[Flight] Serialize top-level Date (#31163)

renderModelDesctructive can sometimes be called direclty on Date values.
When this happens we don't first call toJSON on the Date value so we
need to explicitly handle the case where where the rendered value is a
Date instance as well. This change updates renderModelDesctructive to
account for sometimes receiving Date instances directly.

Author: gnoff

packages/react-client/src/__tests__/ReactFlight-test.js

@@ -661,6 +661,18 @@ describe('ReactFlight', () => {
       `);
   });
 
+  it('can transport Date as a top-level value', async () => {
+    const date = new Date(0);
+    const transport = ReactNoopFlightServer.render(date);
+
+    let readValue;
+    await act(async () => {
+      readValue = await ReactNoopFlightClient.read(transport);
+    });
+
+    expect(readValue).toEqual(date);
+  });
+
   it('can transport Error objects as values', async () => {
     function ComponentClient({prop}) {
       return `

packages/react-server/src/ReactFlightServer.js

@@ -1962,6 +1962,12 @@ function serializeUndefined(): string {
   return '$undefined';
 }
 
+function serializeDate(date: Date): string {
+  // JSON.stringify automatically calls Date.prototype.toJSON which calls toISOString.
+  // We need only tack on a $D prefix.
+  return '$D' + date.toJSON();
+}
+
 function serializeDateFromDateJSON(dateJSON: string): string {
   // JSON.stringify automatically calls Date.prototype.toJSON which calls toISOString.
   // We need only tack on a $D prefix.
@@ -2779,6 +2785,14 @@ function renderModelDestructive(
       }
     }
 
+    // We put the Date check low b/c most of the time Date's will already have been serialized
+    // before we process it in this function but when rendering a Date() as a top level it can
+    // end up being a Date instance here. This is rare so we deprioritize it by putting it deep
+    // in this function
+    if (value instanceof Date) {
+      return serializeDate(value);
+    }
+
     // Verify that this is a simple plain object.
     const proto = getPrototypeOf(value);
     if (
@@ -3646,6 +3660,10 @@ function renderConsoleValue(
     return serializeBigInt(value);
   }
 
+  if (value instanceof Date) {
+    return serializeDate(value);
+  }
+
   return 'unknown type ' + typeof value;
 }