From c792642d76ef5f985f2b51c52e92e39311b8f830 Mon Sep 17 00:00:00 2001
From: agra <alex@swipelab.co>
Date: Wed, 27 May 2026 19:05:16 +0300
Subject: [PATCH] =?UTF-8?q?ffi=20M5.A.next.4A.bare.1.A:=20bare=20$args=20?=
 =?UTF-8?q?=E2=80=94=20expected-failing=20test?=
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Step 4A final slice's lock-in. `$args` (whole pack) as a bare
expression should evaluate to a comptime `[]Type` slice value
— the whole pack passed through as data so builder fns can
walk it.

Today's parser arm (commit fd03b58, M5.A.next.4.3) requires
the `[<int_literal>]` form: bare `$<pack_name>` hits the
focused "expected '[' after '$<pack_name>'" diagnostic I added
when wiring the indexed access.

`examples/170-pack-bare-value.sx` exercises four call shapes
of a pack-fn whose body binds `list := $args` then returns
`list.len`. Expected output (post-fix) is "0/1/3/4" per call.
Today the parser rejection diff makes the test fail —
209/209 + 1 expected-failing = 210 total.

Cadence shape 2: expected output is the WORKING shape; pre-fix
the parser-error diff fails. Next commit lands the parser
extension + AST node + lowering and the test flips green.
---
 examples/170-pack-bare-value.sx         | 35 +++++++++++++++++++++++++
 tests/expected/170-pack-bare-value.exit |  1 +
 tests/expected/170-pack-bare-value.txt  |  4 +++
 3 files changed, 40 insertions(+)
 create mode 100644 examples/170-pack-bare-value.sx
 create mode 100644 tests/expected/170-pack-bare-value.exit
 create mode 100644 tests/expected/170-pack-bare-value.txt

diff --git a/examples/170-pack-bare-value.sx b/examples/170-pack-bare-value.sx
new file mode 100644
index 0000000..675a43d
--- /dev/null
+++ b/examples/170-pack-bare-value.sx
@@ -0,0 +1,35 @@
+// Variadic heterogeneous type packs — step 4 final slice (4A
+// bare): `$args` referenced bare (without `[...]` indexing) in
+// expression position should evaluate to a comptime `[]Type`
+// slice value — the whole pack passed through as data so
+// builder fns can walk it.
+//
+// Use case (eventual): step 5's generic Into(Block) impl body
+//   convert :: (self: Closure(..$args) -> $R) -> Block {
+//       #insert build_block_convert($args, $R);
+//   }
+// where `build_block_convert(args: []Type, ret: Type) -> string`
+// is a regular sx fn the interp executes — it walks `args` to
+// emit a trampoline fn matching the per-mono signature.
+//
+// Today the parser-arm I wrote for `$<ident>[<int>]` (commit
+// fd03b58, M5.A.next.4.3) REQUIRES the `[` after the pack
+// name; bare `$args` hits a focused diagnostic. This file
+// pins that rejection. Next commit makes the `[` optional —
+// no `[` yields a `comptime_pack_ref` AST node which lowering
+// converts to a `[N x Type]` aggregate of `const_type` values.
+
+#import "modules/std.sx";
+
+len_of :: (..$args) -> s64 {
+    list := $args;
+    return list.len;
+}
+
+main :: () -> s32 {
+    print("{}\n", len_of());
+    print("{}\n", len_of(42));
+    print("{}\n", len_of(1, 2, 3));
+    print("{}\n", len_of("a", true, 3.14, "b"));
+    return 0;
+}
diff --git a/tests/expected/170-pack-bare-value.exit b/tests/expected/170-pack-bare-value.exit
new file mode 100644
index 0000000..573541a
--- /dev/null
+++ b/tests/expected/170-pack-bare-value.exit
@@ -0,0 +1 @@
+0
diff --git a/tests/expected/170-pack-bare-value.txt b/tests/expected/170-pack-bare-value.txt
new file mode 100644
index 0000000..dded520
--- /dev/null
+++ b/tests/expected/170-pack-bare-value.txt
@@ -0,0 +1,4 @@
+0
+1
+3
+4