Fish Shell Announces Plan to Transition from C++ to Rust

Fish is a user‑friendly command‑line shell for Linux and macOS, offering powerful features out‑of‑the‑box without requiring additional configuration.

The fish author recently submitted a pull request stating the intention to rewrite the project in Rust, describing the effort as a "port" rather than a full rewrite because the migration will be incremental, converting modules one by one while maintaining compatibility via FFI.

Reasons for the transition include:

Developers dislike C++ and CMake, and there is no clear path to abandon the legacy toolchain, leading to increasing development pain each year.

C++ is becoming a legacy language, making it harder to attract contributors, whereas Rust has an active, growing community.

Rust provides the language features needed for concurrent function execution.

Rewriting in Rust will help fish remain modern and valuable.

To demonstrate feasibility, the PR already ports several components—FLOG, theme monitor, wgetopt, builtin_wait, and others—into Rust. The Rust code lives in a crate linked to the existing C++ code via FFI.

Developers can build the mixed codebase by:

Installing Rust 1.67 or newer.

Running the usual cmake build, optionally using corrosion to handle the Rust parts.

For a detailed description of the Rust rewrite plan, see the documentation at https://github.com/ridiculousfish/fish-shell/blob/riir/doc_internal/fish-riir-plan.md .