Build: Allow license header check to be customized

This change allows setting which license families are approved, as well
as adding matchers for additional license types.

buildSrc/src/main/groovy/org/elasticsearch/gradle/precommit/LicenseHeadersTask.groovy

@@ -23,6 +23,7 @@ import org.apache.rat.anttasks.SubstringLicenseMatcher
 import org.apache.rat.license.SimpleLicenseFamily
 import org.elasticsearch.gradle.AntTask
 import org.gradle.api.file.FileCollection
+import org.gradle.api.tasks.Input
 import org.gradle.api.tasks.OutputFile
 import org.gradle.api.tasks.SourceSet
 
@@ -44,6 +45,16 @@ public class LicenseHeadersTask extends AntTask {
      */
     protected List<FileCollection> javaFiles
 
+    /** Allowed license families for this project. */
+    @Input
+    List<String> approvedLicenses = ['Apache', 'Generated']
+
+    /**
+     * Additional license families that may be found. The key is the license category name (5 characters),
+     * followed by the family name and the value list of patterns to search for.
+     */
+    protected Map<String, String> additionalLicenses = [:]
+
     LicenseHeadersTask() {
         description = "Checks sources for missing, incorrect, or unacceptable license headers"
         // Delay resolving the dependencies until after evaluation so we pick up generated sources
@@ -53,6 +64,13 @@ public class LicenseHeadersTask extends AntTask {
         }
     }
 
+    public void additionalLicense(String categoryName, String familyName, String pattern) {
+        if (categoryName.length() != 5) {
+            throw new IllegalArgumentException("License category name must be exactly 5 characters, got ${categoryName}");
+        }
+        additionalLicenses.put("${categoryName}${familyName}", pattern);
+    }
+
     @Override
     protected void runAnt(AntBuilder ant) {
         ant.project.addTaskDefinition('ratReport', Report)
@@ -98,9 +116,20 @@ public class LicenseHeadersTask extends AntTask {
                pattern(substring: "ANTLR GENERATED CODE")
             }
 
+            // license types added by the project
+            for (Map.Entry<String, String[]> additional : additionalLicenses.entrySet()) {
+                String category = additional.getKey().substring(0, 5)
+                String family = additional.getKey().substring(5)
+                substringMatcher(licenseFamilyCategory: category,
+                                 licenseFamilyName: family) {
+                    pattern(substring: additional.getValue())
+                }
+            }
+
             // approved categories
-               approvedLicense(familyName: "Apache")
+            for (String licenseFamily : approvedLicenses) {
-               approvedLicense(familyName: "Generated")
+                approvedLicense(familyName: licenseFamily)
+            }
         }
 
         // check the license file for any errors, this should be fast.