Add ansible-core version string parsing (#3068)

Core developers change the `ansible --version` output a bit. Changes
in this commit make sure molecule can parse both pre- and
post-ansible-core version strings.

.github/workflows/tox.yml

@@ -25,17 +25,17 @@ jobs:
           - tox_env: lint
           - tox_env: docs
           - tox_env: py36
-            PREFIX: PYTEST_REQPASS=427
+            PREFIX: PYTEST_REQPASS=429
           - tox_env: py37
-            PREFIX: PYTEST_REQPASS=427
+            PREFIX: PYTEST_REQPASS=429
           - tox_env: py38
-            PREFIX: PYTEST_REQPASS=427
+            PREFIX: PYTEST_REQPASS=429
           - tox_env: py39
-            PREFIX: PYTEST_REQPASS=427
+            PREFIX: PYTEST_REQPASS=429
           - tox_env: py36-devel
-            PREFIX: PYTEST_REQPASS=427
+            PREFIX: PYTEST_REQPASS=429
           - tox_env: py39-devel
-            PREFIX: PYTEST_REQPASS=427
+            PREFIX: PYTEST_REQPASS=429
           - tox_env: packaging
           - tox_env: eco
           - tox_env: dockerfile

src/molecule/config.py

@@ -466,12 +466,20 @@ def ansible_version(version: str = "") -> Version:
     """
     if not version:
         proc = run_command(["ansible", "--version"], quiet=True)
-        if proc.returncode == 0:
-            version = proc.stdout.splitlines()[0].split()[1]
-        else:
+        if proc.returncode != 0:
             LOG.fatal(
                 "Unable to find a working copy of ansible executable. Read https://molecule.readthedocs.io/en/latest/installation.html\n%s",
                 proc,
             )
             sysexit(RC_SETUP_ERROR)
+
+        # First line of the `ansible --version` output is:
+        #
+        #  1. `ansible <version>` on ansible < 2.10 and on ansible-base.
+        #  2. `ansible [core <version>]` on ansible-core.
+        #
+        # The code below grabs the last component in that line and strips trailing ] if
+        # present.
+        version = proc.stdout.splitlines()[0].split()[-1].rstrip("]")
+
     return Version(version)

src/molecule/test/unit/test_config.py

@@ -360,3 +360,22 @@ def test_write_config(config_instance):
     config_instance.write()
 
     assert os.path.isfile(config_instance.config_file)
+
+
+@pytest.mark.parametrize(
+    "input,output",
+    [
+        ("ansible 2.9.18", "2.9.18"),  # ansible < 2.10 and ansible-base
+        ("ansible [core 2.11.0b1.post0]", "2.11.0b1.post0"),  # ansible-core
+    ],
+)
+def test_ansible_version_parsing(mocker, input, output):
+    run_command = mocker.patch.object(config, "run_command")
+    run_command.return_value.returncode = 0
+    run_command.return_value.stdout = input + "\nother stuff\n  here\n"
+
+    # Results from ansible_version are cached, so we need to kill the cache before each
+    # test so that we can actually test parsing of different strings.
+    config.ansible_version.cache_clear()
+
+    assert output == str(config.ansible_version())