Introduction

We still need to cover the basics and a bit of internals of the FIP (Flint Interop Protocol) here, especially what it is. The FIP is, as it's name suggests, is a protocol for interoperability. The base idea is very simple: Flint handles all extern code as a black box and communicates with separate Interop Modules over the FIP to find out who provides a given symbol.

FIP is a small, extensible IPC protocol between the Flint Compiler (the master) and one or more Interop Modules (IMs). Each IM is a helper program that understands a specific language (for example fip-c for C). The compiler asks IMs for symbol information, asks them to compile/produce objects, and receives responses back. Treat the IMs as language-specific assistants: Flint does not try to parse, compile or understand every language by itself - it asks the IMs to do the language work and then consumes the results.

The Flint Compiler also communicates with the IMs about which ABIs they support. For now, every single IM (there only exists fip-c yet) uses the C ABI for function calls. But since the FIP is an abstraction over FFI in general, we could have different ABIs for every single extern function you define.

Key properties you can rely on:

  • Master / IM separation: The Flint compiler is the master. IMs are external processes specialized per language; the master talks to them over FIP messages (stdio communication)
  • Extensible by language: Each IM knows its own language, nothing more. fip-c is the C IM and it only understands C code; other IMs can be added for other languages
  • Config-driven: Each IM is configured by its own TOML file (e.g. fip-c.toml) and the project-level .fip directory stores cache, metadata and auto-generated "binding" files
  • Object outputs: IMs can compile sources code and return object files that the compiler links into the final binary. This keeps debug info intact and makes stepping into native code possible from a debugger
  • Binding-less usage: Because IMs can parse headers and produce objects, you can call C code from Flint without ever hand-writing bindings

In this chapter you will learn how to configure and use the FIP effectively.