Add an "opt-out" global switch to retain second fetch

README.adoc

@@ -166,6 +166,11 @@ Show the entire commit summary in changes::
   With the release of git plugin 4.0, the default was changed to show the complete change summary.
   Administrators that want to restore the old behavior may disable this setting.
 
+[[preserve-second-fetch-during-checkout]]
+Preserve second fetch during checkout::
+
+  If checked the checkout step will not avoid the second fetch.
+
 [#repository-browser]
 === Repository Browser
 

src/main/java/hudson/plugins/git/GitSCM.java

@@ -438,6 +438,11 @@ public boolean isUseExistingAccountWithSameEmail() {
         return (gitDescriptor != null && gitDescriptor.isUseExistingAccountWithSameEmail());
     }
 
+    public boolean isRedundantFetchAllowed() {
+        DescriptorImpl gitDescriptor = getDescriptor();
+        return (gitDescriptor != null && gitDescriptor.isRedundantFetchAllowed());
+    }
+
     @Whitelisted
     public BuildChooser getBuildChooser() {
         BuildChooser bc;
@@ -835,7 +840,6 @@ public GitClient createClient(TaskListener listener, EnvVars environment, Run<?,
 
         String gitExe = getGitExe(n, listener);
         Git git = Git.with(listener, environment).in(ws).using(gitExe);
-
         GitClient c = git.getClient();
         for (GitSCMExtension ext : extensions) {
             c = ext.decorate(this,c);
@@ -1133,7 +1137,9 @@ private void retrieveChanges(Run build, GitClient git, TaskListener listener) th
                 cmd.execute();
                 // determine if second fetch is required
                 CloneOption option = extensions.get(CloneOption.class);
-                removeRedundantFetch = determineRedundantFetch(option, rc);
+                if (!isRedundantFetchAllowed()) {
+                    removeRedundantFetch = determineRedundantFetch(option, rc);
+                }
             } catch (GitException ex) {
                 ex.printStackTrace(listener.error("Error cloning remote repo '" + rc.getName() + "'"));
                 throw new AbortException("Error cloning remote repo '" + rc.getName() + "'");
@@ -1519,6 +1525,7 @@ public static final class DescriptorImpl extends SCMDescriptor<GitSCM> {
         private boolean useExistingAccountWithSameEmail;
 //        private GitClientType defaultClientType = GitClientType.GITCLI;
         private boolean showEntireCommitSummaryInChanges;
+        private boolean allowSecondFetch;
 
         public DescriptorImpl() {
             super(GitSCM.class, GitRepositoryBrowser.class);
@@ -1642,6 +1649,12 @@ public void setUseExistingAccountWithSameEmail(boolean useExistingAccountWithSam
             this.useExistingAccountWithSameEmail = useExistingAccountWithSameEmail;
         }
 
+        public boolean isRedundantFetchAllowed() { return allowSecondFetch; }
+
+        public void setAllowSecondFetch(boolean allowSecondFetch) {
+            this.allowSecondFetch = allowSecondFetch;
+        }
+
         /**
          * Old configuration of git executable - exposed so that we can
          * migrate this setting to GitTool without deprecation warnings.

src/main/resources/hudson/plugins/git/GitSCM/global.jelly

@@ -16,6 +16,9 @@
     <f:entry field="showEntireCommitSummaryInChanges">
       <f:checkbox title="${%Show the entire commit summary in changes}" name="showEntireCommitSummaryInChanges" checked="${descriptor.showEntireCommitSummaryInChanges}"/>
     </f:entry>
+    <f:entry field="allowSecondFetch">
+      <f:checkbox title="${%Preserve second fetch during checkout}" name="allowSecondFetch" checked="${descriptor.allowSecondFetch}"/>
+    </f:entry>
     <!--
     <f:entry title="${%Default git client implementation}" field="defaultClientType">
         <select>

src/test/java/hudson/plugins/git/GitSCMTest.java

@@ -517,6 +517,42 @@ public void testRetainRedundantFetch() throws Exception {
         assertRedundantFetchIsUsed(build, refspec);
     }
 
+    /*
+    * When "Preserve second fetch during checkout" is checked in during configuring Jenkins,
+    * the second fetch should be retained
+    */
+    @Test
+    @Issue("JENKINS-49757")
+    public void testRetainRedundantFetchIfSecondFetchIsAllowed() throws Exception {
+        String refspec = "+refs/heads/*:refs/remotes/*";
+        List<UserRemoteConfig> repos = new ArrayList<>();
+        repos.add(new UserRemoteConfig(testRepo.gitDir.getAbsolutePath(), "origin", refspec, null));
+
+        /* Without honor refspec on initial clone */
+        FreeStyleProject projectWithMaster = setupProject(repos, Collections.singletonList(new BranchSpec("master")), null, false, null);
+
+        GitSCM scm = (GitSCM) projectWithMaster.getScm();
+        final DescriptorImpl descriptor = (DescriptorImpl) scm.getDescriptor();
+        assertThat("Redundant fetch is skipped by default", scm.isRedundantFetchAllowed(), is(false));
+        descriptor.setAllowSecondFetch(true);
+        assertThat("Redundant fetch should be allowed", scm.isRedundantFetchAllowed(), is(true));
+
+        if (random.nextBoolean()) {
+            /* Randomly enable shallow clone, should not alter test assertions */
+            CloneOption cloneOptionMaster = new CloneOption(false, null, null);
+            cloneOptionMaster.setDepth(1);
+            ((GitSCM) projectWithMaster.getScm()).getExtensions().add(cloneOptionMaster);
+        }
+
+        // create initial commit
+        final String commitFile1 = "commitFile1";
+        commit(commitFile1, johnDoe, "Commit in master");
+
+        FreeStyleBuild build = build(projectWithMaster, Result.SUCCESS);
+
+        assertRedundantFetchIsUsed(build, refspec);
+    }
+
     // Checks if the second fetch is being avoided
     private void assertRedundantFetchIsSkipped(FreeStyleBuild build, String refSpec) throws IOException {
         assertRedundantFetchCount(build, refSpec, 1);