Add more c-extension env-vars to default pass_env (#2818)

docs/changelog/2818.bugfix.rst

@@ -0,0 +1,3 @@
+Add ``CC``, ``CFLAGS``, ``CCSHARED``, ``CXX``, ``CPPFLAGS``, ``LDFLAGS``, ``PKG_CONFIG`` and ``PKG_CONFIG_SYSROOT_DIR``
+to the default passed through environment variables list as these are needed for building various C-extensions
+- by :user:`gaborbernat`.

src/tox/tox_env/api.py

@@ -211,7 +211,13 @@ def _default_pass_env(self) -> list[str]:
             "LANGUAGE",  # localization
             "CURL_CA_BUNDLE",  # curl certificates
             "SSL_CERT_FILE",  # https certificates
+            "CC",  # C compiler command
+            "CFLAGS",  # C compiler flags
+            "CCSHARED",  # compiler flags used to build a shared library
+            "CXX",  # C++ compiler command
+            "CPPFLAGS",  # C++ compiler flags
             "LD_LIBRARY_PATH",  # location of libs
+            "LDFLAGS",  # linker flags
         ]
         if sys.stdout.isatty():  # if we're on a interactive shell pass on the TERM
             env.append("TERM")

src/tox/tox_env/python/api.py

@@ -118,7 +118,8 @@ def _default_pass_env(self) -> list[str]:
                     "NUMBER_OF_PROCESSORS",  # multiprocessing.cpu_count()
                 ],
             )
-        env.extend(["PKG_CONFIG_PATH"])  # used by binary extensions during installation
+        binary_extension_build = ["PKG_CONFIG", "PKG_CONFIG_PATH", "PKG_CONFIG_SYSROOT_DIR"]
+        env.extend(binary_extension_build)  # used by binary extensions during installation
         env.extend(["REQUESTS_CA_BUNDLE"])
         return env
 

tests/session/cmd/test_show_config.py

@@ -115,10 +115,11 @@ def test_pass_env_config_default(tox_project: ToxProjectCreator, stdout_is_atty:
     pass_env = outcome.env_conf("py")["pass_env"]
     is_win = sys.platform == "win32"
     expected = (
-        (["COMSPEC"] if is_win else [])
-        + ["CURL_CA_BUNDLE", "LANG", "LANGUAGE", "LD_LIBRARY_PATH"]
+        ["CC", "CCSHARED", "CFLAGS"]
+        + (["COMSPEC"] if is_win else [])
+        + ["CPPFLAGS", "CURL_CA_BUNDLE", "CXX", "LANG", "LANGUAGE", "LDFLAGS", "LD_LIBRARY_PATH"]
         + (["MSYSTEM", "NUMBER_OF_PROCESSORS", "PATHEXT"] if is_win else [])
-        + ["PIP_*", "PKG_CONFIG_PATH"]
+        + ["PIP_*", "PKG_CONFIG", "PKG_CONFIG_PATH", "PKG_CONFIG_SYSROOT_DIR"]
         + (["PROCESSOR_ARCHITECTURE"] if is_win else [])
         + (["PROGRAMDATA"] if is_win else [])
         + (["PROGRAMFILES"] if is_win else [])