[kixelated]

Problem

Debug of std's iterator sources and several collection iterators was refused, so an adaptor over one (for example char::decode_utf16([..]), which wraps an array's IntoIter) failed to translate. #515 covered the adaptors; this covers what they wrap.

Approach

Extends iter_debug in ts/src/lower/fmt.rs, which #515's peel_iter-based adaptor Debug already reaches through wrapped. Each new arm writes std's private fields as std's impl does, from the runtime iterator's own state:

• Once, option::{Iter, IterMut, IntoIter}, and result::{Iter, IterMut, IntoIter}: rt.fmtIterOption, the item left as an Option inside std's wrapper structs (Once { inner: IntoIter { inner: Item { opt } } }). Its item is written as the iterator's item type, so a &mut to a value JS copies is read through its place.
• FromFn and RepeatWith: their names, without closures, as std writes them. Successors: the item it yields next.
• An array's IntoIter: the list it has left, as a Vec's.
• CharIndices: its front offset and Chars. A String's Drain: what it has left.
• A slice's Windows, Chunks, ChunksExact, RChunks, RChunksExact: rt.fmtParts, what the parts left cover, the remainder, and the size. PartsIter now tracks whether a read past the end emptied it, as std's Windows::nth, nth_back, and next_back set v to [].
• A slice's Split and its nine forms: rt.fmtSplit, what is left to split and finished, a &mut one emptying its slice as it finishes, and a splitn's GenericSplitN with its count.
• A HashSet's set operations: the list a clone yields, as std's debug_list().entries(self.clone()).
• A slice's ChunksMut and its forms are refused at their span: std writes their *mut [T] as an address.

Tested differentially in fmt::sources of the shapes fixture, plain, {:#?}, and {:x?}, fresh, read from either end, and past the end. A reject fixture covers ChunksMut.

Impact

• New runtime exports: fmtIterOption, fmtIterClone, fmtSuccessors, fmtParts, fmtSplit, fmtCharIndices, fmtStringDrain. No breaking changes.
• Consumer: moq translates Debug derives over its types; any field or adaptor holding one of these iterators now translates instead of refusing.

Alternatives

• One generic runtime writer driven by a field list from the driver: rejected, since each kind's state (cleared windows, taken splits, sentinel Nones) is computed differently anyway.

Follow-ups

The quest is rewritten to what remains: str's searcher iterators (Split, Lines, SplitWhitespace, Matches) write CharSearcher and TwoWaySearcher state the runtime does not keep; a BTreeSet's set operations write std's strategy; ExtractIfs write a peeked item; and iter::repeat, repeat_n, and once_with are not translated at all yet.

Review

• Harness: quest review, Codex gpt-6.1-sol, medium effort.
• Round 1 (head b088112): 1 finding, refuted: ts/src/lower/library.rs:2995 (nested Vec capacity in clone_from) is not in this branch's diff. It is main's fix(ts): keep a nested Vec's capacity where clone_from writes over it #533, which the old merge base lacked.
• Round 2 (head 3b14318, after merging main): no findings.
• Since then, only conflict-free merges of origin/main (feat(ts): translate a slice's as_chunks_mut and as_rchunks_mut #529, fix(ts): translate the crate's own iterator held as a value, taken by value or by std's &mut self methods #540), ending at head 7a1260b. just ci passed on that head.

🤖 Generated with Claude Code

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Commits

Reviewing files that changed from the base of the PR and between fd9ec1e and 7a1260b.

Files selected for processing: 17

• quest/m3/README.md
• quest/m3/ts-iter-source-debug.md
• ts/README.md
• ts/fixtures/lang/shapes/expected/core/bool.ts
• ts/fixtures/lang/shapes/expected/core/option.ts
• ts/fixtures/lang/shapes/expected/fmt.ts
• ts/fixtures/lang/shapes/expected/lib.ts
• ts/fixtures/lang/shapes/src/fmt.rs
• ts/fixtures/lang/shapes/src/lib.rs
• ts/fixtures/reject/census.txt
• ts/fixtures/reject/expected.txt
• ts/fixtures/reject/src/fmt.rs
• ts/fixtures/reject/ts.toml
• ts/runtime/rt.ts
• ts/runtime/rt/iter.ts
• ts/runtime/rt/str.ts
• ts/src/lower/fmt.rs

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