Add autoenv, automatic environment setup

Using a hook, automatically detect when `.enter` and `.exit` scripts
and source them when changing the shells current directory.

autoenv/autoenv.plugin.zsh

@@ -0,0 +1,74 @@
+# Automatically update the environment when the current working directory
+# changes, this is a reimplementation of the ideas found in the repository
+# https://github.com/Tarrasch/zsh-autoenv stripped down to suit my specific
+# needs.
+
+# Global entered directories array.
+_autoenv_entered=()
+
+# Source an enter script and add its directory to the global entered
+# directories array.
+_autoenv_enter() {
+  local entered=$1
+  # If entered has already been sourced, return.
+  (( ${+_autoenv_entered[$entered]} )) && return
+  # If the enter script is not authorized, return.
+  _autoenv_authorized $entered/.enter || return
+  # Source the enter script.
+  source $entered/.enter
+  # Add the entered directory to the global entered array.
+  _autoenv_entered+=$entered
+}
+
+# Source an exit script and remove its directory from the global entered
+# directories array.
+_autoenv_exit() {
+  local entered=$1
+  # If the exit script is not authorized, return.
+  _autoenv_authorized $entered/.exit || return
+  # Source the exit script.
+  source $entered/.exit
+  # Remove the entered directory from the global entered array.
+  _autoenv_entered-=$entered
+}
+
+# Find a directory containing a .enter file by searching up the directory tree
+# starting in the current directory.
+_autoenv_find_enter() {
+  local current=$PWD
+  # If an enter script is found in the current directory, return it.
+  [ -f $current/.enter ] && return $current
+  # Loop until an enter script or the root directory is found.
+  while true; do
+    # Walk up one directory and make the path absolute.
+    local next=$current/..; local next=${next:A}
+    # If the current directory equals the next directory, return.
+    [[ $current == $next ]] && return || local current=$next
+    # If an enter script is found in the current directory, return it.
+    [ -f $current/.enter ] && return $current
+  done
+}
+
+# A chpwd hook function which automatically sources enter and exit scripts to
+# setup local environments for directory and its subdirectories.
+_autoenv_chpwd() {
+  local entered
+  # Loop over the entered directory stack.
+  for entered in _autoenv_entered; do
+    # If the the current directory was previously entered then exit.
+    # TODO: Verify what this condition expression actually does.
+    ! [[ $PWD/ == $entered/* ]] && _autoenv_exit $entered
+  done
+  # Find the nearest enter script directory.
+  local enter=`_autoenv_find_enter`
+  # If the enter file doesn't exist, return.
+  ! [ -f $enter ] $enter && return
+  _autoenv_enter $enter
+}
+
+# Register the autoenv chpwd hook.
+autoload -U add-zsh-hook
+add-zsh-hook _autoenv_chpwd
+
+# Ensure autoenv is activated in the current directory on first load.
+_autoenv_chpwd

zshrc

@@ -10,6 +10,7 @@ source-plugin() {
 source-plugin zsh-autosuggestions
 source-plugin zsh-history-substring-search
 source-plugin zsh-syntax-highlighting
+source-plugin autoenv
 
 # Disable non end-of-line autosuggest accept widgets
 ZSH_AUTOSUGGEST_ACCEPT_WIDGETS=(end-of-line vi-end-of-line)