# Ceres Solver - A fast non-linear least squares minimizer

# Copyright 2017 Google Inc. All rights reserved.

# http://ceres-solver.org/

#

# Redistribution and use in source and binary forms, with or without

# modification, are permitted provided that the following conditions are met:

#

# * Redistributions of source code must retain the above copyright notice,

#   this list of conditions and the following disclaimer.

# * Redistributions in binary form must reproduce the above copyright notice,

#   this list of conditions and the following disclaimer in the documentation

#   and/or other materials provided with the distribution.

# * Neither the name of Google Inc. nor the names of its contributors may be

#   used to endorse or promote products derived from this software without

#   specific prior written permission.

#

# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

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#

# Author: alexs.mac@gmail.com (Alex Stewart)

# Adds Ceres' C++11 requirements to a target such that they are exported when

# the target is exported (if the version of CMake supports it).

#

#    add_ceres_cxx11_requirements_to_target( [target1 [target2 [...]]] )

function(add_ceres_cxx11_requirements_to_target)

  include(CheckCXXCompilerFlag)

  check_cxx_compiler_flag("-std=c++11" COMPILER_HAS_CXX11_FLAG)

  foreach(TARGET ${ARGN})

    if (NOT TARGET ${TARGET})

      message(FATAL_ERROR "Specified target to append Ceres C++11 requirements "

        "to: ${TARGET} is not a declared CMake target.")

    endif()

    if (COMPILER_HAS_CXX11_FLAG)

      # IMPORTANT: It is not sufficient to specify the

      #            CXX_STANDARD/CXX_STANDARD_REQUIRED target properties

      #            as these target properties are NOT exported.

      if (CMAKE_VERSION VERSION_LESS "2.8.12")

        # CMake version < 2.8.12 does not support target_compile_options(), warn

        # user that they will have to add compile flags to their own projects

        # manually.

        message(WARNING "-- Warning: Detected CMake version: ${CMAKE_VERSION} "

          "< 2.8.12, which is the minimum required for compile options to be "

          "included in an exported CMake target and the detected. compiler "

          "requires -std=c++11. The client is responsible for adding "

          "-std=c++11 when linking against: ${TARGET}.")

      elseif (COMMAND target_compile_features)

        # CMake >= 3.1, use new target_compile_features() to specify Ceres'

        # C++11 requirements as used in the public API.  This assumes that

        # C++11 STL features are available if the specified features are

        # available.  We do not use the cxx_std_11 feature to specify this as

        # this did not come in until CMake 3.8.

        #

        # The reason to prefer using target_compile_features() if it exists is

        # that this handles 'upgrading' of the C++ standard required more

        # gracefully, e.g. if a client of Ceres requires C++14, but Ceres was

        # compiled against C++11 then target_compile_options() may not work as

        # expected.

        target_compile_features(

          ${TARGET} PUBLIC cxx_alignas cxx_alignof cxx_constexpr)

      else()

        # CMake version >= 2.8.12 && < 3.1 supports target_compile_options()

        # but not target_compile_features(). For these intermediary versions,

        # we use target_compile_options() to manually specify the C++11 flag and

        # export it for client targets that depend on the target iff they are

        # NOT compiling for C.  We check for not C, rather than C++ as

        # LINKER_LANGUAGE is often NOTFOUND and then uses the default (C++).

        target_compile_options(${TARGET} PUBLIC

          $<$<NOT:$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>>:-std=c++11>)

      endif()

    endif()

  endforeach()

endfunction()