What are Toolchains?

Toolchains in programming are a set of software development tools that help in project building.

They decouple rule logic from platform-based selection of tools, allowing for more flexible and efficient development. Toolchains are designed to solve the problem of needing different compilers for different targets depending on the platform they’re being built for and on. The toolchain framework adds an extra level of indirection, declaring an abstract dependency on a family of targets (a toolchain type), and automatically resolving this to a particular target (a toolchain) based on the applicable platform constraints. This eliminates the need for the rule author or the target author to know the complete set of available platforms and toolchains.

For more information on the toolchain framework, you can read the Bazel guide on toolchains.