Re: Fix psql pager selection for wrapped expanded output

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.

> +# 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.

--
Erik Wienhold