Automatic type conversion not being applied

1

Why can’t automatic type conversion happen here?

typedef PluginSpec = {
    final name:String;
    final ?cmd:String;
    final ?event:String;
}

abstract Plugin(PluginSpec) {
    @:from
    public static inline function from(spec:PluginSpec):Plugin {
        return untyped __lua__("{{0}, cmd = {1}, event = {2}, config = {3}}", spec.name, spec.cmd, spec.event, spec.config);
    };
}

typedef Plugins = lua.Table.Table<Int, Plugin>;

extern class Packer {
    inline static function init(plugins:Plugins):Void { ... }
}

When I try to use it like this:

import lua.Table.create as t;

function main() {
    Packer.init(t([{name: "wbthomason/packer.nvim", cmd: "", event: ""}]));

or this

import lua.Table.create as t;

function main() {
    final plugins:Plugins = t([{name: "wbthomason/packer.nvim", cmd: "", event: ""}]);
    Packer.init(plugins);

It says the types do not align.

src/kickstart/Pure.hx:7: characters 2-84 : error: { name : String, event : String, cmd : String } should be plugins.Plugin
src/kickstart/Pure.hx:7: characters 2-84 : ... have: lua.Table<..., { name, event, cmd }>
src/kickstart/Pure.hx:7: characters 2-84 : ... want: plugins.Plugins<>
2

Might be because cmd and event are optional in the PluginSpec type, meaning their types are Null?

3

Haxe can’t infer too many type conversions at once. Sometimes you have to explicitly tell it to convert a type. (Last I checked, this is intentional, to avoid edge cases where it might make the wrong inference.)

Here, you can either tell it that the array is an Array<Plugin>, or you can tell it that the first item in the array is a Plugin, because it always assumes the remaining items match the first.

You can either do this using a variable declaration, or with type check syntax. I strongly discourage using a cast, because that could suppress actual errors.

4

Indeed the problem was (well, it still is) the depth of “type hops”. I solved it by removing one nest level:

// This does not work
  typedef Plugins = lua.Table.Table<Int, Plugin>;
  inline static function init(plugins:Plugins):Void { ... } 
// This works, no extra type declaration, inline it
  inline static function init(plugins:Array< Plugin >):Bool {