Allow use without pre-activation of virtualenv

Fixes: #1507

src/ansiblelint/__main__.py

@@ -32,11 +32,15 @@
 
 from enrich.console import should_do_markup
 
+# pylint: disable=unused-import
+import ansiblelint._preimport  # must be kept before other ansiblelint imports!
+
+# pylint: enable=unused-import
 from ansiblelint import cli
 from ansiblelint.app import App
 from ansiblelint.color import console, console_options, reconfigure, render_yaml
 from ansiblelint.config import options
-from ansiblelint.constants import ANSIBLE_MISSING_RC, EXIT_CONTROL_C_RC
+from ansiblelint.constants import EXIT_CONTROL_C_RC
 from ansiblelint.file_utils import abspath, cwd, normpath
 from ansiblelint.prerun import check_ansible_presence, prepare_environment
 from ansiblelint.skip_utils import normalize_tag
@@ -81,15 +85,12 @@ def initialize_options(arguments: Optional[List[str]] = None) -> None:
     new_options.cwd = pathlib.Path.cwd()
 
     if new_options.version:
-        ansible_version, err = check_ansible_presence()
+        ansible_version, _ = check_ansible_presence(exit_on_error=True)
         print(
             "ansible-lint {ver!s} using ansible {ansible_ver!s}".format(
                 ver=__version__, ansible_ver=ansible_version
             )
         )
-        if err:
-            _logger.error(err)
-            sys.exit(ANSIBLE_MISSING_RC)
         sys.exit(0)
 
     if new_options.colored is None:

src/ansiblelint/_preimport.py

@@ -0,0 +1,11 @@
+"""Code that must run before other imports."""
+import os
+import sys
+
+# Hack to allow a venv installed ansible-lint be called from outside the venv
+paths = [x for x in os.environ.get("PATH", "").split(":") if x]
+py_path = os.path.dirname(sys.executable)
+if py_path not in paths:
+    paths.insert(0, py_path)
+    os.environ["PATH"] = ":".join(paths)
+    print(f"WARNING: PATH altered to include {py_path}", file=sys.stderr)

tox.ini

@@ -27,6 +27,8 @@ deps =
 commands =
   # safety measure to assure we do not accidentally run tests with broken dependencies
   {envpython} -m pip check
+  # Ensure that ansible-lint can be called w/o activated virtualenv
+  env -i HOME="$HOME" {envdir}/bin/ansible-lint --version
   # We add coverage options but not making them mandatory as we do not want to force
   # pytest users to run coverage when they just want to run a single test with `pytest -k test`
   {envpython} -m pytest \
@@ -58,6 +60,7 @@ setenv =
   PRE_COMMIT_COLOR = always
   FORCE_COLOR = 1
 allowlist_externals =
+  env
   sh
   tox
 # both options needed to workaround https://github.com/tox-dev/tox/issues/2197