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@@ -5119,6 +5119,60 @@ It should print `bun 0.4.0__dev` or something similar. You will want to add `packages/debug-bun-darwin-arm64/` or `packages/debug-bun-darwin-x64/` to your `$PATH` so you can run `bun-debug` from anywhere. +#### JavaScript builtins + +When you change anything in `src/bun.js/builtins/js/*`, you need to run this: + +```bash +make clean-bindings generate-builtins && make bindings -j12 +``` + +That inlines the JavaScript code into C++ headers using the same builtins generator script that Safari uses. + +#### Code generation scripts + +Bun leverages a lot of code generation scripts + +[./src/bun.js/bindings/headers.h](./src/bun.js/bindings/headers.h) has bindings to & from Zig <> C++ code. This file is generated by running the following: + +```bash +make headers +``` + +This ensures that the types for Zig and the types for C++ match up correctly, by using comptime reflection over functions exported/imported. + +TypeScript files that end with `*.classes.ts` are another code generation script. They generate C++ boilerplate for classes implemented in Zig. The generated code lives in: + +- [src/bun.js/bindings/ZigGeneratedClasses.cpp](src/bun.js/bindings/ZigGeneratedClasses.cpp) +- [src/bun.js/bindings/ZigGeneratedClasses.h](src/bun.js/bindings/ZigGeneratedClasses.h) +- [src/bun.js/bindings/generated_classes.zig](src/bun.js/bindings/generated_classes.zig) + +To generate the code, run: + +```bash +make codegen +``` + +Lastly, we also have a [code generation script](src/bun.js/scripts/generate-jssink.js) for our native stream implementations. + +To run that, run: + +```bash +make generate-sink +``` + +You probably won't need to run that one much. + +### Modifying ESM core modules + +How to modify ESM modules like `node:fs`, `node:path`, `node:stream`, `bun:sqlite`: + +ESM modules implemented in JavaScript live in `*.exports.js` within src/bun.js. + +While bun is in beta, you can modify them at runtime in release builds via the environment variable `BUN_OVERRIDE_MODULE_PATH`. + +This will look at a folder for a file with the same name as in src/bun.js/\*.exports.js and if it exists, it will use that instead. This is useful for testing changes to the ESM modules without needing to compile Bun. + #### Troubleshooting (macOS) If you see an error when compiling `libarchive`, run this: |