Infer virtual type definition from renderer arguments.

.changeset/quiet-mammals-look.md

@@ -0,0 +1,5 @@
+---
+"haunted": minor
+---
+
+Infer `virtual` type definition from renderer arguments.

src/virtual.ts

@@ -3,26 +3,31 @@ import {
   DirectiveParameters,
   ChildPart,
   PartInfo,
-} from "lit-html/directive.js";
-import { noChange } from "lit-html";
-import { AsyncDirective } from "lit-html/async-directive.js";
+} from "lit/directive.js";
+import { noChange } from "lit";
+import { AsyncDirective } from "lit/async-directive.js";
 import { GenericRenderer } from "./core";
 import { BaseScheduler } from "./scheduler";
 
 const includes = Array.prototype.includes;
 
-interface Renderer extends GenericRenderer<ChildPart> {
-  (this: ChildPart, ...args: unknown[]): unknown | void;
+interface Renderer<T extends unknown[]> extends GenericRenderer<ChildPart> {
+  (this: ChildPart, ...args: T): unknown | void;
 }
 
-const partToScheduler: WeakMap<ChildPart, Scheduler> = new WeakMap();
-const schedulerToPart: WeakMap<Scheduler, ChildPart> = new WeakMap();
+const partToScheduler: WeakMap<ChildPart, Scheduler<any>> = new WeakMap();
+const schedulerToPart: WeakMap<Scheduler<any>, ChildPart> = new WeakMap();
 
-class Scheduler extends BaseScheduler<object, ChildPart, Renderer, ChildPart> {
-  args!: unknown[];
+class Scheduler<T extends unknown[]> extends BaseScheduler<
+  object,
+  ChildPart,
+  Renderer<T>,
+  ChildPart
+> {
+  args!: T;
   setValue: Function;
 
-  constructor(renderer: Renderer, part: ChildPart, setValue: Function) {
+  constructor(renderer: Renderer<T>, part: ChildPart, setValue: Function) {
     super(renderer, part);
     this.state.virtual = true;
     this.setValue = setValue;
@@ -43,10 +48,19 @@ class Scheduler extends BaseScheduler<object, ChildPart, Renderer, ChildPart> {
   }
 }
 
-function makeVirtual(): any {
-  function virtual(renderer: Renderer) {
+interface VirtualRenderer<T extends unknown[]> {
+  (this: ChildPart, ...args: T): unknown | void;
+}
+export interface Virtual {
+  <T extends unknown[]>(renderer: VirtualRenderer<T>): (
+    ...values: T
+  ) => unknown;
+}
+
+function makeVirtual(): Virtual {
+  function virtual<T extends unknown[]>(renderer: VirtualRenderer<T>) {
     class VirtualDirective extends AsyncDirective {
-      cont: Scheduler | undefined;
+      cont: Scheduler<T> | undefined;
 
       constructor(partInfo: PartInfo) {
         super(partInfo);
@@ -56,19 +70,23 @@ function makeVirtual(): any {
       update(part: ChildPart, args: DirectiveParameters<this>) {
         this.cont = partToScheduler.get(part);
         if (!this.cont || this.cont.renderer !== renderer) {
-          this.cont = new Scheduler(renderer, part, (r: unknown) => {
-            this.setValue(r);
-          });
+          this.cont = new Scheduler(
+            renderer as Renderer<T>,
+            part,
+            (r: unknown) => {
+              this.setValue(r);
+            }
+          );
           partToScheduler.set(part, this.cont);
           schedulerToPart.set(this.cont, part);
           teardownOnRemove(this.cont, part);
         }
         this.cont.args = args;
         this.cont.update();
-        return this.render(args);
+        return this.render(...args);
       }
 
-      render(args: unknown) {
+      render(...args: T) {
         return noChange;
       }
     }
@@ -79,8 +97,8 @@ function makeVirtual(): any {
   return virtual;
 }
 
-function teardownOnRemove(
-  cont: BaseScheduler<object, ChildPart, Renderer, ChildPart>,
+function teardownOnRemove<T extends unknown[]>(
+  cont: BaseScheduler<object, ChildPart, Renderer<T>, ChildPart>,
   part: ChildPart,
   node = part.startNode
 ): void {