Let a node work out its own ports

Ports that vary per node already existed, but only for the three nested-behavior
types, and the rule for them sat as a switch on type names in nested.ts – the
one place in the project that knew node types by name. It dissolves into two
optional contracts on NodeDef, so a type carries its own rule:

  declaresPorts  the node holds an editable list, shown as a section in the
                 inspector – behavior start/end, and now Pack/Expand
  derivePorts    the node computes them from its settings – Sequence from a
                 count, Run behavior from the behavior it names

Sequence gains an Outputs setting (2 to 26). Its keys stay a, b, c and count on
with d, e, so the edges of the sequences already out there survive.

A param can now take a port away, and the edge on it would stay: it draws as
nothing yet survives every save, and comes back to life if the port returns.
SetNodeParamCommand takes those edges with it, which also closes the same leak
that switching a Run behavior node's target has always had.

The port editor addresses its node by id rather than by type, so two Pack nodes
can live in one graph, and it calls the rows Fields when they are not a
behavior's signature.

src/core/commands/graphCommands.ts

@@ -114,8 +114,15 @@ export class MoveNodeCommand implements Command {
   }
 }
 
-/** Sets a node param or the inline value of an unconnected data input. */
+/**
+ * Sets a node param or the inline value of an unconnected data input. A param can decide how many
+ * ports the node has, so this takes the edges of ports the new value does away with: an edge on a
+ * port that is gone draws as nothing but survives every save, and comes back to life if the port
+ * ever returns.
+ */
 export class SetNodeParamCommand extends SetBagValueCommand<GraphNode> {
+  private orphans: Removed<GraphEdge>[] = [];
+
   constructor(
     private readonly assetId: string,
     private readonly nodeId: string,
@@ -125,6 +132,27 @@ export class SetNodeParamCommand extends SetBagValueCommand<GraphNode> {
     super(key, `Set ${key}`);
   }
 
+  override execute(project: Project): void {
+    super.execute(project);
+    const graph = requireBehavior(project, this.assetId).graph;
+    const node = requireNode(project, this.assetId, this.nodeId);
+    const def = resolveDef(node, behaviorLookup(project));
+    if (!def) return;
+    const outputs = new Set(def.outputs.map((p) => p.key));
+    const inputs = new Set(def.inputs.map((p) => p.key));
+    this.orphans = removeWhere(
+      graph.edges,
+      (e) =>
+        (e.from.node === this.nodeId && !outputs.has(e.from.port)) ||
+        (e.to.node === this.nodeId && !inputs.has(e.to.port)),
+    );
+  }
+
+  override undo(project: Project): void {
+    super.undo(project);
+    restoreAt(requireBehavior(project, this.assetId).graph.edges, this.orphans);
+  }
+
   protected override resolveTarget(project: Project): GraphNode {
     return requireNode(project, this.assetId, this.nodeId);
   }

src/core/commands/portCommands.ts

@@ -2,12 +2,14 @@ import {
   BEHAVIOR_PARAM,
   BEHAVIOR_START,
   type DeclaredPort,
+  findNode,
   type Graph,
   type GraphEdge,
   type GraphNode,
+  isTerminalNode,
   isValidPortName,
+  requireNodeDef,
   RUN_BEHAVIOR,
-  terminalNode,
 } from '../graph';
 import type { PropertyValue } from '../model/Properties';
 import type { Project } from '../model/Project';
@@ -15,7 +17,6 @@ import { type Removed, removeFirst, removeWhere, restoreAt } from '../util/list'
 import { type Command, CommandError } from './Command';
 import { requireBehavior } from './require';
 
-/** Where a declared port shows up: on the terminal node itself, and on every node calling it. */
 interface PortSite {
   graph: Graph;
   nodeId: string;
@@ -24,20 +25,20 @@ interface PortSite {
 }
 
 /**
- * A start node's port is an output there and an input on the calling node; an end node's port the
- * other way round. Every site has to be kept in step, or an edge would hang on a port that is gone.
+ * Where a change to `node`'s declaration has to be mirrored. For most nodes that is the node
+ * itself. A behavior's terminal is the exception: its ports are also ports of every node calling
+ * the behavior – facing the other way, because what a start node hands out the caller passes in.
  */
-function portSites(project: Project, assetId: string, terminalType: string): PortSite[] {
+function portSites(project: Project, assetId: string, node: GraphNode): PortSite[] {
   const asset = requireBehavior(project, assetId);
-  const sites: PortSite[] = [];
-  const terminal = terminalNode(asset.graph, terminalType);
-  const onStart = terminalType === BEHAVIOR_START;
-  if (terminal) sites.push({ graph: asset.graph, nodeId: terminal.id, asInput: !onStart });
+  const asInput = requireNodeDef(node.type).declaresPorts === 'inputs';
+  const sites: PortSite[] = [{ graph: asset.graph, nodeId: node.id, asInput }];
+  if (!isTerminalNode(node)) return sites;
   for (const other of project.assets) {
     if (other.type !== 'behavior') continue;
-    for (const node of other.graph.nodes) {
-      if (node.type !== RUN_BEHAVIOR || node.params[BEHAVIOR_PARAM] !== assetId) continue;
-      sites.push({ graph: other.graph, nodeId: node.id, asInput: onStart });
+    for (const caller of other.graph.nodes) {
+      if (caller.type !== RUN_BEHAVIOR || caller.params[BEHAVIOR_PARAM] !== assetId) continue;
+      sites.push({ graph: other.graph, nodeId: caller.id, asInput: node.type === BEHAVIOR_START });
     }
   }
   return sites;
@@ -50,9 +51,10 @@ function edgesOnPort(site: PortSite, key: string): (edge: GraphEdge) => boolean
       : edge.from.node === site.nodeId && edge.from.port === key;
 }
 
-function requireTerminal(project: Project, assetId: string, terminalType: string): GraphNode {
-  const node = terminalNode(requireBehavior(project, assetId).graph, terminalType);
-  if (!node) throw new CommandError('The behavior has no start or end node');
+/** The node whose declaration is being edited; a terminal is addressed by id like any other. */
+function requirePortNode(project: Project, assetId: string, nodeId: string): GraphNode {
+  const node = findNode(requireBehavior(project, assetId).graph, nodeId);
+  if (!node) throw new CommandError(`Node ${nodeId} not found`);
   return node;
 }
 
@@ -75,14 +77,14 @@ export class AddPortCommand implements Command {
 
   constructor(
     private readonly assetId: string,
-    private readonly terminalType: string,
+    private readonly nodeId: string,
     private readonly port: DeclaredPort,
   ) {
     this.label = `Add ${port.key}`;
   }
 
   execute(project: Project): void {
-    const node = requireTerminal(project, this.assetId, this.terminalType);
+    const node = requirePortNode(project, this.assetId, this.nodeId);
     if (!isValidPortName(this.port.key)) throw new CommandError(INVALID_NAME);
     if ((node.ports ?? []).some((p) => p.key === this.port.key))
       throw new CommandError(`"${this.port.key}" already exists`);
@@ -90,7 +92,7 @@ export class AddPortCommand implements Command {
   }
 
   undo(project: Project): void {
-    const node = requireTerminal(project, this.assetId, this.terminalType);
+    const node = requirePortNode(project, this.assetId, this.nodeId);
     node.ports = (node.ports ?? []).filter((p) => p.key !== this.port.key);
   }
 }
@@ -104,15 +106,15 @@ export class RemovePortCommand implements Command {
 
   constructor(
     private readonly assetId: string,
-    private readonly terminalType: string,
+    private readonly nodeId: string,
     private readonly key: string,
   ) {
     this.label = `Remove ${key}`;
   }
 
   execute(project: Project): void {
-    const sites = portSites(project, this.assetId, this.terminalType);
-    const node = requireTerminal(project, this.assetId, this.terminalType);
+    const node = requirePortNode(project, this.assetId, this.nodeId);
+    const sites = portSites(project, this.assetId, node);
     const ports = [...(node.ports ?? [])];
     const removed = removeFirst(ports, (p) => p.key === this.key);
     if (!removed) throw new CommandError(`Port "${this.key}" not found`);
@@ -134,7 +136,7 @@ export class RemovePortCommand implements Command {
 
   undo(project: Project): void {
     if (!this.removed) return;
-    const node = requireTerminal(project, this.assetId, this.terminalType);
+    const node = requirePortNode(project, this.assetId, this.nodeId);
     const ports = [...(node.ports ?? [])];
     restoreAt(ports, [this.removed]);
     node.ports = ports;
@@ -152,7 +154,7 @@ export class RenamePortCommand implements Command {
 
   constructor(
     private readonly assetId: string,
-    private readonly terminalType: string,
+    private readonly nodeId: string,
     private readonly from: string,
     private readonly to: string,
   ) {
@@ -169,8 +171,8 @@ export class RenamePortCommand implements Command {
 
   private rename(project: Project, from: string, to: string): void {
     if (from === to) return;
-    const sites = portSites(project, this.assetId, this.terminalType);
-    const node = requireTerminal(project, this.assetId, this.terminalType);
+    const node = requirePortNode(project, this.assetId, this.nodeId);
+    const sites = portSites(project, this.assetId, node);
     if (!isValidPortName(to)) throw new CommandError(INVALID_NAME);
     const ports = node.ports ?? [];
     if (!ports.some((p) => p.key === from)) throw new CommandError(`Port "${from}" not found`);

src/core/graph/GraphInterpreter.ts

@@ -1,12 +1,6 @@
 import { edgesInto, edgesOutOf, type Graph, type GraphNode } from './Graph';
-import {
-  BEHAVIOR_END,
-  BEHAVIOR_START,
-  type BehaviorLookup,
-  NO_BEHAVIORS,
-  resolveDef,
-  terminalNode,
-} from './nested';
+import { type BehaviorLookup, NO_BEHAVIORS } from './lookup';
+import { BEHAVIOR_END, BEHAVIOR_START, resolveDef, terminalNode } from './nested';
 import type { NodeContext } from './NodeContext';
 import { type CallResult, hasExecInput, inlineValue, isEventNode, type RepeatResult } from './NodeRegistry';
 import type { Value } from './values';

src/core/graph/NodeRegistry.ts

@@ -1,6 +1,7 @@
 import type { PropertyBag, PropertyValue } from '../model/Properties';
 import type { PropertyDef } from '../properties/PropertySchema';
 import type { PortType } from './Graph';
+import type { BehaviorLookup } from './lookup';
 import type { NodeContext } from './NodeContext';
 import { asBoolean, asNumber, asString, type Value } from './values';
 
@@ -41,6 +42,19 @@ export interface RunResult {
   call?: CallResult;
 }
 
+/** What a node may compute its ports from: its own settings, and the behaviors around it. */
+export interface PortSource {
+  params: PropertyBag;
+  behaviors: BehaviorLookup;
+}
+
+/** Ports a single node has on top of the fixed ones of its type, and a label naming what it does. */
+export interface DerivedShape {
+  label?: string;
+  inputs?: PortDef[];
+  outputs?: PortDef[];
+}
+
 /** Palette, port rendering, connection validation and inspector fields are all derived from this. */
 export interface NodeDef {
   type: string;
@@ -56,6 +70,16 @@ export interface NodeDef {
    * still offers them. Without it a switched-off repeat is two rows of "0" on every key node.
    */
   hiddenParams?(params: PropertyBag): string[];
+  /**
+   * Which side the ports this node declares for itself (`GraphNode.ports`) appear on. Setting it
+   * is what gives a node the port editor in the inspector.
+   */
+  declaresPorts?: 'inputs' | 'outputs';
+  /**
+   * Ports this node computes beyond the fixed and the declared ones – how many outputs a Sequence
+   * offers, which values the behavior a call node names takes. `resolveDef` applies it.
+   */
+  derivePorts?(source: PortSource): DerivedShape;
   /**
    * Pure data nodes are evaluated on demand when a downstream input needs their value; exec nodes
    * run when the flow reaches them. Event nodes have no `run` – the interpreter seeds their outputs.

src/core/graph/dropTarget.ts

@@ -1,5 +1,6 @@
 import { edgesInto, findNode, type Graph, type PortType, portsCompatible } from './Graph';
-import { type BehaviorLookup, resolveDef } from './nested';
+import type { BehaviorLookup } from './lookup';
+import { resolveDef } from './nested';
 import type { NodeDef } from './NodeRegistry';
 
 /** One end of an edge being dragged: a port on a node, seen from its own side. */

src/core/graph/index.ts

@@ -3,6 +3,7 @@ import './nodes';
 
 export * from './dropTarget';
 export * from './Graph';
+export * from './lookup';
 export * from './nested';
 export * from './NodeContext';
 export * from './NodeRegistry';

src/core/graph/lookup.ts

@@ -0,0 +1,13 @@
+import type { PropertyBag } from '../model/Properties';
+import type { Graph } from './Graph';
+
+/** What running another behavior's graph in place needs: its nodes, its variable defaults, its name. */
+export interface BehaviorProgram {
+  name: string;
+  graph: Graph;
+  defaults: PropertyBag;
+}
+
+export type BehaviorLookup = (assetId: string) => BehaviorProgram | null;
+
+export const NO_BEHAVIORS: BehaviorLookup = () => null;

src/core/graph/nested.ts

@@ -1,5 +1,6 @@
-import { type PropertyBag, textOf } from '../model/Properties';
+import { textOf } from '../model/Properties';
 import { type DeclaredPort, declaredPortType, type Graph, type GraphNode } from './Graph';
+import type { BehaviorLookup } from './lookup';
 import { nodeDef, type NodeDef, type PortDef } from './NodeRegistry';
 
 export const BEHAVIOR_START = 'BehaviorStart';
@@ -8,17 +9,6 @@ export const RUN_BEHAVIOR = 'RunBehavior';
 
 export const BEHAVIOR_PARAM = 'behavior';
 
-/** What running another behavior's graph in place needs: its nodes, its variable defaults, its name. */
-export interface BehaviorProgram {
-  name: string;
-  graph: Graph;
-  defaults: PropertyBag;
-}
-
-export type BehaviorLookup = (assetId: string) => BehaviorProgram | null;
-
-export const NO_BEHAVIORS: BehaviorLookup = () => null;
-
 /** Identifier-like, and not `exec`: that key belongs to the fixed flow port of every terminal node. */
 export function isValidPortName(name: string): boolean {
   return /^[A-Za-z_][A-Za-z0-9_]*$/.test(name) && name !== 'exec';
@@ -37,34 +27,31 @@ export function isTerminalNode(node: GraphNode): boolean {
   return isTerminalType(node.type);
 }
 
-export function portsOf(port: DeclaredPort): PortDef {
+export function portDefOf(port: DeclaredPort): PortDef {
   return { key: port.key, label: port.key, type: declaredPortType(port.kind) };
 }
 
-function declaredOf(graph: Graph | undefined, type: string): PortDef[] {
+/** The ports the start (or end) node of `graph` declares, as seen from a node calling it. */
+export function declaredPorts(graph: Graph | undefined, type: string): PortDef[] {
   const node = graph && terminalNode(graph, type);
-  return (node?.ports ?? []).map(portsOf);
+  return (node?.ports ?? []).map(portDefOf);
 }
 
 /**
- * The node definition as it applies to *this* node. Identical to the registered one for every fixed
- * type; the three nested-behavior types grow ports from a declaration instead – the start and end
- * node from their own, the call node from those of the behavior it names.
+ * The node definition as it applies to *this* node: identical to the registered one, unless the
+ * type declares ports per node (`declaresPorts`) or computes them (`derivePorts`).
  */
 export function resolveDef(node: GraphNode, lookup: BehaviorLookup): NodeDef | undefined {
   const def = nodeDef(node.type);
-  if (!def) return undefined;
-  const own = (node.ports ?? []).map(portsOf);
-  if (node.type === BEHAVIOR_START) return { ...def, outputs: [...def.outputs, ...own] };
-  if (node.type === BEHAVIOR_END) return { ...def, inputs: [...def.inputs, ...own] };
-  if (node.type !== RUN_BEHAVIOR) return def;
-  const program = lookup(String(node.params[BEHAVIOR_PARAM] ?? ''));
+  if (!def || (!def.declaresPorts && !def.derivePorts)) return def;
+  const own = def.declaresPorts ? (node.ports ?? []).map(portDefOf) : [];
+  const side = (which: 'inputs' | 'outputs') => (def.declaresPorts === which ? own : []);
+  const grown = def.derivePorts?.({ params: node.params, behaviors: lookup }) ?? {};
   return {
     ...def,
-    // The graph reads as what it does, not as a row of identical "Run behavior" boxes.
-    label: program ? program.name : def.label,
-    inputs: [...def.inputs, ...declaredOf(program?.graph, BEHAVIOR_START)],
-    outputs: [...def.outputs, ...declaredOf(program?.graph, BEHAVIOR_END)],
+    label: grown.label ?? def.label,
+    inputs: [...def.inputs, ...side('inputs'), ...(grown.inputs ?? [])],
+    outputs: [...def.outputs, ...side('outputs'), ...(grown.outputs ?? [])],
   };
 }
 

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

@@ -0,0 +1,23 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { asStruct } from '../../values';
+import { struct } from '../shared';
+
+/**
+ * Takes a bundle apart into one output per field. The fields are declared on the node itself, the
+ * same way a behavior's start node declares what it takes – which is what makes its ports follow
+ * the shape instead of being fixed by the type.
+ */
+export const ExpandStruct: NodeDef = {
+  type: 'ExpandStruct',
+  label: 'Expand',
+  category: 'data',
+  description:
+    'Reads the fields of a struct, one output per field. A field the struct does not carry ' +
+    'reads as empty.',
+  inputs: [struct('value')],
+  outputs: [],
+  params: [],
+  declaresPorts: 'outputs',
+  // A declared output the struct has no field for is simply absent from the cache, and reads as empty.
+  run: (_ctx, inputs) => ({ outputs: { ...asStruct(inputs.value) } }),
+};

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

@@ -0,0 +1,24 @@
+import type { FieldValue } from '../../../model/Properties';
+import type { NodeDef } from '../../NodeRegistry';
+import { asField } from '../../values';
+import { struct } from '../shared';
+
+/**
+ * Bundles its declared inputs into one struct, so a group of values travels along a single edge
+ * instead of one edge per part. The counterpart of Expand.
+ */
+export const PackStruct: NodeDef = {
+  type: 'PackStruct',
+  label: 'Pack',
+  category: 'data',
+  description: 'Bundles named values into one struct, one input per field.',
+  inputs: [],
+  outputs: [struct('value')],
+  params: [],
+  declaresPorts: 'inputs',
+  run: (_ctx, inputs) => {
+    const fields: Record<string, FieldValue> = {};
+    for (const [field, value] of Object.entries(inputs)) fields[field] = asField(value);
+    return { outputs: { value: fields } };
+  },
+};

src/core/graph/nodes/flow/BehaviorEnd.ts

@@ -17,5 +17,6 @@ export const BehaviorEnd: NodeDef = {
   inputs: [exec()],
   outputs: [],
   params: [],
+  declaresPorts: 'inputs',
   run: (_ctx, inputs) => ({ outputs: inputs }),
 };

src/core/graph/nodes/flow/BehaviorStart.ts

@@ -16,4 +16,5 @@ export const BehaviorStart: NodeDef = {
   inputs: [],
   outputs: [exec()],
   params: [],
+  declaresPorts: 'outputs',
 };

src/core/graph/nodes/flow/RunBehavior.ts

@@ -1,11 +1,12 @@
 import type { NodeDef } from '../../NodeRegistry';
-import { BEHAVIOR_PARAM, RUN_BEHAVIOR } from '../../nested';
+import { textOf } from '../../../model/Properties';
+import { BEHAVIOR_END, BEHAVIOR_PARAM, BEHAVIOR_START, declaredPorts, RUN_BEHAVIOR } from '../../nested';
 import { exec } from '../shared';
 
 /**
- * Runs another behavior's graph in place, from its start node to its end node. The ports come from
- * those two nodes (see `nested.ts`); the interpreter does the call, because only it can hold a
- * second graph's pulse.
+ * Runs another behavior's graph in place, from its start node to its end node. Its ports are those
+ * the named behavior declares; the interpreter does the call, because only it can hold a second
+ * graph's pulse.
  */
 export const RunBehavior: NodeDef = {
   type: RUN_BEHAVIOR,
@@ -17,8 +18,17 @@ export const RunBehavior: NodeDef = {
   inputs: [exec()],
   outputs: [exec()],
   params: [{ key: BEHAVIOR_PARAM, label: 'Behavior', kind: 'asset', default: '', assetTypes: ['behavior'] }],
+  derivePorts: (source) => {
+    const program = source.behaviors(textOf(source.params[BEHAVIOR_PARAM] ?? ''));
+    return {
+      // The graph reads as what it does, not as a row of identical "Run behavior" boxes.
+      label: program?.name,
+      inputs: declaredPorts(program?.graph, BEHAVIOR_START),
+      outputs: declaredPorts(program?.graph, BEHAVIOR_END),
+    };
+  },
   run: (_ctx, inputs, params) => ({
-    call: { behaviorId: String(params[BEHAVIOR_PARAM] ?? ''), inputs },
+    call: { behaviorId: textOf(params[BEHAVIOR_PARAM] ?? ''), inputs },
     next: 'exec',
   }),
 };

src/core/graph/nodes/flow/Sequence.ts

@@ -1,13 +1,45 @@
+import type { PropertyBag } from '../../../model/Properties';
 import type { NodeDef } from '../../NodeRegistry';
+import { asNumber } from '../../values';
 import { exec } from '../shared';
 
+const COUNT = 'count';
+/** Below two outputs a Sequence is just a link, so two are fixed and the rest are derived. */
+const FIXED = 2;
+/** One letter per output, so `a` stays `a` – the alphabet is what sets the ceiling. */
+const MAX = 26;
+
+export function sequenceKey(index: number): string {
+  return String.fromCharCode(97 + index);
+}
+
+export function sequenceCount(params: PropertyBag): number {
+  const count = Math.round(asNumber(params[COUNT] ?? 3));
+  return Math.max(FIXED, Math.min(MAX, count));
+}
+
+function outputAt(index: number) {
+  return exec(sequenceKey(index), String(index + 1));
+}
+
+/**
+ * The keys are `a`, `b`, `c`, … rather than `out1`…`outN`: those three are what every Sequence
+ * saved so far names its outputs, and renaming them would drop the edges hanging on them.
+ */
 export const Sequence: NodeDef = {
   type: 'Sequence',
   label: 'Sequence',
   category: 'flow',
   description: 'Runs its outputs one after another.',
   inputs: [exec()],
-  outputs: [exec('a', '1'), exec('b', '2'), exec('c', '3')],
-  params: [],
-  run: () => ({ next: ['a', 'b', 'c'] }),
+  outputs: [outputAt(0), outputAt(1)],
+  params: [
+    { key: COUNT, label: 'Outputs', kind: 'number', default: 3, min: FIXED, max: MAX, step: 1, decimals: 0 },
+  ],
+  derivePorts: ({ params }) => ({
+    outputs: Array.from({ length: sequenceCount(params) - FIXED }, (_, i) => outputAt(FIXED + i)),
+  }),
+  run: (_ctx, _inputs, params) => ({
+    next: Array.from({ length: sequenceCount(params) }, (_, i) => sequenceKey(i)),
+  }),
 };

src/core/graph/nodes/index.ts

@@ -44,6 +44,7 @@ import { NumberLiteral } from './data/Number';
 import { ObjectByName } from './data/ObjectByName';
 import { Or } from './data/Or';
 import { Owner } from './data/Owner';
+import { PackStruct } from './data/PackStruct';
 import { Parent } from './data/Parent';
 import { Random } from './data/Random';
 import { Round } from './data/Round';
@@ -57,6 +58,7 @@ import { ToNumber } from './data/ToNumber';
 import { ToText } from './data/ToText';
 import { Concat } from './data/Concat';
 import { Count } from './data/Count';
+import { ExpandStruct } from './data/ExpandStruct';
 import { Fill } from './data/Fill';
 import { IndexOf } from './data/IndexOf';
 import { ItemAt } from './data/ItemAt';
@@ -157,6 +159,9 @@ export const BUILT_IN_NODES: readonly NodeDef[] = [
   SubList,
   Concat,
   IndexOf,
+  // data: structs
+  PackStruct,
+  ExpandStruct,
   // data: vectors and input
   Length,
   Distance,

src/core/model/behaviorPrograms.ts

@@ -1,4 +1,4 @@
-import type { BehaviorLookup } from '../graph/nested';
+import type { BehaviorLookup } from '../graph/lookup';
 import { resolveAssetProps } from '../properties/resolve';
 import { findAsset, type Project } from './Project';