Add support for disabling configuration

[ZyX-I]

For testing purposes it would be handy to disable loading of some configuration files. I would suggest adding -R/--no-rc switch for disabling loading files from /etc and $XDG_CONFIG_HOME and -D/--no-defaults for disabling loading from /usr/share/fish.

[zanchey]

--no-rc is a reasonable idea, and you can fake it to a degree by running fish with XDG_CONFIG_HOME set to /tmp or similar.

--no-defaults will result in a poorly functioning fish as much of the initialisation work is done in PREFIX/share/fish/config.fish.

[mqudsi]

I imagine --no-defaults could ignore config.fish, though I think it currently has some dependencies on other files in the share directory.

[faho]

I imagine --no-defaults could ignore config.fish

Well.... maybe.

As it currently is, I wouldn't recommend it.

I've actually been running fish in this configuration - I test stuff by building via cmake, and then run it directly without installing, which leaves the prefix wrong.

b0368fd improves the situation somewhat, though there' still a bunch of stuff that I wouldn't recommend running without:

• No $fish_function_path means no type or eval. Also no . or : (from share/config.fish).

• Absolutely no command-not-found handler means not even an error message when a command does not exist

• The fallback key bindings are unusably sparse - not even \x7f ("del") is bound, meaning my backspace doesn't work. Also no arrows.

I'm assuming not setting the locale or $PATH is alright.

[mqudsi]

I imagine it'd be OK to add the standard /{,usr/}{,local/}{,s}bin? Or at least /{,usr/}bin?

(I run fish directly from ./build/fish but I also have it installed locally, so the incorrect paths end up resolving anyway.)

[faho]

I imagine it'd be OK to add the standard /{,usr/}{,local/}{,s}bin? Or at least /{,usr/}bin?

Not $PATH, that's just inherited and usually okay. $fish_function_path, which is what fish uses to find its functions.

(Though yes, we would have to think about universal variables like $fish_user_paths)

[faho]

Wow, that was quite confused of me!

Let me try that again:

We do the following things to $PATH in share/config.fish:

• Add /usr/xpg4/bin on Solaris (does fish currently work on Solaris?)

• $fish_user_paths

• Read /etc/paths if "path_helper" exists

In addition, if $PATH is unset/empty, we set it to "/usr/bin" and "/bin" in C++. If it contains anything, we don't manipulate it.

I imagine it'd be OK to add the standard /{,usr/}{,local/}{,s}bin?

I don't think I've heard of those being missing by accident, so I don't think that'd really help. Plus hardcoding would make it quite hard to remove on purpose.

I took the same approach when it came to setting the locale - we only do that if none of the locale vars is defined, even though I strongly suggest running at least with UTF-8 encoding.

[mqudsi]

See #5417

[rdorbala]

+1 for this.
I want to launch swaywm using a startup ~/.config/fish/conf.d/sway.fish as described in https://github.com/swaywm/sway/wiki#login-managers
But if I also want to use standalone fish scripts with shebang line

#! /usr/bin/env fish

Probably I can work around this by transforming the scripts into fish functions