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Fuzzing CDT: Finding, reproducing, and reporting bugs

Introduction

This is a tutorial on how to write a fuzzer for a non-trivial real-world library, namely Artem Amirkhanov's CDT. It is a library for computing Constrained Delaunay Triangulations (CDTs, hence the name of the library). We will be working from the 9d99b32ae56b26cd2781678dc4405c98b8679a9f commit, since that is what I originally wrote the fuzzer for, and that way, we will be able to rediscover the same bugs I found back then.

If you want to follow along, clone the library using

$ git clone https://github.com/artem-ogre/CDT
$ cd CDT

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A tale of a build system bug

Prologue

So, for a long time, I've had issues with GCC on Windows. It worked fine, on the first build, but whenever I made changes and wanted to build it again, I would get the following error message

ninja: error: FindFirstFileExA(c/:/path/to/project): The filename, directory name, or volume label syntax is incorrect.

and had to delete the contents of the build directory and build it again from scratch.

Obviously, that was too much of a hassle, so I just used MSVC and ignored it. Recently, I decided to look into it again, and hopefully fix it.

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The confusion with std::is_constant_evaluated, hopefully cleared up

Disclaimer: I am not on the committee, and while I have done my due diligence, I could easily have missed something. This is also not an attack on anyone. As stated the confusion is quite understandable, and the talk mentioned generally does a good job of introducing some small features of C++20, even if it does contain a minor mistake.

Introduction

This is inspired by Timur Doumler's C++20: The small things given at CppCon 2019 where, at 48:00, somebody points out a mistake on

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What we want to do

Lets say we have a library that is part of a larger CMake project, and we want to seperate it out so it can be used in more projects. For the sake of convenience lets say it is already largely seperate from the parent project, i.e. in its own directory with a CMakeLists.txt, and referenced with add_subdirectory from the parent project.

In order to fully seperate it we need to:

1. Make it buildable on its own. If it has depencies, it needs to use find_package itself to find them. If it has