fix(caching): guard isError values before calling

src/__tests__/server.caching.test.ts

@@ -363,6 +363,32 @@ describe('memo', () => {
     await expect(updateLog(logAsync)).resolves.toMatchSnapshot('async');
   });
 
+  it('should return cached sync objects with isError: true without calling them', () => {
+    let callCount = 0;
+    const memoized = memo((value: string) => {
+      callCount += 1;
+
+      return { isError: true, value, callCount };
+    }, { cacheLimit: 1, cacheErrors: true });
+
+    expect(memoized('a')).toEqual({ isError: true, value: 'a', callCount: 1 });
+    expect(memoized('a')).toEqual({ isError: true, value: 'a', callCount: 1 });
+    expect(callCount).toBe(1);
+  });
+
+  it('should return sync objects with isError: true when cacheErrors is false', () => {
+    let callCount = 0;
+    const memoized = memo((value: string) => {
+      callCount += 1;
+
+      return { isError: true, value, callCount };
+    }, { cacheLimit: 1, cacheErrors: false });
+
+    expect(memoized('a')).toEqual({ isError: true, value: 'a', callCount: 1 });
+    expect(memoized('a')).toEqual({ isError: true, value: 'a', callCount: 2 });
+    expect(callCount).toBe(2);
+  });
+
   it('should handle clear() without callback', () => {
     const mockDebug = jest.fn();
     const options = { cacheLimit: 1, debug: mockDebug };

src/server.caching.ts

@@ -310,7 +310,7 @@ const memo = <TArgs extends unknown[], TReturn = unknown>(
           cache: [...cache]
         });
 
-        return cachedValue();
+        return typeof cachedValue === 'function' ? cachedValue() : cachedValue;
       }
 
       debug({