, to: string): FieldRename | undefined =>
+    isType ? { structType: asset.id, path, from, to } : undefined;
   for (const def of asset.variables) {
     const edit: VariableEditing = {
-      rename: (next) => run(new RenameVariableCommand(asset.id, def.key, next)),
+      rename: (next) => run(new RenameVariableCommand(asset.id, def.key, next), renamed([], def.key, next)),
       remove: () => run(new RemoveVariableCommand(asset.id, def.key)),
       renameField: (path, field, next) =>
-        run(new RenameStructFieldCommand(asset.id, def.key, field.key, next, path)),
+        run(
+          new RenameStructFieldCommand(asset.id, def.key, field.key, next, path),
+          renamed([def.key, ...path], field.key, next),
+        ),
       removeField: (path, field) => run(new RemoveStructFieldCommand(asset.id, def.key, field.key, path)),
       addField: (path, kind) =>
         run(
@@ -246,13 +271,49 @@ export function buildVariables(
           }
         : undefined;
     const value = values[def.key] ?? def.default;
+    const typing = structTyping(host, asset, def.key);
     host.fields.set(
       def.key,
-      buildVariable(host, def, value, assetHandlers(host, asset.id, def), { edit, keep }),
+      buildVariable(host, def, value, assetHandlers(host, asset.id, def), { edit, typing, keep }),
     );
   }
 }
 
+/**
+ * The type picker of a struct variable and of its struct fields (#253): own fields, a Struct asset,
+ * or a new Struct asset made from the fields it holds now. Inside a Struct asset the types that
+ * hold that asset are not offered – the default of such a field would never end.
+ */
+function structTyping(host: InspectorHost, owner: VariableOwnerAsset, key: string): StructTyping {
+  const project = () => host.state.project;
+  const run = (command: Command): void => void host.state.execute(command);
+  return {
+    typeName: (structType) => structAssetOf(project(), structType)?.name ?? null,
+    menu: (path, structType) => {
+      const current = structAssetOf(project(), structType);
+      const target = { kind: 'variable', ownerId: owner.id, key, path } as const;
+      const types = project().assets.filter(
+        (a) => a.type === 'struct' && !(owner.type === 'struct' && containsType(project(), a.id, owner.id)),
+      );
+      const entries: MenuEntry[] = [
+        { label: 'Own fields', current: !current, onSelect: () => run(new SetStructTypeCommand(target, '')) },
+        ...types.map((type) => ({
+          label: type.name,
+          current: type.id === current?.id,
+          onSelect: () => run(new SetStructTypeCommand(target, type.id)),
+        })),
+        { separator: true },
+        {
+          label: 'Make struct type',
+          disabled: current !== undefined,
+          onSelect: () => run(new MakeStructTypeCommand(owner.id, key, path)),
+        },
+      ];
+      return entries;
+    },
+  };
+}
+
 /** Opens the variables of `owner` in a Variables tab of their own, or brings up the one they have. */
 export function openVariablesButton(host: InspectorHost, owner: VariablesOwner): Button {
   return new Button('Open', {

src/editor/inspector/nodeSection.ts

@@ -18,13 +18,17 @@ import {
   resolveDef,
   STATE_TRANSITION,
   stateName,
+  STRUCT_TYPE_PARAM,
+  STRUCT_TYPE_SETTING,
   TRANSITION_PARAM,
   variablesSourceOf,
 } from '../../core/graph';
 import type { GraphAsset } from '../../core/model/Asset';
 import { graphLookup } from '../../core/model/graphLookup';
 import { findGraphAsset, type Project } from '../../core/model/Project';
-import { textOf } from '../../core/model/Properties';
+import { type PropertyValue, textOf } from '../../core/model/Properties';
+import { isTypedNode, nodeStructType, structAssetOf } from '../../core/model/structTypes';
+import { SetStructTypeCommand } from '../../core/commands/structTypeCommands';
 import type { PropertyDef } from '../../core/properties/PropertySchema';
 import { Label } from '../../ui';
 import { createFieldRow, type FieldHandlers } from './fieldFactory';
@@ -63,7 +67,8 @@ export function nodeSignature(project: Project, assetId: string, nodeId: string)
         .join(',')
     : `${textOf(node.params[TRANSITION_PARAM] ?? '')}:${textOf(node.params[MACHINE_PORT] ?? '')}`;
   // The source names which declarations the port menu offers, so switching it has to rebuild.
-  const source = variablesSourceOf(node.params);
+  const typeName = structAssetOf(project, nodeStructType(node))?.name ?? '';
+  const source = `${variablesSourceOf(node.params)}:${nodeStructType(node)}:${typeName}`;
   const choices = variableChoices(project, assetId, node)
     .map((v) => v.key)
     .join(',');
@@ -94,25 +99,34 @@ export function buildNodeSection(host: InspectorHost, assetId: string, nodeId: s
   addNote(host, def.description);
   const problem = callProblem(node, graphLookup(host.state.project), assetId);
   if (problem) addNote(host, problem, 'warning');
-  const addSetting = (param: PropertyDef) => {
+  const addSetting = (param: PropertyDef, handlers = paramHandlers(host, assetId, nodeId, param)) => {
-    const row = createFieldRow(
+    const row = createFieldRow(host, param, node.params[param.key] ?? param.default, handlers);
-      host,
-      param,
-      node.params[param.key] ?? param.default,
-      paramHandlers(host, assetId, nodeId, param),
-    );
     host.fields.set(`param:${param.key}`, row);
     host.body.add(row.row);
   };
   // Both draw their settings inside the port section: a setting decides what the menu offers.
   const ownSettings = declaresPropertyPorts(node.type) || declaresVariablePorts(node.type);
+  // The type of a Pack/Expand decides its fields (#253), so it stands above them – and picking one
+  // rewrites the ports, which a plain param edit would not.
+  const typed = isTypedNode(node);
+  if (typed) {
+    const pick = (value: PropertyValue) => {
+      const target = { kind: 'node', assetId, nodeId } as const;
+      host.state.execute(new SetStructTypeCommand(target, textOf(value)));
+    };
+    addSetting(STRUCT_TYPE_SETTING, { onInput: () => {}, onChange: pick });
+  }
   if (declaresVariablePorts(node.type)) buildVariablePortSection(host, assetId, node, addSetting);
   else if (ownSettings) buildPropertyPortSection(host, assetId, node, addSetting);
-  else if (def.declaresPorts) buildPortSection(host, assetId, node, variablesOf(asset));
+  else if (def.declaresPorts) {
+    const typeName = structAssetOf(host.state.project, nodeStructType(node))?.name ?? null;
+    buildPortSection(host, assetId, node, variablesOf(asset), typeName);
+  }
 
-  if (!ownSettings && def.params.length > 0) {
+  const settings = def.params.filter((param) => !(typed && param.key === STRUCT_TYPE_PARAM));
+  if (!ownSettings && settings.length > 0) {
     addTitle(host, 'SETTINGS');
-    for (const param of def.params) {
+    for (const param of settings) {
       if (param.key === TRANSITION_PARAM && node.type === STATE_TRANSITION)
         buildTransitionPicker(host, assetId, node, asset.graph);
       else addSetting(param);

src/editor/inspector/portSection.ts

@@ -202,6 +202,7 @@ export function buildPortSection(
   assetId: string,
   node: GraphNode,
   variables: readonly PropertyDef[] = [],
+  typeName: string | null = null,
 ): void {
   const onStart = node.type === BEHAVIOR_START;
   const noun = isTerminalNode(node) ? (onStart ? 'Input' : 'Output') : 'Field';
@@ -209,6 +210,19 @@ export function buildPortSection(
 
   const header = new HStack({ gap: Theme.gap, align: 'center' });
   header.add(new Label(`${noun.toUpperCase()}S`, { style: 'title' }), 1);
+  // With a Struct asset as its type the fields are that asset's (#253): changed there, not here.
+  if (typeName !== null) {
+    host.body.add(header);
+    addNote(host, `The fields of ${typeName}. Change them there.`, 'small');
+    for (const port of node.ports ?? []) {
+      const row = new HStack({ gap: Theme.gap, align: 'center' });
+      row.minHeight = Theme.rowHeight;
+      row.add(markLabel(port.kind));
+      row.add(new Label(port.key, { style: 'muted', width: NAME_WIDTH, padding: Theme.fieldPadding }), 1);
+      host.body.add(row);
+    }
+    return;
+  }
   if (noun === 'Field') addShapePicker(host, assetId, node, variables, header);
   const add = new Dropdown(`+ ${noun}`, { variant: 'ghost' });
   add.onClick = () => {

src/editor/inspector/variableRows.ts

@@ -8,6 +8,7 @@ import {
   Icon,
   Label,
   Menu,
+  type MenuEntry,
   type MenuItem,
   Spacer,
   TextField,
@@ -56,8 +57,19 @@ export interface VariableKeep {
   set: (on: boolean) => void;
 }
 
+/**
+ * The type of a struct (#253), offered where its declaration is edited. `path` names the struct
+ * from the variable down, as for `VariableEditing`.
+ */
+export interface StructTyping {
+  /** The Struct asset the struct follows, or null while it holds its own fields – a deleted type too. */
+  typeName: (structType: string | undefined) => string | null;
+  menu: (path: readonly string[], structType: string | undefined) => MenuEntry[];
+}
+
 export interface VariableOptions {
   edit?: VariableEditing;
+  typing?: StructTyping;
   keep?: VariableKeep;
   /** ↺/↑ on the first row: an override covers a whole struct, so its fields share them. */
   actions?: RowActions;
@@ -74,14 +86,16 @@ export function buildVariable(
   handlers: FieldHandlers,
   options: VariableOptions = {},
 ): FieldRow {
-  const { edit, keep, actions } = options;
+  const { edit, typing, keep, actions } = options;
   const name = nameCell(def.key, 0, edit && ((next) => edit.rename(next)));
   const head = gridRow(0, markLabel(def.kind), name);
   let setValue: (next: PropertyValue) => void = () => {};
   let below: Widget | undefined;
+  // A struct with a type has the type's fields: they are changed on the Struct asset, not here.
+  const typed = def.kind === 'struct' ? (typing?.typeName(def.structType) ?? null) : null;
   if (def.kind === 'struct') {
     head.add(new Spacer(), 1);
-    if (edit) head.add(addFieldMenu(edit, []));
+    if (edit && typed === null) head.add(addFieldMenu(edit, []));
   } else {
     const field = createField(host, def, value, handlers);
     setValue = addValue(head, field);
@@ -94,8 +108,18 @@ export function buildVariable(
   if (below) host.body.add(indentedBy(below, 1));
 
   if (def.kind === 'struct') {
+    if (typing) host.body.add(typeRow(1, typed, () => typing.menu([], def.structType)));
     if (def.fields.length === 0) addNote(host, 'No fields yet.', 'small');
-    setValue = structFieldRows(host, def.fields, [], value, handlers, edit);
+    const own = typed === null;
+    setValue = structFieldRows(
+      host,
+      def.fields,
+      [],
+      value,
+      handlers,
+      own ? edit : undefined,
+      own ? typing : undefined,
+    );
   }
 
   return {
@@ -132,17 +156,33 @@ function structFieldRows(
   value: PropertyValue,
   handlers: FieldHandlers,
   edit: VariableEditing | undefined,
+  typing: StructTyping | undefined,
 ): (next: PropertyValue) => void {
   const setters = new Map<string, (item: PropertyValue) => void>();
   for (const field of fields) {
     const row = fieldRow(field, path, edit);
     const item = structFieldValue(value, field);
     if (field.kind === 'struct') {
+      const inner = [...path, field.key];
+      const typed = typing?.typeName(field.structType) ?? null;
       row.add(new Spacer(), 1);
-      if (edit) row.add(addFieldMenu(edit, [...path, field.key]));
+      if (edit && typed === null) row.add(addFieldMenu(edit, inner));
       if (edit) row.add(removeButton(() => edit.removeField(path, field)));
       host.body.add(row);
-      setters.set(field.key, structFieldRows(host, field.fields, [...path, field.key], item, handlers, edit));
+      if (typing) host.body.add(typeRow(inner.length + 1, typed, () => typing.menu(inner, field.structType)));
+      const own = typed === null;
+      setters.set(
+        field.key,
+        structFieldRows(
+          host,
+          field.fields,
+          inner,
+          item,
+          handlers,
+          own ? edit : undefined,
+          own ? typing : undefined,
+        ),
+      );
       continue;
     }
     const own = handlers.structFieldHandlers?.([...path, field.key], field) ?? READ_ONLY;
@@ -163,6 +203,16 @@ function fieldRow(field: StructFieldDef, path: readonly string[], edit: Variable
   return gridRow(depth, markLabel(field.kind), name);
 }
 
+/** Which Struct asset a struct follows, as a row of its own under the struct's head. */
+function typeRow(depth: number, typeName: string | null, menu: () => MenuEntry[]): HStack {
+  const picker = new Dropdown(typeName ?? 'Own fields', { variant: 'ghost' });
+  picker.onClick = () => new Menu(menu()).openBelow(picker);
+  const name = new Label('Type', { style: 'muted', width: nameWidth(depth), padding: Theme.fieldPadding });
+  const row = gridRow(depth, new Spacer(MARK_WIDTH), name);
+  row.add(picker, 1);
+  return row;
+}
+
 /** Indent, mark and name – sized so that whatever follows starts on the value column at any depth. */
 function gridRow(depth: number, mark: Widget, name: Widget): HStack {
   const row = new HStack({ gap: Theme.gap, align: 'center' });

src/editor/panels/assetGroups.ts

@@ -12,6 +12,7 @@ export const ASSET_GROUP_LABELS: Record<AssetType, string> = {
   text: 'Texts',
   behavior: 'Behaviors',
   variables: 'Variables',
+  struct: 'Structs',
   collider: 'Colliders',
   rigidbody: 'Rigidbodies',
   container: 'Containers',

src/editor/panels/assetIcons.ts

@@ -23,6 +23,7 @@ import shader from './icons/shader.svg?raw';
 import sound from './icons/sound.svg?raw';
 import sprite from './icons/sprite.svg?raw';
 import statemachine from './icons/statemachine.svg?raw';
+import struct from './icons/struct.svg?raw';
 import text from './icons/text.svg?raw';
 import texture from './icons/texture.svg?raw';
 import tile from './icons/tile.svg?raw';
@@ -48,6 +49,7 @@ export const ASSET_ICON_SVG: Record<AssetType, string> = {
   sound,
   sprite,
   statemachine,
+  struct,
   text,
   texture,
   tile,

src/editor/panels/icons/struct.svg

@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="-8 -8 16 16" width="16" height="16">
+  <!-- A record: a box of rows, one per field, each a name and its value. -->
+  <rect x="-6.5" y="-6.5" width="13" height="13" rx="1.5" fill="none" stroke="currentColor" stroke-width="1.25" />
+  <path d="M-6.5 -2.2 L6.5 -2.2 M-6.5 2.2 L6.5 2.2 M-1 -6.5 L-1 6.5" fill="none" stroke="currentColor" stroke-width="1" />
+  <circle cx="-3.8" cy="-4.35" r="0.9" fill="currentColor" />
+  <circle cx="-3.8" cy="0" r="0.9" fill="currentColor" />
+  <circle cx="-3.8" cy="4.35" r="0.9" fill="currentColor" />
+</svg>

src/editor/variables/VariablesEditor.ts

@@ -4,6 +4,7 @@
  * One editor for every such tab, pointed at the target of the one showing, like the asset editors.
  */
 import type { Container } from 'pixi.js';
+import { isVariableOwner } from '../../core/model/Asset';
 import { findObject } from '../../core/model/hierarchy';
 import { findAsset } from '../../core/model/Project';
 import { Label, ScrollContainer, Theme, ui, VStack, HStack } from '../../ui';
@@ -20,7 +21,7 @@ function ownerOf(state: EditorState, target: Extract<ValuesTarget, { kind: 'vari
   const { owner } = target;
   if (owner.kind === 'asset') {
     const asset = findAsset(state.project, owner.assetId);
-    return asset?.type === 'behavior' || asset?.type === 'variables' ? { asset, name: asset.name } : null;
+    return isVariableOwner(asset) ? { asset, name: asset.name } : null;
   }
   const view = viewOf(state.project, owner.holderId);
   const object = view && findObject(view, owner.objectId);
@@ -32,7 +33,8 @@ function ownerOf(state: EditorState, target: Extract<ValuesTarget, { kind: 'vari
 export function valuesTitle(state: EditorState, target: ValuesTarget, live?: LiveVariables): string | null {
   if (target.kind === 'list') return resolveList(state, target.slot, live)?.title ?? null;
   const owner = ownerOf(state, target);
-  return owner ? `${owner.name} · Variables` : null;
+  if (!owner) return null;
+  return `${owner.name} · ${owner.asset.type === 'struct' ? 'Fields' : 'Variables'}`;
 }
 
 export class VariablesEditor extends VStack {

tests/core/struct-types.test.ts

@@ -0,0 +1,356 @@
+/**
+ * Struct assets as types (#253): a struct variable, a struct field or a `Pack`/`Expand` naming one
+ * takes on its fields, and every change to the asset reaches all of them – values, overrides,
+ * ports and edges – as one undo step.
+ */
+import { describe, expect, it } from 'vitest';
+import {
+  CreateAssetCommand,
+  DeleteAssetCommand,
+  SetAssetPropertyCommand,
+} from '../../src/core/commands/assetCommands';
+import { SetOverrideCommand } from '../../src/core/commands/sceneObjectCommands';
+import {
+  MakeStructTypeCommand,
+  SetStructTypeCommand,
+  WithStructTypes,
+} from '../../src/core/commands/structTypeCommands';
+import {
+  AddStructFieldCommand,
+  AddVariableCommand,
+  RemoveVariableCommand,
+  RenameStructFieldCommand,
+  RenameVariableCommand,
+} from '../../src/core/commands/variableCommands';
+import type { Command } from '../../src/core/commands/Command';
+import { STRUCT_TYPE_PARAM } from '../../src/core/graph/nested';
+import type { BehaviorAsset, StructAsset } from '../../src/core/model/Asset';
+import { structTypeUsages, typedSites } from '../../src/core/model/structTypes';
+import type { StructDef } from '../../src/core/properties/PropertySchema';
+import { deserializeProject, serializeProject } from '../../src/core/store/serialize';
+import { graphEditor, makeBehavior, makeSpriteScene, place, type SceneFixture } from '../helpers';
+
+/** `Loot` = { Name: "Coin", Amount: 1 } */
+function lootType(f: SceneFixture): StructAsset {
+  const create = new CreateAssetCommand('struct', 'Loot');
+  f.stack.execute(create);
+  const id = create.asset.id;
+  f.stack.execute(new AddVariableCommand(id, 'Name', 'text'));
+  f.stack.execute(new AddVariableCommand(id, 'Amount', 'number'));
+  f.stack.execute(new SetAssetPropertyCommand(id, 'Name', 'Coin'));
+  f.stack.execute(new SetAssetPropertyCommand(id, 'Amount', 1));
+  return create.asset as StructAsset;
+}
+
+/** A behavior with a struct variable `drop` typed `Loot`. */
+function dropper(f: SceneFixture, loot: StructAsset): BehaviorAsset {
+  const behavior = makeBehavior(f, 'Chest');
+  f.stack.execute(new AddVariableCommand(behavior.id, 'drop', 'struct'));
+  f.stack.execute(
+    new SetStructTypeCommand({ kind: 'variable', ownerId: behavior.id, key: 'drop', path: [] }, loot.id),
+  );
+  return behavior;
+}
+
+const drop = (behavior: BehaviorAsset) => behavior.variables.find((v) => v.key === 'drop') as StructDef;
+
+/** An edit of the type's fields, carried to its users the way the inspector does it. */
+const onType = (
+  f: SceneFixture,
+  command: Command,
+  rename?: ConstructorParameters<typeof WithStructTypes>[1],
+) => f.stack.execute(new WithStructTypes(command, rename));
+
+describe('a struct typed by a Struct asset', () => {
+  it('takes on its fields and starts at its defaults', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = dropper(f, loot);
+    expect(drop(chest)).toMatchObject({
+      structType: loot.id,
+      fields: [
+        { key: 'Name', kind: 'text' },
+        { key: 'Amount', kind: 'number' },
+      ],
+    });
+    expect(chest.props.drop).toEqual({ Name: 'Coin', Amount: 1 });
+    expect(drop(chest).default).toEqual({ Name: 'Coin', Amount: 1 });
+  });
+
+  it('gets a field added to the type, at the default the type declares', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = dropper(f, loot);
+    onType(f, new AddVariableCommand(loot.id, 'Rare', 'boolean'));
+    expect(drop(chest).fields.map((x) => x.key)).toEqual(['Name', 'Amount', 'Rare']);
+    expect(chest.props.drop).toEqual({ Name: 'Coin', Amount: 1, Rare: false });
+  });
+
+  it('loses a field removed from the type, and gets it back with one undo', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = dropper(f, loot);
+    f.stack.execute(new SetAssetPropertyCommand(chest.id, 'drop', { Name: 'Gem', Amount: 7 }));
+    onType(f, new RemoveVariableCommand(loot.id, 'Amount'));
+    expect(chest.props.drop).toEqual({ Name: 'Gem' });
+    expect(drop(chest).fields.map((x) => x.key)).toEqual(['Name']);
+    f.stack.undo();
+    expect(chest.props.drop).toEqual({ Name: 'Gem', Amount: 7 });
+    expect(drop(chest).fields.map((x) => x.key)).toEqual(['Name', 'Amount']);
+  });
+
+  it('keeps every value of a renamed field: the own one, the default and the override', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = dropper(f, loot);
+    f.stack.execute(new SetAssetPropertyCommand(chest.id, 'drop', { Name: 'Gem', Amount: 7 }));
+    const placed = place(f, chest.id, { x: 0, y: 0 });
+    f.stack.execute(new SetOverrideCommand(f.sceneId, placed, 'drop', { Name: 'Ruby', Amount: 3 }));
+    onType(f, new RenameVariableCommand(loot.id, 'Amount', 'Count'), {
+      structType: loot.id,
+      path: [],
+      from: 'Amount',
+      to: 'Count',
+    });
+    expect(chest.props.drop).toEqual({ Name: 'Gem', Count: 7 });
+    expect(f.object(placed).overrides.drop).toEqual({ Name: 'Ruby', Count: 3 });
+    expect(loot.props).toEqual({ Name: 'Coin', Count: 1 });
+    f.stack.undo();
+    expect(chest.props.drop).toEqual({ Name: 'Gem', Amount: 7 });
+    expect(f.object(placed).overrides.drop).toEqual({ Name: 'Ruby', Amount: 3 });
+  });
+
+  it('keeps the values that fit when a struct is given a type', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = makeBehavior(f, 'Chest');
+    f.stack.execute(new AddVariableCommand(chest.id, 'drop', 'struct'));
+    f.stack.execute(new AddStructFieldCommand(chest.id, 'drop', { key: 'Name', kind: 'text' }));
+    f.stack.execute(new AddStructFieldCommand(chest.id, 'drop', { key: 'Old', kind: 'number' }));
+    f.stack.execute(new SetAssetPropertyCommand(chest.id, 'drop', { Name: 'Gem', Old: 4 }));
+    f.stack.execute(
+      new SetStructTypeCommand({ kind: 'variable', ownerId: chest.id, key: 'drop', path: [] }, loot.id),
+    );
+    expect(chest.props.drop).toEqual({ Name: 'Gem', Amount: 1 });
+    f.stack.undo();
+    expect(chest.props.drop).toEqual({ Name: 'Gem', Old: 4 });
+    expect(drop(chest).fields.map((x) => x.key)).toEqual(['Name', 'Old']);
+    expect(drop(chest).structType).toBeUndefined();
+  });
+
+  it('types a struct field deep inside a variable, and renames reach it there', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = makeBehavior(f, 'Chest');
+    f.stack.execute(new AddVariableCommand(chest.id, 'room', 'struct'));
+    f.stack.execute(
+      new AddStructFieldCommand(chest.id, 'room', { key: 'prize', kind: 'struct', fields: [] }),
+    );
+    f.stack.execute(
+      new SetStructTypeCommand(
+        { kind: 'variable', ownerId: chest.id, key: 'room', path: ['prize'] },
+        loot.id,
+      ),
+    );
+    expect(chest.props.room).toEqual({ prize: { Name: 'Coin', Amount: 1 } });
+    onType(f, new RenameVariableCommand(loot.id, 'Name', 'Title'), {
+      structType: loot.id,
+      path: [],
+      from: 'Name',
+      to: 'Title',
+    });
+    expect(chest.props.room).toEqual({ prize: { Title: 'Coin', Amount: 1 } });
+  });
+
+  it('carries a type inside a type: Chest holds Loot, a rename in Loot reaches a Chest value', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chestType = new CreateAssetCommand('struct', 'ChestType');
+    f.stack.execute(chestType);
+    const chestId = chestType.asset.id;
+    f.stack.execute(new AddVariableCommand(chestId, 'inside', 'struct'));
+    f.stack.execute(
+      new SetStructTypeCommand({ kind: 'variable', ownerId: chestId, key: 'inside', path: [] }, loot.id),
+    );
+    const user = makeBehavior(f, 'User');
+    f.stack.execute(new AddVariableCommand(user.id, 'box', 'struct'));
+    f.stack.execute(
+      new SetStructTypeCommand({ kind: 'variable', ownerId: user.id, key: 'box', path: [] }, chestId),
+    );
+    expect(user.props.box).toEqual({ inside: { Name: 'Coin', Amount: 1 } });
+    f.stack.execute(new SetAssetPropertyCommand(user.id, 'box', { inside: { Name: 'Gem', Amount: 9 } }));
+    onType(f, new RenameVariableCommand(loot.id, 'Amount', 'Count'), {
+      structType: loot.id,
+      path: [],
+      from: 'Amount',
+      to: 'Count',
+    });
+    expect(user.props.box).toEqual({ inside: { Name: 'Gem', Count: 9 } });
+    onType(f, new AddVariableCommand(loot.id, 'Rare', 'boolean'));
+    expect(user.props.box).toEqual({ inside: { Name: 'Gem', Count: 9, Rare: false } });
+  });
+
+  it('renames a field of a struct field inside the type', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    onType(f, new AddVariableCommand(loot.id, 'pool', 'struct'));
+    onType(f, new AddStructFieldCommand(loot.id, 'pool', { key: 'min', kind: 'number' }));
+    const chest = dropper(f, loot);
+    f.stack.execute(
+      new SetAssetPropertyCommand(chest.id, 'drop', { Name: 'Gem', Amount: 2, pool: { min: 5 } }),
+    );
+    onType(f, new RenameStructFieldCommand(loot.id, 'pool', 'min', 'low'), {
+      structType: loot.id,
+      path: ['pool'],
+      from: 'min',
+      to: 'low',
+    });
+    expect(chest.props.drop).toEqual({ Name: 'Gem', Amount: 2, pool: { low: 5 } });
+  });
+
+  it('refuses a type that would hold itself, directly or through another type', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    f.stack.execute(new AddVariableCommand(loot.id, 'self', 'struct'));
+    expect(() =>
+      f.stack.execute(
+        new SetStructTypeCommand({ kind: 'variable', ownerId: loot.id, key: 'self', path: [] }, loot.id),
+      ),
+    ).toThrow(/cannot be a field/);
+    const bag = new CreateAssetCommand('struct', 'Bag');
+    f.stack.execute(bag);
+    f.stack.execute(new AddVariableCommand(bag.asset.id, 'loot', 'struct'));
+    f.stack.execute(
+      new SetStructTypeCommand({ kind: 'variable', ownerId: bag.asset.id, key: 'loot', path: [] }, loot.id),
+    );
+    expect(() =>
+      f.stack.execute(
+        new SetStructTypeCommand({ kind: 'variable', ownerId: loot.id, key: 'self', path: [] }, bag.asset.id),
+      ),
+    ).toThrow(/cannot be a field/);
+  });
+
+  it('keeps the last fields as its own when the type is deleted', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = dropper(f, loot);
+    expect(structTypeUsages(f.project, loot.id)).toEqual({ places: 1, nodes: 0 });
+    f.stack.execute(new DeleteAssetCommand(loot.id));
+    expect(drop(chest).fields.map((x) => x.key)).toEqual(['Name', 'Amount']);
+    expect(chest.props.drop).toEqual({ Name: 'Coin', Amount: 1 });
+    const loaded = deserializeProject(serializeProject(f.project));
+    const reloaded = loaded.assets.find((a) => a.id === chest.id) as BehaviorAsset;
+    expect(reloaded.props.drop).toEqual({ Name: 'Coin', Amount: 1 });
+  });
+
+  it('survives saving and loading, and a stale copy in a file is brought in line on load', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = dropper(f, loot);
+    const raw = serializeProject(f.project) as { assets: Record<string, unknown>[] };
+    const stored = raw.assets.find((a) => a.id === chest.id) as {
+      variables: Record<string, unknown>[];
+      props: Record<string, unknown>;
+    };
+    expect(stored.variables[0]).toMatchObject({ structType: loot.id });
+    stored.variables[0]!.fields = [{ key: 'Name', kind: 'text' }];
+    stored.props.drop = { Name: 'Gem' };
+    const loaded = deserializeProject(raw);
+    const reloaded = loaded.assets.find((a) => a.id === chest.id) as BehaviorAsset;
+    expect(reloaded.variables[0]).toMatchObject({
+      structType: loot.id,
+      fields: [{ key: 'Name' }, { key: 'Amount' }],
+    });
+    expect(reloaded.props.drop).toEqual({ Name: 'Gem', Amount: 1 });
+  });
+
+  it('makes a type out of a struct that holds its own fields, reading as it did before', () => {
+    const f = makeSpriteScene();
+    const chest = makeBehavior(f, 'Chest');
+    f.stack.execute(new AddVariableCommand(chest.id, 'drop', 'struct'));
+    f.stack.execute(new AddStructFieldCommand(chest.id, 'drop', { key: 'Name', kind: 'text' }));
+    f.stack.execute(new AddStructFieldCommand(chest.id, 'drop', { key: 'enabled', kind: 'boolean' }));
+    f.stack.execute(new SetAssetPropertyCommand(chest.id, 'drop', { Name: 'Gem', enabled: true }));
+    const make = new MakeStructTypeCommand(chest.id, 'drop', []);
+    f.stack.execute(make);
+    const type = f.project.assets.find((a) => a.id === make.assetId) as StructAsset;
+    expect(type).toMatchObject({ type: 'struct', name: 'drop', props: { Name: 'Gem', enabled: true } });
+    expect(type.variables.map((v) => `${v.key}:${v.kind}`)).toEqual(['Name:text', 'enabled:boolean']);
+    expect(drop(chest).structType).toBe(type.id);
+    expect(chest.props.drop).toEqual({ Name: 'Gem', enabled: true });
+    f.stack.undo();
+    expect(f.project.assets.some((a) => a.id === make.assetId)).toBe(false);
+    expect(drop(chest).structType).toBeUndefined();
+    f.stack.redo();
+    expect(drop(chest).structType).toBe(make.assetId);
+  });
+});
+
+describe('Pack and Expand with a type', () => {
+  it('take the fields as ports, and a rename keeps the edges and the typed-in value', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const behavior = makeBehavior(f, 'G');
+    const g = graphEditor(f, behavior);
+    const pack = g.addNode('PackStruct');
+    const expand = g.addNode('ExpandStruct');
+    f.stack.execute(
+      new SetStructTypeCommand({ kind: 'node', assetId: behavior.id, nodeId: pack.id }, loot.id),
+    );
+    f.stack.execute(
+      new SetStructTypeCommand({ kind: 'node', assetId: behavior.id, nodeId: expand.id }, loot.id),
+    );
+    expect(pack.ports).toEqual([
+      { key: 'Name', kind: 'text' },
+      { key: 'Amount', kind: 'number' },
+    ]);
+    expect(expand.params[STRUCT_TYPE_PARAM]).toBe(loot.id);
+    const log = g.addNode('Log');
+    g.connect(expand, 'Amount', log, 'message');
+    const number = g.addNode('Number');
+    g.connect(number, 'value', pack, 'Amount');
+    pack.params.Name = 'Gem';
+    onType(f, new RenameVariableCommand(loot.id, 'Amount', 'Count'), {
+      structType: loot.id,
+      path: [],
+      from: 'Amount',
+      to: 'Count',
+    });
+    expect(pack.ports?.map((p) => p.key)).toEqual(['Name', 'Count']);
+    expect(behavior.graph.edges.map((e) => `${e.from.port}>${e.to.port}`).sort()).toEqual([
+      'Count>message',
+      'value>Count',
+    ]);
+    onType(f, new RemoveVariableCommand(loot.id, 'Name'));
+    expect(pack.ports?.map((p) => p.key)).toEqual(['Count']);
+    expect(pack.params.Name).toBeUndefined();
+    f.stack.undo();
+    expect(pack.params.Name).toBe('Gem');
+    onType(f, new RemoveVariableCommand(loot.id, 'Count'));
+    expect(behavior.graph.edges).toHaveLength(0);
+    f.stack.undo();
+    expect(behavior.graph.edges).toHaveLength(2);
+  });
+});
+
+describe('typed places', () => {
+  it('are found at any depth, and a typed struct is not looked into', () => {
+    const f = makeSpriteScene();
+    const loot = lootType(f);
+    const chest = dropper(f, loot);
+    f.stack.execute(new AddVariableCommand(chest.id, 'room', 'struct'));
+    f.stack.execute(
+      new AddStructFieldCommand(chest.id, 'room', { key: 'prize', kind: 'struct', fields: [] }),
+    );
+    f.stack.execute(
+      new SetStructTypeCommand(
+        { kind: 'variable', ownerId: chest.id, key: 'room', path: ['prize'] },
+        loot.id,
+      ),
+    );
+    expect(typedSites(f.project).map((s) => [s.def.key, s.path.join('.')])).toEqual([
+      ['drop', ''],
+      ['room', 'prize'],
+    ]);
+  });
+});

tools/e2e/04-assets.mjs

@@ -94,7 +94,7 @@ export async function assets(t) {
   );
   check(
     'every asset type is offered once, each group sorted by label',
-    placeable.length + library.length === 22 &&
+    placeable.length + library.length === 23 &&
       String(placeable) === String([...placeable].sort()) &&
       String(library) === String([...library].sort()),
     JSON.stringify({ placeable, library }),
@@ -453,7 +453,7 @@ export async function assets(t) {
 async function addMenuOnRightClick(t) {
   const { check, json, shot, click, clickText, press, undo, showTab } = t;
   const addRows = (rows) =>
-    Array.isArray(rows) && rows.filter(Boolean).length === 22 && rows.includes('Sprite');
+    Array.isArray(rows) && rows.filter(Boolean).length === 23 && rows.includes('Sprite');
   const heading = await json("__gm.assetRowShown('group:scene')");
   const sceneFolded = async () =>
     !(await json('__gm.assetGroups()')).find((g) => g.type === 'scene').expanded;

tools/e2e/54-struct-types.mjs

@@ -0,0 +1,280 @@
+/**
+ * Struct assets as types (#253), with the real mouse: a Struct asset made from the + menu and its
+ * fields declared in the inspector, a behavior's struct variable typed by it, an `Expand` pointed at
+ * it through its Type setting – then a field of the asset renamed, and the new name has to show up
+ * in the variable, in a placed object's override and on the `Expand` port with its edge. "Make
+ * struct type" turns a struct's own fields into an asset; deleting the asset leaves the fields.
+ *
+ * Everything it adds carries an `st54` id or is an asset it made, and goes again at the end.
+ */
+import { MAKE_OBJECT } from './lib/scaffold.mjs';
+
+export async function structTypes(t) {
+  const {
+    check,
+    json,
+    evaluate,
+    mutate,
+    click,
+    clickText,
+    press,
+    typeText,
+    sleep,
+    settle,
+    shot,
+    select,
+    undo,
+  } = t;
+  const inOverlay = async (text) => {
+    const box = await json('__gm.overlayRect()');
+    const hits = (await json(`__gm.locateAll(${JSON.stringify(text)})`)) ?? [];
+    return (
+      hits.find((h) => h.x >= box.x && h.x <= box.x + box.w && h.y >= box.y && h.y <= box.y + box.h) ?? null
+    );
+  };
+  const press_ = async (at, what) => {
+    if (!at) throw new Error(`nothing to click: ${what}`);
+    await click(at.x, at.y);
+    await sleep(150);
+  };
+  /** A menu entry, always the last drawn: the panels behind a menu carry the same words. */
+  const pick = async (label) => press_(await json(`__gm.locate(${JSON.stringify(label)}, true)`), label);
+  /**
+   * Types into the text field showing `text`, replacing it. The rightmost hit: the inspector is the
+   * right-hand panel, and an open graph shows the same names on its ports.
+   */
+  const retype = async (text, next) => {
+    const hits = (await json(`__gm.locateAll(${JSON.stringify(text)})`)) ?? [];
+    await press_(hits.sort((a, b) => b.x - a.x)[0], text);
+    await press('a', { ctrl: true });
+    await typeText(next);
+    await press('Enter');
+    await sleep(150);
+  };
+  const asset = (id) => json(`__gm.state.project.assets.find((a) => a.id === ${JSON.stringify(id)}) ?? null`);
+  const chest = () => asset('st54-chest');
+  const variable = async (key) => (await chest()).variables.find((v) => v.key === key);
+  const override = () =>
+    json("__gm.state.activeScene.objects.find((o) => o.id === 'st54-obj')?.overrides.drop ?? null");
+  const expand = async () => (await chest()).graph.nodes.find((n) => n.id === 'st54-expand');
+  const edgeFrom = async () =>
+    (await chest()).graph.edges.find((e) => e.id === 'st54-edge')?.from.port ?? null;
+
+  // A behavior with two structs holding their own fields, an Expand and a Log in its graph, and one
+  // placed object overriding `drop`.
+  await mutate(`
+    const p = __gm.state.project;
+    const scene = __gm.state.activeScene;
+    p.assets.push({
+      id: 'st54-chest',
+      type: 'behavior',
+      name: 'Chest 54',
+      props: { enabled: true, runInEditor: false, drop: { Title: 'Gem' }, bag: { Gold: 5 } },
+      variables: [
+        { key: 'drop', label: 'drop', kind: 'struct', default: { Title: '' }, fields: [{ key: 'Title', kind: 'text' }] },
+        { key: 'bag', label: 'bag', kind: 'struct', default: { Gold: 0 }, fields: [{ key: 'Gold', kind: 'number' }] },
+      ],
+      graph: {
+        nodes: [
+          { id: 'st54-expand', type: 'ExpandStruct', x: 0, y: 0, params: {} },
+          { id: 'st54-log', type: 'Log', x: 240, y: 0, params: {} },
+        ],
+        edges: [],
+      },
+    });
+    ${MAKE_OBJECT}
+    const placed = make('st54-obj', 'st54-chest', '', 400, 'Chest 54');
+    placed.overrides = { drop: { Title: 'Ruby' } };
+    scene.objects.push(placed);
+  `);
+
+  // 54a. The + menu makes a Struct; its inspector declares fields as a Variables asset declares
+  //      variables, and each field has a default.
+  await t.showTab('scene');
+  await clickText('+');
+  const offered = (await json('__gm.menuRows()')) ?? [];
+  const entry = await inOverlay('Struct');
+  check('the + menu offers Struct', offered.includes('Struct') && Boolean(entry), JSON.stringify(offered));
+  if (!entry) return;
+  await press_(entry, 'Struct');
+  await settle();
+  const lootId = (
+    await json("__gm.state.project.assets.filter((a) => a.type === 'struct').map((a) => a.id)")
+  ).at(-1);
+  await mutate(`__gm.state.project.assets.find((a) => a.id === ${JSON.stringify(lootId)}).name = 'Loot 54'`);
+  const row = await json(`__gm.assetRow(${JSON.stringify(lootId)})`);
+  await press_(row, 'the Loot 54 row');
+  check(
+    'a new Struct selects itself and says it has no fields',
+    (await t.has('FIELDS')) && (await t.has('+ Field')) && (await t.has('No fields yet.')),
+  );
+  await clickText('+ Field');
+  await pick('Text');
+  await retype('field1', 'Title');
+  await clickText('+ Field');
+  await pick('Number');
+  await retype('field1', 'Amount');
+  await press_(await json("__gm.inspectorField('Title')"), 'Title value');
+  await typeText('Coin');
+  await press('Enter');
+  await press_(await json("__gm.inspectorField('Amount')"), 'Amount value');
+  await press('a', { ctrl: true });
+  await typeText('7');
+  await press('Enter');
+  await sleep(150);
+  const loot = await asset(lootId);
+  check(
+    '+ Field, a new name and a value give the struct its fields and their defaults',
+    JSON.stringify(loot.variables.map((v) => `${v.key}:${v.kind}`)) === '["Title:text","Amount:number"]' &&
+      JSON.stringify(loot.props) === '{"Title":"Coin","Amount":7}',
+    JSON.stringify({ variables: loot.variables.map((v) => v.key), props: loot.props }),
+  );
+  await shot('01-struct-fields');
+
+  // 54b. A struct variable picks the type under its head. It takes the type's fields, keeps what
+  //      fits of its value and cannot grow fields of its own any more.
+  await select({ kind: 'asset', assetId: 'st54-chest' });
+  await sleep(150);
+  const addsBefore = ((await json("__gm.locateAll('+ Field')")) ?? []).length;
+  const typeRows = ((await json("__gm.locateAll('Own fields')")) ?? []).sort((a, b) => a.y - b.y);
+  check(
+    'each struct variable has a Type row reading "Own fields"',
+    typeRows.length === 2,
+    JSON.stringify(typeRows),
+  );
+  await press_(typeRows[0], 'Type of drop');
+  await pick('Loot 54');
+  const drop = await variable('drop');
+  const props = (await chest()).props;
+  check(
+    'picking Loot 54 gives drop its fields, keeps "Gem" and fills Amount with the default 7',
+    drop.structType === lootId &&
+      JSON.stringify(drop.fields.map((f) => f.key)) === '["Title","Amount"]' &&
+      JSON.stringify(props.drop) === '{"Title":"Gem","Amount":7}',
+    JSON.stringify({ drop, value: props.drop }),
+  );
+  check(
+    'and the placed override takes the shape as well',
+    JSON.stringify(await override()) === '{"Title":"Ruby","Amount":7}',
+    JSON.stringify(await override()),
+  );
+  const addsAfter = ((await json("__gm.locateAll('+ Field')")) ?? []).length;
+  check(
+    'a typed struct offers no + Field, its row names the type',
+    addsBefore === 2 && addsAfter === 1 && (await t.has('Loot 54')),
+    JSON.stringify({ addsBefore, addsAfter }),
+  );
+  await shot('02-typed-variable');
+
+  // 54c. Expand's Type setting points it at the asset: its ports are the fields.
+  await select({ kind: 'node', assetId: 'st54-chest', nodeId: 'st54-expand' });
+  await sleep(150);
+  await press_(await json("__gm.inspectorField('Type')"), 'Type of Expand');
+  // The asset picker names the kind after each asset.
+  await pick('Loot 54 (struct)');
+  const ports = (await expand()).ports ?? [];
+  check(
+    'Expand with the type has one output per field, and its fields are not edited there',
+    JSON.stringify(ports.map((p) => p.key)) === '["Title","Amount"]' &&
+      (await t.has('The fields of Loot 54. Change them there.')) &&
+      !(await t.has('+ Field')),
+    JSON.stringify(ports),
+  );
+  await mutate(`
+    const graph = __gm.state.project.assets.find((a) => a.id === 'st54-chest').graph;
+    graph.edges.push({ id: 'st54-edge', from: { node: 'st54-expand', port: 'Amount' }, to: { node: 'st54-log', port: 'message' } });
+  `);
+  await shot('03-typed-expand');
+
+  // 54d. Renaming a field on the asset reaches every place of the type in one step, values kept.
+  await select({ kind: 'asset', assetId: lootId });
+  await sleep(150);
+  await retype('Amount', 'Count');
+  const renamed = {
+    fields: (await variable('drop')).fields.map((f) => f.key),
+    value: (await chest()).props.drop,
+    override: await override(),
+    ports: ((await expand()).ports ?? []).map((p) => p.key),
+    edge: await edgeFrom(),
+  };
+  check(
+    'renaming Amount to Count reaches the variable, its value, the override, the port and its edge',
+    JSON.stringify(renamed) ===
+      JSON.stringify({
+        fields: ['Title', 'Count'],
+        value: { Title: 'Gem', Count: 7 },
+        override: { Title: 'Ruby', Count: 7 },
+        ports: ['Title', 'Count'],
+        edge: 'Count',
+      }),
+    JSON.stringify(renamed),
+  );
+  await undo();
+  const back = {
+    fields: (await variable('drop')).fields.map((f) => f.key),
+    value: (await chest()).props.drop,
+    override: await override(),
+    edge: await edgeFrom(),
+  };
+  check(
+    'one undo takes the rename back everywhere',
+    JSON.stringify(back) ===
+      JSON.stringify({
+        fields: ['Title', 'Amount'],
+        value: { Title: 'Gem', Amount: 7 },
+        override: { Title: 'Ruby', Amount: 7 },
+        edge: 'Amount',
+      }),
+    JSON.stringify(back),
+  );
+
+  // 54e. "Make struct type" turns the fields bag holds by itself into a Struct asset.
+  await select({ kind: 'asset', assetId: 'st54-chest' });
+  await sleep(150);
+  await press_(await json("__gm.locate('Own fields')"), 'Type of bag');
+  await pick('Make struct type');
+  const bag = await variable('bag');
+  const made = await asset(bag.structType ?? '');
+  check(
+    'Make struct type makes a Struct asset of bag, its value becoming the defaults',
+    made?.type === 'struct' &&
+      made.name === 'bag' &&
+      JSON.stringify(made.props) === '{"Gold":5}' &&
+      JSON.stringify((await chest()).props.bag) === '{"Gold":5}',
+    JSON.stringify({ bag, made }),
+  );
+
+  // 54f. Deleting the type asks first and says what happens; the places keep the fields.
+  const lootRow = await json(`__gm.assetRow(${JSON.stringify(lootId)})`);
+  await click(lootRow.x, lootRow.y, 'right');
+  await sleep(150);
+  await pick('Delete…');
+  const detail = '1 struct(s) and 1 Pack/Expand node(s) use it and keep its fields as their own.';
+  check('the delete dialog counts the places using the type', await t.has(detail));
+  await shot('04-delete-dialog');
+  await pick('Delete');
+  const kept = await variable('drop');
+  check(
+    'after deleting, drop keeps Title and Amount and its value',
+    (await asset(lootId)) === null &&
+      JSON.stringify(kept.fields.map((f) => f.key)) === '["Title","Amount"]' &&
+      JSON.stringify((await chest()).props.drop) === '{"Title":"Gem","Amount":7}',
+    JSON.stringify(kept),
+  );
+  await select({ kind: 'asset', assetId: 'st54-chest' });
+  await sleep(150);
+  check(
+    'and its Type row reads "Own fields" again, with + Field back',
+    ((await json("__gm.locateAll('+ Field')")) ?? []).length === 1 && (await t.has('Own fields')),
+  );
+
+  // Clean up.
+  await evaluate('__gm.state.select(null)');
+  await mutate(`
+    const p = __gm.state.project;
+    const scene = __gm.state.activeScene;
+    scene.objects = scene.objects.filter((o) => o.id !== 'st54-obj');
+    const made = ${JSON.stringify(made?.id ?? '')};
+    p.assets = p.assets.filter((a) => a.id !== 'st54-chest' && a.id !== made && a.id !== ${JSON.stringify(lootId)});
+  `);
+}

tools/e2e/index.mjs

@@ -56,6 +56,7 @@ import { snapshots } from './50-snapshots.mjs';
 import { clipboard } from './51-clipboard.mjs';
 import { hierarchyGroups } from './52-hierarchy-groups.mjs';
 import { curves } from './53-curves.mjs';
+import { structTypes } from './54-struct-types.mjs';
 
 export const STEPS = [
   hierarchy,
@@ -111,4 +112,5 @@ export const STEPS = [
   clipboard,
   hierarchyGroups,
   curves,
+  structTypes,
 ];