Automatically select light/dark theme based on `color-palette-update-notifications`

[cor]

Is your feature request related to a problem? Please describe.

Most modern operating systems and desktop environments do support Dark and Light themes, this includes at least MacOS, Windows, KDE Plasma, Gnome, and probably others.

Some even support switching from dark to light and light to dark mode based on sun rise / sun set.

In order to not make the terminal emulator look bad after such switch, we must enable the applications inside the terminal to detect when the terminal has updated the color palette. This may happen either due to the operating system having changed the current theme or simply because the user has explicitly requested to reconfigure the currently used theme (e.g. because the user requested to change the terminal profile, also containing a different color scheme).

Describe the solution you'd like
Adopt the color-palette-update-notifications standard.

Describe alternatives you've considered
All other solutions are kinda bad. It's good that we finally have a standard for this.

Additional context
Already supported by Ghostty, Kitty, Neovim, Tmux.
WezTerm, Zellij, and Helix are adding support at the moment.

[stefanhaller]

Lazygit doesn't have a concept of light or dark themes; it is your terminal emulator that does. And as you say, many of them have support for this already or are adding support for it, so I'm not sure what you think is left for lazygit to do here.

[cor]

Lazygit doesn't have a concept of light or dark themes; it is your terminal emulator that does. And as you say, many of them have support for this already or are adding support for it, so I'm not sure what you think is left for lazygit to do here.

Currently, lazygit only allows you to have one theme configured:

lazygit/docs/Config.md

Line 112 in 19ac926

theme:

You can however override this theme by doing something like this on startup:

lazygit/docs/Config.md

Line 746 in 19ac926

lazygit --use-config-file="$HOME/.base_lg_conf,$HOME/.light_theme_lg_conf"

but that is an inferior solution, as it means that if you launch Lazygit with your "light theme configuration", and then switch your OS to dark mode, any instance of lazygit that was spawned before the switch will be stuck in the wrong theme.

The ideal solution would be to have two themes in the config, a dark_theme and a light_theme, and implement the color-palette-update-notifications protocol such that currently running instances automatically change on OS theme switch

[stefanhaller]

I see. So the main feature request is not so much to support automatic switching of light/dark themes, but to add a distinction between light and dark themes in the first place; that's probably the bigger challenge, because it involves some design work (for example, to make it so that the distinction is only relevant for people who care about it, but keep it convenient for those who don't. Personally I don't, and I would like to keep setting my colors unconditionally without having to care about putting them in the right sub-theme).

Once we have that, adding the automatic switching shouldn't be a big deal.

[Dom324]

Another quirk is that the theme information should be ideally passed down to the diff engine, e.g. pager: delta --dark vs pager: delta --light.
(though ideally the diff engine itself would also have support for CSI 2031, and then this isn't needed)

[rbhanot4739]

I think delta does support detecting the terminal colors and adjusting its light/dark color presets based on them and it seems to work as expected when used as a native pager for git. However, when used as a pager for lazygit the delta color preset does not seem to be applied correctly which means when system switches from dark to light mode or vice-versa I have to manually update the lazygit config to add --dark or --light to the pager settings.

Not sure if there is a better way to handle that.

[pricci1]

Related: #4550