The MoonBit Update——0401

Announcement
1

MoonBit Update

  • inspect function added for the Show interface in expect testing with the following signature:
pub fn inspect(
  obj : Show,
  ~content : String = "",
  ~loc : SourceLoc = _,
  ~args_loc : ArgsLoc = _) -> Result[Unit, String]

:warning: This API is currently unstable and may be changed to the expect function in the future.

For example, in the following code:

fn add(x: Int, y: Int) -> Int {
  x + y
}

test {
  inspect(add(1, 2))?
}

test {
  (add(3, 4) |> inspect)?
}

After executing moon test -u, the file is automatically updated to:

fn add(x: Int, y: Int) -> Int {
  x + y
}

test {
  inspect(add(1, 2), ~content="3")?
}

test {
  (add(3, 4) |> inspect(~content="7"))?
}
  • Move compiler builtins to moonbitlang/core

Some fundamental MoonBit definitions, previously maintained inside the MoonBit compiler, is now migrated to moonbitlang/core

  • Alert pragma supported

MoonBit now supports writing multiple pragma in the top-level doc comments. All pragma start with @ and occupy a line by themselves.

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Currently, function and method alert pragma are supported. If functions or methods marked with alert are used, a warning will be generated. This mechanism can be used to mark functions as deprecated or unsafe. The format for alert pragmas is @alert id "explanation string", where id can be any identifier.

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  • Supported marking intrinsics in pragmas. For example, after the following code in the standard library was marked as intrinsic, the JavaScript backend would use the String(..) function to convert floating-point numbers into strings. We will add support for more functions as intrinsics in the future.
/// @intrinsic %f64.to_string
pub fn to_string(self : Double) -> String {
  double_to_string(self)
}
  • Added ArgsLoc, used to automatically insert the position of each argument in the source code.
fn test_args_loc(a: Int, b: Int, ~args_loc : ArgsLoc = _) -> Unit {
  println(args_loc)
}

fn init {
  test_args_loc(1, 2)
  // Output: [Some(path/to/xx.mbt:6:17-6:18), Some(path/to/xx.mbt:6:20-6:21), None]
}

  • Improved the completeness check for pattern matching.

  • Improved moonfmt

    • Adjusted the print format for function for loops; semicolons are no longer printed in special cases.

    • For cases of poor readability due to nested if/match, extra parentheses were added after formatting. The effects before and after formatting are as follows:

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  • Enhanced the performance and size of the generated code.

    • Introduced optimizations to eliminate local aliases, thus avoiding the generation of unnecessary local variables.

    • Introduced constant propagation optimizations.

    • Optimized the type declaration part of the generated wasm code, reducing redundant type declarations.

  • Adjusted string encoding to UTF-16.

IDE Update

  • The VSCode plugin supported installing or updating the MoonBit toolchain.

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Build System Update

  • Supported custom function export names in the moon.pkg.json file using the ["link"][BACKEND]["exports"] field, and by default, not all pub functions are exported anymore. It is now required to explicitly specify them in the exports. Additionally, linking non-main packages through the link field is now supported.

For example, creating a new project with moon new hello results in the following directory structure:

.
├── README.md
├── lib
│   ├── hello.mbt
│   ├── hello_test.mbt
│   └── moon.pkg.json
├── main
│   ├── main.mbt
│   └── moon.pkg.json
└── moon.mod.json

In the past, executing moon build would only generate a wasm file for the main package. Now, the link field in moon.pkg.json supports generating wasm files for non-main packages. The link field can be a boolean value:

{
  "link": true //  Indicates that the current package needs to be linked
}

Or an object, which allows setting link options for different backends like wasm or wasm-gc. Currently, only the exports option is supported. Exports is an array of strings that includes the functions to be exported and their names:

{
  "link": {
    "wasm": {
      "exports": [
        "hello" // This exports the function hello as hello
      ]
    },
    "wasm-gc": {
      "exports": [
        "hello:hello_wasm_gc" // This exports the function hello as hello_wasm_gc
      ]
    }
  }
}

If the content of lib/moon.pkg.json is modified to:

{
  "link": {
    "wasm": {
      "exports": [
        "hello"
      ]
    }
  }
}

Then executing moon build --output-wat, the output in target/wasm/release/build/lib/lib.wat will include the following content:

(func $username/hello/lib.hello.fn/1 (export "hello") (result i32)
 (i32.const 10000))

Where (export "hello") indicates the configuration took effect.