Use deactivate to tell if in virtual environment

This patch makes it so the combined definition of $VIRTUAL_ENV and
existence of the shell function deactivate environment are used to tell
whether a virtual environment is active.

This was done to fix some issues where the plugin collided with other
virtual environment managers like Direnv. Direnv sets $VIRTUAL_ENV but
crucially does not create the disable shell function, which makes sense,
as Direnv manages that for the user.

Previosly, the plugin would not discover the virtual environment created
by Direnv and (since Direnv set VIRTUAL_ENV) decide that it should leave
the virtual environment. This would print an error message as deactivate
is not defined by Direnv.

Author: linnnus

README.md

@@ -20,10 +20,14 @@ How it works
 The heart of this plugin is the following table, corresponding to the logic in
 `_autovenv_update`.
 
-|                                | No active venv (`$VIRTUAL_ENV` is unset) | Active venv (`$VIRTUAL_ENV` is set) |
-|-------------------------------:|------------------------------------------|-------------------------------------|
-| PWD has virtual environment    | Activate it                              | Switch if they aren't the same      |
-| PWD has no virtual environment | Do nothing                               | Deactivate it                       |
+|                                | No active venv (`deactivate` is unset) | Active venv (`deactivate` is set) |
+|-------------------------------:|----------------------------------------|-----------------------------------|
+| PWD has virtual environment    | Activate it                            | Switch if they aren't the same\*  |
+| PWD has no virtual environment | Do nothing                             | Deactivate it                     |
+
+\* The path of the virtual env discovered from `$PWD` is compared to the one
+specified py `$VIRTUAL_ENV`. If they are dissimilar, the latter is deactivated
+and the former is activated.
 
 The rest of the logic should be pretty clear from the source code (as clear as
 shell script can be, that is).

autovenv.plugin.zsh

@@ -1,9 +1,12 @@
+# FIXME: direnv messes this up
+# FIXME: sometimes VIRTUAL_ENV is set when we aren't in virtual env, like with 'nix shell' or subshells (?). maybe use deactivate function as signifier instead?
+
 # Perform an update (leaving, entering, switching virtual environments).
 _autovenv_update () {
 	env_path="$(_autovenv_find_env_path)"
 
 	if [ -n "$env_path" ]; then
-		if [ -v VIRTUAL_ENV ]; then
+		if _autovenv_in_virtual_env; then
 			if [ "${env_path:P}" != "${VIRTUAL_ENV:P}" ]; then
 				echo "autovenv: switching from $VIRTUAL_ENV -> $env_path"
 				deactivate
@@ -16,13 +19,19 @@ _autovenv_update () {
 			_autovenv_post-activate_sanity_check "$env_path"
 		fi
 	else
-		if [ -v VIRTUAL_ENV ]; then
+		if _autovenv_in_virtual_env; then
 			echo "autovenv: leaving virtual environment at $VIRTUAL_ENV"
 			deactivate
 		fi
 	fi
 }
 
+# Check wether a virtual environment is currently active.
+_autovenv_in_virtual_env () {
+	typeset -f deactivate >/dev/null && [ -v VIRTUAL_ENV ]
+	return $?
+}
+
 _autovenv_post-activate_sanity_check () {
 	local env_path="$1"
 
@@ -55,6 +64,15 @@ _autovenv_post-activate_sanity_check () {
 			thinks it's in the old location. The autovenv plugin will behave
 			strangely becuase of this.
 		EOF
+
+	# Check that deactivate function was defined.
+	if ! typeset -f deactivate >/dev/null; then
+		cat >&2 <<-EOF
+			autovenv: warning: $env_path/bin/activate did not define the shell
+			function \`disable\`. The autovenv plugin uses this variable to detect
+			if it's inside a virtual environment and won't work without it.
+		EOF
+		return
 	fi
 }
 

create_examples.sh

@@ -44,3 +44,13 @@ mkdir $'example-special \t\n!characters '
 cd    $'example-special \t\n!characters '
 "$PYTHON" -m virtualenv .venv
 cd ..
+
+# Create one managed by direnv, if available.
+# The plugin should NOT activate in here.
+if command -v direnv >/dev/null; then
+	mkdir example-direnv
+	cd example-direnv
+	echo 'layout python3' >.envrc
+	direnv allow
+	cd ..
+fi