bpo-34715: Revert "Simplify PyInit_timezone. (GH-9323)" (GH-9366)

This reverts commit afde1c1a.

Modules/timemodule.c

@@ -1522,6 +1522,29 @@ PyDoc_STRVAR(get_clock_info_doc,
 \n\
 Get information of the specified clock.");
 
+#if !defined(HAVE_TZNAME) || defined(__GLIBC__) || defined(__CYGWIN__)
+static void
+get_zone(char *zone, int n, struct tm *p)
+{
+#ifdef HAVE_STRUCT_TM_TM_ZONE
+    strncpy(zone, p->tm_zone ? p->tm_zone : "   ", n);
+#else
+    tzset();
+    strftime(zone, n, "%Z", p);
+#endif
+}
+
+static int
+get_gmtoff(time_t t, struct tm *p)
+{
+#ifdef HAVE_STRUCT_TM_TM_ZONE
+    return p->tm_gmtoff;
+#else
+    return timegm(p) - t;
+#endif
+}
+#endif /* !defined(HAVE_TZNAME) || defined(__GLIBC__) || defined(__CYGWIN__) */
+
 static void
 PyInit_timezone(PyObject *m) {
     /* This code moved from PyInit_time wholesale to allow calling it from
@@ -1540,35 +1563,65 @@ PyInit_timezone(PyObject *m) {
 
     And I'm lazy and hate C so nyer.
      */
+#if defined(HAVE_TZNAME) && !defined(__GLIBC__) && !defined(__CYGWIN__)
     PyObject *otz0, *otz1;
     tzset();
     PyModule_AddIntConstant(m, "timezone", timezone);
 #ifdef HAVE_ALTZONE
     PyModule_AddIntConstant(m, "altzone", altzone);
-#elif defined(HAVE_STRUCT_TM_TM_ZONE)
+#else
+    PyModule_AddIntConstant(m, "altzone", timezone-3600);
+#endif
+    PyModule_AddIntConstant(m, "daylight", daylight);
+    otz0 = PyUnicode_DecodeLocale(tzname[0], "surrogateescape");
+    otz1 = PyUnicode_DecodeLocale(tzname[1], "surrogateescape");
+    PyModule_AddObject(m, "tzname", Py_BuildValue("(NN)", otz0, otz1));
+#else /* !HAVE_TZNAME || __GLIBC__ || __CYGWIN__*/
     {
-        static const time_t YEAR = (365 * 24 + 6) * 3600;
+#define YEAR ((time_t)((365 * 24 + 6) * 3600))
         time_t t;
         struct tm p;
         long janzone, julyzone;
+        char janname[10], julyname[10];
         t = (time((time_t *)0) / YEAR) * YEAR;
         _PyTime_localtime(t, &p);
-        janzone = -p.tm_gmtoff;
+        get_zone(janname, 9, &p);
+        janzone = -get_gmtoff(t, &p);
+        janname[9] = '\0';
         t += YEAR/2;
         _PyTime_localtime(t, &p);
-        julyzone = -p.tm_gmtoff;
-
-        // DST is reversed in the southern hemisphere.
-        PyModule_AddIntConstant(m, "altzone",
-            (janzone < julyzone) ? janzone : julyzone);
-    }
-#else
-    PyModule_AddIntConstant(m, "altzone", timezone-3600);
-#endif
-    PyModule_AddIntConstant(m, "daylight", daylight);
-    otz0 = PyUnicode_DecodeLocale(tzname[0], "surrogateescape");
-    otz1 = PyUnicode_DecodeLocale(tzname[1], "surrogateescape");
-    PyModule_AddObject(m, "tzname", Py_BuildValue("(NN)", otz0, otz1));
+        get_zone(julyname, 9, &p);
+        julyzone = -get_gmtoff(t, &p);
+        julyname[9] = '\0';
+
+        if( janzone < julyzone ) {
+            /* DST is reversed in the southern hemisphere */
+            PyModule_AddIntConstant(m, "timezone", julyzone);
+            PyModule_AddIntConstant(m, "altzone", janzone);
+            PyModule_AddIntConstant(m, "daylight",
+                                    janzone != julyzone);
+            PyModule_AddObject(m, "tzname",
+                               Py_BuildValue("(zz)",
+                                             julyname, janname));
+        } else {
+            PyModule_AddIntConstant(m, "timezone", janzone);
+            PyModule_AddIntConstant(m, "altzone", julyzone);
+            PyModule_AddIntConstant(m, "daylight",
+                                    janzone != julyzone);
+            PyModule_AddObject(m, "tzname",
+                               Py_BuildValue("(zz)",
+                                             janname, julyname));
+        }
+    }
+#ifdef __CYGWIN__
+    tzset();
+    PyModule_AddIntConstant(m, "timezone", _timezone);
+    PyModule_AddIntConstant(m, "altzone", _timezone-3600);
+    PyModule_AddIntConstant(m, "daylight", _daylight);
+    PyModule_AddObject(m, "tzname",
+                       Py_BuildValue("(zz)", _tzname[0], _tzname[1]));
+#endif /* __CYGWIN__ */
+#endif /* !HAVE_TZNAME || __GLIBC__ || __CYGWIN__*/
 }