`FetchContent` only introduced in CMake >= 3.11

[mitchallain]

It seems like the FetchContent cmake module was introduced in CMake >= 3.11, however the CMakeLists.txt cites version 3.5.1 as the minimum, and notably ubuntu bionic package repositories only provide 3.10.

Introduced in commit 617743b just prior to 3.6.1 release.

BehaviorTree.CPP/CMakeLists.txt

Lines 113 to 122 in e6f241c

	elseif(BUILD_UNIT_TESTS)
	include(FetchContent)
	FetchContent_Declare(
	googletest
	URL https://github.com/google/googletest/archive/609281088cfefc76f9d0ce82e1ff6c30cc3591e5.zip
	)
	# For Windows: Prevent overriding the parent project's compiler/linker settings
	set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
	FetchContent_MakeAvailable(googletest)
	endif()

[mitchallain]

Not sure if reverting for older CMake versions would be satisfactory for you:

elseif(BUILD_UNIT_TESTS)
    if(${CMAKE_VERSION} VERSION_LESS "3.11.0")
      find_package(GTest REQUIRED)
    else()
      include(FetchContent)
      FetchContent_Declare(
        googletest
        URL https://github.com/google/googletest/archive/609281088cfefc76f9d0ce82e1ff6c30cc3591e5.zip
      )
      # For Windows: Prevent overriding the parent project's compiler/linker settings
      set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
      FetchContent_MakeAvailable(googletest)
    endif()
endif()

[facontidavide]

@mitchallain thanks, I will implement this solution