Custom js generator, dce and typedefs

[benmerckx]

When enabling DCE, a custom js generator receives only those concrete types that need to be generated. However it also receives every typedef included in the class path (even in unused modules). I'm generating Typescript definitions - and some of these typedefs reference concrete types that are not part of the generation (making Typescript upset). So I'm looking to either have unused typedefs not pass through to the generate call or for a way to check during generation if a typedef is in use?

#if macro
import haxe.macro.Compiler;
import haxe.macro.JSGenApi;
#end

typedef Unused = {a: Int}

class Main {
  #if macro
  static function generate(api: JSGenApi) {
    for (type in api.types)
      switch type {
        case TType(t, _): trace(t);
        default:
      }
  }
  public static function use() {
    Compiler.setCustomJSGenerator(generate);
  }
  #end
  static function main() {
    trace('hello');
  }
}

$ haxe --macro Main.use() --main Main --js out.js --dce full
Main.hx:13: Unused
Main.hx:13: Iterator
Main.hx:13: Iterable
Main.hx:13: KeyValueIterator
Main.hx:13: KeyValueIterable
Main.hx:13: js.lib.ObjectPrototype
Main.hx:13: js.lib.ObjectPropertyDescriptor

[RealyUniqueName]

I guess the issue is that onGenerate macros get executed before DCE (check the line numbers): https://github.com/HaxeFoundation/haxe/blob/87ceafc689e36cec327923f24a709adbfd85c6cf/src/filters/filters.ml#L881 https://github.com/HaxeFoundation/haxe/blob/87ceafc689e36cec327923f24a709adbfd85c6cf/src/filters/filters.ml#L911

[RealyUniqueName]

@Simn Do you know why do we have it before dce?

[Simn]

I know absolutely nothing about custom JS generators.

[benmerckx]

I guess the issue is that onGenerate macros get executed before DCE (check the line numbers):

The js generation is actually called at a later stage than onGenerate:

#if macro
import haxe.macro.Compiler;
import haxe.macro.JSGenApi;
import haxe.macro.Context;
#end

typedef Unused = UnusedConcrete;

class UnusedConcrete {}

class Main {
  #if macro
  static function generate(api: JSGenApi) {
    trace('js generate');
    for (type in api.types)
      switch type {
        case TInst(_.get() => {name: name}, _) | TType(_.get() => {name: name}, _):
          if (name.substr(0, 2) == 'Un')
            trace(name);
        default:
      }
  }
  public static function use() {
    Context.onGenerate(_ -> trace('onGenerate'));
    Compiler.setCustomJSGenerator(generate);
  }
  #end
  static function main() {
    trace('hello');
  }
}

$ haxe --macro Main.use() --main Main --js out.js
Main.hx:24: onGenerate
Main.hx:14: js generate
Main.hx:19: Unused
Main.hx:19: UnusedConcrete

With dce the unused class UnusedConcrete is not passed to the generate call, but the typedef referencing it is:

$ haxe --macro Main.use() --main Main --js out.js --dce full
Main.hx:24: onGenerate
Main.hx:14: js generate
Main.hx:19: Unused