Fix dependency check for ignored licenses (#104736)

if there are no dependencies declared and the license file is marked as
ignored, no exception should be thrown and dependencylicense check
should pass.

Fixes issues we identified in #104628

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/precommit/DependencyLicensesTask.java

@@ -28,6 +28,7 @@
 
 import java.io.File;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
@@ -187,7 +188,7 @@ public void checkDependencies() {
         }
         File licensesDirAsFile = licensesDir.get().getAsFile();
         if (dependencies.isEmpty()) {
-            if (licensesDirAsFile.exists()) {
+            if (licensesDirAsFile.exists() && allIgnored() == false) {
                 throw new GradleException("Licenses dir " + licensesDirAsFile + " exists, but there are no dependencies");
             }
             return; // no dependencies to check
@@ -227,6 +228,10 @@ public void checkDependencies() {
         sources.forEach((item, exists) -> failIfAnyMissing(item, exists, "sources"));
     }
 
+    private boolean allIgnored() {
+        return Arrays.asList(getLicensesDir().listFiles()).stream().map(f -> f.getName()).allMatch(ignoreFiles::contains);
+    }
+
     // This is just a marker output folder to allow this task being up-to-date.
     // The check logic is exception driven so a failed tasks will not be defined
     // by this output but when successful we can safely mark the task as up-to-date.

build-tools-internal/src/test/java/org/elasticsearch/gradle/internal/precommit/DependencyLicensesTaskTests.java

@@ -63,8 +63,17 @@ public void execute(DependencyLicensesTask dependencyLicensesTask) {
     public void givenProjectWithLicensesDirButNoDependenciesThenShouldThrowException() throws Exception {
         expectedException.expect(GradleException.class);
         expectedException.expectMessage(containsString("exists, but there are no dependencies"));
+        getLicensesDir(project).mkdir();
+        createFileIn(getLicensesDir(project), "groovy-LICENSE.txt", PERMISSIVE_LICENSE_TEXT);
+        task.get().checkDependencies();
+    }
 
+    @Test
+    public void givenProjectWithLicensesDirButAllIgnoreFileAndNoDependencies() throws Exception {
         getLicensesDir(project).mkdir();
+        String licenseFileName = "cloudcarbonfootprint-LICENSE.txt";
+        createFileIn(getLicensesDir(project), licenseFileName, PERMISSIVE_LICENSE_TEXT);
+        task.get().ignoreFile(licenseFileName);
         task.get().checkDependencies();
     }