export easily nameable constraint

Author: uhyo

generated/lib.dom.d.ts

@@ -34084,11 +34084,7 @@ declare function setTimeout(
 
 /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/structuredClone) */
 declare function structuredClone<
-  const T extends BetterTypeScriptLibInternals.StructuredClone.NeverOrUnknown<
-    BetterTypeScriptLibInternals.StructuredClone.StructuredCloneOutput<
-      BetterTypeScriptLibInternals.StructuredClone.AvoidCyclicConstraint<T>
-    >
-  >,
+  const T extends BetterTypeScriptLibInternals.StructuredClone.Constraint<T>,
 >(
   value: T,
   options?: StructuredSerializeOptions,
@@ -34863,7 +34859,13 @@ declare namespace BetterTypeScriptLibInternals {
 
     type AvoidCyclicConstraint<T> = [T] extends [infer R] ? R : never;
 
-    // 上限が不正にきつくなっているのを無視する
     type NeverOrUnknown<T> = [T] extends [never] ? never : unknown;
+
+    export type Constraint<T> =
+      BetterTypeScriptLibInternals.StructuredClone.NeverOrUnknown<
+        BetterTypeScriptLibInternals.StructuredClone.StructuredCloneOutput<
+          BetterTypeScriptLibInternals.StructuredClone.AvoidCyclicConstraint<T>
+        >
+      >;
   }
 }

lib/lib.dom.d.ts

@@ -176,18 +176,20 @@ declare namespace BetterTypeScriptLibInternals {
 
     type AvoidCyclicConstraint<T> = [T] extends [infer R] ? R : never;
 
-    // 上限が不正にきつくなっているのを無視する
     type NeverOrUnknown<T> = [T] extends [never] ? never : unknown;
+
+    export type Constraint<T> =
+      BetterTypeScriptLibInternals.StructuredClone.NeverOrUnknown<
+        BetterTypeScriptLibInternals.StructuredClone.StructuredCloneOutput<
+          BetterTypeScriptLibInternals.StructuredClone.AvoidCyclicConstraint<T>
+        >
+      >;
   }
 }
 
 /** [MDN Reference](https://developer.mozilla.org/docs/Web/API/structuredClone) */
 declare function structuredClone<
-  const T extends BetterTypeScriptLibInternals.StructuredClone.NeverOrUnknown<
-    BetterTypeScriptLibInternals.StructuredClone.StructuredCloneOutput<
-      BetterTypeScriptLibInternals.StructuredClone.AvoidCyclicConstraint<T>
-    >
-  >,
+  const T extends BetterTypeScriptLibInternals.StructuredClone.Constraint<T>,
 >(
   value: T,
   options?: StructuredSerializeOptions,

tests/src/dom.ts

@@ -115,4 +115,25 @@ const test = async (url: string) => {
     // @ts-expect-error
     const p = structuredClone(() => 1);
   }
+  // unions
+  {
+    function getData() {
+      if (Math.random() > 0.5) {
+        return { a: 5, b: null };
+      } else {
+        return { a: null, b: "hello" };
+      }
+    }
+    expectType<{ a: number; b: null } | { a: null; b: string }>(
+      structuredClone(getData()),
+    );
+  }
+  // generic functions
+  {
+    function func1<
+      T extends BetterTypeScriptLibInternals.StructuredClone.Constraint<T>,
+    >(obj: T) {
+      return structuredClone(obj);
+    }
+  }
 }