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Use Fetchcontent instead of ExternalProject #3314

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Apr 21, 2021
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Use Fetchcontent instead of ExternalProject #3314

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5065389
Use Fetchcontent instead of ExternalProject
Vollstrecker Mar 13, 2021
38c316f
Changes like Requested.
Vollstrecker Apr 14, 2021
c79eb87
Mention to explicitely set the option to it's default.
Vollstrecker Apr 14, 2021
8043818
Use URL instead of git-repo
Vollstrecker Apr 20, 2021
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62 changes: 10 additions & 52 deletions googletest/README.md
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Expand Up @@ -85,69 +85,27 @@ main build can be done a few different ways:
is just a little more complex, but doesn't have the limitations of the other
methods.

The last of the above methods is implemented with a small piece of CMake code in
a separate file (e.g. `CMakeLists.txt.in`) which is copied to the build area and
then invoked as a sub-build _during the CMake stage_. That directory is then
pulled into the main build with `add_subdirectory()`. For example:
The last of the above methods is implemented with a small piece of CMake code so
the code is pulled into the main build.
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I might disambiguate the second use of "code" here:

"The last of the above methods is implemented with a small piece of CMake code that downloads and pulls the GoogleTest code into the main build."

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"small piece of CMake" would be sufficient, I think. Or CMake script.


New file `CMakeLists.txt.in`:
Just add to your `CMakeLists.txt`:

```cmake
cmake_minimum_required(VERSION 2.8.12)

project(googletest-download NONE)

include(ExternalProject)
ExternalProject_Add(googletest
GIT_REPOSITORY https://github.com/google/googletest.git
GIT_TAG master
SOURCE_DIR "${CMAKE_CURRENT_BINARY_DIR}/googletest-src"
BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/googletest-build"
CONFIGURE_COMMAND ""
BUILD_COMMAND ""
INSTALL_COMMAND ""
TEST_COMMAND ""
include (FetchContent)
FetchContent_Declare(
googletest
GIT_REPOSITORY https://github.com/google/googletest.git
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In our CMake Quickstart we use URL instead of GIT_REPOSITORY and GIT_TAG to avoid downloading the full Git history and instead download the code at a specific release. Could we use that approach here too?

Suggested change
GIT_REPOSITORY https://github.com/google/googletest.git
# Specify the commit you depend on and update it regularly.
URL https://github.com/google/googletest/archive/609281088cfefc76f9d0ce82e1ff6c30cc3591e5.zip

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Sure, make sense if users should stick with a specific version. For myself, I prefer the git, diskspace isn't that big problems nowadays and I like to see if something breaks as early as possible.

)
```

Existing build's `CMakeLists.txt`:

```cmake
# Download and unpack googletest at configure time
configure_file(CMakeLists.txt.in googletest-download/CMakeLists.txt)
execute_process(COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" .
RESULT_VARIABLE result
WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/googletest-download )
if(result)
message(FATAL_ERROR "CMake step for googletest failed: ${result}")
endif()
execute_process(COMMAND ${CMAKE_COMMAND} --build .
RESULT_VARIABLE result
WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/googletest-download )
if(result)
message(FATAL_ERROR "Build step for googletest failed: ${result}")
endif()

# Prevent overriding the parent project's compiler/linker
# settings on Windows
set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)

# Add googletest directly to our build. This defines
# the gtest and gtest_main targets.
add_subdirectory(${CMAKE_CURRENT_BINARY_DIR}/googletest-src
${CMAKE_CURRENT_BINARY_DIR}/googletest-build
EXCLUDE_FROM_ALL)
FetchContent_MakeAvailable(googletest)

# Now simply link against gtest or gtest_main as needed. Eg
add_executable(example example.cpp)
target_link_libraries(example gtest_main)
add_test(NAME example_test COMMAND example)
```

Note that this approach requires CMake 2.8.2 or later due to its use of the
`ExternalProject_Add()` command. The above technique is discussed in more detail
in [this separate article](http://crascit.com/2015/07/25/cmake-gtest/) which
also contains a link to a fully generalized implementation of the technique.
Note that this approach requires CMake 3.14 or later due to its use of the
`FetchContent_MakeAvailable()` command.

##### Visual Studio Dynamic vs Static Runtimes

Expand Down