Only use tox_cleanup hook when it is possible

src/tox_current_env/hooks.py

@@ -85,10 +85,15 @@ def unsupported_raise(config, venv):
         return
     regular = not (config.option.current_env or config.option.print_deps_only)
     if regular and is_current_env_link(venv):
+        if hasattr(tox.hookspecs, "tox_cleanup"):
             raise tox.exception.ConfigError(
                 "Looks like previous --current-env or --print-deps-only tox run didn't finish the cleanup. "
                 "Run tox run with --recreate (-r) or manually remove the environment in .tox."
             )
+        else:
+            raise tox.exception.ConfigError(
+                "Regular tox run after --current-env or --print-deps-only tox run is not supported without --recreate (-r)."
+            )
     elif config.option.current_env and is_proper_venv(venv):
         raise tox.exception.ConfigError(
             "--current-env after regular tox run is not supported without --recreate (-r)."
@@ -166,6 +171,8 @@ def tox_runtest(venv, redirect):
         return True
 
 
+if hasattr(tox.hookspecs, "tox_cleanup"):
+
     @tox.hookimpl
     def tox_cleanup(session):
         """Remove the fake virtualenv not to collide with regular tox

tests/test_integration.py

@@ -6,6 +6,8 @@ import subprocess
 import sys
 import textwrap
 
+from packaging import version
+
 import pytest
 
 
@@ -37,6 +39,8 @@ def is_available(python):
     return True
 
 
+TOX_VERSION = version.parse(tox("--version").stdout.split(" ")[0])
+
 needs_py3678 = pytest.mark.skipif(
     not is_available("python3.6")
     or not is_available("python3.7")
@@ -44,6 +48,10 @@ needs_py3678 = pytest.mark.skipif(
     reason="This test needs all of python3.6, python3.7 and python3.8 to be available in $PATH",
 )
 
+needs_tox38 = pytest.mark.skipif(
+    TOX_VERSION < version.parse("3.8"), reason="This test needs at least tox 3.8"
+)
+
 
 def test_native_toxenv_current_env():
     result = tox("-e", NATIVE_TOXENV, "--current-env")
@@ -195,6 +203,7 @@ def test_regular_run_native_toxenv():
         assert len(list(sitelib.glob(f"{pkg}-*.dist-info"))) == 1
 
 
+@needs_tox38
 def test_regular_after_current_is_supported():
     result = tox("-e", NATIVE_TOXENV, "--current-env")
     assert result.stdout.splitlines()[0] == NATIVE_EXECUTABLE
@@ -214,6 +223,7 @@ def test_regular_after_killed_current_is_not_supported():
     assert "--recreate" in result.stderr
 
 
+@needs_tox38
 def test_regular_after_first_deps_only_is_supported():
     result = tox("-e", NATIVE_TOXENV, "--print-deps-only")
     assert result.stdout.splitlines()[0] == "six"

tox.ini

@@ -4,6 +4,7 @@ envlist = {py36,py37,py38}-tox{35,release,master}
 [testenv]
 deps=
     pytest
+    packaging
     tox35: tox >=3.5,<3.6
     toxrelease: tox
     toxmaster: git+https://github.com/tox-dev/tox.git@master