nix-shell should either preserve TERMINFO and TERM or neither

[bennofs]

Right now, nix-shell will inherit $TERM from the environment, even if --pure is used. However, it does not preserve the value of $TERMINFO, which leads to a situation where $TERM is set to an invalid value in the inner shell. So either:

• inherit both $TERMINFO and $TERM
• do not inherit either $TERMINFO or $TERM (perhaps set $TERM = xterm? that seems to work most of the cases)

Example:

I have $TERM set to rxvt-unicode-256color on my system, with $TERMINFO being /nix/store/dj4m8kaylm598bsybri8vkw3a8mv447m-rxvt-unicode-with-perl-with-unicode3-9.22-terminfo/share/terminfo, which provides the terminfo file for that $TERM value. If I now use nix-shell, weird effects occur like a double prompt or backspace not working correctly, because $TERM is inherited but $TERMINFO is not, so bash no longer finds the terminfo file for that $TERM value.

[bennofs]

In case anyone is looking for a workaround, on NixOS you can add the following to your ~/.bashrc to make the nix-shell use the terminfo database from the system:

if [ -n "$IN_NIX_SHELL" ]; then
  export TERMINFO=/run/current-system/sw/share/terminfo

  # Reload terminfo
  real_TERM=$TERM; TERM=xterm; TERM=$real_TERM; unset real_TERM
fi

[langston-barrett]

I can reproduce this error on Nix 1.11.4. Using zsh, I found this to be a suitable workaround:

nix-shell . --pure --run "export TERM=xterm; zsh"

[copumpkin]

cc @shlevy @domenkozar @edolstra

[shlevy]

Seems reasonable to me.

[edolstra]

I guess we should also preserve TERMINFO_DIRS.

[unode]

Unsetting TERM works for me.

...until I run into some software that relies on TERM.

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[bew]

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[egasimus]

So that's why my shells act weird sometimes. Huh.

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