factor out internals_version.h from internals.h (no functional changes)

include/pybind11/detail/internals.h

@@ -10,6 +10,7 @@
 #pragma once
 
 #include "common.h"
+#include "internals_version.h"
 #include "platform_abi_id.h"
 
 #if defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)
@@ -22,34 +23,6 @@
 #include <mutex>
 #include <thread>
 
-/// Tracks the `internals` and `type_info` ABI version independent of the main library version.
-///
-/// Some portions of the code use an ABI that is conditional depending on this
-/// version number.  That allows ABI-breaking changes to be "pre-implemented".
-/// Once the default version number is incremented, the conditional logic that
-/// no longer applies can be removed.  Additionally, users that need not
-/// maintain ABI compatibility can increase the version number in order to take
-/// advantage of any functionality/efficiency improvements that depend on the
-/// newer ABI.
-///
-/// WARNING: If you choose to manually increase the ABI version, note that
-/// pybind11 may not be tested as thoroughly with a non-default ABI version, and
-/// further ABI-incompatible changes may be made before the ABI is officially
-/// changed to the new version.
-#ifndef PYBIND11_INTERNALS_VERSION
-#    if PY_VERSION_HEX >= 0x030C0000 || defined(_MSC_VER)
-// Version bump for Python 3.12+, before first 3.12 beta release.
-// Version bump for MSVC piggy-backed on PR #4779. See comments there.
-#        define PYBIND11_INTERNALS_VERSION 5
-#    else
-#        define PYBIND11_INTERNALS_VERSION 4
-#    endif
-#endif
-
-// This requirement is mainly to reduce the support burden (see PR #4570).
-static_assert(PY_VERSION_HEX < 0x030C0000 || PYBIND11_INTERNALS_VERSION >= 5,
-              "pybind11 ABI version 5 is the minimum for Python 3.12+");
-
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 using ExceptionTranslator = void (*)(std::exception_ptr);

include/pybind11/detail/internals_version.h

@@ -0,0 +1,33 @@
+// Copyright (c) 2024 The pybind Community.
+
+#pragma once
+
+#include "common.h"
+
+/// Tracks the `internals` and `type_info` ABI version independent of the main library version.
+///
+/// Some portions of the code use an ABI that is conditional depending on this
+/// version number.  That allows ABI-breaking changes to be "pre-implemented".
+/// Once the default version number is incremented, the conditional logic that
+/// no longer applies can be removed.  Additionally, users that need not
+/// maintain ABI compatibility can increase the version number in order to take
+/// advantage of any functionality/efficiency improvements that depend on the
+/// newer ABI.
+///
+/// WARNING: If you choose to manually increase the ABI version, note that
+/// pybind11 may not be tested as thoroughly with a non-default ABI version, and
+/// further ABI-incompatible changes may be made before the ABI is officially
+/// changed to the new version.
+#ifndef PYBIND11_INTERNALS_VERSION
+#    if PY_VERSION_HEX >= 0x030C0000 || defined(_MSC_VER)
+// Version bump for Python 3.12+, before first 3.12 beta release.
+// Version bump for MSVC piggy-backed on PR #4779. See comments there.
+#        define PYBIND11_INTERNALS_VERSION 5
+#    else
+#        define PYBIND11_INTERNALS_VERSION 4
+#    endif
+#endif
+
+// This requirement is mainly to reduce the support burden (see PR #4570).
+static_assert(PY_VERSION_HEX < 0x030C0000 || PYBIND11_INTERNALS_VERSION >= 5,
+              "pybind11 ABI version 5 is the minimum for Python 3.12+");