feat(ts): translate Debug of std's iterator adaptors and a str's escapes

quest/m3/README.md

@@ -22,9 +22,10 @@ generic std gap is planned here even when moq never calls it.
 - [Waiting: drop the lang fixture's mul_add allowance](/quest/m3/ts-fma-allowance.md) - the differential fails on any `mul_add` difference again once wasm32's `fma` rounds exactly
 - [Waiting: type-check in process with tsrs](/quest/m3/ts-tsrs.md) - rust2-ts checks bindings through tsrs instead of `tsc` once it is a stable library
 - [A slice of one byte behind any &mut](/quest/m3/ts-slice-of-one.md) - `slice::from_mut` and `array::from_mut` of a `&mut u8` translate
-- [Debug of std's iterator adaptors](/quest/m3/ts-iter-adaptor-debug.md) - `Debug` of `Map`, `Zip`, `Peekable`, `DecodeUtf16`, and the other adaptors writes what std's does
 - [Waiting: a slice object for a mutable part of other values](/quest/m3/ts-slice-object.md) - waits on a moq profile showing the `Proxy` view's traps matter, then decides on an `rt.ByteSlice`-like form
 - [Port the workflow guard to kixelated/quest](/quest/m3/quest-workflow-guard.md) - quest's environment guard parses YAML as this repository's does
+- [An adaptor of the crate's own iterator held as a value](/quest/m3/ts-own-iter-value.md) - `map` and the other adaptors of a fieldless enum that implements `Iterator`, taken by value, translate
+- [Debug of std's other iterators](/quest/m3/ts-iter-source-debug.md) - `Debug` of `Once`, `Repeat`, `FromFn`, an array's `IntoIter`, and std's other iterators writes what std's does
 - [A vector keeps the capacity its pushes grew as it shrinks](/quest/m3/ts-vec-clear-capacity.md) - every step that drops a pushed `Vec`'s length keeps its capacity, as std guarantees
 - [A vector's exact capacity as it shrinks](/quest/m3/ts-vec-exact-capacity.md) - a deque made from a `Vec` splits its slices where std's does
 - [A B-tree's searches call Ord as std's do](/quest/m3/ts-btree-search-order.md) - a B-tree's lookups and inserts call a key's own `Ord` in std's order and number

quest/m3/ts-iter-source-debug.md

@@ -0,0 +1,18 @@
+# [S] Debug of std's other iterators
+
+## Goal
+
+[rust2-ts](/ts/README.md) translates `Debug` of std's iterators that still have no
+mapping, so an adaptor over one writes what std's does instead of being refused:
+iterator sources such as `Once`, `Repeat`, `RepeatN`, `FromFn`, `Successors`,
+`OnceWith`, and `RepeatWith`, an array's and an `Option`'s or `Result`'s iterators, and
+`str`'s iterators other than `Chars` and `Bytes`. Proven by differential tests against
+native Rust.
+
+## Plan
+
+Found while translating `Debug` of the adaptors: `char::decode_utf16([..])` refuses at
+its span, as `Debug` of `array::IntoIter` has no mapping. Read each of std's impls, which
+write private fields of their own (`Once { inner: IntoIter { inner: Item { opt } } }`),
+and survey which share a shape before choosing how the runtime writes them, as
+`iter_debug` and `adaptor_debug` in `src/lower/fmt.rs` do.

quest/m3/ts-own-iter-value.md

@@ -0,0 +1,16 @@
+# [S] An adaptor of the crate's own iterator held as a value
+
+## Goal
+
+[rust2-ts](/ts/README.md) translates an adaptor taking by value an iterator of the
+crate's own whose JS value is copied, as a fieldless enum's is, such as
+`Toggle::Ready.map(f)`, so its `next` reads and writes the iterator's place. Proven by
+differential tests against native Rust.
+
+## Plan
+
+Found while translating `Debug` of std's adaptors: `toggle.map(|x| x)` of a fieldless
+enum that implements `Iterator` fails to type-check, as `rt.iterFrom` is given the enum's
+value where its `next` takes a `rt.Place`; `(&mut toggle).map(|x| x)` translates. Find
+where `into_iter` of an owned iterator of the crate's own makes its source, and give it
+the place its `next` reads through.

ts/README.md

@@ -277,7 +277,11 @@ collections writes their items in the order each iterates, a hash map's or set's
 and of their iterators and `Chars` the items each has left, in std's wrapper; a deque's
 `Iter` and `IterMut` write the two slices of its buffer they have left, swapped as std's
 swap them, and its `Drain` its counts; a list's `Iter` and `IterMut` write what is left and
-its length, as std's do. `Debug` of `Bound`, `Ordering`, `Reverse`, and `ControlFlow` is
+its length, as std's do. `Debug` of std's iterator adaptors, `Map` through `Flatten`,
+`DecodeUtf16`, and a `str`'s escapes, writes their fields as std's does, each iterator it
+wraps by its own `Debug`, no closure, and the state each keeps, such as what a `Peekable` peeked, what a
+`Skip` has left to skip, and the countdown std's `StepBy` of a small unsigned range keeps
+in its end. `Debug` of `Bound`, `Ordering`, `Reverse`, and `ControlFlow` is
 their derived one, whichever way each is held, and a guard of a cell or a lock, mapped or
 not, writes what it lends by its own `Debug` and `Display`. `Debug` of a `Cell`, a
 `RefCell`, a `Mutex`, and an `RwLock` writes what each holds, or `<borrowed>` and