luau-analyze: add --definitions=<file> option for loading type definition files

[nurpax]

Add the ability to load a type definition file before type checking.

This is useful in projects that'd like to declare their own types (such as types declared by their game engine's Luau integration code) and linting their scripts using 'luau-analyze'.

This is modeled to behave similar to the luau-lsp.types.definitionFiles in the Luau LSP project (https://github.com/JohnnyMorganz/luau-lsp).

Usage example:

  luau-analyze --definitions=engine_types.d.luau some_script.luau

---

I also implemented small example project that motivates why and how to use type definition files. The project declares some functionality in Zig, exposes the Zig functions to Luau, and declares the added object types so that luau-analyze can be used to type check any scripts written against this code: https://github.com/nurpax/luau-zig-example/tree/main/src. Summary of the example source files:

• Player.zig (first ten lines)
• types.d.luau
• main.luau <- this uses the "engine" and this is the file that would be luau-analyzed. Without the --definitions flag, it's hard to lint this file because the engine's types are missing.

[vegorov-rbx]

Thank you for your interest in improving Luau, but we have definition file support in .luaurc files on our roadmap, so we are not going to merge this contribution.
#418

[alexmccord]

Closing this. I think --definitions=<file> as a command line argument is a little brittle, since it means you have to setup your command line invocations correctly to get type checking to do the right thing. I'd much rather the path to a definition be added in the source tree itself.