Adds check for license headers and unused imports

.github/workflows/main.yml

@@ -23,6 +23,8 @@ jobs:
       - uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633 # v4.1.2
         with:
           submodules: recursive
+        # Need to also fetch origin/master for the "rachetFrom" functionality of the "spotless" gradle plugin
+      - run: git fetch origin/master
       - uses: gradle/wrapper-validation-action@b231772637bb498f11fdbc86052b6e8a8dc9fc92 # v2.1.2
       - name: Use java ${{ matrix.java }}
         uses: actions/setup-java@99b8673ff64fbf99d8d325f52d9a5bdedb8483e9 # v4.2.1

build.gradle.kts

@@ -30,8 +30,8 @@ plugins {
     id("org.cyclonedx.bom") version "1.7.2"
     id("com.github.spotbugs") version "5.0.13"
     id("org.jlleitschuh.gradle.ktlint") version "11.3.2"
-    // TODO: more static analysis. E.g.:
-    // id("com.diffplug.spotless") version "6.11.0"
+
+    id("com.diffplug.spotless") version "6.11.0"
 
     // Used for generating the third party attribution document
     id("com.github.jk1.dependency-license-report") version "2.5"
@@ -99,6 +99,57 @@ licenseReport {
     )
 }
 
+/**
+ * This is the `git remote` name that corresponds to amazon-ion/ion-java.
+ * It is used for applying the "spotless" checks only to things that are changed
+ * compared to the master branch of the source repo.
+ */
+val sourceRepoRemoteName: String by lazy {
+    val git = System.getenv("GIT_CLI") ?: "git"
+
+    fun String.isSourceRepo(): Boolean {
+        val url = "$git remote get-url ${this@isSourceRepo}".runCommand()
+        return "amazon-ion/ion-java" in url || "amzn/ion-java" in url
+    }
+
+    "$git remote".runCommand().lines().firstOrNull { it.isSourceRepo() }
+        ?: throw Exception(
+            """
+            |No git remote found for amazon-ion/ion-java. Try again after running:
+            |
+            |    git remote add -f <name> https://github.com/amazon-ion/ion-java/
+            """.trimMargin()
+        )
+}
+
+fun String.runCommand(workingDir: File = rootProject.projectDir): String {
+    val parts = this.split("\\s".toRegex())
+    val proc = ProcessBuilder(*parts.toTypedArray())
+        .directory(workingDir)
+        .redirectOutput(ProcessBuilder.Redirect.PIPE)
+        .redirectError(ProcessBuilder.Redirect.PIPE)
+        .start()
+    proc.waitFor(30, TimeUnit.SECONDS)
+    return proc.inputStream.bufferedReader().readText()
+}
+
+spotless {
+    ratchetFrom("$sourceRepoRemoteName/master")
+
+    val shortFormLicenseHeader = """
+        // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+        // SPDX-License-Identifier: Apache-2.0
+    """.trimIndent()
+
+    java {
+        licenseHeader(shortFormLicenseHeader)
+        removeUnusedImports()
+    }
+    kotlin {
+        licenseHeader(shortFormLicenseHeader)
+    }
+}
+
 tasks {
     withType<JavaCompile> {
         options.encoding = "UTF-8"

src/main/java/com/amazon/ion/_Private_Trampoline.kt

@@ -1,3 +1,5 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
 package com.amazon.ion
 
 /**