[DO NOT MERGE] test: regenerate bindings with rescript-bindgen #168 (@tag variants)

[jagguji]

⚠️ DO NOT MERGE. A test build for juspay/rescript-bindgen#168, which is still open. package.json deliberately still pins bindgen 1.3.0, so src/ here cannot be reproduced from the pinned generator — merging would break this repo's "same blend version always produces byte-identical bindings" guarantee. Real adoption is a separate package.json bump PR once #168 ships.

Regenerated against the pkg.pr.new build of rescript-bindgen#168, which maps a nested discriminated union to a @tag variant instead of a flattened record.

Which build produced this

resolved:       https://pkg.pr.new/@juspay/rescript-bindgen@168
version string: 1.3.0
extract.mjs:    908a40b9cd780091

The version string is not proof — a pkg.pr.new build reports the version it branched from, so node_modules reads 1.3.0 either way. The resolved URL and hash are what identify it. (An earlier local attempt silently used a stale preview whose hash was 137c08b0…; same version string, different code.)

The diff — 4 files, +28/−41

DataTableTypes.rowAnimationConfig — record → @tag variant:

@tag("transitionType")
type rowAnimationConfig =
  | @as("bezier") Bezier({enterDuration: float, enterOffset: float, duration: float, bezier: (float, float, float, float)})
  | @as("spring") Spring({enterDuration: float, enterOffset: float, stiffness: float, damping: float, mass: float})

MenuV2Types.menuV2FlatRow — 6 %identity externals and 3 per-arm records → one matchable variant, retiring 3 ⚪ loose type_: string fields. Reading an arm was previously an unchecked cast; it is now compiler-verified.

BlendDesignSystemBindings.flattenMenuV2Groups returns the variant. Shared types 3360 → 3356.

Verification

check	result
npm run generate	exit 0
components	226 · ✅ 219 usable · 🔍 7 review · 🛑 0 broken — identical to baseline
npm run build	432 modules compile

Both arms construct, and the runtime object is flat with the real tag — exactly what the library reads:

{ transitionType: "bezier", enterDuration: 0.32, enterOffset: 12, duration: 0.4,
  bezier: [0.32, 0.72, 0, 1] }

Pattern matching compiles to a bare tag check, no wrapper:

if (cfg.transitionType === "bezier") { ... }

The #134 crash shape now fails to compile:

let bad: DataTableTypes.rowAnimationConfig = Bezier({ enterDuration: 0.32, enterOffset: 12.0 })
                                             ^
Some required record fields are missing: duration bezier.

That is the binding half of #134 closed at compile time, rather than relying on the runtime guard in juspay/blend-design-system#1653.

Migration notes for testing

This is a breaking change for existing consumers of both types.

rowAnimationConfig was a record; it is now a variant:

// before
{enterDuration: 0.32, enterOffset: 12.0, transitionType: Bezier}
// after
Bezier({enterDuration: 0.32, enterOffset: 12.0, duration: 0.4, bezier: (0.32, 0.72, 0.0, 1.0)})

MenuV2Types.MenuV2FlatRow.t and its from*/as* externals are gone — replace the casts with a switch.

One ergonomic wrinkle worth knowing: pattern matching needs the type in scope, or the constructors don't resolve:

let describe = (cfg: DataTableTypes.rowAnimationConfig) =>
  switch cfg {
  | Bezier({duration}) => ...
  | Spring({stiffness}) => ...
  }

Without the annotation you get "The variant constructor Bezier can't be found." Normal ReScript behaviour for a variant declared in another module, but it will be the first thing anyone hits.

Known issue in the candidate, not surfaced here

rescript-bindgen#168 has an open blocker: a self-referential discriminated union (type T = {kind:'leaf',…} | {kind:'branch', children: T[]}) recurses without bound and the component is dropped from the output entirely. blend has recursive types (MenuItemType.subMenu) and discriminated unions (MenuV2FlatRow) but never both in one type, so this regeneration cannot surface it. A green result here is not evidence that bug is fixed.

🤖 Generated with Claude Code

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@juspay/rescript-blend@138

commit: b5e7ea0

[jagguji]

Superseded by #139, which merged the same regeneration via the published @juspay/rescript-bindgen@1.4.0-beta.0 — src/ there is byte-identical to this preview build. Shipped as 0.0.37-1 under next. This branch was never meant to merge (package.json here still pins bindgen 1.3.0, so its src/ is not reproducible from the pin).