[JENKINS-76026] Do not show merges in changelog (jenkinsci#1327)

Git client 6.3.1 adapted the git client plugin to support command line
git 2.51.0 where the "whatchanged" command has been deprecated.  However,
the change introduced an inconsistency between the CLI git implementation
and the JGit implementation.

Prior to git client plugin 6.3.1, the changelog skipped merge commits
in all cases.

With git client 6.3.1, the CLI git changelog includes merge commits.
With git client 6.3.1, the JGit changelog does not include merge commits.

Testing done:

* Confirmed the bug with interactive testing of git client plugin 6.3.1
* Wrote an automated test that shows the inconsistency
* Confirmed that the automated test fails with git client 6.3.1 and
  passes with the fix

(cherry picked from commit 358e279)

Author: MarkEWaite

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

@@ -1297,7 +1297,8 @@ 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

@@ -1350,15 +1350,16 @@ public void execute() throws GitException {
                         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();
                 }
@@ -1400,7 +1401,7 @@ private String statusOf(DiffEntry d) {
          *      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
      */