feat(ts): translate Debug of std's iterator sources, Option's, Result's, and an array's iterators, and a slice's parts

quest/m3/README.md

@@ -24,7 +24,7 @@ generic std gap is planned here even when moq never calls it.
 - [Waiting: 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 once a consumer calls them
 - [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
-- [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
+- [Debug of std's other iterators](/quest/m3/ts-iter-source-debug.md) - `Debug` of `str`'s searcher iterators, a `BTreeSet`'s set operations, `ExtractIf`, and `repeat`, `repeat_n`, and `once_with` 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

@@ -1,18 +1,29 @@
-# [S] Debug of std's other iterators
+# [M] 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.
+[rust2-ts](/ts/README.md) translates `Debug` of the std iterators that still have no
+mapping, writing what std's does instead of being refused: `str`'s iterators other than
+`Chars`, `Bytes`, `CharIndices`, and the escapes (`Split` and its forms, `Lines`,
+`SplitWhitespace`, `Matches`, `MatchIndices`), a `BTreeSet`'s set operations, and each
+`ExtractIf`. `iter::repeat`, `repeat_n`, and `once_with`, which are not translated at all
+yet, translate with their `Debug`. 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.
+The sources, `Option`'s, `Result`'s, and an array's iterators, a slice's parts, and a hash
+set's operations landed on `iter_debug` in `src/lower/fmt.rs`; extend it the same way.
+
+What is left writes private state the runtime does not keep in std's shape:
+
+- `str`'s searcher iterators write their searcher's fields: a `CharSearcher`'s
+  `finger` and `finger_back` in UTF-8 bytes, a `StrSearcher`'s `TwoWaySearcher` state
+  (`crit_pos`, `period`, `byteset`, `memory`), and an empty needle's flags. The runtime
+  searches in UTF-16 code units by a `Pattern`, so it would track std's state beside its
+  own, or search as std does.
+- A `BTreeSet`'s `Difference` and `Intersection` write which strategy std picked
+  (`Stitch`, `Search`, `Iterate`, `Answer`) and its iterators, `Search` the whole other
+  set; `Union` and `SymmetricDifference` their `MergeIterInner`'s peeked item. The runtime
+  already picks std's strategy, so its state may map over.
+- `Vec`'s, `LinkedList`'s, and a B-tree's `ExtractIf` write the item they peek at; a hash
+  map's and set's write `ExtractIf { .. }` once their `extract_if` translates.

ts/README.md

@@ -296,7 +296,12 @@ its length, as std's do. `Debug` of std's iterator adaptors, `Map` through `Flat
 `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`, `AssertUnwindSafe`, and `ControlFlow` is
+in its end. So does `Debug` of std's sources, `Once`, `FromFn`, `RepeatWith`, and
+`Successors`, an `Option`'s, a `Result`'s, and an array's iterators, a `CharIndices`, a
+`String`'s `Drain`, and a slice's `Windows`, chunks, and splits, each writing what is left of
+its slice as std's does, emptied where std's `nth` past the end empties a `Windows`; a hash
+set's operations write the list a clone yields. A slice's `chunks_mut` and its forms are
+refused, as std writes their slice's address. `Debug` of `Bound`, `Ordering`, `Reverse`, `AssertUnwindSafe`, 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

ts/fixtures/lang/shapes/expected/core/bool.ts

@@ -1,6 +1,7 @@
 // Generated by rust2-ts. Do not edit.
 
 import * as rt from "../rt.ts";
+import type * as Pair from "../fmt.Pair.ts";
 import type * as Void from "../shapes.Void.ts";
 
 export function thenSome$0ztng9q(self: boolean, t: rt.Result<rt.u16, Void.Void>): rt.Result<rt.u16, Void.Void> | undefined {
@@ -10,6 +11,20 @@ export function thenSome$0ztng9q(self: boolean, t: rt.Result<rt.u16, Void.Void>)
 	return t;
 }
 
+export function thenSome$1ou04rm(self: boolean, t: Pair.Pair): Pair.Pair | undefined {
+	if (!self) {
+		return undefined;
+	}
+	return t;
+}
+
+export function thenSome$0n2gkz4(self: boolean, t: rt.i32): rt.i32 | undefined {
+	if (!self) {
+		return undefined;
+	}
+	return t;
+}
+
 export function thenSome$0d5am30(self: boolean, t: rt.u8): rt.u8 | undefined {
 	if (!self) {
 		return undefined;

ts/fixtures/lang/shapes/expected/core/option.ts

@@ -57,6 +57,13 @@ export function map$18z3v8h(self: Dir.Dir | undefined, _: (a0: Dir.Dir) => rt.u8
 	return from$convert_From_shapes_Dir_u8(self);
 }
 
+export function map$0phsnvg(self: rt.u8 | undefined, _: (a0: rt.u8) => rt.u8 | undefined): rt.u8 | undefined | rt.None {
+	if (self === undefined) {
+		return rt.None;
+	}
+	return self;
+}
+
 export function mapOr$1a3irjf(self: rt.ByteVec | undefined, default_: rt.u8, f: (a0: rt.ByteVec) => rt.u8): rt.u8 {
 	if (self === undefined) {
 		return default_;
@@ -106,6 +113,13 @@ export function okOr$1vxk0yk(self: rt.u8 | undefined, err: rt.u8): rt.Result<rt.
 	return rt.Ok(self);
 }
 
+export function andThen$1bd14ex(self: rt.u8 | undefined, f: (a0: rt.u8) => rt.u8 | undefined | rt.None): rt.u8 | undefined | rt.None {
+	if (self === undefined) {
+		return rt.None;
+	}
+	return f(self);
+}
+
 export function clone$0hmts8n(self: rt.u16[] | undefined): rt.u16[] | undefined {
 	if (self === undefined) {
 		return undefined;