Prevent users from enabling auto commit (#1290)

Zio-kafka applications always pre-fetch data so that user streams can
process the data asynchronously. This is not compatible with auto
commit. When auto commit is enabled, the consumer will automatically
commit batches _before_ they are processed by the user streams.

An unaware user might accidentally enable auto commit and lose data
during rebalances.

Solves #1289.

zio-kafka-test/src/test/scala/zio/kafka/consumer/ConsumerSettingsSpec.scala

@@ -0,0 +1,24 @@
+package zio.kafka.consumer
+
+import zio._
+import zio.kafka.ZIOSpecDefaultSlf4j
+import zio.test._
+import zio.test.Assertion._
+
+object ConsumerSettingsSpec extends ZIOSpecDefaultSlf4j {
+
+  override def spec: Spec[TestEnvironment with Scope, Throwable] =
+    suite("ConsumerSettingsSpec")(
+      test("accepts no auto.commit") {
+        ZIO.attempt(ConsumerSettings(List("host"))) *> assertCompletesZIO
+      },
+      test("accepts disabled auto.commit") {
+        ZIO.attempt(ConsumerSettings(List("host")).withProperty("enable.auto.commit", "false")) *> assertCompletesZIO
+      },
+      test("rejects auto.commit") {
+        val settings = ZIO.attempt(ConsumerSettings(List("host")).withProperty("enable.auto.commit", "true")).exit
+        assertZIO(settings)(failsWithA[IllegalArgumentException])
+      }
+    )
+
+}

zio-kafka/src/main/scala/zio/kafka/consumer/Consumer.scala

@@ -197,7 +197,7 @@ object Consumer {
   /**
    * Create a zio-kafka Consumer from an org.apache.kafka KafkaConsumer
    *
-   * You are responsible for creating and closing the KafkaConsumer
+   * You are responsible for creating and closing the KafkaConsumer. Make sure auto.commit is disabled.
    */
   def fromJavaConsumer(
     javaConsumer: JConsumer[Array[Byte], Array[Byte]],

zio-kafka/src/main/scala/zio/kafka/consumer/ConsumerSettings.scala

@@ -33,6 +33,11 @@ final case class ConsumerSettings(
   runloopMetricsSchedule: Schedule[Any, Unit, Long] = Schedule.fixed(500.millis),
   authErrorRetrySchedule: Schedule[Any, Throwable, Any] = Schedule.recurs(5) && Schedule.spaced(500.millis)
 ) {
+  // Parse booleans in a way compatible with how Kafka does this in org.apache.kafka.common.config.ConfigDef.parseType:
+  require(
+    properties.get(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG).forall(_.toString.trim.equalsIgnoreCase("false")),
+    "Because zio-kafka does pre-fetching, auto commit is not supported"
+  )
 
   /**
    * Tunes the consumer for high throughput.