Build: Integrate Scalafix to auto-fix unused Scala imports

.baseline/scala/.scalafix.conf

@@ -0,0 +1,23 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+rules = [RemoveUnused]
+RemoveUnused.imports = true
+RemoveUnused.privates = false
+RemoveUnused.locals = false
+RemoveUnused.patternvars = false
+RemoveUnused.params = false

baseline.gradle

@@ -187,6 +187,21 @@ subprojects {
   }
 
   pluginManager.withPlugin('scala') {
+    apply plugin: 'io.github.cosmicsilence.scalafix'
+
+    scalafix {
+      configFile = file("${rootDir}/.baseline/scala/.scalafix.conf")
+      semanticdb {
+        autoConfigure = true
+      }
+    }
+
+    // When running scalafix, downgrade unused import errors to warnings so that
+    // compilation succeeds and SemanticDB is produced for Scalafix to process.
+    boolean scalafixRun = gradle.startParameter.taskNames.any {
+      it.toLowerCase().contains('scalafix')
+    }
+
     tasks.withType(ScalaCompile).configureEach { scalaCompile ->
       if (scalaVersion?.startsWith("2.12")) {
         scalaCompile.scalaCompileOptions.additionalParameters = [
@@ -196,8 +211,8 @@ subprojects {
         ]
       } else if (scalaVersion?.startsWith("2.13")) {
         scalaCompile.scalaCompileOptions.additionalParameters = [
-                "-Wconf:cat=unused:error",
-                "-Wunused:imports"
+                "-Wunused:imports",
+                scalafixRun ? "-Wconf:cat=unused:warning" : "-Wconf:cat=unused:error",
         ]
       }
     }

build.gradle

@@ -33,6 +33,7 @@ buildscript {
     classpath 'me.champeau.jmh:jmh-gradle-plugin:0.7.3'
     classpath 'gradle.plugin.io.morethan.jmhreport:gradle-jmh-report:0.9.6'
     classpath "com.github.alisiikh:gradle-scalastyle-plugin:3.5.0"
+    classpath 'io.github.cosmicsilence:gradle-scalafix:0.2.6'
     classpath 'org.revapi:gradle-revapi:1.8.0'
     classpath 'com.gorylenko.gradle-git-properties:gradle-git-properties:2.5.7'
     classpath 'com.palantir.gradle.gitversion:gradle-git-version:4.3.0'

site/docs/contribute.md

@@ -111,6 +111,7 @@ Iceberg is built using Gradle with Java 17 or 21.
 * To invoke a build and run tests: `./gradlew build`
 * To skip tests: `./gradlew build -x test -x integrationTest`
 * To fix code style: `./gradlew spotlessApply`
+* To fix Scala unused imports: `./gradlew scalafix`
 * To build particular Spark/Flink Versions: `./gradlew build -DsparkVersions=3.5,4.0 -DflinkVersions=1.20,2.0`
 
 Iceberg table support is organized in library modules:
@@ -303,6 +304,12 @@ In order to automatically fix Java code style issues, please use `./gradlew spot
 since that version is compatible with JDK 8. When formatting the code in the IDE, there is a slight chance that it will produce slightly different results. In such a case please run `./gradlew spotlessApply`
 as CI will check the style against **google-java-format** 1.7.
 
+For Scala code, unused imports are treated as compilation errors. To automatically remove unused imports, run [Scalafix](https://scalacenter.github.io/scalafix/):
+
+```bash
+./gradlew scalafix -DsparkVersions=4.0 -DscalaVersion=2.13
+```
+
 ### Copyright
 
 Each file must include the Apache license information as a header.