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

> Philip Oakley <philipoakley@iee.email> writes:
>
>>>  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.