Empty lines in /etc/paths.d cause . to appear in PATH on macOS Mojave

[strayer]

I recently discovered that my PATH contains a . between the default paths of macOS from /etc/paths*:

sh-3.2$ sh -c 'env HOME=$(mktemp -d) /usr/local/bin/fish'
Welcome to fish, the friendly interactive shell
strayer@wolf359 /U/s/.config> echo $PATH
/usr/local/bin /usr/bin /bin /usr/sbin /sbin /opt/X11/bin /Applications/VMware Fusion.app/Contents/Public /Library/TeX/texbin . /Applications/Wireshark.app/Contents/MacOS
strayer@wolf359 /U/s/.config> echo $fish_user_paths

One of the files in /etc/paths.d contains empty lines (/etc/paths.d/TeX to be specific):

strayer@wolf359 /U/s/.config> cat /etc/paths /etc/paths.d/*
/usr/local/bin
/usr/bin
/bin
/usr/sbin
/sbin
/opt/X11/bin
/Applications/VMware Fusion.app/Contents/Public/Library/TeX/texbin


/Applications/Wireshark.app/Contents/MacOS

When I manually remove these empty lines, the dot doesn't appear in PATH anymore:

sh-3.2$ sh -c 'env HOME=$(mktemp -d) /usr/local/bin/fish'
Welcome to fish, the friendly interactive shell
strayer@wolf359 /U/s/.config> echo $PATH
/usr/local/bin /usr/bin /bin /usr/sbin /sbin /opt/X11/bin /Applications/VMware Fusion.app/Contents/Public /Library/TeX/texbin /Applications/Wireshark.app/Contents/MacOS

fish version, installed via Homebrew:

strayer@wolf359 ~> fish --version
fish, version 3.0.2
strayer@wolf359 ~> echo $version
3.0.2

TERM: xterm-256color
macOS Mojave 10.14.4 (18E226)
Terminal: iTerm2 Build 3.3.0beta2

[floam]

Can reproduce.

[floam]

There is a small problem with the logic causing empty elements to be put into $PATH for empty lines. And I did not know this until now but we translate these to . on purpose.

/// Ensure the content of the magic path env vars is reasonable. Specifically, that empty path
/// elements are converted to explicit "." to make the vars easier to use in fish scripts.
static void init_path_vars() {
    // Do not replace empties in MATHPATH - see #4158.
    fix_colon_delimited_var(L"PATH", env_stack_t::globals());
    fix_colon_delimited_var(L"CDPATH", env_stack_t::globals());
}

[floam]

I don't understand this business of sticking . into $PATH or $CDPATH here.. for the sake of aiding fish scripting? What am I not getting? If someone prepended an empty component to $PATH, they'd be in a potentially dangerous situation when in a directory with unfortunately-named binaries.

[floam]

Oh, I didn't realize that empty $PATH components usually are equivalent to . in most shells.

[faho]

Does the official path_helper thing handle this in the same way?

[floam]

Yes. Blank lines are ignored.

[floam]

path_helper.c