Basic usage

This tutorial explains how to add a third party dependency with subpatch to a git repository.

In this tutorial the superproject is a simple C-library project that contains a function that adds two numbers. The subproject (=third party dependency) is the GoogleTest test library for C and C++ projects.

Prerequisites

To follow the tutorial you need the following setup

• Basic knowledge of git and the command line
• git installed
• subpatch installed (See Installation for the details)
• (optional) cmake and a c/c++ compiler installed

Cloning the example repository

First you need to clone the example repository. It's the superproject that contains minimal C library. On the command line execute

$ git clone https://github.com/lengfeld/subpatch-example0
$ cd subpatch-example0

If interested, have a look at the README.md file.

(optional) Buliding the C project

If you want, you can also build the C library and test the example program. You need cmake and a c/c++ compiler for that. Execute the commands

$ cmake -B build .
$ cmake --build build
$ build/prog 9 7
16

Adding the third party dependency

The example project contains the file test.cc. It is currently unused, because the GoogleTest dependency is missing. You will add it shortly.

As a good practice you should add all third party dependencies in a subfolder called external. To add the dependency execute the commands

$ mkdir external
$ cd external
$ subpatch add https://github.com/google/googletest -r v1.15.2

The last command takes some seconds to execute. It downloads the git repository and extract the files. It uses revision v1.15.2 of the git repository. It's a git tag that points to the current latest release of googletest.

When the command finishes it prints the message

Adding subproject 'https://github.com/google/googletest' into 'googletest'... Done.
- To inspect the changes, use `git status` and `git diff --staged`.
- If you want to keep the changes, commit them with `git commit`.
- If you want to revert the changes, execute `git reset --merge`.

The message contains three different options. To see what subpatch added to the git index, execute

$ git status

There are around 240 new files. Commit them by executing

$ cd ..
$ git commit -m "external: Adding GooglTest dependency"

Info: Apart from the files of the third party dependency subpatch also adds some metadata to the superproject. You can find it a the root directory of the git repository in the file .subpatch. For this tutorial the content looks like

[subpatch "external/googletest"]
    url = https://github.com/google/googletest

(optional) Enable and build the tests

After adding the GoogleTest dependency, you can build and execute the tests. Open the CMakeLists.txt file and enable them. You can find the needed cmake configuration already in the file, just remove the comments. Now the last lines of the file should look like

# Tests
add_subdirectory(external/googletest gtest)
add_executable(test test.cc)
target_link_libraries(test GTest::gtest_main add)
include(GoogleTest)
gtest_discover_tests(test)

After that you can build and run the tests with

$ cmake --build build
$ build/test

Executing the last command will perform all tests and show the test results. All tests should pass!

Congratulations

Congratulations! You have added your first subproject with subpatch.