feat(python): Auto-activate venv when cd'ing into directory

plugins/python/README.md

@@ -22,8 +22,18 @@ plugins=(... python)
 
 ## Virtual environments
 
-The plugin provides two utilities to manage Python venvs:
+The plugin provides three utilities to manage Python venvs:
 
 - `mkv [name]`: make a new virtual environment called `name` (default: `venv`) in current directory.
 
 - `vrun [name]`: activate virtual environment called `name` (default: `venv`) in current directory.
+
+- `auto_vrun`: Automatically activate the venv virtual environment when
+  cd’ing into a directory containing `venv/bin/activate`, and
+  automatically deactivate the venv virtual environment when cd’ing into
+  any other directory.
+  - Set the environment variable `VENV_NAME` to auto-activate on a
+  different venv name. (Example: `VENV_NAME=.venv`).
+  - Set the environment variable `DISABLE_AUTO_VRUN` to anything to
+  deactivate `auto_vrun`. (Example: `DISABLE_AUTO_VRUN=true`) Unset
+  `DISABLE_AUTO_VRUN` to re-enable.

plugins/python/python.plugin.zsh

@@ -81,3 +81,18 @@ function mkv() {
   echo >&2 "Created venv in '${venvpath}'"
   vrun "${name}"
 }
+
+# Virtual environment is assumed to be named "venv".
+# Set VENV_NAME to another name if you use a different name, maybe ".venv".
+# To disable, set DISABLE_AUTO_VRUN to anything. Unset to re-enable.
+auto_vrun() {
+    [ $DISABLE_AUTO_VRUN ] && return 0
+    local venvpath=${VENV_NAME:-'venv'}
+    if [ -e "${venvpath}/bin/activate" ]; then
+        source "${venvpath}/bin/activate" > /dev/null 2>&1
+    else
+        [ -n "$(command -v deactivate)" ] && deactivate > /dev/null 2>&1
+    fi
+}
+add-zsh-hook chpwd auto_vrun
+auto_vrun