Un-escape backslashes before populating os.environ

Related to #1656

Author: jayvdb

src/tox/config/__init__.py

@@ -408,6 +408,19 @@ def __setitem__(self, name, value):
         self.definitions[name] = value
         self.resolved[name] = value
 
+    def items(self):
+        return [(name, self.__getitem__(name)) for name in self.definitions]
+
+    def export(self):
+        # post-process items to avoid internal syntax/semantics
+        # such as {} being escaped using \{\}, suitable for use with
+        # os.environ .
+        return {
+            name: re.sub(r"\\({|})", r"\1", value)
+            for name, value in self.items()
+            if value is not self._DUMMY
+        }
+
 
 @tox.hookimpl
 def tox_addoption(parser):

src/tox/venv.py

@@ -493,7 +493,7 @@ def _get_os_environ(self, is_test_command=False):
             env = os.environ.copy()
 
         # in any case we honor per-testenv setenv configuration
-        env.update(self.envconfig.setenv)
+        env.update(self.envconfig.setenv.export())
 
         env["VIRTUAL_ENV"] = str(self.path)
         return env

tests/unit/test_venv.py

@@ -777,13 +777,17 @@ def test_env_variables_added_to_pcall(tmpdir, mocksession, newconfig, monkeypatc
     monkeypatch.setenv("YY", "456")
     config = newconfig(
         [],
-        """\
+        r"""
         [testenv:python]
         commands=python -V
         passenv = x123
         setenv =
             ENV_VAR = value
+            ESCAPED_VAR = \{value\}
+            ESCAPED_VAR2 = \\{value\\}
             PYTHONPATH = value
+            TTY_VAR = {tty:ON_VALUE:OFF_VALUE}
+            COLON = {:}
         """,
     )
     mocksession._clearmocks()
@@ -799,6 +803,10 @@ def test_env_variables_added_to_pcall(tmpdir, mocksession, newconfig, monkeypatc
         assert env is not None
         assert "ENV_VAR" in env
         assert env["ENV_VAR"] == "value"
+        assert env["ESCAPED_VAR"] == "{value}"
+        assert env["ESCAPED_VAR2"] == r"\{value\}"
+        assert env["COLON"] == ";" if sys.platform == "win32" else ":"
+        assert env["TTY_VAR"] == "OFF_VALUE"
         assert env["VIRTUAL_ENV"] == str(venv.path)
         assert env["X123"] == "123"
         assert "PYTHONPATH" in env