docs(metatype): make_enum done; note deferred free-form-construction gaps

current/CHECKPOINT-METATYPE.md

@@ -4,6 +4,19 @@ Companion to [PLAN-METATYPE.md](PLAN-METATYPE.md). Update after every step (one
 step at a time, per the cadence rule).
 
 ## Last completed step
+**`make_enum(name, variants: []EnumVariant) -> Type`** — the general enum
+constructor over `declare`/`define`, minting a nominal enum from a variant list
+passed as a VALUE (not a hardcoded literal). Pure sx in `meta.sx`, no compiler
+machinery — the open-ended form the channel-result constructors are special cases
+of. Because `variants` is an ordinary comptime value, a non-generic builder
+assembles it in a local before minting; `examples/0620` (`build_level` fills a
+local array → `make_enum` mints `Level`) exercises `define` decoding a value-arg
+SLICE (`decodeVariantElements`' slice branch) vs. the inline `.[ … ]` array the
+0614–0618 examples pass directly. No compiler change (locks existing capability).
+Suite green (678). See "make_enum follow-ups" under Next step for the deferred
+free-form-construction gaps (subslice/List at comptime, generic-type-fn locals).
+
+## Prior step
 **`type_info($T)` reflection — enum round-trip.** Reflect a type INTO a `TypeInfo`
 value (the inverse of `define`'s decode), so `define(declare(n), type_info(T))`
 mints a byte-identical copy with NO literal variant list.
@@ -28,7 +41,7 @@ mints a byte-identical copy with NO literal variant list.
 `examples/0619` locks it (source enum `circle:f64 / rect:i64 / empty` reflected →
 reconstructed → constructs + matches). Full suite green (676 examples + units).
 
-## Prior step
+## Earlier step
 **Self-reference — recursive enums via `declare("Name")` + `*Name`.** The
 `declare`/`define` floor now supports self-referential types.
 
@@ -59,7 +72,8 @@ traversal)**; `field_type` reflection `0616`. Full suite green (674 examples).
 ## Current state
 - `modules/std/meta.sx`: `EnumVariant` / `EnumInfo{ name, variants }` / `TypeInfo`
   data types; `declare` / `define` / `type_info` / `field_type` `#builtin`s;
-  `RecvResult($T)` / `TryResult($T)` sx constructors over `define(declare(), …)`.
+  `RecvResult($T)` / `TryResult($T)` + the general `make_enum(name, variants)` sx
+  constructors over `define(declare(), …)`.
 - Compiler primitives only: `declare`/`define` (construction), `field_type`
   (reflection). No constructor-name knowledge anywhere in the compiler — every
   named constructor is sx. `declare(name)` carries the type name (compile-time
@@ -75,16 +89,28 @@ shifts every `.ir` snapshot. On-demand import keeps the prelude clean.
 
 ## Next step
 Pick any (independent):
-- **`make_enum(variants: []EnumVariant)`** sx helper over a COMPUTED (non-literal)
-  variant list — exercises the interpreter decoding a value-arg slice in `define`.
-  **UNBLOCKED** (issue 0140 fixed — decode failures now surface a clean diagnostic
-  at the construction site instead of a panic/cascade). Remaining work: a computed
-  (pointer-backed) `[]EnumVariant` slice from a local var / `List` still does not
-  DECODE in `defineEnum`/`decodeVariantElements` — that decoder needs to follow a
-  `slot_ptr`/`heap_ptr` data field (today it only reads an inline `.aggregate`).
-  Probes: `.sx-tmp/probe_me2.sx` (sliced local array → bail "TypeError"),
-  `.sx-tmp/probe_makeenum.sx` (List → bail "struct_get: base has no fields"); the
-  inline-literal-param form already works (`.sx-tmp/probe_me3.sx`).
+- **Widen `type_info` / `TypeInfo` past `` `enum ``** — struct/tuple variants:
+  add `` .`struct ``/`` .`tuple `` to the `TypeInfo` enum in `meta.sx`, teach
+  `reflectTypeInfo` to build them, and teach `defineEnum` (→ a `defineType`) to
+  decode them. Round-trips a struct through `define` once it lands.
+- **Validation + loud diagnostics** (remaining) — duplicate variant names, a
+  `declare()` never `define()`d (hard error at end of comptime), use-before-define.
+
+### make_enum follow-ups (deferred capability gaps — NOT crashes; clean diagnostics)
+`make_enum` itself is DONE (see Last completed step). Two adjacent capabilities
+would let the variant list be built more freely; both currently error cleanly
+(post-0140) rather than crash, so they're enhancements, not blockers:
+- **Comptime slice over a non-string aggregate.** `arr[..]` over a `[]EnumVariant`
+  array bails — the interp's `.subslice` op (`interp.zig:~1235`) only supports
+  STRING bases. Needed for `vs[..]`-style construction. Probe `.sx-tmp/probe_me2.sx`.
+- **Comptime `List` growth.** Building variants via `List(EnumVariant).append` at
+  comptime bails ("struct_get: base has no fields") — the allocator/List protocol
+  path isn't fully interp-evaluable. Probe `.sx-tmp/probe_makeenum.sx`.
+- **Generic type-fn body locals.** A *generic* `($T) -> Type` comptime-evals only
+  its return EXPRESSION (`generic.zig:1760`, `findReturnTypeExpr`), so a local
+  before the return is unresolved. Workaround: build the list inline in the return,
+  or use a non-generic `() -> Type` builder (whose whole body is evaluated — this
+  is what `examples/0620` uses). Probe `.sx-tmp/probe_me5.sx`.
 - **Widen `type_info` / `TypeInfo` past `` `enum ``** — struct/tuple variants:
   add `` .`struct ``/`` .`tuple `` to the `TypeInfo` enum in `meta.sx`, teach
   `reflectTypeInfo` to build them, and teach `defineEnum` (→ a `defineType`) to
@@ -105,6 +131,13 @@ Pick any (independent):
   `examples/1178` locks it).
 
 ## Log
+- **`make_enum` done.** General enum constructor `make_enum(name, variants:
+  []EnumVariant) -> Type` in `meta.sx` (pure sx over declare/define). A non-generic
+  builder assembles the variant list in a local, then mints from it —
+  `examples/0620` exercises `define`'s value-arg SLICE decode. No compiler change.
+  Suite green (678). Deferred free-form gaps (subslice/List at comptime,
+  generic-type-fn locals) noted under Next step — all clean diagnostics now, not
+  crashes (post-0140), so enhancements rather than blockers.
 - **issue 0140 fixed.** A comptime type-construction bail (`declare`/`define`/
   reflection) used to panic at LLVM emission ("unresolved type reached LLVM
   emission") or hide behind a cascade — `evalComptimeType` swallowed the interp's