// Variadic heterogeneous type packs — `..$args` — impl matching
// lock-in.
//
// Step 1d slice for the pack feature (see
// ~/.claude/plans/lets-see-options-for-merry-dijkstra.md). Pins
// today's concrete-only impl-matching behaviour: a user-declared
// `impl Into(Block) for Closure(..$args) -> $R` does NOT match
// any concrete closure source type. The xx cast site hits the
// existing "no `Into(Block) for <src>` impl" diagnostic even
// though the pack impl is reachable.
//
// Next commit (1d.B) teaches `tryUserConversion` /
// `registerParamImpl` to walk a second `param_impl_pack_map`
// when the concrete-key miss happens. Pack impls bind their
// `$args` and `$R` to the concrete source closure's tail types
// and return; monomorphisation proceeds against those bindings.
//
// The `Closure(i32, bool) -> bool` shape is not covered by
// stdlib's hand-rolled impls (only `Closure() -> void` and
// `Closure(bool) -> void`) and not covered by 96-block-multi-arg's
// `Closure(i32, *void) -> void` impl, so the pack impl is the
// only candidate.

#import "modules/std.sx";
#import "modules/ffi/objc_block.sx";

impl Into(Block) for Closure(..$args) -> $R {
    convert :: (self: Closure(..$args) -> $R) -> Block {
        .{
            isa = @_NSConcreteStackBlock,
            flags = 0,
            reserved = 0,
            invoke = null,
            descriptor = xx @__sx_block_descriptor,
            sx_env = self.env,
            sx_fn = self.fn_ptr,
        }
    }
}

main :: () -> i32 {
    cl := (a: i32, b: bool) => true;
    b : *Block = xx cl;
    print("pack impl match ok\n");
    return 0;
}
