Added support for getting the merge base (#288).

src/main/java/org/gitlab4j/api/RepositoryApi.java

@@ -16,6 +16,7 @@ import javax.ws.rs.core.Response;
 
 import org.gitlab4j.api.GitLabApi.ApiVersion;
 import org.gitlab4j.api.models.Branch;
+import org.gitlab4j.api.models.Commit;
 import org.gitlab4j.api.models.CompareResults;
 import org.gitlab4j.api.models.Contributor;
 import org.gitlab4j.api.models.Tag;
@@ -742,4 +743,40 @@ public class RepositoryApi extends AbstractApi {
     public Stream<Contributor> getContributorsStream(Object projectIdOrPath) throws GitLabApiException {
         return (getContributors(projectIdOrPath, getDefaultPerPage()).stream());
     }
+
+    /**
+     * Get the common ancestor for 2 or more refs (commit SHAs, branch names or tags).
+     *
+     * <pre><code>GitLab Endpoint: GET /projects/:id/repository/merge_base</code></pre>
+     *
+     * @param projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance
+     * @param refs a List of 2 or more refs (commit SHAs, branch names or tags)
+     * @return the Commit instance containing the common ancestor
+     * @throws GitLabApiException if any exception occurs
+     */
+    public Commit getMergeBase(Object projectIdOrPath, List<String> refs) throws GitLabApiException {
+        GitLabApiForm queryParams = new GitLabApiForm().withParam("refs", refs, true);
+        Response response = get(Response.Status.OK, queryParams.asMap(), "projects",
+                getProjectIdOrPath(projectIdOrPath), "repository", "merge_base");
+        return (response.readEntity(Commit.class));
+    }
+
+    /**
+     * Get an Optional instance with the value of the common ancestor
+     * for 2 or more refs (commit SHAs, branch names or tags).
+     *
+     * <pre><code>GitLab Endpoint: GET /projects/:id/repository/merge_base</code></pre>
+     *
+     * @param projectIdOrPath the project in the form of an Integer(ID), String(path), or Project instance
+     * @param refs a List of 2 or more refs (commit SHAs, branch names or tags)
+     * @return an Optional instance with the Commit instance containing the common ancestor as the value
+     * @throws GitLabApiException if any exception occurs
+     */
+    public Optional<Commit> getOptionalMergeBase(Object projectIdOrPath, List<String> refs) throws GitLabApiException {
+        try {
+            return (Optional.ofNullable(getMergeBase(projectIdOrPath, refs)));
+        } catch (GitLabApiException glae) {
+            return (GitLabApi.createOptionalFromException(glae));
+        }
+    }
 }

src/test/java/org/gitlab4j/api/TestRepositoryApi.java

@@ -12,6 +12,7 @@ import java.io.InputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
+import java.util.Arrays;
 import java.util.List;
 
 import org.gitlab4j.api.models.Branch;
@@ -54,6 +55,8 @@ public class TestRepositoryApi {
     }
 
     private static final String TEST_BRANCH_NAME = "feature/test_branch";
+    private static final String TEST_BRANCH1 = "feature/test_branch1";
+    private static final String TEST_BRANCH2 = "feature/test_branch2";
     private static final String TEST_PROTECT_BRANCH_NAME = "feature/protect_branch";
     private static GitLabApi gitLabApi;
 
@@ -101,6 +104,16 @@ public class TestRepositoryApi {
                 } catch (GitLabApiException ignore) {
                 }
 
+                try {
+                    gitLabApi.getRepositoryApi().deleteBranch(project.getId(), TEST_BRANCH1);
+                } catch (GitLabApiException ignore) {
+                }
+
+                try {
+                    gitLabApi.getRepositoryApi().deleteBranch(project.getId(), TEST_BRANCH2);
+                } catch (GitLabApiException ignore) {
+                }
+
                 gitLabApi.getRepositoryApi().deleteBranch(project.getId(), TEST_PROTECT_BRANCH_NAME);
 
             } catch (GitLabApiException ignore) {
@@ -200,4 +213,20 @@ public class TestRepositoryApi {
         assertNotNull(unprotectedBranch);
         assertFalse(unprotectedBranch.getProtected());
     }
+
+    @Test
+    public void testMergeBase() throws GitLabApiException {
+
+        Project project = gitLabApi.getProjectApi().getProject(TEST_NAMESPACE, TEST_PROJECT_NAME);
+        assertNotNull(project);
+
+        Branch branch1 = gitLabApi.getRepositoryApi().createBranch(project.getId(), TEST_BRANCH1, "master");
+        assertNotNull(branch1);
+        Branch branch2 = gitLabApi.getRepositoryApi().createBranch(project.getId(), TEST_BRANCH2, "master");
+        assertNotNull(branch2);
+
+        List<String> refs = Arrays.asList(TEST_BRANCH1, TEST_BRANCH2);
+        Commit mergeBase = gitLabApi.getRepositoryApi().getMergeBase(project, refs);
+        assertNotNull(mergeBase);
+    }
 }