Fail on blanks in passed env vars

Avoids to oversee pass_env/passenv going from blank to comma separated list
Resolves #2658

docs/changelog/2658.feature.rst

@@ -0,0 +1 @@
+Fail on ''pass_env/passenv'' entries containing blanks, detecting missing commas

src/tox/tox_env/api.py

@@ -21,7 +21,7 @@
 from tox.execute.request import ExecuteRequest
 from tox.journal import EnvJournal
 from tox.report import OutErr, ToxHandler
-from tox.tox_env.errors import Recreate, Skip
+from tox.tox_env.errors import Fail, Recreate, Skip
 from tox.tox_env.info import Info
 from tox.tox_env.installer import Installer
 from tox.util.path import ensure_empty_dir
@@ -131,6 +131,12 @@ def register_config(self) -> None:
         )
 
         def pass_env_post_process(values: list[str]) -> list[str]:
+            blank_values = [v for v in values if " " in v or "\t" in v]
+            if blank_values:
+                raise Fail(
+                    f"pass_env/passenv variable can't have values containing "
+                    f"blanks like {blank_values}; a comma is possibly missing",
+                )
             values.extend(self._default_pass_env())
             return sorted({k: None for k in values}.keys())
 

tests/tox_env/test_tox_env_api.py

@@ -80,6 +80,26 @@ def test_tox_env_pass_env_literal_miss() -> None:
     assert not env
 
 
+def test_tox_env_pass_env_fail(tox_project: ToxProjectCreator) -> None:
+    prj = tox_project(
+        {
+            "tox.ini": """[testenv]
+    passenv = MYENV YOURENV, THEIRENV
+    commands=python -c 'import os; print("MYENV", os.getenv("MYENV"))'""",
+        },
+    )
+
+    result = prj.run("r")
+
+    result.assert_failed(1)
+    out = (
+        r"py: failed with pass_env/passenv variable can't have values "
+        r"containing blanks like \['MYENV YOURENV'\]; "
+        r"a comma is possibly missing.*"
+    )
+    result.assert_out_err(out=out, err="", regex=True)
+
+
 @pytest.mark.parametrize("glob", ["*", "?"])
 @pytest.mark.parametrize("char", ["a", "A"])
 def test_tox_env_pass_env_match_ignore_case(char: str, glob: str) -> None: