[Bug tui/30337] [gdb/tui] TUI in ansi terminal has off-by-one width problem

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30337

--- Comment #6 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=deb1ba4e38bf1427d4297b1e9b3e5e73cbc9e456

commit deb1ba4e38bf1427d4297b1e9b3e5e73cbc9e456
Author: Tom de Vries <tdevries@suse.de>
Date:   Sun Apr 30 13:06:23 2023 +0200

    [gdb/tui] Fix TUI resizing for TERM=ansi

    With TERM=ansi, when resizing a TUI window from LINES/COLUMNS 31/118
    (maximized) to 20/78 (de-maximized), I get a garbled screen (that ^L
doesn't
    fix) and a message:
    ...
    @@ resize done 0, size = 77x20
    ...
    with the resulting width being 77 instead of the expected 78.

    [ The discrepancy also manifests in CLI, filed as PR30346. ]

    The discrepancy comes from tui_resize_all, where we ask readline for the
    screen size:
    ...
       rl_get_screen_size (&screenheight, &screenwidth);
    ...

    As it happens, when TERM is set to ansi, readline decides that the terminal
    cannot auto-wrap lines, and reserves one column to deal with that, and as a
    result reports back one less than the actual screen width:
    ...
    $ echo $COLUMNS
    78
    $ TERM=xterm gdb -ex "show width" -ex q
    Number of characters gdb thinks are in a line is 78.
    $ TERM=ansi  gdb -ex "show width" -ex q
    Number of characters gdb thinks are in a line is 77.
    ...

    In tui_resize_all, we need the actual screen width, and using a screenwidth
of
    one less than the actual value garbles the screen.

    This is currently not causing trouble in testing because we have a
workaround
    in place in proc Term::resize.  If we disable the workaround:
    ...
    -       stty columns [expr {$_cols + 1}] < $::gdb_tty_name
    +       stty columns $_cols < $::gdb_tty_name
    ...
    and dump the screen we get the same type of screen garbling:
    ...
        0 +---------------------------------------+|
        1                                         ||
        2                                         ||
        3                                         ||
    ...

    Another way to reproduce the problem is using command "maint info screen".
    After starting gdb with TERM=ansi, entering TUI, and issuing the command,
we
    get:
    ...
    Number of characters curses thinks are in a line is 78.
    ...
    and after maximizing and demaximizing the window we get:
    ...
    Number of characters curses thinks are in a line is 77.
    ...
    If we use TERM=xterm, we do get the expected 78.

    Fix this by:
    - detecting when readline will report back less than the actual screen
width,
    - accordingly setting a new variable readline_hidden_cols,
    - using readline_hidden_cols in tui_resize_all to fix the resize problem,
and
    - removing the workaround in Term::resize.

    The test-case gdb.tui/empty.exp serves as regression test.

    I've applied the same fix in tui_async_resize_screen, the new test-case
    gdb.tui/resize-2.exp serves as a regression test for that change.  Without
    that fix, we have:
    ...
    FAIL: gdb.tui/resize-2.exp: again: gdb width 80
    ...

    Tested on x86_64-linux.

    PR tui/30337
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30337

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