[JENKINS-43507] Add some helper methods

src/main/java/jenkins/scm/api/trait/SCMTrait.java

@@ -24,8 +24,14 @@
 
 package jenkins.scm.api.trait;
 
+import edu.umd.cs.findbugs.annotations.CheckForNull;
+import edu.umd.cs.findbugs.annotations.NonNull;
+import edu.umd.cs.findbugs.annotations.Nullable;
 import hudson.DescriptorExtensionList;
 import hudson.model.AbstractDescribableImpl;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.Set;
 import jenkins.model.Jenkins;
 
 /**
@@ -54,4 +60,80 @@
         return Jenkins.getActiveInstance().getDescriptorList(specialization);
     }
 
+    /**
+     * Converts the supplied list of {@link SCMTrait} instances into a list where there is at most one instance of
+     * each trait.
+     *
+     * @param list the list to apply the constraint to.
+     * @param <T>  type of {@link SCMTrait}.
+     * @return a new list that contains the first instance of any type of trait in the supplied list.
+     * @since 2.2.0
+     */
+    @NonNull
+    public static <T extends SCMTrait<?>> ArrayList<T> asSetList(@CheckForNull Iterable<? extends T> list) {
+        ArrayList<T> result = new ArrayList<T>();
+        if (list != null) {
+            Set<Class> seen = new HashSet<Class>();
+            for (T trait : list) {
+                if (trait == null) {
+                    continue;
+                }
+                if (seen.contains(trait.getClass())) {
+                    continue;
+                }
+                seen.add(trait.getClass());
+                result.add(trait);
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Converts the supplied instance and list of {@link SCMTrait} instances into a list where there is at most one
+     * instance of each trait.
+     *
+     * @param list the list to apply the constraint to.
+     * @param <T>  type of {@link SCMTrait}.
+     * @return a new list that contains the first instance of any type of trait in the supplied list.
+     * @since 2.2.0
+     */
+    public static <T extends SCMTrait<?>> ArrayList<T> asSetList(@NonNull T first, @CheckForNull Iterable<? extends T> list) {
+        ArrayList<T> result = new ArrayList<T>();
+        result.add(first);
+        if (list != null) {
+            Set<Class> seen = new HashSet<Class>();
+            seen.add(first.getClass());
+            for (T trait : list) {
+                if (trait == null) {
+                    continue;
+                }
+                if (seen.contains(trait.getClass())) {
+                    continue;
+                }
+                seen.add(trait.getClass());
+                result.add(trait);
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Finds the trait of the required type.
+     *
+     * @param traits the traits to search.
+     * @param clazz  the type of trait.
+     * @param <T>    the type of trait.
+     * @return the matching trait from the supplied traits or {@code null} if there is no matching trait.
+     * @since 2.2.0
+     */
+    @CheckForNull
+    public static <T extends SCMTrait<?>> T find(@NonNull Iterable<?> traits, @NonNull Class<T> clazz) {
+        for (Object trait : traits) {
+            if (clazz.isInstance(trait)) {
+                return clazz.cast(trait);
+            }
+        }
+        return null;
+    }
+
 }

src/test/java/jenkins/scm/impl/mock/MockSCMNavigator.java

@@ -61,7 +61,7 @@
     @DataBoundConstructor
     public MockSCMNavigator(String controllerId, List<SCMTrait<?>> traits) {
         this.controllerId = controllerId;
-        this.traits = new ArrayList<SCMTrait<?>>(traits);
+        this.traits = SCMTrait.asSetList(traits);
     }
 
     public MockSCMNavigator(String controllerId, SCMTrait<?>... traits) {
@@ -71,7 +71,7 @@ public MockSCMNavigator(String controllerId, SCMTrait<?>... traits) {
     public MockSCMNavigator(MockSCMController controller, List<SCMTrait<?>> traits) {
         this.controllerId = controller.getId();
         this.controller = controller;
-        this.traits = new ArrayList<SCMTrait<?>>(traits);
+        this.traits = SCMTrait.asSetList(traits);
     }
 
     public MockSCMNavigator(MockSCMController controller, SCMTrait<?>... traits) {

src/test/java/jenkins/scm/impl/mock/MockSCMSource.java

@@ -29,7 +29,6 @@
 import edu.umd.cs.findbugs.annotations.NonNull;
 import edu.umd.cs.findbugs.annotations.Nullable;
 import hudson.Extension;
-import hudson.RestrictedSince;
 import hudson.model.Action;
 import hudson.model.TaskListener;
 import hudson.scm.SCM;
@@ -59,13 +58,12 @@
 import jenkins.scm.api.trait.SCMSourceRequest;
 import jenkins.scm.api.trait.SCMSourceTrait;
 import jenkins.scm.api.trait.SCMSourceTraitDescriptor;
+import jenkins.scm.api.trait.SCMTrait;
 import jenkins.scm.impl.ChangeRequestSCMHeadCategory;
 import jenkins.scm.impl.TagSCMHeadCategory;
 import jenkins.scm.impl.UncategorizedSCMHeadCategory;
 import org.apache.commons.io.IOUtils;
 import org.jenkinsci.Symbol;
-import org.kohsuke.accmod.Restricted;
-import org.kohsuke.accmod.restrictions.NoExternalUse;
 import org.kohsuke.stapler.DataBoundConstructor;
 import org.kohsuke.stapler.QueryParameter;
 
@@ -79,7 +77,7 @@
     public MockSCMSource(String controllerId, String repository, List<SCMSourceTrait> traits) {
         this.controllerId = controllerId;
         this.repository = repository;
-        this.traits = new ArrayList<SCMSourceTrait>(traits);
+        this.traits = SCMTrait.asSetList(traits);
     }
 
     public MockSCMSource(String controllerId, String repository, SCMSourceTrait... traits) {
@@ -90,7 +88,7 @@ public MockSCMSource(MockSCMController controller, String repository, List<SCMSo
         this.controllerId = controller.getId();
         this.controller = controller;
         this.repository = repository;
-        this.traits = new ArrayList<SCMSourceTrait>(traits);
+        this.traits = SCMTrait.asSetList(traits);
     }
 
     public MockSCMSource(MockSCMController controller, String repository, SCMSourceTrait... traits) {