Use user's default shell in Zed's terminal

[snokpok]

Context:

• I did some digging and found that Alacritty (which we forked) by default does not use the user's $SHELL, but instead uses what's specified in /etc/passwd if any. This PR starts it with $SHELL by default if $SHELL is set.

Release Notes:

• Fixed https://github.com/zed-industries/zed/issues/5320

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[maxdeviant]

Adding @mikayla-maki as a reviewer, as she is more familiar with the terminal code 😄

[frou]

Aside: is /etc/passwd even relevant on macOS? I think the actual source of truth is whatever it is the following command consults dscl . -read $HOME UserShell

[Un1q32]

Aside: is /etc/passwd even relevant on macOS? I think the actual source of truth is whatever it is the following command consults dscl . -read $HOME UserShell

~~IIRC macOS uses /etc/master.passwd for that stuff, which uses a different format, but an /etc/passwd file is automatically generated for compatibility with programs that read /etc/passwd~~

Nevermind, I think this is true for older versions but on my mac /etc/passwd and /etc/master.passwd contain default info, my user isn't even in there and root has a default shell of /bin/sh instead of /bin/zsh

[mrnugget]

• I did some digging and found that Alacritty (which we forked) by default does not use the user's $SHELL, but instead uses what's specified in /etc/passwd if any. This PR starts it with $SHELL by default if $SHELL is set.

This code in alacritty tells me that they do check $SHELL first:

https://github.com/alacritty/alacritty/blob/7c046f5ae664f746c5f5a4bbe18c0e89f5702305/alacritty_terminal/src/tty/unix.rs#L136-L158

I'm wondering whether the problem isn't that $SHELL isn't set at this point yet?

[mikayla-maki]

Yeah, this PR isn't correct. I debugged this with a user several months ago and it turned out Zed wasn't loading the SHELL environment variable somehow. The relevant code is in main.rs.