bash: use zsh if in a nix-shell

.bashrc

@@ -1,8 +1,12 @@
 #!/bin/bash
 
-# Blake's bashrc 99.99% of this is the default bashrc for manjaro, I just liked
-# it so I took it. The main job of this is to load my basic shell
-# configuration, which works in any `sh`-compatible shell
+# Blake's bashrc
+
+# ZSH supremacy
+
+# 99.99% of this is the default bashrc for manjaro, I just liked it so I took
+# it, and I don't use bash enough to care. The main job of this is to load my
+# basic shell configuration, which works in any POSIX shell.
 
 # If not running interactively, don't do anything
 [[ $- != *i* ]] && return
@@ -13,6 +17,11 @@ export SHELL_CONFIG_DIR="${SHELL_CONFIG_DIR:-"${XDG_CONFIG_HOME:-"$HOME/.config"
 # Source standard shell configuration
 [ -f "$SHELL_CONFIG_DIR/shrc" ] && source "$SHELL_CONFIG_DIR/shrc"
 
+# if in nix shell, run zsh instead of bash - not sure if there's a better way to do this
+if ! "${FORCE_BASH:-false}" && [ -n "$IN_NIX_SHELL" ]; then
+   SHELL="/etc/profiles/per-user/$USER/bin/zsh" exec zsh
+fi
+
 ### Manjaro default bashrc >>>
 colors() {
 	local fgc bgc vals seq0