[JENKINS-76026] Do not show merges in changelog

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

@@ -8,7 +8,7 @@
  * Command builder for generating changelog in the format {@code GitSCM} expects.
  *
  * <p>
- * The output format is that of <code>git log --raw</code>, which looks something like this:
+ * The output format is that of <code>git log --raw --no-merges</code>, which looks something like this:
  *
  * <pre>
  * commit dadaf808d99c4c23c53476b0c48e25a181016300

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

@@ -1300,7 +1300,8 @@ public void abort() {
 
             @Override
             public void execute() throws GitException, InterruptedException {
-                ArgumentListBuilder args = new ArgumentListBuilder(gitExe, "log", "--raw", "--no-abbrev", "-M");
+                ArgumentListBuilder args =
+                        new ArgumentListBuilder(gitExe, "log", "--raw", "--no-merges", "--no-abbrev", "-M");
                 if (isAtLeastVersion(1, 8, 3, 0)) {
                     args.add("--format=" + RAW);
                 } else {

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

@@ -1394,15 +1394,16 @@
                         this.includes("HEAD");
                     }
                     for (RevCommit commit : walk) {
-                        // git log --raw doesn't show the merge commits unless -m is given
+                        // git log --raw --no-merges doesn't show merge commits
                         if (commit.getParentCount() > 1) {
                             continue;
                         }
 
                         formatter.format(commit, null, pw, true);
                     }
                 } catch (IOException e) {
-                    throw new GitException("Error: jgit log --raw in " + workspace + " " + e.getMessage(), e);
+                    throw new GitException(
+                            "Error: jgit log --raw --no-merges in " + workspace + " " + e.getMessage(), e);
                 } finally {
                     closeResources();
                 }
@@ -1444,7 +1445,7 @@
          *      Commit to format.
          * @param parent
          *      Optional parent commit to produce the diff against. This only matters
-         *      for merge commits, and git-log behaves differently with respect to this.
+         *      for merge commits and git-log behaves differently with respect to this.
          */
         @SuppressFBWarnings(
                 value = "VA_FORMAT_STRING_USES_NEWLINE",

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

@@ -1710,6 +1710,64 @@ public void testChangeLogAbort() throws Exception {
         assertTrue("No SHA1 in " + writer, writer.toString().contains(sha1));
     }
 
+    @Test
+    public void testChangelogSkipsMerges() throws Exception {
+        int counter = 0;
+        workspace.touch(testGitDir, "file-skips-merges-" + counter, "changelog skips merges " + counter);
+        testGitClient.add("file-skips-merges-" + counter);
+        testGitClient.commit("skips-merges-" + counter++);
+        String rootCommit = testGitClient.revParse("HEAD").name();
+
+        // Create branches a, b, and common that will merge a and b
+        testGitClient.branch("branch-A"); // Create branch-A without switching to it
+        testGitClient.branch("branch-B"); // Create branch-B without switching to it
+        testGitClient.branch("common"); // common branch that will merge branch-A and branch-B
+
+        testGitClient.checkoutBranch("branch-A", rootCommit); // Switch to branch-A
+        workspace.touch(testGitDir, "file-branch-A", "branch-A file " + counter++);
+        testGitClient.add("file-branch-A");
+        testGitClient.commit("file-branch-A on branch-A");
+        String branchACommit = testGitClient.revParse("HEAD").name();
+
+        testGitClient.checkoutBranch("branch-B", rootCommit); // Switch to branch-B
+        workspace.touch(testGitDir, "file-branch-B", "branch-B file " + counter++);
+        testGitClient.add("file-branch-B");
+        testGitClient.commit("file-branch-B on branch-B");
+        String branchBCommit = testGitClient.revParse("HEAD").name();
+
+        String mergeMessage = "Merged branch-B into common";
+        testGitClient.checkoutBranch("common", rootCommit); // Switch to common branch
+        testGitClient
+                .merge()
+                .setRevisionToMerge(ObjectId.fromString(branchACommit))
+                .execute();
+        testGitClient
+                .merge()
+                .setRevisionToMerge(ObjectId.fromString(branchBCommit))
+                .setMessage(mergeMessage)
+                .execute();
+        String mergedCommit = testGitClient.revParse("HEAD").name();
+
+        workspace.touch(testGitDir, "file-skips-merges-" + counter, "changelog skips merges " + counter);
+        testGitClient.add("file-skips-merges-" + counter);
+        testGitClient.commit("skips-merges-" + counter++);
+        String finalCommit = testGitClient.revParse("HEAD").name();
+
+        // Calculate the changelog
+        StringWriter writer = new StringWriter();
+        testGitClient.changelog().to(writer).execute();
+        String changelog = writer.toString();
+
+        // Confirm the changelog includes expected commits
+        assertThat(changelog, containsString("commit " + branchACommit));
+        assertThat(changelog, containsString("commit " + branchBCommit));
+        assertThat(changelog, containsString("commit " + finalCommit));
+
+        // Confirm the changelog does not include the merge commit
+        assertThat(changelog, not(containsString("commit " + mergedCommit)));
+        assertThat(changelog, not(containsString(mergeMessage)));
+    }
+
     /**
      * inline ${@link hudson.Functions#isWindows()} to prevent a transient remote classloader issue
      */