[kixelated]

Problem

A crate function returning Result<Option<u64>, E>, such as Decoder::varint_opt, made an rt.Ok per call. #385's result slot refused any Ok payload containing an enum, and the scalar layer held an Option of a number as a flag plus the number, even though its JS value, T | undefined, is never an object.

Approach

• Shape::Leaf now covers an Option of a number (an integer of any width, a float, bool, char, or a shared reference to one). That is one JS value, so a held local keeps it as one part, and number counts it as one.
• As a result, a Result whose Ok is numbers alone, with such Options among them, qualifies for the slot. Examples: Result<Option<u64>, E>, Result<(Option<u8>, u64), E>, Result<(u64, Option<i128>), E>, and Result<(Option<u16>, &[u8]), E>.
• When the payload is an Option, the callee writes it to out$Option_<T>.p and returns the error or undefined, as out$bool already does. When the first part is a plain number, the existing return path is unchanged.
• Other snapshots: varintOpt and its caller in codec, made$Option_u8 and unset in cells and shapes, and an ok_or in splits whose Option<u8> error is now one part, so option_okOr and its rt.Result drop out.
• Bench: expected/bench.ts and everything it calls are unchanged (no bench workload calls varint_opt). No just ts bench workload runs different code, so none can be slower.
• Differential cases (returns::options) cover Option of u8 through u128, usize, i8 through i128 with their MIN/MAX, f32 (including -0) and f64, both including NaN, plus bool and char. Each has None, Some(0), an error, and arbitrary bytes. They also cover: a result returned as is and through ?, an Option first or last in a tuple and beside a slice, a drop that rewrites the slot, two results held at once, results kept in a Vec and through a fn pointer, and a loop.

Impact

• The translator's output: a function only translated code calls, returning a Result of numbers in which an Option of a number counts as one, returns its error or undefined and leaves the Ok in a lib.ts slot such as out$Option_u64. ts/MIGRATE.md's existing entry is updated. Roots are unchanged.

Alternatives

• Return the Option itself, with null meaning an error (the error goes in the slot), to skip the slot write on success, as a plain number's first part does. Dropped: it adds a second sentinel to every slot path, and no bench workload calls varint_opt to measure it against (moq-net calls it 8 times, against 249 for varint).
• Keep Option<u64> as a flag plus its number inside the slot. Dropped: that writes two fields, and take_apart and build_plain would need enum support.

Follow-ups

None. An Option of a tuple or slice in the slot (its JS value is an object) has no consumer in moq-net.

Review

• Reviewer: Codex gpt-6.1-sol at medium effort (quest review), round 1 on head d60a6e86, 0 findings. Since then the only changes are conflict-free merges of origin/main (Folds from the back, and a crate's own folds #463, feat(ts): translate a pointer to a struct whose last field is a trait object #493, feat(ts): accept an empty iterator of mutable references as a place source #497), giving head adab4b0a.
• Checks: just ci passes on adab4b0a, and just ts moq translates and type-checks moq-net.

🤖 Generated with Claude Code

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Commits

Reviewing files that changed from the base of the PR and between 8c7a301 and adab4b0.

Files selected for processing: 23

• quest/m3/README.md
• quest/m3/ts-option-slot.md
• ts/MIGRATE.md
• ts/README.md
• ts/fixtures/codec/expected/coding/decode.Decoder.ts
• ts/fixtures/codec/expected/harness.ts
• ts/fixtures/codec/expected/lib.ts
• ts/fixtures/lang/cells/expected/cells.ts
• ts/fixtures/lang/cells/expected/lib.ts
• ts/fixtures/lang/returns/expected/core/bool.ts
• ts/fixtures/lang/returns/expected/core/option.ts
• ts/fixtures/lang/returns/expected/core/result.ts
• ts/fixtures/lang/returns/expected/lib.ts
• ts/fixtures/lang/returns/expected/returns.Error.ts
• ts/fixtures/lang/returns/expected/returns.Opted.ts
• ts/fixtures/lang/returns/expected/returns.ts
• ts/fixtures/lang/returns/src/lib.rs
• ts/fixtures/lang/returns/src/returns.rs
• ts/fixtures/lang/shapes/expected/lib.ts
• ts/fixtures/lang/shapes/expected/shapes.ts
• ts/fixtures/lang/splits/expected/core/option.ts
• ts/fixtures/lang/splits/expected/splits.ts
• ts/src/lower/mir/scalar.rs

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