bpo-39413: Implement os.unsetenv() on Windows (GH-18163)

The os.unsetenv() function is now also available on Windows.

2 files changed, 108 insertions, 41 deletions

diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index 13a69cd..0f5995e 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -6125,7 +6125,43 @@ exit:
 
 #endif /* ((defined(HAVE_SETENV) || defined(HAVE_PUTENV)) && !defined(MS_WINDOWS)) */
 
-#if defined(HAVE_UNSETENV)
+#if defined(MS_WINDOWS)
+
+PyDoc_STRVAR(os_unsetenv__doc__,
+"unsetenv($module, name, /)\n"
+"--\n"
+"\n"
+"Delete an environment variable.");
+
+#define OS_UNSETENV_METHODDEF    \
+    {"unsetenv", (PyCFunction)os_unsetenv, METH_O, os_unsetenv__doc__},
+
+static PyObject *
+os_unsetenv_impl(PyObject *module, PyObject *name);
+
+static PyObject *
+os_unsetenv(PyObject *module, PyObject *arg)
+{
+    PyObject *return_value = NULL;
+    PyObject *name;
+
+    if (!PyUnicode_Check(arg)) {
+        _PyArg_BadArgument("unsetenv", "argument", "str", arg);
+        goto exit;
+    }
+    if (PyUnicode_READY(arg) == -1) {
+        goto exit;
+    }
+    name = arg;
+    return_value = os_unsetenv_impl(module, name);
+
+exit:
+    return return_value;
+}
+
+#endif /* defined(MS_WINDOWS) */
+
+#if (defined(HAVE_UNSETENV) && !defined(MS_WINDOWS))
 
 PyDoc_STRVAR(os_unsetenv__doc__,
 "unsetenv($module, name, /)\n"
@@ -6157,7 +6193,7 @@ exit:
     return return_value;
 }
 
-#endif /* defined(HAVE_UNSETENV) */
+#endif /* (defined(HAVE_UNSETENV) && !defined(MS_WINDOWS)) */
 
 PyDoc_STRVAR(os_strerror__doc__,
 "strerror($module, code, /)\n"
@@ -8773,4 +8809,4 @@ exit:
 #ifndef OS__REMOVE_DLL_DIRECTORY_METHODDEF
     #define OS__REMOVE_DLL_DIRECTORY_METHODDEF
 #endif /* !defined(OS__REMOVE_DLL_DIRECTORY_METHODDEF) */
-/*[clinic end generated code: output=6f42d8be634f5942 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=0348cbdff48691e3 input=a9049054013a1b77]*/
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 6a68752..3a8e6aa 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -10083,23 +10083,9 @@ posix_putenv_dict_setitem(PyObject *name, PyObject *value)
 
 
 #ifdef MS_WINDOWS
-/*[clinic input]
-os.putenv
-
-    name: unicode
-    value: unicode
-    /
-
-Change or add an environment variable.
-[clinic start generated code]*/
-
-static PyObject *
-os_putenv_impl(PyObject *module, PyObject *name, PyObject *value)
-/*[clinic end generated code: output=d29a567d6b2327d2 input=ba586581c2e6105f]*/
+static PyObject*
+win32_putenv(PyObject *name, PyObject *value)
 {
-    const wchar_t *env;
-    Py_ssize_t size;
-
     /* Search from index 1 because on Windows starting '=' is allowed for
        defining hidden environment variables. */
     if (PyUnicode_GET_LENGTH(name) == 0 ||
@@ -10108,36 +10094,68 @@ os_putenv_impl(PyObject *module, PyObject *name, PyObject *value)
         PyErr_SetString(PyExc_ValueError, "illegal environment variable name");
         return NULL;
     }
-    PyObject *unicode = PyUnicode_FromFormat("%U=%U", name, value);
+    PyObject *unicode;
+    if (value != NULL) {
+        unicode = PyUnicode_FromFormat("%U=%U", name, value);
+    }
+    else {
+        unicode = PyUnicode_FromFormat("%U=", name);
+    }
     if (unicode == NULL) {
         return NULL;
     }
 
-    env = PyUnicode_AsUnicodeAndSize(unicode, &size);
-    if (env == NULL)
-        goto error;
+    Py_ssize_t size;
+    /* PyUnicode_AsWideCharString() rejects embedded null characters */
+    wchar_t *env = PyUnicode_AsWideCharString(unicode, &size);
+    Py_DECREF(unicode);
+
+    if (env == NULL) {
+        return NULL;
+    }
     if (size > _MAX_ENV) {
         PyErr_Format(PyExc_ValueError,
                      "the environment variable is longer than %u characters",
                      _MAX_ENV);
-        goto error;
-    }
-    if (wcslen(env) != (size_t)size) {
-        PyErr_SetString(PyExc_ValueError, "embedded null character");
-        goto error;
+        PyMem_Free(env);
+        return NULL;
     }
 
-    if (_wputenv(env)) {
+    /* _wputenv() and SetEnvironmentVariableW() update the environment in the
+       Process Environment Block (PEB). _wputenv() also updates CRT 'environ'
+       and '_wenviron' variables, whereas SetEnvironmentVariableW() does not.
+
+       Prefer _wputenv() to be compatible with C libraries using CRT
+       variables and CRT functions using these variables (ex: getenv()). */
+    int err = _wputenv(env);
+    PyMem_Free(env);
+
+    if (err) {
         posix_error();
-        goto error;
+        return NULL;
     }
-    Py_DECREF(unicode);
 
     Py_RETURN_NONE;
+}
+#endif
 
-error:
-    Py_DECREF(unicode);
-    return NULL;
+
+#ifdef MS_WINDOWS
+/*[clinic input]
+os.putenv
+
+    name: unicode
+    value: unicode
+    /
+
+Change or add an environment variable.
+[clinic start generated code]*/
+
+static PyObject *
+os_putenv_impl(PyObject *module, PyObject *name, PyObject *value)
+/*[clinic end generated code: output=d29a567d6b2327d2 input=ba586581c2e6105f]*/
+{
+    return win32_putenv(name, value);
 }
 /* repeat !defined(MS_WINDOWS) to workaround an Argument Clinic issue */
 #elif (defined(HAVE_SETENV) || defined(HAVE_PUTENV)) && !defined(MS_WINDOWS)
@@ -10186,7 +10204,23 @@ os_putenv_impl(PyObject *module, PyObject *name, PyObject *value)
 #endif  /* defined(HAVE_SETENV) || defined(HAVE_PUTENV) */
 
 
-#ifdef HAVE_UNSETENV
+#ifdef MS_WINDOWS
+/*[clinic input]
+os.unsetenv
+    name: unicode
+    /
+
+Delete an environment variable.
+[clinic start generated code]*/
+
+static PyObject *
+os_unsetenv_impl(PyObject *module, PyObject *name)
+/*[clinic end generated code: output=54c4137ab1834f02 input=4d6a1747cc526d2f]*/
+{
+    return win32_putenv(name, NULL);
+}
+/* repeat !defined(MS_WINDOWS) to workaround an Argument Clinic issue */
+#elif defined(HAVE_UNSETENV) && !defined(MS_WINDOWS)
 /*[clinic input]
 os.unsetenv
     name: FSConverter
@@ -10199,16 +10233,13 @@ static PyObject *
 os_unsetenv_impl(PyObject *module, PyObject *name)
 /*[clinic end generated code: output=54c4137ab1834f02 input=2bb5288a599c7107]*/
 {
-#ifndef HAVE_BROKEN_UNSETENV
-    int err;
-#endif
-
 #ifdef HAVE_BROKEN_UNSETENV
     unsetenv(PyBytes_AS_STRING(name));
 #else
-    err = unsetenv(PyBytes_AS_STRING(name));
-    if (err)
+    int err = unsetenv(PyBytes_AS_STRING(name));
+    if (err) {
         return posix_error();
+    }
 #endif
 
 #ifdef PY_PUTENV_DICT