Scarb vs Cargo

The entire Cairo and Starknet developer experience, starting with the Regenesis, is taking huge inspiration from the Rust ecosystem. As a part of that, the Cairo language, since 1.0, bases on Rust's syntax and partially semantics. Naturally, then, Scarb is designed to be as close as possible to Cargo and mimic its behaviour wherever it makes sense. There are some differences, though, and this document outlines them.

Scope

Scarb aims to be a little more minimal than Cargo, and it avoids including big features in main binary that are outside Scarb's scope, which is to be a build toolchain and package manager for Cairo.

The primary example of this is testing. Cargo comes with a built-in test and benchmark runners, which take a sizeable chunk of Cargo's code base. Scarb pushes to externalize such things into Scarb's extensions. Scarb's bundled distribution of testing framework, Cairo Language Server and the Cairo Runner are regular extensions. Currently, for simplicity these are temporarily included in Scarb's release archives, but this will change in the future.

Extensibility

Scarb is a bit more open to extensibility. Technically, both Scarb and Cargo have very similar mechanisms for writing extensions, but with Scarb exposes this feature in the documentation more prominently. The extension interfaces are also a bit easier to work with.

On top of that, Scarb has NPM-style scripts, while Cargo has an [alias] feature that is much more limited and also is hidden in Cargo config (.cargo/config.toml), rather than Cargo.toml/Scarb.toml directly.

Compilation model

Cairo's compilation model is different from Rust's. The Cairo compiler takes a flat list of packages to compile together, while in Rust, there is an explicit linking phase, and it is possible to form trees of linked objects (which Cargo does extensively). The consequence of this is that in Rust it is possible to link two semver-incompatible versions of the same package x (say, 1.0.0 and 2.0.0) together, while in Cairo, this would generate compilation errors, because only one package can define a global path x. For those familiar with Elixir, in this aspect, Cairo is much more similar to Elixir than to Rust.

Version resolution

In the end, we plan to use a different version resolution algorithm than Cargo. Scarb will use PubGrub, while Cargo is using a custom backtracking algorithm.