Re: [PATCH] [gdb/cli] Add maint info screen

[John Baldwin <jhb@FreeBSD.org>]

On 4/17/23 7:09 AM, Tom de Vries via Gdb-patches wrote:
> While working on PRs tui/30337 and cli/30346 I came across various notions of
> width in gdb, as reported by gdb, readline, curses and the environment
> variables.
> 
> As for gdb, readline and the environment variables, the way things work
> is:
> - Gdb asks readline to detect screen size,
> - readline sets the actual screen size in the environment variables
>    COLUMNS and LINES,
> - readline reports back a screen size to gdb, which may have one column
>    less than the actual screen size, to deal with lack of auto-wrap.
>    This becomes gdb's notion of screen size (in other words the point where
>    we can expect the gdb command line to wrap),
> - Gdb then explicitly sets readline's screen size, which readline itself may
>    adjust to deal with lack of auto-wrap.  This becomes readlines notion
>    of screen size (well, internally the unadjusted one, but it'll report back
>    the adjusted one).
> 
> Add a command "maint info screen" that prints these notions, both for width
> and height.
> 
> For TERM=xterm we have:
> ...
> $ TERM=xterm gdb -ex "maint info screen"
> Number of characters gdb thinks are in a line is 118.
> Number of characters readline reports are in a line is 118.
> Number of characters curses thinks are in a line is 118.
> Number of characters environment thinks are in a line is 118 (COLUMNS).
> Number of lines gdb thinks are in a page is 27.
> Number of lines readline reports are in a page is 27.
> Number of lines curses thinks are in a page is 27.
> Number of lines environment thinks are in a page is 27 (LINES).
> ...
> 
> And for TERM=ansi:
> ...
> $ TERM=ansi gdb -ex "maint info screen"
> Number of characters gdb thinks are in a line is 117.
> Number of characters readline reports are in a line is 116.
> Number of characters curses thinks are in a line is 118.
> Number of characters environment thinks are in a line is 118 (COLUMNS).
> Number of lines gdb thinks are in a page is 27.
> Number of lines readline reports are in a page is 27.
> Number of lines curses thinks are in a page is 27.
> Number of lines environment thinks are in a page is 27 (LINES).
> ...
> 
> [ The fact that we have "characters readline reports are in a line is 116" is
> is due to gdb making readline adjust twice for the lack of auto-wrap, this is
> PR cli/30346.
> 
> Likewise we can detect tui/30337 by doing a resize in TUI mode and doing
> "maint info screen":
> ...
> Number of characters characters curses thinks are in a line is 110.
> Number of characters environment thinks are in a line is 111 (COLUMNS). ]
> 
> And for TERM=ansi, with width and heigth set to 0:
> ...
> Number of characters gdb thinks are in a line is 4294967295 (unlimited).
> Number of characters readline reports are in a line is 32766 (unlimited - 1).
> Number of characters curses thinks are in a line is 118.
> Number of characters environment thinks are in a line is 118 (COLUMNS).
> Number of lines gdb thinks are in a page is 4294967295 (unlimited).
> Number of lines readline reports are in a page is 32767 (unlimited).
> Number of lines curses thinks are in a page is 27.
> Number of lines environment thinks are in a page is 27 (LINES).
> ...
> 
> [ Note that when doing a resize by say maximizing or de-maximizing a terminal,
> all reported values are updated, except for curses when not in TUI mode.
> 
> Maybe that means there's a bug.  If not, then maybe we should not print
> the curses lines unless in TUI mode, or annotate those lines such that it's
> clear that the values may be not up-to-date. ]
> 
> I'd like to use this command in the regression test for PR cli/30346.
> 
> Tested on x86_64-linux.

I was building GDB in a Linux x86-64 VM that didn't have curses-dev installed and
this change causes GDB to no longer build:

   CXX    utils.o
/git/gdb/gdb/utils.c: In function ‘void maintenance_info_screen(const char*, int)’:
/git/gdb/gdb/utils.c:1310:14: error: ‘COLS’ was not declared in this scope
  1310 |              COLS);
       |              ^~~~
/git/gdb/gdb/utils.c:1331:15: error: ‘LINES’ was not declared in this scope; did you mean ‘LONGEST’?
  1331 |               LINES);
       |               ^~~~~
       |               LONGEST
make[2]: *** [Makefile:1920: utils.o] Error 1

-- 
John Baldwin