Macros in Fir

Fir macros are fully deterministic programs that are distributed separately and that can introspect into the using program’s type-checked AST definitions. Deterministic execution of macros is necessary to be able to Cache macro results in the language server and between compilation of a package during development. Avoid the issues with build scripts in many languages that can run arbitrary code when compiling a package, causing all kinds of security nightmares. Potentially distribute packages with macros fully expanded. This makes dependency trees smaller as importing a package doesn’t bring in its macro dependencies. Avoid leaking compiling platform details into generated code, which makes cross-compilation difficult. Separate distribution is not a requirement but it simplifies the implementation quite significantly, and it’s also a good idea from a software design point of view: With macros in the same package with the use sites, you have to compile some parts of the package with…