build: Enforce scalafix check in CI

.github/actions/java-test/action.yaml

@@ -49,7 +49,7 @@ runs:
     - name: Run Maven compile
       shell: bash
       run: |
-        ./mvnw -B compile test-compile scalafix:scalafix -Psemanticdb ${{ inputs.maven_opts }}
+        ./mvnw -B compile test-compile scalafix:scalafix -Dscalafix.mode=CHECK -Psemanticdb ${{ inputs.maven_opts }}
 
     - name: Run tests
       shell: bash

DEVELOPMENT.md

@@ -84,3 +84,7 @@ in the respective source code, e.g., `CometTPCHQueryBenchmark`.
 ## Debugging
 Comet is a multi-language project with native code written in Rust and JVM code written in Java and Scala.
 It is possible to debug both native and JVM code concurrently as described in the [DEBUGGING guide](DEBUGGING.md)
+
+## Submitting a Pull Request
+Comet uses `cargo fmt`, [Scalafix](https://github.com/scalacenter/scalafix) and [Spotless](https://github.com/diffplug/spotless/tree/main/plugin-maven) to 
+automatically format the code. Before submitting a pull request, you can simply run `make format` to format the code.

Makefile

@@ -38,6 +38,7 @@ clean:
 bench:
 	cd core && RUSTFLAGS="-Ctarget-cpu=native" cargo bench $(filter-out $@,$(MAKECMDGOALS))
 format:
+	cd core && cargo fmt
 	./mvnw compile test-compile scalafix:scalafix -Psemanticdb $(PROFILES)
 	./mvnw spotless:apply $(PROFILES)
 

spark/src/main/scala/org/apache/comet/CometSparkSessionExtensions.scala

@@ -26,7 +26,6 @@ import org.apache.spark.internal.Logging
 import org.apache.spark.network.util.ByteUnit
 import org.apache.spark.sql.SparkSession
 import org.apache.spark.sql.SparkSessionExtensions
-import org.apache.spark.sql.catalyst.expressions.AttributeReference
 import org.apache.spark.sql.catalyst.rules.Rule
 import org.apache.spark.sql.comet._
 import org.apache.spark.sql.comet.execution.shuffle.{CometColumnarShuffle, CometNativeShuffle}

spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala

@@ -28,7 +28,7 @@ import org.apache.spark.sql.catalyst.expressions.objects.StaticInvoke
 import org.apache.spark.sql.catalyst.optimizer.NormalizeNaNAndZero
 import org.apache.spark.sql.catalyst.plans.physical.{HashPartitioning, Partitioning, SinglePartition}
 import org.apache.spark.sql.catalyst.util.CharVarcharCodegenUtils
-import org.apache.spark.sql.comet.{CometHashAggregateExec, CometPlan, CometSinkPlaceHolder, DecimalPrecision}
+import org.apache.spark.sql.comet.{CometSinkPlaceHolder, DecimalPrecision}
 import org.apache.spark.sql.execution
 import org.apache.spark.sql.execution._
 import org.apache.spark.sql.execution.aggregate.HashAggregateExec

spark/src/test/scala/org/apache/comet/CometCastSuite.scala

@@ -90,13 +90,13 @@ class CometCastSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     Range(0, len).map(_ => chars.charAt(r.nextInt(chars.length))).mkString
   }
 
-  private def fuzzCastFromString(chars: String, maxLen: Int, toType: DataType) {
+  private def fuzzCastFromString(chars: String, maxLen: Int, toType: DataType): Unit = {
     val r = new Random(0)
     val inputs = Range(0, 10000).map(_ => genString(r, chars, maxLen))
     castTest(inputs.toDF("a"), toType)
   }
 
-  private def castTest(input: DataFrame, toType: DataType) {
+  private def castTest(input: DataFrame, toType: DataType): Unit = {
     withTempPath { dir =>
       val df = roundtripParquet(input, dir)
         .withColumn("converted", col("a").cast(toType))

spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala

@@ -24,7 +24,7 @@ import java.util
 import org.apache.hadoop.fs.Path
 import org.apache.spark.sql.{CometTestBase, DataFrame, Row}
 import org.apache.spark.sql.execution.adaptive.AdaptiveSparkPlanHelper
-import org.apache.spark.sql.functions.{expr, lit}
+import org.apache.spark.sql.functions.expr
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.internal.SQLConf.SESSION_LOCAL_TIMEZONE
 import org.apache.spark.sql.types.{Decimal, DecimalType, StructType}