refactor: remove FASTElementTemplateInput

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: janechu

packages/fast-element/DESIGN.md

@@ -103,7 +103,7 @@ registry.
 - `onAttributeChangedCallback()` is the standard handler that processes attribute changes. During the prerendered bind, it is temporarily swapped to a no-op (see above) to avoid redundant processing of server-rendered attribute values.
 - Exposes `addBehavior` / `removeBehavior` for dynamic `HostBehavior` management (used by `ElementStyles`).
 
-`FASTElementDefinition` wraps all the metadata for a custom element class: its tag name, template, styles, and observed attribute list. It is created by `FASTElement.compose()` (which returns `Promise<FASTElementDefinition>`, always resolving immediately) and registered globally via `fastElementRegistry`. `PartialFASTElementDefinition.template` may be either a concrete `ElementViewTemplate` or a `FASTElementTemplateResolver` function that receives the composed definition and returns the concrete template (sync or async). `FASTElement.define()` returns `Promise<TType>` — resolving immediately for complete definitions or definitions without an initial template, and resolving async template resolver functions only after extensions have had a chance to update the definition. `FASTElementDefinition.register()` returns `Promise<Function>` — resolving when a definition with the given name has been registered.
+`FASTElementDefinition` wraps all the metadata for a custom element class: its tag name, template, styles, and observed attribute list. It is created by `FASTElement.compose()` (which returns `Promise<FASTElementDefinition>`, always resolving immediately) and registered globally via `fastElementRegistry`. `PartialFASTElementDefinition.template` may be either a concrete `ElementViewTemplate<InstanceType<TType>>` or a `FASTElementTemplateResolver<TType>` function that receives the composed definition and returns the concrete template (sync or async). `FASTElementDefinition.template` always stores the concrete `ElementViewTemplate<InstanceType<TType>>` after composition or resolver settlement. `FASTElement.define()` returns `Promise<TType>` — resolving immediately for complete definitions or definitions without an initial template, and resolving async template resolver functions only after extensions have had a chance to update the definition. `FASTElementDefinition.register()` returns `Promise<Function>` — resolving when a definition with the given name has been registered.
 
 #### Extensions
 

packages/fast-element/docs/api-report.api.md

@@ -443,7 +443,7 @@ export class FASTElementDefinition<TType extends Constructable<HTMLElement> = Co
     readonly registry: CustomElementRegistry;
     shadowOptions?: ShadowRootOptions;
     readonly styles?: ElementStyles;
-    template?: ElementViewTemplate;
+    template?: ElementViewTemplate<InstanceType<TType>>;
     readonly type: TType;
 }
 
@@ -734,8 +734,7 @@ export interface PartialFASTElementDefinition<TType extends Constructable<HTMLEl
     readonly registry?: CustomElementRegistry;
     readonly shadowOptions?: Partial<ShadowRootOptions> | null;
     readonly styles?: ComposableStyles | ComposableStyles[];
-    // Warning: (ae-forgotten-export) The symbol "FASTElementTemplateInput" needs to be exported by the entry point index.d.ts
-    readonly template?: FASTElementTemplateInput<TType>;
+    readonly template?: ElementViewTemplate<InstanceType<TType>> | FASTElementTemplateResolver<TType>;
 }
 
 // @public

packages/fast-element/src/components/element-controller.ts

@@ -227,7 +227,9 @@ export class ElementController<TElement extends HTMLElement = HTMLElement>
                 this._template = (this.source as any).resolveTemplate();
             } else if (definition.template) {
                 // 3. Default to the static definition.
-                this._template = definition.template ?? null;
+                this._template =
+                    (definition.template as ElementViewTemplate<TElement> | undefined) ??
+                    null;
             }
         }
 

packages/fast-element/src/components/fast-definitions.ts

@@ -74,7 +74,7 @@ export type FASTElementTemplateResolver<
     | ElementViewTemplate<InstanceType<TType>>
     | Promise<ElementViewTemplate<InstanceType<TType>>>;
 
-type FASTElementTemplateInput<
+type FASTElementTemplateSource<
     TType extends Constructable<HTMLElement> = Constructable<HTMLElement>,
 > = ElementViewTemplate<InstanceType<TType>> | FASTElementTemplateResolver<TType>;
 
@@ -96,7 +96,7 @@ const extensionRegistries = new WeakMap<
 function isFASTElementTemplateResolver<
     TType extends Constructable<HTMLElement> = Constructable<HTMLElement>,
 >(
-    value: FASTElementTemplateInput<TType> | undefined,
+    value: FASTElementTemplateSource<TType> | undefined,
 ): value is FASTElementTemplateResolver<TType> {
     return isFunction(value);
 }
@@ -239,7 +239,9 @@ export interface PartialFASTElementDefinition<
     /**
      * The template, or template resolver, for the custom element.
      */
-    readonly template?: FASTElementTemplateInput<TType>;
+    readonly template?:
+        | ElementViewTemplate<InstanceType<TType>>
+        | FASTElementTemplateResolver<TType>;
 
     /**
      * The styles to associate with the custom element.
@@ -321,7 +323,7 @@ export class FASTElementDefinition<
     /**
      * The template to render for the custom element.
      */
-    public template?: ElementViewTemplate;
+    public template?: ElementViewTemplate<InstanceType<TType>>;
 
     /**
      * The styles to associate with the custom element.

sites/website/src/docs/3.x/api/fast-element.fastelementdefinition.md

@@ -352,7 +352,7 @@ _(Optional)_ The styles to associate with the custom element.
 
 </td><td>
 
-[ElementViewTemplate](../fast-element.elementviewtemplate/)
+[ElementViewTemplate](../fast-element.elementviewtemplate/)<!-- -->&lt;InstanceType&lt;TType&gt;&gt;
 
 
 </td><td>

sites/website/src/docs/3.x/api/fast-element.fastelementdefinition.template.md

@@ -20,5 +20,5 @@ The template to render for the custom element.
 **Signature:**
 
 ```typescript
-template?: ElementViewTemplate;
-```
+template?: ElementViewTemplate<InstanceType<TType>>;
+```

sites/website/src/docs/3.x/api/fast-element.fastelementtemplateresolver.md

@@ -0,0 +1,25 @@
+---
+id: "fast-element.fastelementtemplateresolver"
+title: "FASTElementTemplateResolver type"
+layout: 3x-api
+eleventyNavigation:
+  key: "api3xfast-element.fastelementtemplateresolver"
+  parent: "api3xfast-element"
+  title: "FASTElementTemplateResolver type"
+navigationOptions:
+  activeKey: "api3xfast-element.fastelementtemplateresolver"
+---
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[@microsoft/fast-element](../fast-element/index.html) &gt; [FASTElementTemplateResolver](../fast-element.fastelementtemplateresolver/index.html)
+
+## FASTElementTemplateResolver type
+
+Resolves an element template from a composed definition.
+
+**Signature:**
+
+```typescript
+export type FASTElementTemplateResolver<TType extends Constructable<HTMLElement> = Constructable<HTMLElement>> = (definition: FASTElementDefinition<TType>) => ElementViewTemplate<InstanceType<TType>> | Promise<ElementViewTemplate<InstanceType<TType>>>;
+```
+**References:** [Constructable](../fast-element.constructable/), [FASTElementDefinition](../fast-element.fastelementdefinition/), [ElementViewTemplate](../fast-element.elementviewtemplate/)

sites/website/src/docs/3.x/api/fast-element.md

@@ -1706,6 +1706,17 @@ The signature of an arrow function capable of being evaluated against source dat
 A callback that receives a FASTElementDefinition during element registration. Extensions are invoked before the element is registered with the platform, allowing plugins to inspect or act on the resolved definition.
 
 
+</td></tr>
+<tr><td>
+
+[FASTElementTemplateResolver](../fast-element.fastelementtemplateresolver/)
+
+
+</td><td>
+
+Resolves an element template from a composed definition.
+
+
 </td></tr>
 <tr><td>
 

sites/website/src/docs/3.x/api/fast-element.partialfastelementdefinition.md

@@ -205,12 +205,12 @@ _(Optional)_ The styles to associate with the custom element.
 
 </td><td>
 
-[ElementViewTemplate](../fast-element.elementviewtemplate/)
+[ElementViewTemplate](../fast-element.elementviewtemplate/)<!-- -->&lt;InstanceType&lt;TType&gt;&gt; | [FASTElementTemplateResolver](../fast-element.fastelementtemplateresolver/)<!-- -->&lt;TType&gt;
 
 
 </td><td>
 
-_(Optional)_ The template to render for the custom element.
+_(Optional)_ The template, or template resolver, for the custom element.
 
 
 </td></tr>

sites/website/src/docs/3.x/api/fast-element.partialfastelementdefinition.template.md

@@ -15,10 +15,10 @@ navigationOptions:
 
 ## PartialFASTElementDefinition.template property
 
-The template to render for the custom element.
+The template, or template resolver, for the custom element.
 
 **Signature:**
 
 ```typescript
-readonly template?: ElementViewTemplate;
-```
+readonly template?: ElementViewTemplate<InstanceType<TType>> | FASTElementTemplateResolver<TType>;
+```