rust-and-c++.md

Rust and C++

Taskwarrior has historically been a C++ project, but as part of an ongoing effort to replace its storage backend it now includes a Rust library called TaskChampion. To develop Taskwarrior, you will need both a C++ compiler and tools, and a Rust toolchain. However, most tasks will only require you to be familiar with one of the two languages.

TaskChampion

TaskChampion implements storage and access to "replicas" containing a user's tasks. It defines an abstract model for this data, and also provides a simple Rust API for manipulating replicas. It also defines a method of synchronizing replicas and provides an implementation of that method in the form of a sync server. TaskChampion provides a C interface via the taskchampion-lib crate.

Other applications, besides Taskwarrior, can use TaskChampion to manage tasks. Applications written in Rust can use the taskchampion crate, while those in other languages may use the taskchampion-lib crate. Taskwarrior is just one application using the TaskChampion interface.

You can build Taskchampion locally by simply running cargo build in the root of this repository. The implementation, including more documentation, is in the rust subdirectory.

Taskwarrior's use of TaskChampion

Taskwarrior's interface to TaskChampion has a few layers:

• The skeletal Rust crate in src/tc/rust brings the symbols from taskchampion-lib under CMake's management. The corresponding header file is included from taskchampion/lib. All of these symbols are placed in the C++ namespace, tc::ffi.
• C++ wrappers for the types from taskchampion-lib are defined in src/tc, ensuring memory safety (with unique_ptr) and adding methods corresponding to the Rust API's methods. The wrapper types are in the C++ namespace, tc.