> On Aug 13, 2019, at 2:54 PM, Christian Gruber <christian.gru...@posteo.de> 
> wrote:
> Am 13.08.19 um 02:45 schrieb John Ralls:
>>> On Aug 12, 2019, at 3:12 PM, Christian Gruber <christian.gru...@posteo.de> 
>>> wrote:
>>> Following my previous thread "[GNC-dev] Contribute to GnuCash development" 
>>> I opened a new topic thread about reworking GoogleTest integration.
>>> At first some investigation results on bug 797344 
>>> <https://bugs.gnucash.org/show_bug.cgi?id=797344>.
>>> In function gnc_gtest_configure() in file 
>>> common/cmake_modules/GncAddTest.cmake the two CMake variables 
>>> GTEST_INCLUDE_DIR and GMOCK_INCLUDE_DIR are set as follows:
>>> find_path(GTEST_INCLUDE_DIR gtest/gtest.h HINTS ${GTEST_ROOT}/include 
>>> ${GMOCK_ROOT}/gtest/include /usr/include)
>>> find_path(GMOCK_INCLUDE_DIR gmock/gmock.h HINTS ${GMOCK_ROOT}/include 
>>> /usr/include)
>>> This means, as long as GTEST_ROOT and GMOCK_ROOT are defined and refer to a 
>>> valid GoogleTest repository, header files gtest.h and gmock.h are found 
>>> there and the two variables GTEST_INCLUDE_DIR and GMOCK_INCLUDE_DIR will 
>>> refer to the include directories within this GoogleTest repository.
>>> In contrast to that the four CMake variables GTEST_MAIN_LIB, 
>>> function gnc_gtest_configure() as follows:
>>> find_library(GTEST_MAIN_LIB gtest_main)
>>> find_library(GTEST_SHARED_LIB gtest)
>>> find_library(GMOCK_MAIN_LIB gmock_main)
>>> find_library(GMOCK_SHARED_LIB gmock)
>>> This means, libraries are always searched in the default CMake search 
>>> paths. Therefore any preinstalled GoogleTest libraries will be found this 
>>> way.
>>> This explains the behaviour described in my bug report.
>>> Now let's come to my ideas regarding rework of GoogleTest integration. 
>>> After further studying CMake files I have two general questions at first.
>>> 1. Why are library targets "gtest" and "gmock" defined in GnuCash build 
>>> system instead of importing them from GoogleTest build results?
>>> In file common/test-core/CMakeLists.txt these two targets are defined via 
>>> add_library(). The same is done within GoogleTest build system in files 
>>> googletest/CMakeLists.txt and googlemock/CMakeLists.txt. So part of the 
>>> CMake build system from GoogleTest repository is copied into GnuCash build 
>>> system.
>>> My idea is to build and install GoogleTest completely independent from 
>>> GnuCash using its own build system and then importing targets via 
>>> find_package() into GnuCash build system. GoogleTest build system provides 
>>> CMake configuration files after installation ready for importing targets 
>>> into other projects.
>>> CMake function find_package() is able to find package GTest via CMake 
>>> configuration files, i.e. prebuilt from source code repository, as well as 
>>> preinstalled libraries from distro using internal CMake module FindGTest 
>>> <https://cmake.org/cmake/help/v3.5/module/FindGTest.html>. Beginning from 
>>> CMake version 3.5 module FindGTest provides imported targets GTest::GTest 
>>> and GTest::Main.
>>> This would avoid mixing of libraries and header files from different 
>>> locations.
>>> Additionally the user doesn't have to define extra environment variables 
>>> GTEST_ROOT and GMOCK_ROOT anymore. Instead the user can configure CMake 
>>> search path using CMake variable CMAKE_PREFIX_PATH, if desired.
>>> And the user can choose, which GoogleTest installation should be used by 
>>> influencing the CMake search path. So the requirement, that one can decide 
>>> whether to use preinstalled GoogleTest libraries from distro or GoogleTest 
>>> installation prebuilt from sources would be fulfilled.
>>> 2. Why is library target "gtest" not used directly instead of variables 
>>> Several test applications are defined via function gnc_add_test() by 
>>> passing a list of sources, include directories and libraries to that 
>>> function. This function gnc_add_test() is defined in file 
>>> common/cmake_modules/GncAddTest.cmake and passes the list of libraries 
>>> (TEST_LIBS_VAR_NAME) after resolving the variable names to CMake function 
>>> target_link_libraries().
>>> My idea is to add library target "gtest" directly to that list of libraries 
>>> instead of variable GTEST_LIB, which is possible since CMake function 
>>> target_link_libraries() can handle libraries as well as CMake targets. The 
>>> advantage is, that you don't have to handle include directories separately 
>>> on your own. When passing CMake targets to function target_link_libraries() 
>>> CMake does all the stuff for you. Include directories defined for that 
>>> target are added automatically, i.e. target_include_directories() doesn't 
>>> have to be invoked to add GTEST_INCLUDE_DIR.
>>> A further advantage is, that all test application targets depend on library 
>>> target "gtest". And if library target "gtest" is not an imported target, it 
>>> would be rebuilt automatically if necessary, when building test 
>>> applications. Currently after any change to GoogleTest sources, e.g. 
>>> checking out another version, you have to rebuilt GoogleTest libraries at 
>>> first via "make gtest" for instance before you can rebuilt test 
>>> applications via "make check" for instance. And if you forget that, you get 
>>> a mix of GoogleTest header files and libraries from different versions.
>>> Unfortunatelly in case of an imported target (see my first question), 
>>> automatic rebuilt is not easily possible. In this case you have to define 
>>> some extra custom command to invoke external GoogleTest build system.
>>> These two questions are important to be answered before proceeding. Are 
>>> there any considerations or constraints, which have to be taken into 
>>> account, e.g. backwards compatibility?
>>> Last there is another question.
>>> 3. Why has GTEST_SRC to be added to the list of sources passed to function 
>>> gnc_add_test()?
>>> Variable GTEST_SRC is set to ${GTEST_SRC_DIR}/src/gtest_main.cc in function 
>>> gnc_gtest_configure() in file common/cmake_modules/GncAddTest.cmake. But as 
>>> far as I can see this source file is already compiled and archived within 
>>> library libgtest_main.a, which is also contained in list of libraries 
>>> passed to function gnc_add_test() via variable GTEST_LIB.
>> Christian,
>> A little history: We started using Googletest 1.7.0 in 2014, when our build 
>> system was based on autotools. The autotools GTest integration was built 
>> from the recommendations of the GTest Readme file of the day 
>> (https://github.com/google/googletest/tree/release-1.7.0). When we begun 
>> using CMake I wrote gnc_gtest_configure mostly as a port from the autotools 
>> configuration before I'd learned much about CMake.
>> 1. Building Googletest from inside the GnuCash build system ensures that it 
>> is built with the same compiler flags as GnuCash itself. C++ used to break 
>> spectacularly if that wasn't done. It's gotten much better about it in 
>> recent years though it's still among the top 10 complaints reported by the 
>> standard committee. It would be my preference to always build directly from 
>> source this way but some Linux bistro packagers insist that we must use the 
>> included package; in some cases those packages provide a shared library 
>> instead of a static one, something that the Googletest developers 
>> specifically recommend against (or at least did back in v1.7).
>> 2. The GTEST_LIBS and GTEST_INCLUDE_DIRS are holdovers from the old 
>> autotools build system. You're correct that using the CMake target would be 
>> better.
>> The only problem with FindGTest is that there's no corresponding FindGMock, 
>> see https://gitlab.kitware.com/cmake/cmake/issues/17365.
>> 3. Because that v1.7.0 Readme doesn't say anything about building 
>> libgtest_main.a, it just said to build gtest-all.cc into libgtest.a. That 
>> readme also warns against even looking at the provided configure.ac, which 
>> does build libgtest_main.a, and says to use the compile-by-hand 
>> instructions. So I did that, promptly got symbol not found errors for the 
>> functions in gtest_main.cc, and simply added that to the source.
> 1. Ok, I understand. That means you not only want GoogleTest to be built from 
> source code. You also want GoogleTest to be built inside GnuCash build system 
> to ensure identical compiler flags. In this case my proposal is not 
> sufficient. Another approach to avoid copying CMake code could be to add 
> GoogleTest build system to GnuCash build system via CMake function 
> add_subdirectory(). Looking into GoogleTest Readme I see, that this is 
> proposed there as well (see "Using CMake" > "Incorporating Into An Existing 
> CMake Project"):
> "If you want to use gtest in a project which already uses CMake, then a more 
> robust and flexible approach is to build gtest as part of that project 
> directly. This is done by making the GoogleTest source code available to the 
> main build and adding it using CMake's `add_subdirectory()` command. This has 
> the significant advantage that the same compiler and linker settings are used 
> between gtest and the rest of your project, so issues associated with using 
> incompatible libraries (eg debug/release), etc. are avoided."
> Furthermore this Readme recommends four different methods to provide source 
> code:
> *   Download the GoogleTest source code manually and place it at a known
>     location. This is the least flexible approach and can make it more 
> difficult
>     to use with continuous integration systems, etc.
> *   Embed the GoogleTest source code as a direct copy in the main project's
>     source tree. This is often the simplest approach, but is also the hardest 
> to
>     keep up to date. Some organizations may not permit this method.
> *   Add GoogleTest as a git submodule or equivalent. This may not always be
>     possible or appropriate. Git submodules, for example, have their own set 
> of
>     advantages and drawbacks.
> *   Use CMake to download GoogleTest as part of the build's configure step. 
> This
>     is just a little more complex, but doesn't have the limitations of the 
> other
>     methods.
> What do you think?
> 2. Regarding GMock you're right. But is GMock already used by any GnuCash 
> test? Searching the code for variable GMOCK_LIB shows no results except in 
> file common/cmake_modules/GncAddTest.cmake, where it is set.
> 3. I see, the Readme doesn't really tell you much about the two libraries 
> libgtest.a and libgtest_main.a and their differences. Looking into the CMake 
> code (googletest/CMakeLists.txt) brings more clarity. Library libgtest.a 
> (target gtest) is defined as follows:
> cxx_library(gtest "${cxx_strict}" src/gtest-all.cc)
> It is built from source file gtest-all.cc. Library libgtest_main.a (target 
> gtest_main) is defined as follows:
> cxx_library(gtest_main "${cxx_strict}" src/gtest_main.cc)
> target_link_libraries(gtest_main PUBLIC gtest)
> It is built from source file gtest-main.cc. That means when linking 
> libgtest_main.a into any test application, you shouldn't need to additionally 
> add gtest_main.cc to the source files of the application.
> Furthermore target gtest is set as a dependency to target gtest_main. That 
> means, when adding gtest_main as a dependency to any application, target 
> gtest is automatically added as well. So you don't need to add both targets, 
> but choose what you want, depending on whether your test application provides 
> its own main function or not. Library libgtest.a (target gtest) is linked in 
> both cases.
> So I would say, passing GTEST_SRC to function gnc_add_test() can be omitted.

I think our distro packagers would object to any option other than relying on 
tools outside of the build system to provide the googletest sources and maybe a 
prebuilt static lib. It's a one-off for the casual builder and easily scripted 
for everyone else. Building gtest is also sufficiently trivial that it's not 
all that interesting to call out to guests own CMakeLists.txt instead of just 
building the two libraries in ours. OTOH it's possible that might change at 
some point, so 

I don't think anyone's actually tried doing a mock with GMock yet. There are 
hand-rolled ones in the QOF tests, but they use the old Glib test facility. 
Most of the C++ work so far has been at the lowest levels so that the C++ 
classes don't have any mockable dependencies. That will change when we get to 
redoing the engine as we'll want to use mock for at least the backend. We don't 
want to remove GMock from the dependencies.

I agree about libgtest_main.a. Would you like to make a PR to remove all of the 
inclusion of gtest_main.cc and GTEST_SRC?

John Ralls

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