Disable problem matcher when tox seems to be running on container

src/tox_gh_actions/plugin.py

@@ -55,8 +55,16 @@ def tox_configure(config):
     config.envlist_default = config.envlist = envlist
     verbosity1("overriding envlist with: {}".format(envlist))
 
-    verbosity2("enabling problem matcher")
-    print("::add-matcher::" + get_problem_matcher_file_path())
+    if is_running_on_container():
+        verbosity2(
+            "not enabling problem matcher as tox seems to be running on a container"
+        )
+        # Trying to add a problem matcher from a container without proper host mount can
+        # cause an error like the following:
+        # Unable to process command '::add-matcher::/.../matcher.json' successfully.
+    else:
+        verbosity2("enabling problem matcher")
+        print("::add-matcher::" + get_problem_matcher_file_path())
 
     if not is_log_grouping_enabled(config):
         verbosity2(
@@ -236,6 +244,21 @@ def is_running_on_actions():
     return os.environ.get("GITHUB_ACTIONS") == "true"
 
 
+def is_running_on_container():
+    # type: () -> bool
+    """Check whether tox is running on a container or not
+
+    Only Linux containers are supported.
+    """
+    cgroup_path = "/proc/1/cgroup"
+    if os.path.exists(cgroup_path):
+        with open(cgroup_path) as f:
+            for line in f:
+                if "containerd" in line:
+                    return True
+    return False
+
+
 def is_log_grouping_enabled(config):
     # type: (Config) -> bool
     """Returns True when the plugin should enable log line grouping

tests/test_plugin.py

@@ -395,6 +395,49 @@ def test_is_running_on_actions(mocker, environ, expected):
     assert plugin.is_running_on_actions() == expected
 
 
+def is_running_on_container_returns_false_on_non_linux(mocker):
+    mocker.patch("tox_gh_actions.plugin.os.path.exists", False)
+    assert not plugin.is_running_on_container()
+
+
+def is_running_on_container_returns_false_on_linux_host(mocker):
+    mocker.patch("tox_gh_actions.plugin.os.path.exists", True)
+    mock_open = mocker.mock_open(read_data="""12:perf_event:/
+11:devices:/init.scope
+10:cpu,cpuacct:/init.scope
+9:freezer:/
+8:pids:/init.scope
+7:memory:/init.scope
+6:cpuset:/
+5:hugetlb:/
+4:blkio:/init.scope
+3:net_cls,net_prio:/
+2:rdma:/
+1:name=systemd:/init.scope
+0::/init.scope""")
+    mocker.patch("tox_gh_actions.plugin.open", mock_open)
+    assert plugin.is_running_on_container()
+
+
+def is_running_on_container_returns_true_on_linux_container(mocker):
+    mocker.patch("tox_gh_actions.plugin.os.path.exists", True)
+    mock_open = mocker.mock_open(read_data="""12:pids:/actions_job/3d81
+11:net_cls,net_prio:/actions_job/3d81
+10:devices:/actions_job/3d81
+9:freezer:/actions_job/3d81
+8:cpuset:/actions_job/3d81
+7:cpu,cpuacct:/actions_job/3d81
+6:memory:/actions_job/3d81
+5:blkio:/actions_job/3d81
+4:perf_event:/actions_job/3d81
+3:rdma:/
+2:hugetlb:/actions_job/3d81
+1:name=systemd:/actions_job/3d81
+0::/system.slice/containerd.service""")
+    mocker.patch("tox_gh_actions.plugin.open", mock_open)
+    assert plugin.is_running_on_container()
+
+
 @pytest.mark.parametrize(
     "environ,parallel,parallel_live,expected",
     [