Re: [PATCH 04/17] add_to_alternates_file: don't add duplicate entries

On 08/10/2015 11:34 AM, Jeff King wrote:

The add_to_alternates_file function blindly uses
hold_lock_file_for_append to copy the existing contents, and
then adds the new line to it. This has two minor problems:

  1. We might add duplicate entries, which are ugly and
     inefficient.

  2. We do not check that the file ends with a newline, in
     which case we would bogusly append to the final line.
     This is quite unlikely in practice, though, as we call
     this function only from git-clone, so presumably we are
     the only writers of the file (and we always add a
     newline).

Instead of using hold_lock_file_for_append, let's copy the
file line by line, which ensures all records are properly
terminated. If we see an extra line, we can simply abort the
update (there is no point in even copying the rest, as we
know that it would be identical to the original).

Do we have reason to expect that a lot of people have alternates files
that already contain duplicate lines? You say that this function is only
called from `git clone`, so I guess the answer is "no".

But if I'm wrong, it might be friendly to de-dup the existing lines
while copying them.

Michael

-- 
Michael Haggerty
mhagger@alum.mit.edu