MergeUtil: Add debug logging to PluggableCommitMessageGenerator

Change-Id: If23c598d9bbaa16d3fa056d8d656b4ab87a34470

java/com/google/gerrit/server/git/MergeUtil.java

@@ -32,6 +32,7 @@ import com.google.gerrit.common.FooterConstants;
 import com.google.gerrit.common.data.LabelType;
 import com.google.gerrit.extensions.registration.DynamicItem;
 import com.google.gerrit.extensions.registration.DynamicSet;
+import com.google.gerrit.extensions.registration.Extension;
 import com.google.gerrit.extensions.restapi.BadRequestException;
 import com.google.gerrit.extensions.restapi.MergeConflictException;
 import com.google.gerrit.extensions.restapi.MethodNotAllowedException;
@@ -125,20 +126,31 @@ public class MergeUtil {
     }
 
     public String generate(
-        RevCommit original, RevCommit mergeTip, Branch.NameKey dest, String current) {
+        RevCommit original, RevCommit mergeTip, Branch.NameKey dest, String originalMessage) {
       requireNonNull(original.getRawBuffer());
       if (mergeTip != null) {
         requireNonNull(mergeTip.getRawBuffer());
       }
-      for (ChangeMessageModifier changeMessageModifier : changeMessageModifiers) {
+
+      int count = 0;
+      String current = originalMessage;
+      for (Extension<ChangeMessageModifier> ext : changeMessageModifiers.entries()) {
+        ChangeMessageModifier changeMessageModifier = ext.get();
+        String className = changeMessageModifier.getClass().getName();
         current = changeMessageModifier.onSubmit(current, original, mergeTip, dest);
-        requireNonNull(
+        checkState(
-            current,
+            current != null,
-            () ->
+            "%s.onSubmit from plugin %s returned null instead of new commit message",
-                String.format(
+            className,
-                    "%s.OnSubmit returned null instead of new commit message",
+            ext.getPluginName());
-                    changeMessageModifier.getClass().getName()));
+        count++;
+        logger.atFine().log(
+            "Invoked %s from plugin %s, message length now %d",
+            className, ext.getPluginName(), current.length());
       }
+      logger.atFine().log(
+          "Invoked %d ChangeMessageModifiers on message with original length %d",
+          count, originalMessage.length());
       return current;
     }
   }

javatests/com/google/gerrit/acceptance/rest/change/SubmitByRebaseAlwaysIT.java

@@ -153,7 +153,8 @@ public class SubmitByRebaseAlwaysIT extends AbstractSubmitByRebase {
             .hasMessageThat()
             .isEqualTo(
                 modifier1.getClass().getName()
-                    + ".OnSubmit returned null instead of new commit message");
+                    + ".onSubmit from plugin modifier-1 returned null instead of new commit"
+                    + " message");
       }
     }
   }