Adding Backfill Id to the config object.

client-base/src/main/kotlin/app/cash/backfila/client/spi/BackfilaParameters.kt

@@ -46,12 +46,14 @@ class BackfilaParametersOperator<T : Any>(
   fun constructBackfillConfig(request: GetNextBatchRangeRequest): BackfillConfig<T> = BackfillConfig(
     constructParameters(request.parameters),
     request.partition_name,
+    request.backfill_id,
     request.dry_run,
   )
 
   fun constructBackfillConfig(request: RunBatchRequest): BackfillConfig<T> = BackfillConfig(
     constructParameters(request.parameters),
     request.partition_name,
+    request.backfill_id,
     request.dry_run,
   )
 

client-base/src/test/java/app/cash/backfila/embedded/JavaBackfilaTest.java

@@ -122,4 +122,15 @@ void twoInstanceBackfill() {
     assertThat(backfillRun.getBackfill().runOrder).containsExactly("a", "b", "c", "e", "f");
     assertThat(datastore.valuesToList()).containsExactly("A", "B", "C", "E", "F");
   }
+
+  @Test
+  void backfillIdIsANumber() {
+    datastore.put("instance", "A", "b", "C");
+
+    var backfillRun = backfila.createWetRun(JavaChangeCaseTestBackfill.class,
+        Map.of("required", ByteString.encodeUtf8("isRequired")));
+    backfillRun.execute();
+    String seenBackfillId = backfillRun.getBackfill().seenBackfillId;
+    assertThat(Integer.parseInt(seenBackfillId)).isNotNull();
+  }
 }

client-base/src/test/java/app/cash/backfila/embedded/JavaChangeCaseTestBackfill.java

@@ -17,6 +17,7 @@
 class JavaChangeCaseTestBackfill extends FixedSetBackfill<CaseParameters> {
   public List<String> runOrder = new ArrayList();
   public CaseParameters seenParameters = null;
+  public String seenBackfillId = null;
 
   @Inject
   public JavaChangeCaseTestBackfill(){
@@ -32,6 +33,7 @@ public ValidateResult<CaseParameters> checkParameters(@NotNull CaseParameters pa
   @Override public void runOne(@NotNull FixedSetRow row,
       @NotNull BackfillConfig<CaseParameters> backfillConfig) {
     seenParameters = backfillConfig.getParameters();
+    seenBackfillId = backfillConfig.getBackfillId();
     runOrder.add(row.getValue());
     if (backfillConfig.getParameters().toUpper) {
       row.setValue(row.getValue().toUpperCase(Locale.ROOT));

client-base/src/test/kotlin/app/cash/backfila/client/FixedSetTest.kt

@@ -25,7 +25,9 @@ class FixedSetTest {
 
   class ToUpperCaseBackfill @Inject constructor() : FixedSetBackfill<NoParameters>() {
     val runOrder = mutableListOf<String>()
+    var seenBackfillId: String? = null
     override fun runOne(row: FixedSetRow, backfillConfig: BackfillConfig<NoParameters>) {
+      seenBackfillId = backfillConfig.backfillId
       runOrder += row.value
       row.value = row.value.toUpperCase(Locale.ROOT)
     }
@@ -49,4 +51,12 @@ class FixedSetTest {
     assertThat(backfillRun.backfill.runOrder).containsExactly("a", "b", "c", "e", "f")
     assertThat(datastore.valuesToList()).containsExactly("A", "B", "C", "E", "F")
   }
+
+  @Test fun `backfillId is a number`() {
+    datastore.put("instance", "a", "b", "c")
+
+    val backfillRun = backfila.createWetRun<ToUpperCaseBackfill>()
+    backfillRun.execute()
+    assertThat(backfillRun.backfill.seenBackfillId?.toInt()).isNotNull()
+  }
 }

client/src/main/kotlin/app/cash/backfila/client/BackfillConfig.kt

@@ -3,6 +3,7 @@ package app.cash.backfila.client
 data class BackfillConfig<Param : Any>(
   val parameters: Param,
   val partitionName: String,
+  val backfillId: String,
   val dryRun: Boolean,
 ) {
   fun prepareConfig() = PrepareBackfillConfig(parameters, dryRun)