[ML] Include 3rd party C++ component notices (#30132)

The overall NOTICE file for the ML X-Pack module should
include the notices from the 3rd party C++ components as
well as the 3rd party Java components.

distribution/archives/build.gradle

@@ -217,6 +217,24 @@ subprojects {
   }
   check.dependsOn checkNotice
 
+  if (project.name == 'zip' || project.name == 'tar') {
+    task checkMlCppNotice {
+      dependsOn buildDist, checkExtraction
+      onlyIf toolExists
+      doLast {
+        // this is just a small sample from the C++ notices, the idea being that if we've added these lines we've probably added all the required lines
+        final List<String> expectedLines = Arrays.asList("Apache log4cxx", "Boost Software License - Version 1.0 - August 17th, 2003")
+        final Path noticePath = archiveExtractionDir.toPath().resolve("elasticsearch-${VersionProperties.elasticsearch}/modules/x-pack/x-pack-ml/NOTICE.txt")
+        final List<String> actualLines = Files.readAllLines(noticePath)
+        for (final String expectedLine : expectedLines) {
+          if (actualLines.contains(expectedLine) == false) {
+            throw new GradleException("expected [${noticePath}] to contain [${expectedLine}] but it did not")
+          }
+        }
+      }
+    }
+    check.dependsOn checkMlCppNotice
+  }
 }
 
 /*****************************************************************************

x-pack/plugin/ml/build.gradle

@@ -64,6 +64,23 @@ artifacts {
     testArtifacts testJar
 }
 
+task extractNativeLicenses(type: Copy) {
+    dependsOn configurations.nativeBundle
+    into "${buildDir}"
+    from {
+        project.zipTree(configurations.nativeBundle.singleFile)
+    }
+    include 'platform/licenses/**'
+}
+project.afterEvaluate {
+    // Add an extra licenses directory to the combined notices
+    project.tasks.findByName('generateNotice').dependsOn extractNativeLicenses
+    project.tasks.findByName('generateNotice').licensesDir new File("${project.buildDir}/platform/licenses")
+    project.tasks.findByName('generateNotice').outputs.upToDateWhen {
+        extractNativeLicenses.state.upToDate
+    }
+}
+
 run {
     plugin xpackModule('core')
 }