Python: use the vendored pybind11

Add a target that resembles what you would get from "normal"
use of pybind11 when following the examples. Link with it.
Drop Boost:Python sources from libcalamares.

3rdparty/pybind11/CMakeLists.txt

@@ -0,0 +1,16 @@
+# === This file is part of Calamares - <https://calamares.io> ===
+#
+#   SPDX-FileCopyrightText: 2023 Adriaan de Groot <groot@kde.org>
+#   SPDX-License-Identifier: BSD-2-Clause
+#
+###
+#
+# This is a very-stripped-down way of getting the bundled pybind11
+
+add_library(pybind11_headers INTERFACE)
+add_library(pybind11::headers ALIAS pybind11_headers)
+
+target_include_directories(pybind11_headers INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/include)
+target_link_libraries(pybind11_headers INTERFACE Python::Python) # Was searched-for at top-level
+
+

CMakeLists.txt

@@ -23,8 +23,9 @@
 #   WITH_<foo>      : try to enable <foo> (these usually default to ON). For
 #                     a list of WITH_<foo> grep CMakeCache.txt after running
 #                     CMake once. These affect the ABI offered by Calamares.
-#                       - PYTHON (enable Python Job modules)
-#                       - QML (enable QML UI View modules)
+#                       - PYBIND11 (use bundled pybind11, default ON, needs WITH_PYTHON)
+#                       - PYTHON (enable Python Job modules, default ON if Python is found)
+#                       - QML (enable QML UI View modules, default ON)
 #                       - QT6 (use Qt6 rather than Qt5, default to OFF)
 #                     The WITH_* options affect the ABI of Calamares: you must
 #                     build (C++) modules for Calamares with the same WITH_*
@@ -80,7 +81,8 @@ option(INSTALL_POLKIT "Install Polkit configuration" ON)
 option(INSTALL_COMPLETION "Install shell completions" OFF)
 # When adding WITH_* that affects the ABI offered by libcalamares,
 # also update libcalamares/CalamaresConfig.h.in
-option(WITH_PYTHON "Enable Python modules API (requires Boost.Python)." ON)
+option(WITH_PYBIND11 "Use bundled pybind11 instead o Boost::Python" ON)
+option(WITH_PYTHON "Enable Python modules API." ON)
 option(WITH_QML "Enable QML UI options." ON)
 option(WITH_QT6 "Use Qt6 instead of Qt5" OFF)
 #
@@ -446,25 +448,30 @@ else()
 endif()
 add_feature_info(yaml-schema BUILD_SCHEMA_TESTING "Validate YAML (config files) with schema.${_schema_explanation}")
 
-if(Python_Development_FOUND)
+if(NOT Python_Development_FOUND)
+    message(STATUS "Disabling Python modules")
+    set(WITH_PYTHON OFF)
+    set(WITH_PYBIND11 OFF)
+endif()
+
+if(WITH_PYTHON AND NOT WITH_PYBIND11)
     find_package(boost_python)
     if(NOT TARGET Boost::python)
         find_package(Boost ${BOOSTPYTHON_VERSION} COMPONENTS python)
-        set_package_properties(Boost PROPERTIES PURPOSE "Boost.Python is used for Python job modules.")
+        set_package_properties(Boost PROPERTIES
+            PURPOSE "Boost.Python is used for Python job modules (because WITH_PYBIND11 is OFF)."
+            TYPE REQUIRED
+        )
     else()
         message(STATUS "Found boost_python with target Boost::python")
         set(Boost_FOUND ON)
     endif()
 endif()
 
-if(NOT Python_Development_FOUND OR NOT Boost_FOUND)
-    message(STATUS "Disabling Boost::Python modules")
-    set(WITH_PYTHON OFF)
-endif()
-
 # Now we know the state of the ABI-options, copy them into "Calamares_"
 # prefixed variables, to match how the variables would-be-named
 # when building out-of-tree.
+set(Calamares_WITH_PYBIND11 ${WITH_PYBIND11})
 set(Calamares_WITH_PYTHON ${WITH_PYTHON})
 set(Calamares_WITH_QML ${WITH_QML})
 set(Calamares_WITH_QT6 ${WITH_QT6})
@@ -595,9 +602,13 @@ include(GNUInstallDirs)
 set(Calamares_LIBRARIES calamares)
 
 add_subdirectory(3rdparty/kdsingleapplication)
+if(WITH_PYBIND11)
+    add_subdirectory(3rdparty/pybind11)
+endif()
 add_subdirectory(src)
 
 add_feature_info(Python ${WITH_PYTHON} "Python job modules")
+add_feature_info(Pybind11 ${WITH_PYBIND11} "Python using bundled pybind11")
 add_feature_info(Qml ${WITH_QML} "QML UI support")
 add_feature_info(Polkit ${INSTALL_POLKIT} "Install Polkit files")
 add_feature_info(KCrash ${BUILD_CRASH_REPORTING} "Crash dumps via KCrash")

src/libcalamares/CMakeLists.txt

@@ -115,8 +115,13 @@ endif()
 #
 #
 if(WITH_PYTHON)
-    target_sources(calamares PRIVATE PythonHelper.cpp PythonJob.cpp PythonJobApi.cpp)
-    target_link_libraries(calamares PRIVATE Python::Python Boost::python)
+    if(WITH_PYBIND11)
+        target_sources(calamares PRIVATE python/Api.cpp python/PythonJob.cpp)
+        target_link_libraries(calamares PRIVATE Python::Python pybind11::headers)
+    else()
+        target_sources(calamares PRIVATE PythonHelper.cpp PythonJob.cpp PythonJobApi.cpp)
+        target_link_libraries(calamares PRIVATE Python::Python Boost::python)
+    endif()
 endif()
 
 ### OPTIONAL GeoIP XML support