ABI stability refers to the ability of a library or executable to maintain binary compatibility with other libraries or executables that depend on it even when the library is updated or changed. This means that any application that relies on a particular library should not break when that library is updated, and conversely, that updating an application should not require updating all of the libraries it depends on.
In the Rust ecosystem, ABI stability is particularly important due to the languages emphasis on system-level programming, where libraries can have a big impact on the efficiency and reliability of a system. ABI instability can have a major impact on developers and users, as they need to recompile and/or update their code each time a library changes.
In Rust, one potential solution to achieve ABI stability is to use a stable ABI for all Rust libraries by default. This would require some cooperation from the compiler, as well as a well-defined and well-documented ABI that can be relied on across different architectures and platforms. Alternatively, Rust could adopt cross-language ABI standards, such as those used by C and C++, to ensure compatibility with existing software and toolchains. This is already partially implemented in Rust through the use of the "C FFI", which allows Rust code to interact with C code in a way that is compatible with the C ABI.
Another potential solution to improve ABI stability is to use versioned symbols, which would allow multiple versions of a library to be installed and used simultaneously. This would enable developers to use newer versions of libraries without worrying about breaking old code, and it would allow system-level software to guarantee that it will work correctly with any installed version of a library. However, this approach requires careful design to ensure that the symbol versioning system is compatible with existing toolchains and that it does not introduce additional complexity or performance overhead.
Finally, another approach to achieve ABI stability is to provide a way to ensure and enforce consistency in the API and ABI of libraries. This can be done through tools that check for ABI compatibility when compiling or linking, and through automated testing to ensure that code changes do not introduce compatibility problems. By making ABI compatibility a core part of the Rust development process, libraries can be built with greater confidence and developers can have greater assurance that their code will continue to work as expected even when dependencies change.