How Go 1.26's source-level inliner works, and how it can help you with self-service API migrations.

GoLang is an open-source programming language developed by Google, known for its simplicity, concurrency support, and performance. Developers can learn about GoLang's syntax, standard library, and concurrency primitives to build efficient and scalable software applications for various domains.

Go 1.26 introduces a source-level inliner as part of the redesigned `go fix` command, enabling self-service API migrations. By annotating deprecated functions with `//go:fix inline`, package authors can instruct the tool to automatically replace calls to old functions with their new equivalents. The post explains how the inliner works and covers six key technical challenges it must handle correctly: parameter elimination, side effects and evaluation order, fallible constant expressions, variable shadowing, unused variables, and defer statements. The inliner is already integrated into gopls for interactive use and has been used to prepare over 18,000 changelists in Google's monorepo.

//go:fix inline and the source-level inliner