fix(equal): account for Weak* objects

- `WeakMap` and `WeakSet` cannot be deeply compared (no `size`, `Symbol.iterator`, etc.)
- `WeakRef` can be dereferenced

Refs #949

testing/asserts.ts

@@ -122,6 +122,14 @@ export function equal(c: unknown, d: unknown): boolean {
       return true;
     }
     if (a && typeof a === "object" && b && typeof b === "object") {
+      if (a instanceof WeakMap || b instanceof WeakMap) {
+        if (!(a instanceof WeakMap && b instanceof WeakMap)) return false;
+        throw new TypeError("cannot compare WeakMap instances");
+      }
+      if (a instanceof WeakSet || b instanceof WeakSet) {
+        if (!(a instanceof WeakSet && b instanceof WeakSet)) return false;
+        throw new TypeError("cannot compare WeakSet instances");
+      }
       if (seen.get(a) === b) {
         return true;
       }
@@ -166,6 +174,10 @@ export function equal(c: unknown, d: unknown): boolean {
         }
       }
       seen.set(a, b);
+      if (a instanceof WeakRef || b instanceof WeakRef) {
+        if (!(a instanceof WeakRef && b instanceof WeakRef)) return false;
+        return compare(a.deref(), b.deref());
+      }
       return true;
     }
     return false;

testing/asserts_test.ts

@@ -153,6 +153,32 @@ Deno.test("testingEqual", function (): void {
   assert(
     !equal({ a: undefined, b: undefined }, { a: undefined }),
   );
+  assertThrows(() => equal(new WeakMap(), new WeakMap()));
+  assertThrows(() => equal(new WeakSet(), new WeakSet()));
+  assert(!equal(new WeakMap(), new WeakSet()));
+  assert(
+    equal(new WeakRef({ hello: "world" }), new WeakRef({ hello: "world" })),
+  );
+  assert(
+    !equal(new WeakRef({ world: "hello" }), new WeakRef({ hello: "world" })),
+  );
+  assert(!equal({ hello: "world" }, new WeakRef({ hello: "world" })));
+  assert(
+    equal(
+      new WeakRef({ hello: "world" }),
+      // deno-lint-ignore ban-types
+      new (class<T extends object> extends WeakRef<T> {})({ hello: "world" }),
+    ),
+  );
+  assert(
+    !equal(
+      new WeakRef({ hello: "world" }),
+      // deno-lint-ignore ban-types
+      new (class<T extends object> extends WeakRef<T> {
+        foo = "bar";
+      })({ hello: "world" }),
+    ),
+  );
 });
 
 Deno.test("testingNotEquals", function (): void {