kgo / changelog: last minute rename from CommitTxn to TxnCommit

This better mirrors TxnOffsetCommit, also in the same api call, and
better mirrors how it's pretty universally Txn then Commit wherever you
see it.

Also fixes the context in GroupTransactSession.End to actually be passed
all the way to the commit function, and documents where it can be used.

pkg/kgo/consumer_group.go

@@ -2289,18 +2289,19 @@ func PreCommitFnContext(ctx context.Context, fn func(*kmsg.OffsetCommitRequest)
 	return context.WithValue(ctx, commitContextFn, fn)
 }
 
-type commitTxnContextFnT struct{}
+type txnCommitContextFnT struct{}
 
-var commitTxnContextFn commitTxnContextFnT
+var txnCommitContextFn txnCommitContextFnT
 
-// PreCommitTxnFnContext attaches fn to the context through WithValue. Using
+// PreTxnCommitFnContext attaches fn to the context through WithValue. Using
 // the context while committing a transaction allows fn to be called just
 // before the commit is issued. This can be used to modify the actual commit,
 // such as by associating metadata with partitions (for transactions, the
 // default internal metadata is the client's current member ID). If fn returns
-// an error, the commit is not attempted.
-func PreCommitTxnFnContext(ctx context.Context, fn func(*kmsg.TxnOffsetCommitRequest) error) context.Context {
-	return context.WithValue(ctx, commitTxnContextFn, fn)
+// an error, the commit is not attempted. This context can be used in either
+// GroupTransactSession.End or in Client.EndTransaction.
+func PreTxnCommitFnContext(ctx context.Context, fn func(*kmsg.TxnOffsetCommitRequest) error) context.Context {
+	return context.WithValue(ctx, txnCommitContextFn, fn)
 }
 
 // CommitRecords issues a synchronous offset commit for the offsets contained

pkg/kgo/txn.go

@@ -287,7 +287,7 @@ func (s *GroupTransactSession) End(ctx context.Context, commit TransactionEndTry
 		var commitErrs []string
 
 		committed := make(chan struct{})
-		g = s.cl.commitTransactionOffsets(context.Background(), postcommit,
+		g = s.cl.commitTransactionOffsets(ctx, postcommit,
 			func(_ *kmsg.TxnOffsetCommitRequest, resp *kmsg.TxnOffsetCommitResponse, err error) {
 				defer close(committed)
 				if err != nil {
@@ -1222,7 +1222,7 @@ func (g *groupConsumer) commitTxn(
 			req.Topics = append(req.Topics, reqTopic)
 		}
 
-		if fn, ok := ctx.Value(commitTxnContextFn).(func(*kmsg.TxnOffsetCommitRequest) error); ok {
+		if fn, ok := ctx.Value(txnCommitContextFn).(func(*kmsg.TxnOffsetCommitRequest) error); ok {
 			if err := fn(req); err != nil {
 				onDone(req, nil, err)
 				return