Formatter formats away `await` on module

[zth]

• Formatting
• Handling let module Dynamic import in expression #6310

Consider this example:

let main = async () => {
  module Utils = await MathUtils

  let twoPlusTwo = Utils.add(2, 2)
  RescriptCore.Console.log(twoPlusTwo)
}

When formatting this, the formatter removes the await on the module.

Playground example (load this and then press format): https://rescript-lang.org/try?version=v11.0.0-beta.1&code=DYUwLgBAtghglgOwgXgjAzgTwQYwgCgEoUA+CAbwCgJoB7AEwFdQIBVMOYdFNAd3kgBZGGAAW7TukrUIoSGF60ACsEboAKop4SuAOhj16+AEwAaCMcIyASiHQ4ATnAAOYAMK0HIXR4TpaoLrAtADm+ArKqhqKVgC+QA

[mununki]

Currently, the builtin_ppx converts the await Module for Pstr_module of module_binding but there is another case for Pexp_letmodule of string loc * module_expr * expression.

$ bsc -dparsetree Import2.res

structure_item 
    Pstr_value Nonrec
    [
      <def>
        pattern 
          Ppat_var "main" 
        expression 
          attribute  "res.async"
            []
          Pexp_fun
          Nolabel
          None
          pattern 
            Ppat_construct "()" 
            None
          expression 
            Pexp_apply
            expression 
              Pexp_ident "Js.Promise.unsafe_async" 
            [
              <arg>
              Nolabel
                expression 
                  attribute  "res.braces"
                    []
                  Pexp_letmodule "Utils" 
                  module_expr 
                    attribute  "res.await"
                      []
                    Pmod_ident "MathUtils"
                    ...

[cristianoc]

The builtin ppx runs after the parser, so it should not affect formatting.

[mununki]

Correct. There are 2 problems. The first is that builtin ppx is not working for Pexp_letmodule and format.

[zth]

@mununki did you have a chance to look further into this?

[mununki]

@zth Yes, I've looked into it. I'm thinking about how to implement it. It's going to be a tricky implementation, because dynamic importing of a module creates a hidden module type, and it's not possible to define a type with an expression.

[mununki]

I couldn't grab an enough time yet. I'll grab a time during this weekend to fix this.