[fabric/core] Add variantConstructor utility for tagged variants

packages/fabric/core/variant/constructor.ts

@@ -0,0 +1,14 @@
+import type { TaggedVariant, VariantTag } from "./variant.ts";
+
+export function variantConstructor<
+  const T extends TaggedVariant<string>,
+>(
+  tag: T[VariantTag],
+) {
+  return <TOpts extends Omit<T, VariantTag>>(options: TOpts) => {
+    return {
+      _tag: tag,
+      ...options,
+    } as const;
+  };
+}

packages/fabric/core/variant/index.ts

@@ -1,2 +1,3 @@
+export * from "./constructor.ts";
 export * from "./match.ts";
 export * from "./variant.ts";