Add option to suppress merge commits diff in showRevision

src/main/java/org/jenkinsci/plugins/gitclient/CliGitAPIImpl.java

@@ -1342,12 +1342,23 @@ public List<String> showRevision(ObjectId from, ObjectId to) throws GitException
         return showRevision(from, to, true);
     }
 
-    /** {@inheritDoc} */
     @Override
     public List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutput)
             throws GitException, InterruptedException {
+        return showRevision(from, to, useRawOutput, false);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutput, Boolean suppressMergeCommitDiff)
+            throws GitException, InterruptedException {
         ArgumentListBuilder args =
-                new ArgumentListBuilder("log", "--full-history", "--no-abbrev", "--format=raw", "-M", "-m");
+                new ArgumentListBuilder("log", "--full-history", "--no-abbrev", "--format=raw", "-M");
+
+        if (!suppressMergeCommitDiff) {
+            args.add("-m");
+        }
+
         if (useRawOutput) {
             args.add("--raw");
         }

src/main/java/org/jenkinsci/plugins/gitclient/GitClient.java

@@ -950,6 +950,31 @@ void submoduleUpdate(boolean recursive, boolean remoteTracking, String reference
     List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutput)
             throws GitException, InterruptedException;
 
+    /**
+     * Given a Revision, show it as if it were an entry from git whatchanged, so that it
+     * can be parsed by GitChangeLogParser.
+     *
+     * <p>
+     * If useRawOutput is true, the '--raw' option will include commit file information to be passed to the
+     * GitChangeLogParser.
+     *
+     * <p>
+     * Changes are computed on the [from..to] range. If {@code from} is null, this prints
+     * just one commit that {@code to} represents.
+     *
+     * <p>
+     * If suppressMergeCommitDiff is false, for merge commit this method reports one diff per each parent.
+     *
+     * @param from a {@link org.eclipse.jgit.lib.ObjectId} object.
+     * @param to a {@link org.eclipse.jgit.lib.ObjectId} object.
+     * @param useRawOutput a {java.lang.Boolean} object.
+     * @param suppressMergeCommitDiff a {java.lang.Boolean} object.
+     * @return The git whatchanged output, in <code>raw</code> format.
+     * @throws hudson.plugins.git.GitException if underlying git operation fails.
+     * @throws java.lang.InterruptedException if interrupted.
+     */
+    List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutput, Boolean suppressMergeCommitDiff)
+            throws GitException, InterruptedException;
     /**
      * Equivalent of "git-describe --tags".
      *

src/main/java/org/jenkinsci/plugins/gitclient/JGitAPIImpl.java

@@ -2438,6 +2438,13 @@ public List<String> showRevision(ObjectId from, ObjectId to) throws GitException
     /** {@inheritDoc} */
     @Override
     public List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutput) throws GitException {
+        return showRevision(from, to, useRawOutput, false);
+    }
+
+    /** {@inheritDoc} */
+    @Override
+    public List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutput, Boolean suppressMergeCommitDiff)
+            throws GitException {
         try (Repository repo = getRepository();
                 ObjectReader or = repo.newObjectReader();
                 RevWalk w = new RevWalk(or)) {
@@ -2457,9 +2464,10 @@ public List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutpu
                     if (c.getParentCount() <= 1 || !useRawOutput) {
                         f.format(c, null, pw, useRawOutput);
                     } else {
-                        // the effect of the -m option, which makes the diff produce for each parent of a merge commit
-                        for (RevCommit p : c.getParents()) {
-                            f.format(c, p, pw, useRawOutput);
+                        if (!suppressMergeCommitDiff) {
+                            for (RevCommit p : c.getParents()) {
+                                f.format(c, p, pw, useRawOutput);
+                            }
                         }
                     }
 

src/main/java/org/jenkinsci/plugins/gitclient/RemoteGitImpl.java

@@ -852,6 +852,12 @@
         return proxy.showRevision(from, to, useRawOutput);
     }
 
+    @Override
+    public List<String> showRevision(ObjectId from, ObjectId to, Boolean useRawOutput, Boolean suppressMergeCommitDiff)
+            throws GitException, InterruptedException {
+        return proxy.showRevision(from, to, useRawOutput);
+    }
+
     /** {@inheritDoc} */
     @Override
     public boolean hasGitModules(String treeIsh) throws GitException, InterruptedException {

src/test/java/org/jenkinsci/plugins/gitclient/GitAPITestUpdate.java

@@ -2046,6 +2046,49 @@ public void testChangelogWithMergeCommitAndMaxLogHistory() throws Exception {
         assertThat(writer.toString(), is(not("")));
     }
 
+    @Issue("JENKINS-23606")
+    @Test
+    public void testSupressMergeCommitDiffInShowRevision() throws Exception {
+        w.init();
+        w.commitEmpty("init");
+
+        final String branchBeforeCommit = "branchBeforeCommit";
+        w.git.branch(branchBeforeCommit);
+
+        final String fileFromBranch = "fileFromBranch";
+        w.git.checkout().ref(branchBeforeCommit).execute();
+        w.touch(fileFromBranch, "content-1");
+        w.git.add(fileFromBranch);
+        w.git.commit("commit-in-branch-before-commit");
+
+        final String fileInMain = "fileInMain";
+        w.git.checkout().ref(defaultBranchName).execute();
+        w.touch(fileInMain, "content-2");
+        w.git.add(fileInMain);
+        w.git.commit("commit-in-main-after-branch-created");
+        String commitSha1 = w.git.revParse("HEAD").name();
+
+        w.git.merge()
+                .setGitPluginFastForwardMode(MergeCommand.GitPluginFastForwardMode.NO_FF)
+                .setRevisionToMerge(w.git.getHeadRev(w.repoPath(), branchBeforeCommit))
+                .execute();
+        String commitSha2 = w.git.revParse("HEAD").name();
+
+        final List<String> defaultBehaviour =
+                w.git.showRevision(ObjectId.fromString(commitSha1), ObjectId.fromString(commitSha2), true);
+        assertTrue(
+                "Default behaviour shows merge commits diffs",
+                defaultBehaviour.stream().anyMatch(e -> e.contains(fileInMain)));
+        assertTrue(
+                "Shows file from merged branch", defaultBehaviour.stream().anyMatch(e -> e.contains(fileFromBranch)));
+
+        final List<String> notShowDiffMerge =
+                w.git.showRevision(ObjectId.fromString(commitSha1), ObjectId.fromString(commitSha2), true, true);
+        assertTrue("Merge commit diffs aren't shown", !notShowDiffMerge.stream().anyMatch(e -> e.contains(fileInMain)));
+        assertTrue(
+                "Shows file from merged branch", notShowDiffMerge.stream().anyMatch(e -> e.contains(fileFromBranch)));
+    }
+
     /**
      * inline ${@link hudson.Functions#isWindows()} to prevent a transient
      * remote classloader issue