Add fish suport to installer

Before this patch, installing Nix using the Fish shell did not
work because Fish wasn't configured to add Nix to the PATH. Some
options in #1512 offered workarounds, but they typically involve
extra plugins or packages.

This patch adds native, out-of-the-box support for the Fish shell.

Note that Fish supports a `conf.d` directory, which is intended
for exactly use cases like this: software projects distributing
shell snippets. This patch takes advantage of it. The installer
doesn't append any Nix loader behavior to any Fish config file.
Because of that, the uninstall process is smooth and a reinstall
obliterates the existing nix.fish files that we place instead of
bothering the user with a backup / manual removal.

Both single-user and multi-user cases are covered. It has been
tested on Ubuntu, and a Mac with MacPorts, homebrew, and the
Fish installer pkg.

Closes #1512

Co-authored-by: Graham Christensen <graham@grahamc.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/scripts/nix-profile-daemon.fish.in b/scripts/nix-profile-daemon.fish.in
new file mode 100644
index 000000000..56d851a9c
--- /dev/null
+++ b/scripts/nix-profile-daemon.fish.in
@@ -0,0 +1,35 @@
+# Only execute this file once per shell.
+if test -n "$__ETC_PROFILE_NIX_SOURCED"
+  return
+end
+
+set __ETC_PROFILE_NIX_SOURCED 1
+
+set --export NIX_PROFILES "@localstatedir@/nix/profiles/default $HOME/.nix-profile"
+
+# Set $NIX_SSL_CERT_FILE so that Nixpkgs applications like curl work.
+if test -n "$NIX_SSH_CERT_FILE"
+  : # Allow users to override the NIX_SSL_CERT_FILE
+else if test -e /etc/ssl/certs/ca-certificates.crt # NixOS, Ubuntu, Debian, Gentoo, Arch
+  set --export NIX_SSL_CERT_FILE /etc/ssl/certs/ca-certificates.crt
+else if test -e /etc/ssl/ca-bundle.pem # openSUSE Tumbleweed
+  set --export NIX_SSL_CERT_FILE /etc/ssl/ca-bundle.pem
+else if test -e /etc/ssl/certs/ca-bundle.crt # Old NixOS
+  set --export NIX_SSL_CERT_FILE /etc/ssl/certs/ca-bundle.crt
+else if test -e /etc/pki/tls/certs/ca-bundle.crt # Fedora, CentOS
+  set --export NIX_SSL_CERT_FILE /etc/pki/tls/certs/ca-bundle.crt
+else if test -e "$NIX_LINK/etc/ssl/certs/ca-bundle.crt" # fall back to cacert in Nix profile
+  set --export NIX_SSL_CERT_FILE "$NIX_LINK/etc/ssl/certs/ca-bundle.crt"
+else if test -e "$NIX_LINK/etc/ca-bundle.crt" # old cacert in Nix profile
+  set --export NIX_SSL_CERT_FILE "$NIX_LINK/etc/ca-bundle.crt"
+else
+  # Fall back to what is in the nix profiles, favouring whatever is defined last.
+  for i in $NIX_PROFILES
+    if test -e "$i/etc/ssl/certs/ca-bundle.crt"
+      set --export NIX_SSL_CERT_FILE "$i/etc/ssl/certs/ca-bundle.crt"
+    end
+  end
+end
+
+fish_add_path --prepend --global "@localstatedir@/nix/profiles/default/bin"
+fish_add_path --prepend --global "$HOME/.nix-profile/bin"