Re: Fix psql pager selection for wrapped expanded output

> On Jul 1, 2026, at 04:34, Erik Wienhold <ewie(at)ewie(dot)name> wrote:
>
> On 2026-06-12 12:01 +0200, Chao Li wrote:
>> While testing “[27da1a796] Improve psql's ability to select pager mode
>> accurately”, I found that the pager doesn’t work for expanded wrapped
>> mode. However, I realized that this is not a new problem introduced by
>> 27da1a796, it didn’t work before 27da1a796 either. Instead, with
>> 27da1a796, we are almost there to make it work.
>>
>> 27da1a796 introduces a new helper count_table_lines(), that takes a
>> per-column-width array. For expanded mode (vertical mode), all columns
>> use the same data width. So we can simply build such a width_wrap
>> array, and move IsPagerNeeded() to after dwidth is computed. Then the
>> pager works in expanded wrapped mode.
>>
>> I tested with this procedure (making the terminal small with ~30 rows):
>> ```
>> \pset pager on
>> \pset columns 25
>> \pset expanded on
>> \pset format wrapped
>> select g AS id, 'name_' || g AS name, repeat('x', g * 5) AS payload from generate_series(1, 10) AS g;
>> ```
>> See the attached patch for details. I’m not going to add this to the
>> v19 open items, as it’s not a v19-new bug.
>
> The changes to print.c look good to me and it works in manual testing.

Thanks for your review and test.

>
>> +# With the 80-column pty, the payload wraps to two lines per row.
>> +# Expanded output also prints one record header per row, plus a trailing
>> +# blank line, so this produces 11 * 3 + 1 = 34 lines.
>> +do_command(
>> + "\\pset expanded on\n\\pset format wrapped\n\\pset columns 80\nSELECT repeat('x',138) AS payload FROM generate_series(1,11);\n",
>
> We can do without \pset columns 80 here since the PTY is already set to
> 80 columns by the test setup on line 82. I'd also change the query to
> return repeat('x', 80) which is sufficiently long for the wrapping to
> occur. It's then also clear that this length is related to the PTY
> width while 138 lacks any meaning IMO.

Agreed and addressed in v2.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/