Check to verify that "copied files" are mentioned in LICENSE

To ensure that files that are known to be mentioned in `LICENSE` are really mentioned in that file, the Gradle plugin introduced in this change verifies this.

The "magic word" `CODE_COPIED_TO_POLARIS` must be present in such files. The presence of the "magic word" triggers a validation that the path of the containing file, relative to the project root directory, must be mentioned in `LICENSE`, prefixed with `* `.

The plugin checks all source directories in projects that have any Java plugin applied. For other projects, the plugin's extension provides a mechanism to add directory sets similar to how `SourceDirectorySet` works, which is used for the root project.

The plugin must be applied on the root project, it adds itself to all other projects. The introduced `checkForCopiedCode` task is added to the `check` task as a dependency.

Files that contain "copied code" need to have the word `CODE_COPIED_TO_POLARIS` anywhere.

Related to apache#903

Author: snazy

aggregated-license-report/build.gradle.kts

@@ -60,3 +60,5 @@ val aggregatedLicenseReportsZip by
     destinationDirectory.set(layout.buildDirectory.dir("distributions"))
     archiveExtension.set("zip")
   }
+
+tasks.register("check")

build-logic/src/main/kotlin/copiedcode/CopiedCodeCheckerExtension.kt

@@ -0,0 +1,104 @@
+/*
+ * 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.
+ */
+
+package copiedcode
+
+import org.gradle.api.Project
+import org.gradle.api.file.RegularFileProperty
+import org.gradle.api.file.SourceDirectorySet
+import org.gradle.api.provider.Property
+import org.gradle.api.provider.SetProperty
+
+abstract class CopiedCodeCheckerExtension(private val project: Project) {
+  /**
+   * Per-project set of additional directories to scan.
+   *
+   * This property is _not_ propagated to subprojects.
+   */
+  val scanDirectories =
+    project.objects.domainObjectContainer(
+      SourceDirectorySet::class.java,
+      { name -> project.objects.sourceDirectorySet(name, name) },
+    )
+
+  /**
+   * By default, this plugin scans all files. The content types that match the regular expression of
+   * this property are excluded, unless a content-type matches one of the regular expressions in
+   * [CopiedCodeCheckerExtension.includedContentTypePatterns].
+   *
+   * See [CopiedCodeCheckerExtension.addDefaultContentTypes],
+   * [CopiedCodeCheckerExtension.includedContentTypePatterns],
+   * [CopiedCodeCheckerExtension.includeUnrecognizedContentType],
+   * [CopiedCodeCheckerExtension.includedContentTypePatterns].
+   */
+  abstract val excludedContentTypePatterns: SetProperty<String>
+  /**
+   * By default, this plugin scans all files. The content types that match the regular expression of
+   * the [copiedcode.CopiedCodeCheckerExtension.excludedContentTypePatterns] property are excluded,
+   * unless a content-type matches one of the regular expressions in this property.
+   *
+   * See [CopiedCodeCheckerExtension.addDefaultContentTypes],
+   * [CopiedCodeCheckerExtension.excludedContentTypePatterns],
+   * [CopiedCodeCheckerExtension.includeUnrecognizedContentType],
+   * [CopiedCodeCheckerExtension.includedContentTypePatterns].
+   */
+  abstract val includedContentTypePatterns: SetProperty<String>
+
+  /**
+   * If a content-type could not be detected, this property, which defaults to `true`, is consulted.
+   *
+   * See [CopiedCodeCheckerPlugin] for details.
+   */
+  abstract val includeUnrecognizedContentType: Property<Boolean>
+
+  /**
+   * The magic "word", if present in a file, meaning "this file has been copied".
+   *
+   * A file is considered as "copied" must contain this magic word. "Word" means that the value must
+   * be surrounded by regular expression word boundaries (`\b`).
+   */
+  abstract val magicWord: Property<String>
+
+  /**
+   * License file to check, configured on the root project. See [CopiedCodeCheckerPlugin] for
+   * details.
+   */
+  abstract val licenseFile: RegularFileProperty
+
+  /** Recommended to use, adds known and used binary content types. */
+  fun addDefaultContentTypes(): CopiedCodeCheckerExtension {
+    // Exclude all images
+    excludedContentTypePatterns.add("image/.*")
+    // But include images built in XML (e.g. image/svg+xml)
+    includedContentTypePatterns.add("\\+xml")
+
+    return this
+  }
+
+  init {
+    includeUnrecognizedContentType.convention(true)
+    magicWord.convention(DEFAULT_MAGIC_WORD)
+  }
+
+  companion object {
+    // String manipulation is intentional - otherwise this source file would be considered as
+    // "copied".
+    val DEFAULT_MAGIC_WORD = "_CODE_COPIED_TO_POLARIS".substring(1)
+  }
+}