add version suffix to internal pybind11 data structures to avoid conflicts with future versions

include/pybind11/cast.h

@@ -34,12 +34,13 @@ PYBIND11_NOINLINE inline internals &get_internals() {
     if (internals_ptr)
         return *internals_ptr;
     handle builtins(PyEval_GetBuiltins());
-    capsule caps(builtins["__pybind11__"]);
+    const char *id = PYBIND11_INTERNALS_ID;
+    capsule caps(builtins[id]);
     if (caps.check()) {
         internals_ptr = caps;
     } else {
         internals_ptr = new internals();
-        builtins["__pybind11__"] = capsule(internals_ptr);
+        builtins[id] = capsule(internals_ptr);
     }
     return *internals_ptr;
 }

include/pybind11/common.h

@@ -110,6 +110,10 @@
 #endif
 
 #define PYBIND11_TRY_NEXT_OVERLOAD ((PyObject *) 1) // special failure return code
+#define PYBIND11_STRINGIFY(x) #x
+#define PYBIND11_TOSTRING(x) PYBIND11_STRINGIFY(x)
+#define PYBIND11_INTERNALS_ID "__pybind11_" \
+    PYBIND11_TOSTRING(PYBIND11_VERSION_MAJOR) "_" PYBIND11_TOSTRING(PYBIND11_VERSION_MINOR) "__"
 
 #define PYBIND11_PLUGIN(name) \
     static PyObject *pybind11_init(); \