for https://github.com/HaxeFoundation/haxe/issues/5255

GenericClass.hx

import haxe.macro.Context;

#if !macro
@:genericBuild(GenericClass.build())
#end
class GenericClass<@:const Content> {
	public static function build () {
		return switch (Context.getLocalType())
		{
			case TInst(_, [TInst(_.get() => { kind: KExpr(macro $v{(s:String)}) }, _)]):
				var c = macro class TestImpl {
					public function new () {
					}
					public function execute () {
						trace($v{s});
					}
				};

				Context.defineType(c);
				return Context.getType("TestImpl");

			default:
				Context.error("Class expected", Context.currentPos());
				null;
		}
	}
}

Test.hx

//@:eager
typedef Sub = GenericClass<"test string from generic build">;

class Test {
	public static function main () {
		new Sub().execute();
	}
}