Use 'getoption' to get the basetemp value instead of private details

changelog/518.bugfix

@@ -0,0 +1 @@
+Fix support of the `--basetemp` pytest option for pytest 5.4.0 and up.

src/xdist/workermanage.py

@@ -252,9 +252,9 @@ def setup(self):
             args = make_reltoroot(self.nodemanager.roots, args)
         if spec.popen:
             name = "popen-%s" % self.gateway.id
-            if hasattr(self.config, "_tmpdirhandler"):
-                basetemp = self.config._tmpdirhandler.getbasetemp()
-                option_dict["basetemp"] = str(basetemp.join(name))
+            basetemp = self.config.getoption("basetemp")
+            if basetemp is not None:
+                option_dict["basetemp"] = str(os.path.join(basetemp, name))
         self.config.hook.pytest_configure_node(node=self)
 
         remote_module = self.config.hook.pytest_xdist_getremotemodule()

testing/acceptance_test.py

@@ -128,6 +128,22 @@ def test_send(tmpdir):
         assert result.ret == 0
         result.stdout.fnmatch_lines(["*1 passed*"])
 
+    def test_basetemp_in_subprocesses_when_specified(self, testdir):
+        basetemp = testdir.tmpdir.join("one-level-down")
+        basetemp.mkdir()
+
+        p1 = testdir.makepyfile(
+            """
+            def test_send(tmpdir):
+                import py
+                assert tmpdir.relto(py.path.local(%r)), tmpdir
+        """
+            % str(basetemp)
+        )
+        result = testdir.runpytest_subprocess(p1, "-n1", "--basetemp", basetemp)
+        assert result.ret == 0
+        result.stdout.fnmatch_lines(["*1 passed*"])
+
     def test_dist_ini_specified(self, testdir):
         p1 = testdir.makepyfile(
             """