rpk: avoid listing offsets for no topics, fix group seek

For rpk group seek, if we seeked in a group that had no topics, we would
list *all* topics (as is the api for list) and then commit a group to
the beginning of *all* topics.

We now only seek if there are topics to seek, otherwise we print the
standard output that no offset was changed.

We also fix this potential seek problem in rpk group describe, but
realistically all groups have topics assigned.

src/go/rpk/pkg/cli/cmd/group/describe.go

@@ -64,8 +64,11 @@ information about the members.
 				out.Die("unable to fetch offsets for any group")
 			}
 
-			listed, err := adm.ListEndOffsets(ctx, described.AssignedPartitions().Topics()...)
-			out.HandleShardError("ListOffsets", err)
+			var listed kadm.ListedOffsets
+			if topics := described.AssignedPartitions().Topics(); len(topics) > 0 {
+				listed, err = adm.ListEndOffsets(ctx, topics...)
+				out.HandleShardError("ListOffsets", err)
+			}
 
 			printDescribed(
 				described,

src/go/rpk/pkg/cli/cmd/group/seek.go

@@ -220,28 +220,33 @@ func seek(
 			tps[topic] = map[int32]struct{}{} // ensure exists
 		}
 		topics := tps.Topics()
-
 		var listed kadm.ListedOffsets
-		var err error
-		switch to {
-		case "start":
-			listed, err = adm.ListStartOffsets(context.Background(), topics...)
-		case "end":
-			listed, err = adm.ListEndOffsets(context.Background(), topics...)
-		default:
-			var milli int64
-			milli, err = strconv.ParseInt(to, 10, 64)
-			out.MaybeDie(err, "unable to parse millisecond %q: %v", to, err)
-			switch len(to) {
-			case 10: // e.g. "1622505600"; sec to milli
-				milli *= 1000
-			case 13: // e.g. "1622505600000", already in milli
-			case 19: // e.g. "1622505600000000000"; nano to milli
-				milli /= 1e6
+		if len(topics) > 0 {
+			var err error
+			switch to {
+			case "start":
+				listed, err = adm.ListStartOffsets(context.Background(), topics...)
+			case "end":
+				listed, err = adm.ListEndOffsets(context.Background(), topics...)
 			default:
-				out.Die("--to timestamp %q is not a second, nor a millisecond, nor a nanosecond", to)
+				var milli int64
+				milli, err = strconv.ParseInt(to, 10, 64)
+				out.MaybeDie(err, "unable to parse millisecond %q: %v", to, err)
+				switch len(to) {
+				case 10: // e.g. "1622505600"; sec to milli
+					milli *= 1000
+				case 13: // e.g. "1622505600000", already in milli
+				case 19: // e.g. "1622505600000000000"; nano to milli
+					milli /= 1e6
+				default:
+					out.Die("--to timestamp %q is not a second, nor a millisecond, nor a nanosecond", to)
+				}
+				listed, err = adm.ListOffsetsAfterMilli(context.Background(), milli, topics...)
+			}
+			if err == nil { // ListOffsets can return ShardErrors, but we want to be entirely successful
+				err = listed.Error()
 			}
-			listed, err = adm.ListOffsetsAfterMilli(context.Background(), milli, topics...)
+			out.MaybeDie(err, "unable to list all offsets successfully: %v", err)
 		}
 		if err == nil { // ListOffsets can return ShardErrors, but we want to be entirely successful
 			err = listed.Error()

src/go/rpk/pkg/cli/cmd/topic/list.go

@@ -52,7 +52,7 @@ information.
 		Run: func(cmd *cobra.Command, topics []string) {
 			// The purpose of the regex flag really is for users to
 			// know what topics they will delete when using regex.
-			// We forbit deleting internal topics (redpanda
+			// We forbid deleting internal topics (redpanda
 			// actually does not expose these currently), so we
 			// make -r and -i incompatible.
 			if internal && re {