Re: [PATCH v4] pretty-formats: add hard truncation, without ellipsis, options

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 26, 2022, 23:19 UTC
Message-ID: <xmqq35a5cnhq.fsf@gitster.g>
In-Reply-To: <f0923db4-7bfe-86d2-7539-c9ebed62fa4f@iee.email>

Philip Oakley <philipoakley@iee.email> writes:

Show 23 quoted lines

>>  in that they may do "[][].." or "[][][]" when told to
>> "trunc" fill a string with four or more double-width letters into a
>> 5 display space.  But the point is at least for these with ellipsis
>> it is fairly clear what the desired behaviour is.
>
> That "is fairly clear" is probably the problem. In retrospect it's not
> clear in the docs that the "%<(N" format is (would appear to be) about
> defining the display width, in terminal character columns, that the
> selected parameter is to be displayed within.
>
> The code already pads the displayed parameter with spaces as required if
> the parameter is shorter than the display width - the else condition in
> pretty.c L1750
>
>>   For "trunc" in
>> the above example, I think the right thing for it to do would be to
>> do "[][].", i.e. consume exactly 5 display columns, and avoid
>> exceeding the given space by not giving two dots but just one.
>
> The existing choice is padding "[][]" with a single space to reach 5
> display chars.
> For the 6-char "[][][]" truncation it is "[][..", i.e. 3 chars from
> "[][][]", then the two ".." dots of the ellipsis.

Here, I realize that I did not explain the scenario well. The message you are responding to was meant to be a clarification of my earlier message and it should have done a better job but apparently I failed. Sorry, and let me try again.

The single example I meant to use to illustrate the scenario I worry about is this. There is a string, in which there are four (or more) letters, each of which occupies two display columns. And '[]' in my earlier messages stood for a SINGLE such letter (I just wanted to stick to ASCII, instead of using East Asian script, for illustration). So "[][.." is not possible (you are chomping the second such letter in half).

I could use East Asian 一二三四 (there are four letters, denoting one, two, three, and four, each occupying two display spaces when typeset in a fixed width font), but to make it easier to see in ASCII only text, let's pretend "[1]", "[2]", "[3]", "[4]" are such letters. You cannot chomp them in the middle (and please pretend each of them occupy two, not three, display spaces).

When the given display space is 6 columns, we can fit 2 such letters plus ".." in the space. If the original string were [1][2][3][4], it is clear trunk and ltrunk can do "[1][2].." (remember [n] stands for a single letter whose width is 2 columns, so that takes 6 columns) and "..[3][4]", respectively. It also is clear that Trunk and Ltrunk can do "[1][2][3]" and "[2][3][4]", respectively. We truncate the given string so that we fill the alloted display columns fully.

If the given display space is 5 columns, the desirable behaviour for trunk and ltrunk is still clear. Instead of consuming two dots, we could use a single dot as the filler. As I said, I suspect that the implementation of trunk and ltrunc does this correctly, though.

My worry is it is not clear what Trunk and Ltrunk should do in that case. There is no way to fit a substring of [1][2][3][4] into 5 columns without any filler.