declaration-site unification check

Main.hx

class Point implements UnifyCheck<{x:Int}> {
	public var x:Int;
}

class Main {
	static function main() {
	}
}

UnifyCheck.hx

@:remove
@:autoBuild(UnifyCheckMacro.build())
interface UnifyCheck<T> {}

UnifyCheckMacro.hx

#if macro
import haxe.macro.Context;
import haxe.macro.Expr;
import haxe.macro.Type;
using haxe.macro.Tools;

class UnifyCheckMacro {
	static function build() {
		var fields = Context.getBuildFields();
		var localClass = Context.getLocalClass().get();
		for (iface in localClass.interfaces) {
			switch iface {
				case {t: _.toString() => "UnifyCheck", params: [type]}:
					// TODO: handle type params
					var thisCT = Context.getLocalType().toComplexType();
					var unifyCT = type.toComplexType();
					fields.push((macro class {
						extern inline function __unifyCheck__() @:pos(Context.currentPos()) ((null : $thisCT) : $unifyCT);
					}).fields[0]);
					break;
				case _:
			}
		}
		return fields;
	}
}
#end