chore: cleanup

.github/workflows/ci.yml

@@ -286,7 +286,10 @@ jobs:
         apt-get install -y git make cmake g++ libeigen3-dev python3-dev python3-pip python3-pytest
 
     - name: Configure for install
-      run: cmake -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") -DPYBIND11_INSTALL=1 -DPYBIND11_TEST=0 .
+      run: >
+        cmake .
+        -DPYBIND11_INSTALL=1 -DPYBIND11_TEST=0
+        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Make and install
       run: make install
@@ -298,7 +301,11 @@ jobs:
       run: mkdir /build-tests
 
     - name: Configure tests
-      run: cmake -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") ../pybind11-tests -DPYBIND11_WERROR=ON
+      run: >
+        cmake ../pybind11-tests
+        -DDOWNLOAD_CATCH=ON
+        -DPYBIND11_WERROR=ON
+        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
       working-directory: /build-tests
 
     - name: Run tests

CMakeLists.txt

@@ -7,8 +7,9 @@
 
 cmake_minimum_required(VERSION 3.7)
 
-# VERSION 3.7...3.18, but some versions of MCVS have a patched CMake 3.11
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
-# that do not work properly with this syntax, so using the following workaround:
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
 if(${CMAKE_VERSION} VERSION_LESS 3.18)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
@@ -26,7 +27,7 @@ foreach(ver ${pybind11_version_defines})
 endforeach()
 
 if(PYBIND11_VERSION_PATCH MATCHES [[([a-zA-Z]+)]])
-  set(PYBIND11_VERSION_TYPE "${CMAKE_MATCH_1}")
+  set(pybind11_VERSION_TYPE "${CMAKE_MATCH_1}")
 endif()
 string(REGEX MATCH "[0-9]+" PYBIND11_VERSION_PATCH "${PYBIND11_VERSION_PATCH}")
 
@@ -40,7 +41,7 @@ include(GNUInstallDirs)
 include(CMakePackageConfigHelpers)
 include(CMakeDependentOption)
 
-message(STATUS "pybind11 v${pybind11_VERSION} ${PYBIND11_VERSION_TYPE}")
+message(STATUS "pybind11 v${pybind11_VERSION} ${pybind11_VERSION_TYPE}")
 
 # Check if pybind11 is being used directly or via add_subdirectory
 if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
@@ -56,9 +57,11 @@ else()
   set(pybind11_system SYSTEM)
 endif()
 
+# Options
 option(PYBIND11_INSTALL "Install pybind11 header files?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_TEST "Build pybind11 test suite?" ${PYBIND11_MASTER_PROJECT})
 option(PYBIND11_CLASSIC_LTO "Use the classic LTO flag algorithm, even on CMake 3.9+" OFF)
+
 cmake_dependent_option(
   USE_PYTHON_INCLUDE_DIR
   "Install pybind11 headers in Python include directory instead of default installation prefix"
@@ -117,8 +120,7 @@ string(REPLACE "include/" "${CMAKE_CURRENT_SOURCE_DIR}/include/" PYBIND11_HEADER
 
 # Classic mode
 
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/tools")
+include("${CMAKE_CURRENT_LIST_DIR}/tools/pybind11Tools.cmake")
-include(pybind11Tools)
 
 # Cache variables so pybind11_add_module can be used in parent projects
 set(PYBIND11_INCLUDE_DIR
@@ -146,10 +148,6 @@ set(PYTHON_IS_DEBUG
     "${PYTHON_IS_DEBUG}"
     CACHE INTERNAL "")
 
-if(PYBIND11_TEST OR (BUILD_TESTING AND PYBIND11_MASTER_PROJECT))
-  add_subdirectory(tests)
-endif()
-
 if(USE_PYTHON_INCLUDE_DIR)
   file(RELATIVE_PATH CMAKE_INSTALL_INCLUDEDIR ${CMAKE_INSTALL_PREFIX} ${PYTHON_INCLUDE_DIRS})
 endif()
@@ -273,3 +271,7 @@ if(PYBIND11_INSTALL)
                                         ${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake)
   endif()
 endif()
+
+if(PYBIND11_TEST OR (BUILD_TESTING AND PYBIND11_MASTER_PROJECT))
+  add_subdirectory(tests)
+endif()

tests/CMakeLists.txt

@@ -7,8 +7,9 @@
 
 cmake_minimum_required(VERSION 3.7)
 
-# VERSION 3.7...3.18, but some versions of VS have a patched CMake 3.11
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
-# that do not work properly with this syntax, so using the following workaround:
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
 if(${CMAKE_VERSION} VERSION_LESS 3.18)
   cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
 else()
@@ -18,6 +19,9 @@ endif()
 # There's no harm in including a project in a project
 project(pybind11_tests CXX)
 
+# Access FindCatch and more
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/../tools")
+
 option(PYBIND11_WERROR "Report all warnings as errors" OFF)
 option(DOWNLOAD_EIGEN "Download EIGEN (requires CMake 3.11+)" OFF)
 set(PYBIND11_TEST_OVERRIDE
@@ -89,12 +93,8 @@ endif()
 
 # Skip test_async for Python < 3.5
 list(FIND PYBIND11_TEST_FILES test_async.cpp PYBIND11_TEST_FILES_ASYNC_I)
-if((PYBIND11_TEST_FILES_ASYNC_I GREATER -1) AND ("${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR}"
+if((PYBIND11_TEST_FILES_ASYNC_I GREATER -1) AND (PYTHON_VERSION VERSION_LESS 3.5))
-                                                 VERSION_LESS 3.5))
+  message(STATUS "Skipping test_async because Python version ${PYTHON_VERSION} < 3.5")
-  message(
-    STATUS
-      "Skipping test_async because Python version ${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR} < 3.5"
-  )
   list(REMOVE_AT PYBIND11_TEST_FILES ${PYBIND11_TEST_FILES_ASYNC_I})
 endif()
 

tests/test_cmake_build/CMakeLists.txt

@@ -8,7 +8,7 @@ function(pybind11_add_build_test name)
       "-DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}"
       "-DPYTHON_EXECUTABLE:FILEPATH=${PYTHON_EXECUTABLE}")
 
-  if(CMAKE_CXX_STANDARD)
+  if(DEFINED CMAKE_CXX_STANDARD)
     list(APPEND build_options "-DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD}")
   endif()
 

tests/test_cmake_build/installed_embed/CMakeLists.txt

@@ -1,4 +1,14 @@
 cmake_minimum_required(VERSION 3.7)
+
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
+if(${CMAKE_VERSION} VERSION_LESS 3.18)
+  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
+else()
+  cmake_policy(VERSION 3.18)
+endif()
+
 project(test_installed_embed CXX)
 
 set(CMAKE_MODULE_PATH "")

tests/test_cmake_build/installed_function/CMakeLists.txt

@@ -1,10 +1,21 @@
 cmake_minimum_required(VERSION 3.7)
+
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
+if(${CMAKE_VERSION} VERSION_LESS 3.18)
+  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
+else()
+  cmake_policy(VERSION 3.18)
+endif()
+
 project(test_installed_module CXX)
 
 set(CMAKE_MODULE_PATH "")
 
 find_package(pybind11 CONFIG REQUIRED)
-message(STATUS "Found pybind11 v${pybind11_VERSION}: ${pybind11_INCLUDE_DIRS}")
+message(
+  STATUS "Found pybind11 v${pybind11_VERSION} ${pybind11_VERSION_TYPE}: ${pybind11_INCLUDE_DIRS}")
 
 pybind11_add_module(test_cmake_build SHARED NO_EXTRAS ../main.cpp)
 

tests/test_cmake_build/installed_target/CMakeLists.txt

@@ -1,4 +1,14 @@
 cmake_minimum_required(VERSION 3.7)
+
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
+if(${CMAKE_VERSION} VERSION_LESS 3.18)
+  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
+else()
+  cmake_policy(VERSION 3.18)
+endif()
+
 project(test_installed_target CXX)
 
 set(CMAKE_MODULE_PATH "")

tests/test_cmake_build/subdirectory_embed/CMakeLists.txt

@@ -1,4 +1,14 @@
 cmake_minimum_required(VERSION 3.7)
+
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
+if(${CMAKE_VERSION} VERSION_LESS 3.18)
+  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
+else()
+  cmake_policy(VERSION 3.18)
+endif()
+
 project(test_subdirectory_embed CXX)
 
 set(PYBIND11_INSTALL

tests/test_cmake_build/subdirectory_function/CMakeLists.txt

@@ -1,4 +1,14 @@
 cmake_minimum_required(VERSION 3.7)
+
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
+if(${CMAKE_VERSION} VERSION_LESS 3.18)
+  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
+else()
+  cmake_policy(VERSION 3.18)
+endif()
+
 project(test_subdirectory_module CXX)
 
 add_subdirectory(${PYBIND11_PROJECT_DIR} pybind11)

tests/test_cmake_build/subdirectory_target/CMakeLists.txt

@@ -1,4 +1,14 @@
 cmake_minimum_required(VERSION 3.7)
+
+# The `cmake_minimum_required(VERSION 3.7...3.18)` syntax does not work with
+# some versions of VS that have a patched CMake 3.11. This forces us to emulate
+# the behavior using the following workaround:
+if(${CMAKE_VERSION} VERSION_LESS 3.18)
+  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
+else()
+  cmake_policy(VERSION 3.18)
+endif()
+
 project(test_subdirectory_target CXX)
 
 add_subdirectory(${PYBIND11_PROJECT_DIR} pybind11)

tools/FindPythonLibsNew.cmake

@@ -140,6 +140,7 @@ string(REGEX REPLACE "\\." ";" _PYTHON_VERSION_LIST ${_PYTHON_VERSION_LIST})
 list(GET _PYTHON_VERSION_LIST 0 PYTHON_VERSION_MAJOR)
 list(GET _PYTHON_VERSION_LIST 1 PYTHON_VERSION_MINOR)
 list(GET _PYTHON_VERSION_LIST 2 PYTHON_VERSION_PATCH)
+set(PYTHON_VERSION "${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR}.${PYTHON_VERSION_PATCH}")
 
 # Make sure all directory separators are '/'
 string(REGEX REPLACE "\\\\" "/" PYTHON_PREFIX "${PYTHON_PREFIX}")

tools/pybind11Config.cmake.in

@@ -1,62 +1,65 @@
-# pybind11Config.cmake
+#[=============================================================================[.rst
-# --------------------
+
-#
+pybind11Config.cmake
-# PYBIND11 cmake module.
+--------------------
-# This module sets the following variables in your project::
+
-#
+PYBIND11 cmake module.
-#   pybind11_FOUND - true if pybind11 and all required components found on the system
+This module sets the following variables in your project::
-#   pybind11_VERSION - pybind11 version in format Major.Minor.Release
+
-#   pybind11_INCLUDE_DIRS - Directories where pybind11 and python headers are located.
+  pybind11_FOUND - true if pybind11 and all required components found on the system
-#   pybind11_INCLUDE_DIR - Directory where pybind11 headers are located.
+  pybind11_VERSION - pybind11 version in format Major.Minor.Release
-#   pybind11_DEFINITIONS - Definitions necessary to use pybind11, namely USING_pybind11.
+  pybind11_INCLUDE_DIRS - Directories where pybind11 and python headers are located.
-#   pybind11_LIBRARIES - compile flags and python libraries (as needed) to link against.
+  pybind11_INCLUDE_DIR - Directory where pybind11 headers are located.
-#   pybind11_LIBRARY - empty.
+  pybind11_DEFINITIONS - Definitions necessary to use pybind11, namely USING_pybind11.
-#   CMAKE_MODULE_PATH - appends location of accompanying FindPythonLibsNew.cmake and
+  pybind11_LIBRARIES - compile flags and python libraries (as needed) to link against.
-#                       pybind11Tools.cmake modules.
+  pybind11_LIBRARY - empty.
-#
+
-#
+
-# Available components: None
+Available components: None
-#
+
-#
+
-# Exported targets::
+Exported targets::
-#
+
-# If pybind11 is found, this module defines the following :prop_tgt:`IMPORTED`
+If pybind11 is found, this module defines the following :prop_tgt:`IMPORTED`
-# interface library targets::
+interface library targets::
-#
+
-#   pybind11::module - for extension modules
+  pybind11::module - for extension modules
-#   pybind11::embed - for embedding the Python interpreter
+  pybind11::embed - for embedding the Python interpreter
-#
+
-# Python headers, libraries (as needed by platform), and the C++ standard
+Python headers, libraries (as needed by platform), and the C++ standard
-# are attached to the target. Set PythonLibsNew variables to influence
+are attached to the target.
-# python detection and CMAKE_CXX_STANDARD (11 or 14) to influence standard
+Classic mode::
-# setting. ::
+
-#
+Set PythonLibsNew variables to influence python detection and
-#   find_package(pybind11 CONFIG REQUIRED)
+CMAKE_CXX_STANDARD to influence standard setting. ::
-#   message(STATUS "Found pybind11 v${pybind11_VERSION}: ${pybind11_INCLUDE_DIRS}")
+
-#
+  find_package(pybind11 CONFIG REQUIRED)
-#   # Create an extension module
+  message(STATUS "Found pybind11 v${pybind11_VERSION} ${pybind11_VERSION_TYPE}: ${pybind11_INCLUDE_DIRS}")
-#   add_library(mylib MODULE main.cpp)
+
-#   target_link_libraries(mylib pybind11::module)
+  # Create an extension module
-#
+  add_library(mylib MODULE main.cpp)
-#   # Or embed the Python interpreter into an executable
+  target_link_libraries(mylib pybind11::module)
-#   add_executable(myexe main.cpp)
+
-#   target_link_libraries(myexe pybind11::embed)
+  # Or embed the Python interpreter into an executable
-#
+  add_executable(myexe main.cpp)
-# Suggested usage::
+  target_link_libraries(myexe pybind11::embed)
-#
+
-# find_package with version info is not recommended except for release versions. ::
+Suggested usage::
-#
+
-#   find_package(pybind11 CONFIG)
+find_package with version info is not recommended except for release versions. ::
-#   find_package(pybind11 2.0 EXACT CONFIG REQUIRED)
+
-#
+  find_package(pybind11 CONFIG)
-#
+  find_package(pybind11 2.0 EXACT CONFIG REQUIRED)
-# The following variables can be set to guide the search for this package::
+
-#
+
-#   pybind11_DIR - CMake variable, set to directory containing this Config file
+The following variables can be set to guide the search for this package::
-#   CMAKE_PREFIX_PATH - CMake variable, set to root directory of this package
+
-#   PATH - environment variable, set to bin directory of this package
+  pybind11_DIR - CMake variable, set to directory containing this Config file
-#   CMAKE_DISABLE_FIND_PACKAGE_pybind11 - CMake variable, disables
+  CMAKE_PREFIX_PATH - CMake variable, set to root directory of this package
-#     find_package(pybind11) when not REQUIRED, perhaps to force internal build
+  PATH - environment variable, set to bin directory of this package
+  CMAKE_DISABLE_FIND_PACKAGE_pybind11 - CMake variable, disables
+    find_package(pybind11) when not REQUIRED, perhaps to force internal build
+#]=============================================================================]
 
 @PACKAGE_INIT@
 
@@ -65,32 +68,35 @@ set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/@CMAKE_INSTALL_INCLUDEDIR@")
 
 set(pybind11_LIBRARY "")
 set(pybind11_DEFINITIONS USING_pybind11)
+set(pybind11_VERSION_TYPE "@pybind11_VERSION_TYPE@")
 
 check_required_components(pybind11)
 
-# Make the FindPythonLibsNew.cmake module available
-list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_LIST_DIR})
 
-include(pybind11Tools)
+include("${CMAKE_CURRENT_LIST_DIR}/pybind11Tools.cmake")
 
 #-----------------------------------------------------------------------------
 # Don't include targets if this file is being picked up by another
 # project which has already built this as a subproject
 #-----------------------------------------------------------------------------
 if(NOT TARGET pybind11::pybind11)
-    include("${CMAKE_CURRENT_LIST_DIR}/pybind11Targets.cmake")
+  include("${CMAKE_CURRENT_LIST_DIR}/pybind11Targets.cmake")
 
-    find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} MODULE REQUIRED)
+  list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
+  find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} MODULE REQUIRED)
+  list(REMOVE_AT CMAKE_MODULE_PATH -1)
 
-    set_property(TARGET pybind11::pybind11 APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES ${PYTHON_INCLUDE_DIRS})
+  set_property(TARGET pybind11::pybind11 APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES ${PYTHON_INCLUDE_DIRS})
-    set_property(TARGET pybind11::pybind11 APPEND PROPERTY INTERFACE_SYSTEM_INCLUDE_DIRECTORIES ${PYTHON_INCLUDE_DIRS})
+  set_property(TARGET pybind11::pybind11 APPEND PROPERTY INTERFACE_SYSTEM_INCLUDE_DIRECTORIES ${PYTHON_INCLUDE_DIRS})
 
-    set_property(TARGET pybind11::embed APPEND PROPERTY INTERFACE_LINK_LIBRARIES ${PYTHON_LIBRARIES})
+  set_property(TARGET pybind11::embed APPEND PROPERTY INTERFACE_LINK_LIBRARIES ${PYTHON_LIBRARIES})
-    set_property(TARGET pybind11::module APPEND PROPERTY INTERFACE_LINK_LIBRARIES
+  set_property(TARGET pybind11::module APPEND PROPERTY INTERFACE_LINK_LIBRARIES
-        "$<$<OR:$<PLATFORM_ID:Windows>,$<PLATFORM_ID:Cygwin>>:$<BUILD_INTERFACE:${PYTHON_LIBRARIES}>>")
+      "$<$<OR:$<PLATFORM_ID:Windows>,$<PLATFORM_ID:Cygwin>>:$<BUILD_INTERFACE:${PYTHON_LIBRARIES}>>")
 
-    get_property(_iid TARGET pybind11::pybind11 PROPERTY INTERFACE_INCLUDE_DIRECTORIES)
+  get_property(_iid TARGET pybind11::pybind11 PROPERTY INTERFACE_INCLUDE_DIRECTORIES)
-    get_property(_ill TARGET pybind11::module PROPERTY INTERFACE_LINK_LIBRARIES)
+  get_property(_ill TARGET pybind11::module PROPERTY INTERFACE_LINK_LIBRARIES)
-    set(pybind11_INCLUDE_DIRS ${_iid})
+  set(pybind11_INCLUDE_DIRS ${_iid})
-    set(pybind11_LIBRARIES ${_ico} ${_ill})
+  set(pybind11_LIBRARIES ${_ico} ${_ill})
+
+  include("${CMAKE_CURRENT_LIST_DIR}/pybind11Tools.cmake")
 endif()

tools/pybind11Tools.cmake

@@ -5,16 +5,6 @@
 # All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
-cmake_minimum_required(VERSION 3.7)
-
-# VERSION 3.7...3.18, but some versions of VS have a patched CMake 3.11
-# that do not work properly with this syntax, so using the following workaround:
-if(${CMAKE_VERSION} VERSION_LESS 3.18)
-  cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-  cmake_policy(VERSION 3.18)
-endif()
-
 # Add a CMake parameter for choosing a desired Python version
 if(NOT PYBIND11_PYTHON_VERSION)
   set(PYBIND11_PYTHON_VERSION
@@ -26,10 +16,12 @@ endif()
 set(Python_ADDITIONAL_VERSIONS
     "3.9;3.8;3.7;3.6;3.5;3.4"
     CACHE INTERNAL "")
-find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} REQUIRED)
+
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
+find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} MODULE REQUIRED)
+list(REMOVE_AT CMAKE_MODULE_PATH -1)
 
 include(CheckCXXCompilerFlag)
-include(CMakeParseArguments)
 
 # Warn or error if old variable name used
 if(PYBIND11_CPP_STANDARD)
@@ -131,7 +123,7 @@ endfunction()
 #
 function(pybind11_add_module target_name)
   set(options MODULE SHARED EXCLUDE_FROM_ALL NO_EXTRAS SYSTEM THIN_LTO)
-  cmake_parse_arguments(ARG "${options}" "" "" ${ARGN})
+  cmake_parse_arguments(PARSE_ARGV 2 ARG "${options}" "" "")
 
   if(ARG_MODULE AND ARG_SHARED)
     message(FATAL_ERROR "Can't be both MODULE and SHARED")
@@ -185,9 +177,14 @@ function(pybind11_add_module target_name)
     _pybind11_add_lto_flags(${target_name} ${ARG_THIN_LTO})
   else()
     include(CheckIPOSupported)
-    check_ipo_supported(RESULT supported OUTPUT error)
+    check_ipo_supported(
+      RESULT supported
+      OUTPUT error
+      LANGUAGES CXX)
     if(supported)
       set_property(TARGET ${target_name} PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
+    else()
+      message(WARNING "IPO is not supported: ${output}")
     endif()
   endif()