[BUILD] Configure scalafmt. Currently, this applies only to Kernel.

.scalafmt.conf

@@ -0,0 +1,48 @@
+# Copyright (2025) The Delta Lake Project Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+align = none
+align.openParenDefnSite = false
+align.openParenCallSite = false
+align.tokens = []
+importSelectors = "singleLine"
+optIn.configStyleArguments = false
+continuationIndent {
+  callSite = 2
+  defnSite = 4
+}
+danglingParentheses {
+  defnSite = false
+  callSite = false
+}
+docstrings {
+  style = Asterisk
+  wrap = no
+}
+literals.hexDigits = upper
+maxColumn = 100
+newlines {
+  beforeCurlyLambdaParams = false
+  source = keep
+}
+rewrite.rules = [Imports]
+rewrite.imports.sort = scalastyle
+rewrite.imports.groups = [
+  ["java\\..*"],
+  ["scala\\..*"],
+  ["io\\.delta\\..*"],
+  ["org\\.apache\\.spark\\.sql\\.delta.*"]
+]
+runner.dialect = scala212
+version = 3.8.6

build.sbt

@@ -157,11 +157,26 @@ lazy val commonSettings = Seq(
   unidocSourceFilePatterns := Nil,
 )
 
-// enforce java code style
-def javafmtCheckSettings() = Seq(
+////////////////////////////
+// START: Code Formatting //
+////////////////////////////
+
+/** Enforce java code style on compile. */
+def javafmtCheckSettings(): Seq[Def.Setting[Task[CompileAnalysis]]] = Seq(
   (Compile / compile) := ((Compile / compile) dependsOn (Compile / javafmtCheckAll)).value
 )
 
+/** Enforce scala code style on compile. */
+def scalafmtCheckSettings(): Seq[Def.Setting[Task[CompileAnalysis]]] = Seq(
+  (Compile / compile) := ((Compile / compile) dependsOn (Compile / scalafmtCheckAll)).value,
+)
+
+// TODO: define fmtAll and fmtCheckAll tasks that run both scala and java fmts/checks
+
+//////////////////////////
+// END: Code Formatting //
+//////////////////////////
+
 /**
  * Note: we cannot access sparkVersion.value here, since that can only be used within a task or
  *       setting macro.
@@ -233,7 +248,7 @@ def runTaskOnlyOnSparkMaster[T](
 }
 
 lazy val connectCommon = (project in file("spark-connect/common"))
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "delta-connect-common",
     commonSettings,
@@ -272,7 +287,7 @@ lazy val connectCommon = (project in file("spark-connect/common"))
   )
 
 lazy val connectClient = (project in file("spark-connect/client"))
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .dependsOn(connectCommon % "compile->compile;test->test;provided->provided")
   .settings(
     name := "delta-connect-client",
@@ -361,7 +376,7 @@ lazy val connectClient = (project in file("spark-connect/client"))
 lazy val connectServer = (project in file("spark-connect/server"))
   .dependsOn(connectCommon % "compile->compile;test->test;provided->provided")
   .dependsOn(spark % "compile->compile;test->test;provided->provided")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "delta-connect-server",
     commonSettings,
@@ -405,7 +420,7 @@ lazy val connectServer = (project in file("spark-connect/server"))
 lazy val spark = (project in file("spark"))
   .dependsOn(storage)
   .enablePlugins(Antlr4Plugin)
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-spark",
     commonSettings,
@@ -493,7 +508,7 @@ lazy val spark = (project in file("spark"))
 
 lazy val contribs = (project in file("contribs"))
   .dependsOn(spark % "compile->compile;test->test;provided->provided")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-contribs",
     commonSettings,
@@ -532,7 +547,7 @@ lazy val contribs = (project in file("contribs"))
 
 lazy val sharing = (project in file("sharing"))
   .dependsOn(spark % "compile->compile;test->test;provided->provided")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "delta-sharing-spark",
     commonSettings,
@@ -558,12 +573,14 @@ lazy val sharing = (project in file("sharing"))
   ).configureUnidoc()
 
 lazy val kernelApi = (project in file("kernel/kernel-api"))
+  .enablePlugins(ScalafmtPlugin)
   .settings(
     name := "delta-kernel-api",
     commonSettings,
     scalaStyleSettings,
     javaOnlyReleaseSettings,
     javafmtCheckSettings,
+    scalafmtCheckSettings,
     Test / javaOptions ++= Seq("-ea"),
     libraryDependencies ++= Seq(
       "org.roaringbitmap" % "RoaringBitmap" % "0.9.25",
@@ -638,6 +655,7 @@ lazy val kernelApi = (project in file("kernel/kernel-api"))
   ).configureUnidoc(docTitle = "Delta Kernel")
 
 lazy val kernelDefaults = (project in file("kernel/kernel-defaults"))
+  .enablePlugins(ScalafmtPlugin)
   .dependsOn(kernelApi)
   .dependsOn(kernelApi % "test->test")
   .dependsOn(storage)
@@ -650,6 +668,7 @@ lazy val kernelDefaults = (project in file("kernel/kernel-defaults"))
     scalaStyleSettings,
     javaOnlyReleaseSettings,
     javafmtCheckSettings,
+    scalafmtCheckSettings,
     Test / javaOptions ++= Seq("-ea"),
     libraryDependencies ++= Seq(
       "org.apache.hadoop" % "hadoop-client-runtime" % hadoopVersion,
@@ -682,7 +701,7 @@ lazy val kernelDefaults = (project in file("kernel/kernel-defaults"))
 // TODO unidoc
 // TODO(scott): figure out a better way to include tests in this project
 lazy val storage = (project in file("storage"))
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-storage",
     commonSettings,
@@ -707,7 +726,7 @@ lazy val storage = (project in file("storage"))
 lazy val storageS3DynamoDB = (project in file("storage-s3-dynamodb"))
   .dependsOn(storage % "compile->compile;test->test;provided->provided")
   .dependsOn(spark % "test->test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-storage-s3-dynamodb",
     commonSettings,
@@ -733,7 +752,7 @@ val icebergSparkRuntimeArtifactName = {
 lazy val testDeltaIcebergJar = (project in file("testDeltaIcebergJar"))
   // delta-iceberg depends on delta-spark! So, we need to include it during our test.
   .dependsOn(spark % "test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "test-delta-iceberg-jar",
     commonSettings,
@@ -763,7 +782,7 @@ val deltaIcebergSparkIncludePrefixes = Seq(
 // scalastyle:off println
 lazy val iceberg = (project in file("iceberg"))
   .dependsOn(spark % "compile->compile;test->test;provided->provided")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-iceberg",
     commonSettings,
@@ -833,7 +852,7 @@ lazy val generateIcebergJarsTask = TaskKey[Unit]("generateIcebergJars", "Generat
 
 lazy val icebergShaded = (project in file("icebergShaded"))
   .dependsOn(spark % "provided")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "iceberg-shaded",
     commonSettings,
@@ -864,7 +883,7 @@ lazy val icebergShaded = (project in file("icebergShaded"))
 
 lazy val hudi = (project in file("hudi"))
   .dependsOn(spark % "compile->compile;test->test;provided->provided")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-hudi",
     commonSettings,
@@ -916,7 +935,7 @@ lazy val hudi = (project in file("hudi"))
 
 lazy val hive = (project in file("connectors/hive"))
   .dependsOn(standaloneCosmetic)
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-hive",
     commonSettings,
@@ -933,7 +952,7 @@ lazy val hive = (project in file("connectors/hive"))
 
 lazy val hiveAssembly = (project in file("connectors/hive-assembly"))
   .dependsOn(hive)
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "delta-hive-assembly",
     Compile / unmanagedJars += (hive / Compile / packageBin / packageBin).value,
@@ -960,7 +979,7 @@ lazy val hiveAssembly = (project in file("connectors/hive-assembly"))
 
 lazy val hiveTest = (project in file("connectors/hive-test"))
   .dependsOn(goldenTables % "test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "hive-test",
     // Make the project use the assembly jar to ensure we are testing the assembly jar that users
@@ -993,7 +1012,7 @@ lazy val hiveTest = (project in file("connectors/hive-test"))
 
 lazy val hiveMR = (project in file("connectors/hive-mr"))
   .dependsOn(hiveTest % "test->test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "hive-mr",
     commonSettings,
@@ -1020,7 +1039,7 @@ lazy val hiveMR = (project in file("connectors/hive-mr"))
 
 lazy val hiveTez = (project in file("connectors/hive-tez"))
   .dependsOn(hiveTest % "test->test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "hive-tez",
     commonSettings,
@@ -1064,7 +1083,7 @@ lazy val hiveTez = (project in file("connectors/hive-tez"))
 
 lazy val hive2MR = (project in file("connectors/hive2-mr"))
   .dependsOn(goldenTables % "test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "hive2-mr",
     commonSettings,
@@ -1095,7 +1114,7 @@ lazy val hive2MR = (project in file("connectors/hive2-mr"))
 
 lazy val hive2Tez = (project in file("connectors/hive2-tez"))
   .dependsOn(goldenTables % "test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "hive2-tez",
     commonSettings,
@@ -1162,7 +1181,7 @@ lazy val hive2Tez = (project in file("connectors/hive2-tez"))
  */
 lazy val standaloneCosmetic = project
   .dependsOn(storage) // this doesn't impact the output artifact (jar), only the pom.xml dependencies
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "delta-standalone",
     commonSettings,
@@ -1182,7 +1201,7 @@ lazy val standaloneCosmetic = project
 lazy val testStandaloneCosmetic = (project in file("connectors/testStandaloneCosmetic"))
   .dependsOn(standaloneCosmetic)
   .dependsOn(goldenTables % "test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "test-standalone-cosmetic",
     commonSettings,
@@ -1199,7 +1218,7 @@ lazy val testStandaloneCosmetic = (project in file("connectors/testStandaloneCos
  * except `ParquetSchemaConverter` are working without `parquet-hadoop` in testStandaloneCosmetic`.
  */
 lazy val testParquetUtilsWithStandaloneCosmetic = project.dependsOn(standaloneCosmetic)
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "test-parquet-utils-with-standalone-cosmetic",
     commonSettings,
@@ -1223,7 +1242,7 @@ def scalaCollectionPar(version: String) = version match {
  * create a separate project to skip the shading.
  */
 lazy val standaloneParquet = (project in file("connectors/standalone-parquet"))
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .dependsOn(standaloneWithoutParquetUtils)
   .settings(
     name := "delta-standalone-parquet",
@@ -1238,7 +1257,7 @@ lazy val standaloneParquet = (project in file("connectors/standalone-parquet"))
 
 /** A dummy project to allow `standaloneParquet` depending on the shaded standalone jar. */
 lazy val standaloneWithoutParquetUtils = project
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "delta-standalone-without-parquet-utils",
     commonSettings,
@@ -1251,7 +1270,7 @@ lazy val standaloneWithoutParquetUtils = project
 lazy val standalone = (project in file("connectors/standalone"))
   .dependsOn(storage % "compile->compile;provided->provided")
   .dependsOn(goldenTables % "test")
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "delta-standalone-original",
     commonSettings,
@@ -1376,7 +1395,7 @@ lazy val compatibility = (project in file("connectors/oss-compatibility-tests"))
 
 lazy val goldenTables = (project in file("connectors/golden-tables"))
   .dependsOn(spark % "test") // depends on delta-spark
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings(
     name := "golden-tables",
     commonSettings,
@@ -1403,7 +1422,7 @@ def sqlDeltaImportScalaVersion(scalaBinaryVersion: String): String = {
 
 lazy val sqlDeltaImport = (project in file("connectors/sql-delta-import"))
   .dependsOn(spark)
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "sql-delta-import",
     commonSettings,
@@ -1435,7 +1454,7 @@ lazy val flink = (project in file("connectors/flink"))
   .dependsOn(standaloneCosmetic % "provided")
   .dependsOn(kernelApi)
   .dependsOn(kernelDefaults)
-  .disablePlugins(JavaFormatterPlugin)
+  .disablePlugins(JavaFormatterPlugin, ScalafmtPlugin)
   .settings (
     name := "delta-flink",
     commonSettings,

kernel/kernel-api/src/test/scala/io/delta/kernel/CloseableIteratorSuite.scala

@@ -21,6 +21,7 @@ import scala.collection.JavaConverters._
 import io.delta.kernel.internal.util.Utils
 import io.delta.kernel.utils.CloseableIterator
 import io.delta.kernel.utils.CloseableIterator.BreakableFilterResult
+
 import org.scalatest.funsuite.AnyFunSuite
 
 class CloseableIteratorSuite extends AnyFunSuite {