Support shallow clone in multibranch Pipeline and resolveScm

README.adoc

@@ -136,6 +136,18 @@ checkout scmGit(
     userRemoteConfigs: [[url: 'https://github.com/jenkinsci/ws-cleanup-plugin']])
 ----
 
+[source,groovy]
+----
+def resolvedSCMBranch = resolveScm(
+  source: gitSource(
+    credentialsId: 'git-cred',
+    traits: [cloneOption(cloneOption(depth: 1, shallow: true)), gitBranchDiscovery()]
+    remote: 'https://github.com/jenkinsci/ws-cleanup-plugin'),
+    targets: ['main', 'master']
+)
+checkout resolvedSCMBranch
+----
+
 ==== Checkout with a narrow refspec
 
 Checkout from the workspace cleanup plugin source repository using https without credentials, the `master` branch, and with a refspec specific to the master branch.

src/main/java/jenkins/plugins/git/AbstractGitSCMSource.java

@@ -404,6 +404,7 @@ private <T, C extends GitSCMSourceContext<C, R>, R extends GitSCMSourceRequest>
                 fetch.tags(context.wantTags());
             }
             fetch = fetch.prune(prune);
+            fetch = fetch.shallow(context.wantShallow()).depth(context.depth());
 
             URIish remoteURI = null;
             try {

src/main/java/jenkins/plugins/git/GitSCMSourceContext.java

@@ -94,6 +94,14 @@ public class GitSCMSourceContext<C extends GitSCMSourceContext<C, R>, R extends
      */
     @NonNull
     private String remoteName = AbstractGitSCMSource.DEFAULT_REMOTE_NAME;
+    /**
+     * Perform shallow clone
+     */
+    private boolean shallow;
+    /**
+     * Shallow clone depth
+     */
+    private Integer depth;
 
     /**
      * Constructor.
@@ -192,6 +200,25 @@ public final String remoteName() {
         return remoteName;
     }
 
+    /**
+     * Returns {@code true} if a limited number of commits will be retrieved when cloning with a GitSCMSource.
+     * A GitSCMSource is most commonly used when defining a multibranch Pipeline.
+     *
+     * @return {@code true} if a limited number of commits will be retrieved
+     */
+    public final boolean wantShallow() {
+        return shallow;
+    }
+
+    /**
+     * Returns shallow clone depth
+     *
+     * @return shallow clone depth
+     */
+    public final Integer depth() {
+        return depth;
+    }
+
     /**
      * Adds a requirement for branch details to any {@link GitSCMSourceRequest} for this context.
      *
@@ -358,6 +385,34 @@ public final List<RefSpec> asRefSpecs() {
         return result;
     }
 
+    /**
+     * Limit the number of commits that will be retrieved when the multibranch Pipeline is cloned.
+     * When shallow clone is enabled, a single commit will be retrieved instead of retrieving all commits.
+     * If more commits are needed, set the depth to a larger value.
+     *
+     * @param shallow {@code true} to perform shallow clone
+     * @return {@code this} for method chaining.
+     */
+    @SuppressWarnings("unchecked")
+    @NonNull
+    public final C shallow(boolean shallow) {
+        this.shallow = shallow;
+        return (C) this;
+    }
+
+    /**
+     * Configures shallow clone depth
+     *
+     * @param depth upper limit to the number of commits included in the repository clone
+     * @return {@code this} for method chaining.
+     */
+    @SuppressWarnings("unchecked")
+    @NonNull
+    public final C depth(Integer depth) {
+        this.depth = depth;
+        return (C) this;
+    }
+
     /**
      * {@inheritDoc}
      */

src/main/java/jenkins/plugins/git/traits/CloneOptionTrait.java

@@ -27,6 +27,8 @@
 
 import hudson.Extension;
 import hudson.plugins.git.extensions.impl.CloneOption;
+import jenkins.plugins.git.GitSCMSourceContext;
+import jenkins.scm.api.trait.SCMSourceContext;
 import jenkins.scm.api.trait.SCMSourceTrait;
 import org.jenkinsci.Symbol;
 import org.kohsuke.stapler.DataBoundConstructor;
@@ -47,6 +49,12 @@ public CloneOptionTrait(CloneOption extension) {
         super(extension);
     }
 
+    @Override
+    protected void decorateContext(SCMSourceContext<?, ?> context) {
+        CloneOption extension = getExtension();
+        ((GitSCMSourceContext<?, ?>) context).shallow(extension.isShallow()).depth(extension.getDepth());
+    }
+
     /**
      * Our {@link hudson.model.Descriptor}
      */

src/test/java/jenkins/plugins/git/traits/CloneOptionTraitTest.java

@@ -0,0 +1,42 @@
+package jenkins.plugins.git.traits;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+import hudson.plugins.git.extensions.impl.CloneOption;
+import jenkins.plugins.git.GitSCMSourceContext;
+
+class CloneOptionTraitTest {
+
+    @Test
+    void testShallowDisabledByDefault() {
+        GitSCMSourceContext<?, ?> context = new GitSCMSourceContext<>(null, null);
+        assertFalse(context.wantShallow());
+        assertNull(context.depth());
+    }
+
+    @Test
+    void testDecorateWithDefaultCloneOption() {
+        GitSCMSourceContext<?, ?> context = new GitSCMSourceContext<>(null, null);
+        CloneOption cloneOption = new CloneOption(false, null, null);
+        CloneOptionTrait cloneOptionTrait = new CloneOptionTrait(cloneOption);
+        cloneOptionTrait.decorateContext(context);
+        assertFalse(context.wantShallow());
+        assertNull(context.depth());
+    }
+
+    @Test
+    void testDecorateCloneOptionWithShallow() {
+        GitSCMSourceContext<?, ?> context = new GitSCMSourceContext<>(null, null);
+        CloneOption cloneOption = new CloneOption(true, null, null);
+        cloneOption.setDepth(10);
+        CloneOptionTrait cloneOptionTrait = new CloneOptionTrait(cloneOption);
+        cloneOptionTrait.decorateContext(context);
+        assertTrue(context.wantShallow());
+        assertEquals(context.depth(), 10);
+    }
+}