mc does not threat TERM=screen.xterm-256color as 256 colored terminal

[Hubbitus]

I use GNU screen and run mc inside them.

$ echo $TERM
$ screen.xterm-256color
$ mc --skin=modarin256root-defbg

┌────────────────────────────── Error ──────────────────────────────┐
│                                                                   │
│ Unable to use 'modarin256root-defbg' skin with 256 colors support │
│                    on non-256 colors terminal.                    │
│                   Default skin has been loaded                    │
│                                                                   │
└───────────────────────────────────────────────────────────────────┘

Run correctly with:

TERM=xterm-256color mc --skin=modarin256root-defbg

Fedora Linux 33

# rpm -q mc screen
mc-4.8.25-3.fc33.x86_64
screen-4.8.0-3.fc33.x86_64

[andrew_b]

$ tput colors

If output is not 256, your terminal actually doesn't support 256 colors.

[Hubbitus]

[root@hubbitus ~]# echo $TERM
screen.xterm-256color
[root@hubbitus ~]# tput colors
256

[andrew_b]

Ok. Next step.

mc -V

[Hubbitus]

# mc -V
GNU Midnight Commander unknown
Built with GLib 2.65.0
Built with S-Lang 2.3.2 with terminfo database
With builtin Editor
With subshell support as default
With support for background operations
With mouse support on xterm and Linux console
With internationalization support
With multiple codepages support
With ext2fs attributes support
Virtual File Systems:
 cpiofs, tarfs, sfs, extfs, ftpfs, sftpfs, fish, smbfs
Data types:
 char: 8; int: 32; long: 64; void *: 64; size_t: 64; off_t: 64;

[zaytsev]

Closed as duplicate of #4143.

[zaytsev]

I have commented in #4143 - it's a distro bug and the workaround is to set the terminal in screenrc.

[andrew_b]

TERM=screen.xterm-256color mc --skin=modarin256root-defbg

This command in the terminal emulator (no screen) runs fine. No any errors.
But the same command in the screen produces error as in the ticket description.

[andrew_b]

To define the number of colors in the terminal, S-Lang tests the "Co" terminal capability. If TERMCAP variable is set, S-Lang gets terminal capability from it. If not, terminfo is used. TERMCAP is set in screen and

$ echo $TERMCAP | tr ':' '\n' | head -1 
SC|screen|VT 100/ANSI X3.64 virtual terminal
$ echo $TERMCAP | tr ':' '\n' | grep Co#
Co#8

Just unset TERMCAP, and mc will work fine with 256-color sckins.

@zaytsev: it's not duplicate. It's invalid.

[Hubbitus]

Sorry, but why $TERMCAP Co terminal capability when TERM=screen.xterm-256color and that is not happened with TERM=xterm-256color??

I can confirm what:

TERM=screen.xterm-256color TERMCAP='' /usr/bin/mc --skin=modarin256root-defbg

also works.

[andrew_b]

There is quite complicated initialization sequence in S-Lang. I can't describe it in details. As I understand correctly, S-Lang checks if TERM value begins with "xterm". There is no check if TERM begins with "screen.xterm". If TERM begins with "xterm", TERMCAP is ignored. If not, TERMCAP is used.

[Hubbitus]

So, really it the bug in the component which set TERMCAP? Is it termcapdb?

[andrew_b]

Replying to Hubbitus:

So, really it the bug in the component which `set TERMCAP? Is it termcapdb?

I don't know.