Open source in installments: moonbit-compiler [jsr-000L]

MoonBit was open sourced on GitHub on December 18th. The current moonbit-compiler is unfortunately a specialized open-source version that is only a small portion of the complete moonbit compiler. This lack is primarily evident in that, out of the four targets supported by moonbit (wasm, wasmgc, js, native), the open-source moonbit-compiler only supports wasmgc.

src/driver_util.ml#L44-L48

type target =
  | Wasm_gc of {
      clam_callback : clam_passes -> Clam.prog -> unit;
      sexp_callback : W.t list -> unit;
    }

Obviously, there is only one data constructor: Wasm_gc.

But we can still give it a try. We can pass the parameter --target wasm to moonc, and it not only fails, but even reports an Internal Compiler Error (ICE).

> dune exec moonc build-package -- /path/to/source/main/main.mbt -is-main -o main.core -target wasm -std-path /path/to/lib/target/wasm/release/bundle
                                        
         --  --
       /  //  / __--------_
      /  //  /_/            \
   ---      -                \ __
  / X        /        ____   /   )
  *_________/__/_____/______/ `--

Oops, the compiler has encountered an unexpected situation.
This is a bug in the compiler.

A bug report containing the error description and relevant code would be
greatly appreciated. You can submit the bug report here:

  https://github.com/moonbitlang/moonbit-docs/issues/new?labels=bug,ICE

Error: File "src/basic_config.ml", line 47, characters 60-66: Assertion failed

Compiler args: _build/install/default/bin/moonc build-package /path/to/source/main/main.mbt -is-main -o main.core -target wasm -std-path /path/to/lib/target/wasm/release/bundle

moonc version: v0.1.20241202+8756d160d

Uh oh, I think this is an error that shouldn't occur. Let's look at what happens where the "Assertion failed" is thrown.

src/basic_config.ml#47

let parse_target_exn = function "wasm-gc" -> Wasm_gc | _ -> assert false

Now we know how "specialized" this open-source version is.

By the way, the function parse_target_exn is called at the point where command-line arguments are parsed (naturally). But at this point, we can see remnants of the full moonbit compiler, which is why I say this is an error that shouldn't occur.

src/driver_config.ml#L189-L195

( "-target",
  Arg.Symbol
    ( [ "wasm-gc"; "wasm"; "js"; "native" ],
      fun target -> Config.target := Basic_config.parse_target_exn target
    ),
  "set compilation target. available targets: wasm, wasm-gc, js, native"
);