Subject: Re: [PATCH 2/2] Documentation/git-log: mention that line-log regex must match in starting revision

From: SZEDER Gábor <[email-masked]>
Date: Wed, 18 Dec 2019 12:09:29 +0100

On Tue, Dec 17, 2019 at 10:28:37PM -0500, Philippe Blain wrote:
> 
> > Le 17 déc. 2019 à 13:16, Junio C Hamano <[email-masked]> a écrit :
> > Even when you specify <start> or <end> as a line number, they must
> > exist in the starting revision or it would be a fatal error.  If we
> > are clarifying with this patch for completeness, I think we should
> > also mention it together.  
> Thanks for the feedback. I did some tests : 

I'll swap the order of your first two tests:

>     git log -L 300,2000000085:Documentation/git-log.txt 
> errors out:
>     fatal: file Documentation/git-log.txt has only 239 lines

Here the entire line range is outside of the file, so there is not
much we can do about it, but error out.

An alternative would be to treat it as an empty line range and then
don't show any commits but exit silently, but I think that would be
confusing ("why didn't I get any output?!"), and telling the user
what's wrong is better ("Ah, ok, I mistyped 192 as 912").

>     git log -L 73,2000000085:Documentation/git-log.txt
> does not error and shows the history from line 73 to the end of the file.

Here there is an overlap between the given line range and the file
(lines 73-239), so we have two possibilities:

  - be strict and error out saying that the <end> doesn't make sense.

  - be lax about it, and interpret the <end> as the end of file.  This
    allows for cases like "I want line log from here to the end of
    file, but instead of finding out the exact number of lines in the
    file I'll just say 999999 that is surely larger than the file, and
    you shall do what I mean".

Those who implemented the line-log feature chose the latter.  I think
it's the better choice.

> But 
>     git log -L 300,-2000000085:Documentation/git-log.txt
> does not error out and shows the history for the whole file. Also,
>     git log -L 1,-2000000085:Documentation/git-log.txt
> does not error out and gives the history for the first line.

These are a variant of the previous case, with the difference that
because of the '-' in <end> it is not an absolute line number but
relative, and is interpreted as that many lines before <start> (i.e.
in this case <start> actually means the end of the line range).

I think the same argument can be made about <end> pointing past the
beginning of the file, though, arguably, it's not as useful, because
the first line as always 1, and '-L 123,-99999' is more keystrokes
than '-L 1,123'.

> So I think that it’s really only regex that must match...