autoenv: look in additional installation locations, redo logic

Fixes #4681
Co-authored-by: Marc Cornellà <marc.cornella@live.com>

plugins/autoenv/README.md

@@ -7,8 +7,14 @@ To use it, add `autoenv` to the plugins array in your zshrc file:
 ```zsh
 plugins=(... autoenv)
 ```
+
+## Functions
+
+* `use_env()`: creates and/or activates a virtualenv. For use in `.env` files.
+  See the source code for details.
+
 ## Requirements
 
 In order to make this work, you will need to have the autoenv installed.
 
-More info on the usage and install: https://github.com/inishchith/autoenv
+More info on the usage and install at [the project's homepage](https://github.com/inishchith/autoenv).

plugins/autoenv/autoenv.plugin.zsh

-# Activates autoenv or reports its failure
+# Initialization: activate autoenv or report its absence
 () {
+local d autoenv_dir install_locations
 if ! type autoenv_init >/dev/null; then
-  for d (~/.autoenv ~/.local/bin /usr/local/opt/autoenv /usr/local/bin); do
+  # Check if activate.sh is in $PATH
+  if (( $+commands[activate.sh] )); then
+    autoenv_dir="${commands[activate.sh]:h}"
+  fi
+
+  # Locate autoenv installation
+  if [[ -z $autoenv_dir ]]; then
+    install_locations=(
+      ~/.autoenv
+      ~/.local/bin
+      /usr/local/opt/autoenv
+      /usr/local/bin
+      /usr/share/autoenv-git
+      ~/Library/Python/bin
+    )
+    for d ( $install_locations ); do
       if [[ -e $d/activate.sh ]]; then
         autoenv_dir=$d
         break
       fi
     done
+  fi
+
+  # Look for Homebrew path as a last resort
+  if [[ -z "$autoenv_dir" ]] && (( $+commands[brew] )); then
+    d=$(brew --prefix)/opt/autoenv
+    if [[ -e $d/activate.sh ]]; then
+      autoenv_dir=$d
+    fi
+  fi
+
+  # Complain if autoenv is not installed
   if [[ -z $autoenv_dir ]]; then 
     cat <<END >&2
 -------- AUTOENV ---------
@@ -17,6 +44,7 @@ In the meantime the autoenv plugin is DISABLED.
 END
     return 1
   fi
+  # Load autoenv
   source $autoenv_dir/activate.sh
 fi
 }
@@ -27,7 +55,7 @@ fi
 # It only performs an action if the requested virtualenv is not the current one.
 
 use_env() {
-    typeset venv
+  local venv
   venv="$1"
   if [[ "${VIRTUAL_ENV:t}" != "$venv" ]]; then
     if workon | grep -q "$venv"; then