Generalize workaround for #271 for more placeholder classes

Fixes #625

docs/changelog.rst

@@ -38,6 +38,10 @@ Version 10.3.2
 
    Fix by user rndblnch on github
 
+* :issue:`625`: Fix crash for calling ``NSIndexSet.alloc().initWithIndex_(0)``
+
+  This "fix" is a workaround for what appears to be a bug in Foundation.
+
 Version 10.3.1
 --------------
 

pyobjc-core/Modules/objc/objc-class.m

@@ -2659,15 +2659,16 @@ static Class _Nullable objc_metaclass_locate(PyObject* meta_class)
         PyType_Ready((PyTypeObject*)result);
     }
 
-    if (strcmp(className, "_NSPlaceholderData") == 0) {
-        /* XXX */
+    if (strncmp(className, "_NSPlaceholder", sizeof("_NSPlaceholder")-1) == 0) {
         /* Workaround for an issue on macOS 10.15: For some
          * reason the call to class_getInstanceVariable crashes
          * when called early in the process, likely due to an
          * incompletely initialized class.
          *
-         * The workaround is hardcoded for this specific class
-         * to avoid issues with other magic classes.
+         * The issue is more widespread in later versions of the OS,
+         * and seems to be related to rewriting Foundation in Swift.
+         *
+         * Issues: #271, #625
          */
         [objc_class class];
     }