cmake: Add PythonQtConfigure.h to map CMake option to public macro

Introduce `PythonQtConfigure.h` to derive `PYTHONQT_USE_RELEASE_PYTHON_FALLBACK`
from the CMake option `PythonQt_USE_RELEASE_PYTHON_FALLBACK`.

Export build-tree binary include dir and install the configured header so
`#include <PythonQtConfigure.h>` works for both build and install trees.

Stop requiring downstreams to set the macro via compile definitions; users can
still override by predefining `PYTHONQT_USE_RELEASE_PYTHON_FALLBACK`.

Author: jcfr

CMakeLists.txt

@@ -267,6 +267,23 @@ foreach(qtlib ${qtlibs})
   endif()
 endforeach()
 
+#-----------------------------------------------------------------------------
+# Configure header
+
+# Map the CMake option `PythonQt_USE_RELEASE_PYTHON_FALLBACK` (camelCase)
+# to a plain variable used by the configured header. The public-facing
+# preprocessor symbol remains `PYTHONQT_USE_RELEASE_PYTHON_FALLBACK`.
+set(PYTHONQT_USE_RELEASE_PYTHON_FALLBACK ${PythonQt_USE_RELEASE_PYTHON_FALLBACK})
+configure_file(
+  src/PythonQtConfigure.h.in
+  ${CMAKE_CURRENT_BINARY_DIR}/src/PythonQtConfigure.h
+  )
+unset(PYTHONQT_USE_RELEASE_PYTHON_FALLBACK)
+
+list(APPEND headers
+  ${CMAKE_CURRENT_BINARY_DIR}/src/PythonQtConfigure.h
+  )
+
 #-----------------------------------------------------------------------------
 # Do wrapping
 pythonqt_wrap_cpp(gen_moc_sources ${moc_sources})
@@ -284,8 +301,8 @@ target_compile_definitions(PythonQt
   PRIVATE
     $<$<BOOL:${PythonQt_DEBUG}>:PYTHONQT_DEBUG>
     $<$<BOOL:${PythonQt_SUPPORT_NAME_PROPERTY}>:PYTHONQT_SUPPORT_NAME_PROPERTY>
-  PUBLIC
-    $<$<BOOL:${PythonQt_USE_RELEASE_PYTHON_FALLBACK}>:PYTHONQT_USE_RELEASE_PYTHON_FALLBACK>
+    # No need to export PYTHONQT_USE_RELEASE_PYTHON_FALLBACK publicly. the
+    # configured header handles consumers.
   )
 
 target_compile_options(PythonQt PRIVATE
@@ -295,6 +312,7 @@ target_compile_options(PythonQt PRIVATE
 target_include_directories(PythonQt
   PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/src>
     $<INSTALL_INTERFACE:${PythonQt_INSTALL_INCLUDE_DIR}>
   PRIVATE
     # Required for use of "QtCore/private/qmetaobjectbuilder_p.h" in "PythonQt.cpp"

src/PythonQtConfigure.h.in

@@ -0,0 +1,45 @@
+/*
+ *
+ *  Copyright (C) 2025 MeVis Medical Solutions AG All Rights Reserved.
+ *  Copyright (C) 2025 Kitware, Inc.
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  Further, this software is distributed without any warranty that it is
+ *  free of the rightful claim of any third person regarding infringement
+ *  or the like.  Any license provided herein, whether implied or
+ *  otherwise, applies only to this software file.  Patent licenses, if
+ *  any, provided herein do not apply to combinations of this program with
+ *  other software, or any other product whatsoever.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ *  Contact information: MeVis Medical Solutions AG, Universitaetsallee 29,
+ *  28359 Bremen, Germany or:
+ *
+ *  http://www.mevis.de
+ *
+ */
+
+#ifndef _PYTHONQTCONFIGURE_H
+#define _PYTHONQTCONFIGURE_H
+
+// If the user has not pre-defined the macro, derive it from the CMake
+// configure-time variable `PYTHONQT_USE_RELEASE_PYTHON_FALLBACK`, which
+// mirrors the `PythonQt_USE_RELEASE_PYTHON_FALLBACK` (camelCase)  CMake
+// option.
+#ifndef PYTHONQT_USE_RELEASE_PYTHON_FALLBACK
+#cmakedefine PYTHONQT_USE_RELEASE_PYTHON_FALLBACK
+#endif
+
+#endif

src/PythonQtPythonInclude.h

@@ -33,6 +33,8 @@
 #ifndef __PythonQtPythonInclude_h
 #define __PythonQtPythonInclude_h
 
+#include <PythonQtConfigure.h>
+
 // Undefine macros that features.h defines to avoid redefinition warning
 #ifdef _POSIX_C_SOURCE
   #undef _POSIX_C_SOURCE