Re: [PATCH v4 20/25] sequencer: refactor write_message()

Johannes Schindelin [off-list ref] writes:

The write_message() function safely writes an strbuf to a file.
Sometimes it is inconvenient to require an strbuf, though: the text to
be written may not be stored in a strbuf, or the strbuf should not be
released after writing.

Let's refactor "safely writing string to a file" into
write_with_lock_file(), and make write_message() use it.

The new function will make it easy to create a new convenience function
write_file_gently() that does not die(); as some of the upcoming callers
of this new function will want to append a newline character, we already
add that flag as parameter to write_with_lock_file().

While at it, roll back the locked files in case of failure, as pointed
out by Hannes Sixt.

Signed-off-by: Johannes Schindelin <redacted>
---
 sequencer.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

Once a helper function starts taking <buf, len> pair, not a strbuf,
it becomes obvious that it does not make much sense to calling
strbuf_release() from the helper.  It is caller's job to do the
memory management of the strbuf it uses to pass information to the
helper, and the current api into write_message() is klunky.

If I were doing this, I would make this into three separate steps:

    - move the strbuf_release(msgbuf) to the caller in
      do_pick_commit();

    - add the missing rollback_lock_file(), which is a bugfix; and
      then finally

    - allow the helper to take not a strbuf but <buf, len> pair as
      parameters.

The end result of this patch achieves two thirds of the above, but
especially given that write_message() only has two call sites in a
single function, I think it is OK and preferrable even to do all
three.