Silence compinit when it finds shared Homebrew stuff

zshrc

@@ -290,8 +290,21 @@ bindkey -e                      # emacs style key bindings
 
 # 10. Completion
 # =============
+
 autoload -Uz compinit
-compinit
+
+# Sharing Homebrew in /usr/local with multiple users on the same machine means
+# that group writable files in /usr/local are deemed insecure. But I'm the only
+# actual user so tell compinit not to bother me about compaudit's complaints.
+is_group_writable() {
+  local ls=$(ls -ld "$1")
+  [[ "${ls:5:1}" = "w" ]]
+}
+if mac && is_group_writable /usr/local/share; then
+  compinit -u
+else
+  compinit
+fi
 
 # 11. SSH Keychain
 # ================