Fix documentation, fix equality check, add tests

Author: qwwdfsad

kotlinx-coroutines-core/common/src/flow/terminal/Reduce.kt

@@ -123,7 +123,7 @@ public suspend fun <T> Flow<T>.first(predicate: suspend (T) -> Boolean): T {
 
 /**
  * The terminal operator that returns the first element emitted by the flow and then cancels flow's collection.
- * Returns [null] if the flow was empty.
+ * Returns `null` if the flow was empty.
  */
 public suspend fun <T : Any> Flow<T>.firstOrNull(): T? {
     var result: Any? = NULL
@@ -135,12 +135,12 @@ public suspend fun <T : Any> Flow<T>.firstOrNull(): T? {
     } catch (e: AbortFlowException) {
         // Do nothing
     }
-    return result.takeUnless { it == NULL } as T?
+    return result.takeUnless { it === NULL } as T?
 }
 
 /**
- * The terminal operator that returns the first element emitted by the flow and then cancels flow's collection.
- * Returns [null] if the flow did not contain an element matching the [predicate].
+ *  The terminal operator that returns the first element emitted by the flow matching the given [predicate] and then cancels flow's collection.
+ * Returns `null` if the flow did not contain an element matching the [predicate].
  */
 public suspend fun <T : Any> Flow<T>.firstOrNull(predicate: suspend (T) -> Boolean): T? {
     var result: Any? = NULL
@@ -154,5 +154,5 @@ public suspend fun <T : Any> Flow<T>.firstOrNull(predicate: suspend (T) -> Boole
     } catch (e: AbortFlowException) {
         // Do nothing
     }
-    return result.takeUnless { it == NULL } as T?
+    return result.takeUnless { it === NULL } as T?
 }

kotlinx-coroutines-core/common/test/AsyncTest.kt

@@ -210,12 +210,6 @@ class AsyncTest : TestBase() {
         finish(13)
     }
 
-    class BadClass {
-        override fun equals(other: Any?): Boolean = error("equals")
-        override fun hashCode(): Int = error("hashCode")
-        override fun toString(): String = error("toString")
-    }
-
     @Test
     fun testDeferBadClass() = runTest {
         val bad = BadClass()

kotlinx-coroutines-core/common/test/TestBase.common.kt

@@ -80,3 +80,8 @@ public fun wrapperDispatcher(context: CoroutineContext): CoroutineContext {
 
 public suspend fun wrapperDispatcher(): CoroutineContext = wrapperDispatcher(coroutineContext)
 
+class BadClass {
+    override fun equals(other: Any?): Boolean = error("equals")
+    override fun hashCode(): Int = error("hashCode")
+    override fun toString(): String = error("toString")
+}

kotlinx-coroutines-core/common/test/WithTimeoutOrNullTest.kt

@@ -152,12 +152,6 @@ class WithTimeoutOrNullTest : TestBase() {
         assertSame(bad, result)
     }
 
-    class BadClass {
-        override fun equals(other: Any?): Boolean = error("Should not be called")
-        override fun hashCode(): Int = error("Should not be called")
-        override fun toString(): String = error("Should not be called")
-    }
-
     @Test
     fun testNullOnTimeout() = runTest {
         expect(1)

kotlinx-coroutines-core/common/test/WithTimeoutTest.kt

@@ -107,12 +107,6 @@ class WithTimeoutTest : TestBase() {
         assertSame(bad, result)
     }
 
-    class BadClass {
-        override fun equals(other: Any?): Boolean = error("Should not be called")
-        override fun hashCode(): Int = error("Should not be called")
-        override fun toString(): String = error("Should not be called")
-    }
-
     @Test
     fun testExceptionOnTimeout() = runTest {
         expect(1)

kotlinx-coroutines-core/common/test/channels/RendezvousChannelTest.kt

@@ -241,12 +241,6 @@ class RendezvousChannelTest : TestBase() {
         finish(12)
     }
 
-    class BadClass {
-        override fun equals(other: Any?): Boolean = error("equals")
-        override fun hashCode(): Int = error("hashCode")
-        override fun toString(): String = error("toString")
-    }
-
     @Test
     fun testProduceBadClass() = runTest {
         val bad = BadClass()

kotlinx-coroutines-core/common/test/flow/terminal/FirstTest.kt

@@ -150,4 +150,14 @@ class FirstTest : TestBase() {
         assertEquals(1, flow.firstOrNull())
         finish(2)
     }
+
+    @Test
+    fun testBadClass() = runTest {
+        val instance = BadClass()
+        val flow = flowOf(instance)
+        assertSame(instance, flow.first())
+        assertSame(instance, flow.firstOrNull())
+        assertSame(instance, flow.first { true })
+        assertSame(instance, flow.firstOrNull { true })
+    }
 }

kotlinx-coroutines-core/common/test/flow/terminal/SingleTest.kt

@@ -17,7 +17,6 @@ class SingleTest : TestBase() {
 
         assertEquals(239L, flow.single())
         assertEquals(239L, flow.singleOrNull())
-
     }
 
     @Test
@@ -63,4 +62,12 @@ class SingleTest : TestBase() {
         assertNull(flowOf<Int?>(null).single())
         assertFailsWith<NoSuchElementException> { flowOf<Int?>().single() }
     }
+
+    @Test
+    fun testBadClass() = runTest {
+        val instance = BadClass()
+        val flow = flowOf(instance)
+        assertSame(instance, flow.single())
+        assertSame(instance, flow.singleOrNull())
+    }
 }