feat: NOPYTHON mode

Author: henryiii

CMakeLists.txt

@@ -41,7 +41,9 @@ include(GNUInstallDirs)
 include(CMakePackageConfigHelpers)
 include(CMakeDependentOption)
 
-message(STATUS "pybind11 v${pybind11_VERSION} ${pybind11_VERSION_TYPE}")
+if(NOT pybind11_QUIETLY)
+  message(STATUS "pybind11 v${pybind11_VERSION} ${pybind11_VERSION_TYPE}")
+endif()
 
 # Check if pybind11 is being used directly or via add_subdirectory
 if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
@@ -60,7 +62,7 @@ endif()
 # Options
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
-option(PYBIND11_CLASSIC_LTO "Use the classic LTO flag algorithm, even on CMake 3.9+" OFF)
+option(PYBIND11_NOPYTHON "Disable search for Python" OFF)
 
 cmake_dependent_option(
   USE_PYTHON_INCLUDE_DIR
@@ -213,5 +215,9 @@ if(PYBIND11_INSTALL)
 endif()
 
 if(PYBIND11_TEST OR (BUILD_TESTING AND PYBIND11_MASTER_PROJECT))
-  add_subdirectory(tests)
+  if(_pybind11_nopython)
+    message(FATAL_ERROR "Cannot activate tests in NOPYTHON mode")
+  else()
+    add_subdirectory(tests)
+  endif()
 endif()

docs/compiling.rst

@@ -234,7 +234,7 @@ available in all modes. The targets provided are:
      An alternative to `INTERPROCEDURAL_OPTIMIZATION` for adding link-time optimization.
 
    ``pybind11::windows_extras``
-     Bigobj and mp for MSVC.
+     ``/bigobj`` and ``/mp`` for MSVC.
 
 Two helper functions are also provided:
 
@@ -276,6 +276,17 @@ Instead of setting properties, you can set ``CMAKE_*`` variables to initialize t
     It can be expecially important to provide or set these properties; the
     :ref:`FAQ <faq:symhidden>` contains an explanation on why these are needed.
 
+Advanced: NOPYTHON mode
+-----------------------
+
+If you want complete control, you can set ``PYBIND11_NOPYTHON`` to completely
+disable Python integration (this also happens if you run ``FindPython2`` and/or
+``FindPython3`` without running ``FindPython``). This gives you complete
+freedom to integrate into an existing system (like `Scikit-Build's
+<https://scikit-build.readthedocs.io>`_ ``PythonExtensions``).
+``pybind11_add_module`` and ``pybind11_extension`` will be unavailable, and the
+targets will be missing any Python specific behavior.
+
 Embedding the Python interpreter
 --------------------------------
 

tools/pybind11Common.cmake

@@ -132,17 +132,50 @@ if(MSVC)
       PROPERTY INTERFACE_COMPILE_OPTIONS $<$<NOT:$<CONFIG:Debug>>:$<$<COMPILE_LANGUAGE:CXX>:/MP>>)
   endif()
 endif()
+
+# ----------------------- Legacy option --------------------------
+
+# Warn or error if old variable name used
+if(PYBIND11_CPP_STANDARD)
+  string(REGEX MATCH [[..$]] VAL "${PYBIND11_CPP_STANDARD}")
+  if(CMAKE_CXX_STANDARD)
+    if(NOT CMAKE_CXX_STANDARD STREQUAL VAL)
+      message(WARNING "CMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD} does not match "
+                      "PYBIND11_CPP_STANDARD=${PYBIND11_CPP_STANDARD}, "
+                      "please remove PYBIND11_CPP_STANDARD from your cache")
+    endif()
+  else()
+    set(supported_standards 11 14 17 20)
+    if("${VAL}" IN_LIST supported_standards)
+      message(WARNING "USE -DCMAKE_CXX_STANDARD=${VAL} instead of PYBIND11_PYTHON_VERSION")
+      set(CMAKE_CXX_STANDARD
+          ${VAL}
+          CACHE STRING "From PYBIND11_CPP_STANDARD")
+    else()
+      message(FATAL_ERROR "PYBIND11_CPP_STANDARD should be replaced with CMAKE_CXX_STANDARD "
+                          "(last two chars: ${VAL} not understood as a valid CXX std)")
+    endif()
+  endif()
+endif()
+
 # --------------------- Python specifics -------------------------
 
-# Check to see which Python mode we are in, new or old python
-if(PYBIND11_FINDPYTHON
-   OR Python_FOUND
-   OR Python3_FOUND
-   OR Python2_FOUND)
+# Check to see which Python mode we are in, new, old, or no python
+if(PYBIND11_NOPYTHON)
+  set(_pybind11_nopython ON)
+  if(NOT pybind11_QUIETLY)
+    message(STATUS "pybind11 in NOPYHTON mode")
+  endif()
+elseif(PYBIND11_FINDPYTHON OR Python_FOUND)
 
   # New mode
   include("${CMAKE_CURRENT_LIST_DIR}/pybind11NewTools.cmake")
 
+elseif(Python3_FOUND OR Python2_FOUND)
+  set(_pybind11_nopython ON)
+  if(NOT pybind11_QUIETLY)
+    message(STATUS "pybind11 in NOPYHTON mode due to Python2/Python3 only being present")
+  endif()
 else()
 
   # Classic mode
@@ -221,11 +254,11 @@ function(_pybind11_generate_lto target prefer_thin_lto)
       TARGET ${target}
       APPEND
       PROPERTY INTERFACE_COMPILE_OPTIONS "$<${genex}:${PYBIND11_LTO_CXX_FLAGS}>")
-    if(NOT is_config)
+    if(NOT is_config AND NOT pybind11_QUIETLY)
       message(STATUS "${target} enabled")
     endif()
   else()
-    if(NOT is_config)
+    if(NOT is_config AND NOT pybind11_QUIETLY)
       message(STATUS "${target} disabled (not supported by the compiler and/or linker)")
     endif()
   endif()

tools/pybind11Config.cmake.in

@@ -75,7 +75,9 @@ Set PythonLibsNew variables to influence python detection and
 CMAKE_CXX_STANDARD to influence standard setting. ::
 
   find_package(pybind11 CONFIG REQUIRED)
-  message(STATUS "Found pybind11 v${pybind11_VERSION} ${pybind11_VERSION_TYPE}: ${pybind11_INCLUDE_DIRS}")
+  if(NOT pybind11_QUIETLY)
+    message(STATUS "Found pybind11 v${pybind11_VERSION} ${pybind11_VERSION_TYPE}: ${pybind11_INCLUDE_DIRS}")
+  endif()
 
   # Create an extension module
   add_library(mylib MODULE main.cpp)

tools/pybind11NewTools.cmake

@@ -14,14 +14,12 @@ if(CMAKE_VERSION VERSION_LESS 3.12)
   message(FATAL_ERROR "You cannot use the new FindPython module with CMake < 3.12")
 endif()
 
-if(NOT Python_FOUND
-   OR Python2_FOUND
-   OR Python3_FOUND)
-
+if(NOT Python_FOUND)
   if(NOT DEFINED Python_FIND_IMPLEMENTATIONS)
     set(Python_FIND_IMPLEMENTATIONS CPython PyPy)
   endif()
 
+  # GitHub Actions like activation
   if(NOT DEFINED Python_ROOT_DIR AND DEFINED ENV{pythonLocation})
     set(Python_ROOT_DIR "$ENV{pythonLocation}")
   endif()
@@ -48,14 +46,14 @@ if(DEFINED Python_INCLUDE_DIRS)
     PROPERTY INTERFACE_INCLUDE_DIRECTORIES $<BUILD_INTERFACE:${Python_INCLUDE_DIRS}>)
 endif()
 
-if(DEFINED Python2_VERSION OR (Python_VERSION AND Python_VERSION VERSION_LESS 3))
+if(DEFINED Python_VERSION AND Python_VERSION VERSION_LESS 3)
   set_property(
     TARGET pybind11::pybind11
     APPEND
     PROPERTY INTERFACE_LINK_LIBRARIES pybind11::python2_no_register)
 endif()
 
-# In CMake 3.18+, you can find these separately, so include an if (also Python2 and Python3, for which we do nothing)
+# In CMake 3.18+, you can find these separately, so include an if
 if(TARGET Python::Python)
   set_property(
     TARGET pybind11::embed
@@ -89,10 +87,6 @@ function(pybind11_add_module target_name)
 
   if(COMMAND Python_add_library)
     python_add_library(${target_name} ${type} WITH_SOABI ${ARG_UNPARSED_ARGUMENTS})
-  elseif(COMMAND Python3_add_library)
-    python3_add_library(${target_name} ${type} WITH_SOABI ${ARG_UNPARSED_ARGUMENTS})
-  elseif(COMMAND Python2_add_library)
-    python2_add_library(${target_name} ${type} WITH_SOABI ${ARG_UNPARSED_ARGUMENTS})
   endif()
 
   target_link_libraries(${target_name} PRIVATE pybind11::headers)
@@ -107,9 +101,7 @@ function(pybind11_add_module target_name)
     target_link_libraries(${target_name} PRIVATE pybind11::windows_extras)
   endif()
 
-  if(DEFINED Python2_VERSION
-     OR Python_VERSION
-     AND Python_VERSION VERSION_LESS 3)
+  if(DEFINED Python_VERSION AND Python_VERSION VERSION_LESS 3)
     target_link_libraries(${target_name} PRIVATE pybind11::python2_no_register)
   endif()
 

tools/pybind11Tools.cmake

@@ -30,29 +30,6 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
 find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} MODULE REQUIRED)
 list(REMOVE_AT CMAKE_MODULE_PATH -1)
 
-# Warn or error if old variable name used
-if(PYBIND11_CPP_STANDARD)
-  string(REGEX MATCH [[..$]] VAL "${PYBIND11_CPP_STANDARD}")
-  if(CMAKE_CXX_STANDARD)
-    if(NOT CMAKE_CXX_STANDARD STREQUAL VAL)
-      message(WARNING "CMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD} does not match "
-                      "PYBIND11_CPP_STANDARD=${PYBIND11_CPP_STANDARD}, "
-                      "please remove PYBIND11_CPP_STANDARD from your cache")
-    endif()
-  else()
-    set(supported_standards 11 14 17 20)
-    if("${VAL}" IN_LIST supported_standards)
-      message(WARNING "USE -DCMAKE_CXX_STANDARD=${VAL} instead of PYBIND11_PYTHON_VERSION")
-      set(CMAKE_CXX_STANDARD
-          ${VAL}
-          CACHE STRING "From PYBIND11_CPP_STANDARD")
-    else()
-      message(FATAL_ERROR "PYBIND11_CPP_STANDARD should be replaced with CMAKE_CXX_STANDARD "
-                          "(last two chars: ${VAL} not understood as a valid CXX std)")
-    endif()
-  endif()
-endif()
-
 # Cache variables so pybind11_add_module can be used in parent projects
 set(PYTHON_INCLUDE_DIRS
     ${PYTHON_INCLUDE_DIRS}