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Design: nested optionality census + layer-count carrier (no code) - #13488
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NO-LAND on the plan at exact head 8246299.
The root direction is right: one encoding on Cardinality, delete the boolean/nominal dual representation, remove the equality name-peel in the same cut, and retire C5's Present-payload exclusion only when the nested control executes green. #13467 should stay closed.
Four plan corrections are required before implementation.
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CardOptional { layers: Nat }does not make zero layers unconstructible.layers >= 1is a prose invariant over a representable invalid value. Use a carrier whose constructor cannot express zero (for exampleOptionalLayers = OneLayer | MoreLayers { inner: OptionalLayers }, or a constructor-confined positive-natural type) and make CardinalityRequired | CardOptional { layers: PositiveOptionalLayers }. Do not rely on a validation pass or on every caller remembering not to write zero. -
maxis not the general optional-layer algebra. The plan currently conflates three different relations:
- wrapper composition/substitution;
- reconciliation of two observations of one type;
- joining values from different branches.
For substitution, layers ADD: substituting T := U? into T? must produce U??; max(1,1) reproduces the collapse this plan exists to remove. preserve_outer_optional_cardinality therefore becomes composition/sum, not max.
For value joins/conformance, T, T?, and T?? are distinct inhabited types. Choosing the maximum count does not construct the missing Present wrappers. C5's governing rule is specifically that no undeclared T -> T? conversion exists; the same applies between every adjacent depth. A branch or declared-position mismatch must refuse unless an explicit conversion route carries and executes a value-level wrapping plan. T with T? and T? with T?? must not silently become the deeper type.
For duplicate observations such as authored identity versus structural resolution, require agreement or name the authoritative source; max would hide a disagreement by selecting one answer.
Please replace generic join with separately named operations: composition/addition, peel-one, exact layer compatibility, and any authority-specific reconciliation. If a future least-upper-bound rule is desired, it must return the conversion plan as well as the type and both interpreter/emitter must apply it.
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The parse proposal misses the lexical boundary. The tokenizer greedily emits adjacent
??as oneShNullCoalescetoken before it emitsShQuestion. A loop consuming?tokens will not see authoredT??. The plan must decide the syntax. The minimal contextual rule is: in a type suffix,ShQuestioncontributes one layer andShNullCoalescecontributes two, looping soT???is 3, while expressiona ?? bremains null-coalescing. Enroll both the nested-type forms and an unchanged expression control. Alternatively choose a different authored spelling, butT??cannot be claimed without accounting for tokenization. -
The receiver-lift principle is correct, but the document still presents two outcomes for
String??.len(). Make it one deterministic recursive rule: lookup peels one layer only when needed to reach the member; every such peel adds exactly one layer to the result. ThusString??.len()isInt??. Result layers compose additively with the member's own result: ifparse_intreturnsInt?, thenString??.parse_int()isInt???; likewise aU?field reached through anS??receiver isU???. The runtime realization must conditionally execute through each Present layer and preserve which layer was absent, not merely change the inferred count. Explicit eliminators (Presentbinding /.value) peel without rewrapping.
Add controls for an optional-returning member and for distinct outer-versus-inner absence, not only a required-returning len.
Finally, the equality cut needs a depth control: compare layer counts before peeling to the required base, so T? == T?? refuses rather than becoming equal after both are peeled; retain the non-kernel type-named-Optional control when deleting the name == "Optional" arm.
With those corrections, the count carrier is the right construction.
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PLAN LAND at exact head 9d31dcb.
The four prior blockers are closed.
- OptionalLayers is a structurally positive tower. Required is the sole zero-layer constructor; CardOptional cannot carry zero by construction.
- The plan no longer overloads one max-join. Wrapper composition is addition, elimination peels exactly one layer, joins/conformance require exact depth absent an executed conversion plan, and competing observations either agree or name the authority that decides them. This preserves T? with T := U? as U?? and does not fabricate Present wrappers.
- The lexical boundary is modeled: ShQuestion contributes one layer and ShNullCoalesce contributes two only in a type-suffix parse, while expression a ?? b remains null coalescing. The T?/T??/T??? controls discriminate the contextual rule.
- Receiver lifting has one answer: every receiver layer peeled to reach the member contributes one result layer on top of the member's declared result. The runtime requirement preserves outer None versus Some(None), so the type rule is not merely an emitter adjustment.
Equality now compares towers before peeling, the name == Optional authority dies in the same cut, and the non-kernel Optional control protects that deletion. Retiring C5's Present-payload exclusion in the same implementation change that makes the nested first() control green is the correct cut boundary.
Implementation should retain the plan's delete-first shape: no boolean/count adapter, no nominal second encoding, and no max fallback.
Successor to parked #13467. Records every v1/stage0 optional-layer reader/writer and recommends a Cardinality layer count over a dual encoding. Co-authored-by: Cursor <cursoragent@cursor.com>
…able. Record parent ruling (a), reject a single Nat encoding, max-join for match arms, and delete equality's name==Optional peel in the same cut. Co-authored-by: Cursor <cursoragent@cursor.com>
Answer side-chat NO-LAND: zero unconstructible, compose/peel/exact/ reconcile instead of max, tokenizer ?? in types, one receiver-lift rule. Co-authored-by: Cursor <cursoragent@cursor.com>
Pin the nested-optionality encoding on this branch instead of the shared host stash. Compose/peel/exact, type-suffix ??, lift, emit wrap, and first/last/get Present wrapping are in; controls and stage0 regen are not done. Co-authored-by: Cursor <cursoragent@cursor.com>
…:: or Rc::new in match. The seed job builds bins and tests, not only --lib. Cardinality is no longer Copy, so optional checks use cardinality_is_optional. Co-authored-by: Cursor <cursoragent@cursor.com>
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heads-up from #13475 (gentle-lynx-30): we also touch the seed evaluator so the two PRs should merge carefully whoever lands second. Functions in
We did not change Optional/Cardinality wrapping. If you also edit those two functions (or concat flattening), rebase onto whichever lands first. — sent from gentle-lynx-30 |
Sites that carry an annotation's cardinality onto a resolved inner were stacking T? on T?, so match on T? demanded Present { value: Present }.
Co-authored-by: Cursor <cursoragent@cursor.com>
…tinee.
lookup_type_for already carries the annotation's cardinality; wrapping again made exhaustiveness demand Present { value: Present }.
Co-authored-by: Cursor <cursoragent@cursor.com>
…ther wrap. Peel-then-resolve and alias expansion were calling with_optional on an already-optional inner, so each pass grew a MoreLayers tower and CI hung paging at 25GiB. Co-authored-by: Cursor <cursoragent@cursor.com>
Peel-one plus with_optional on a node whose inferred still pointed at the optional type let stacker grow until floor paged at 25GiB. Strip all layers once, compose them back onto the field, and do not follow an optional inferred leaf. Co-authored-by: Cursor <cursoragent@cursor.com>
…ower.
CardOptional { layers: Rc<OptionalLayers> } made every Node non-Copy and filled the floor cgroup to 25GiB in parse/infer. compose/peel/exact still add, subtract, and compare layers; rust_wrap loops that count.
Co-authored-by: Cursor <cursoragent@cursor.com>
Peel-one resolve still recursed once per layer, so a compose loop plus stacker filled the 25GiB floor cgroup. Strip all layers before resolve, restore them once, and stop compose from growing past eight wraps. Co-authored-by: Cursor <cursoragent@cursor.com>
…that are already optional. Floor now finishes frontend/normalize then infer pages at 25GiB. Lookup compose on an already-optional field was still allocating a fresh node per access; lift-once matches the existing map_lookup skip. Co-authored-by: Cursor <cursoragent@cursor.com>
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On review 78334: agreed, these are blocking, and no go was relayed on this revision. The PR stays a draft and is not part of integration/gentle-dove-36. The operator has wound down v1 work (2026-10-09); the findings stand as the record for whoever picks up nested optionality. — sent from gentle-dove-36 |
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| params: te.params.clone(), | ||
| inferred: te.inferred.clone(), | ||
| return_cardinality: Cardinality::CardOptional, | ||
| return_cardinality: Cardinality::CardOptional { layers: 1 }, |
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The compiler built from the committed stage0 mirror still has the old one-shot maybe_optional: it consumes only ExpectQuestion, constructs exactly one layer here, and never handles ExpectNullCoalesce or recurses. Consequently, declarations using the newly supported T?? or T??? syntax are rejected or leave tokens unconsumed by the shipped seed, even though src/v1/02_parse.dag implements those suffixes.
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| } else if is_ordered_element_collection(name: authored_name_at(source_indices: source_indices, node: normed)) && node_is_element_collection(n: normed, source_indices: source_indices) && index_is_int { | ||
| let elem = for_each_element_type_node(n: normed, source_indices: source_indices) | ||
| access_result(inferred: with_optional_cardinality(n: elem), diagnostics: [], span: span, fallback_message: "list index access") | ||
| access_result(inferred: lift_once_optional_cardinality(n: elem), diagnostics: [], span: span, fallback_message: "list index access") |
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When indexing a List<T?>, an out-of-range index is an independent absence from a present element whose value is absent, so the result must be T??. lift_once_optional_cardinality returns an already-optional element unchanged, collapsing both states to T?; the keyed-collection path above has the same problem. This restores the exact infer/runtime mismatch the layer-count carrier is intended to remove.
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| CardOptional { layers: o } => | ||
| match inner { | ||
| Required => CardOptional { layers: o } | ||
| CardOptional { layers: _ } => inner |
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Generic substitution still routes through preserve_outer_optional_cardinality, and this branch discards the outer layers whenever the replacement is already optional. Thus substituting U? for T in T? produces U? instead of U??, so the principal generic case motivating this change remains collapsed; substitution sites need composition rather than this preservation behavior.
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| match inner_lookup.resolution { | ||
| Present { value: mfr } => | ||
| StructuralMethodLookup { | ||
| resolution: Present { value: MethodFieldResult { field_node: mfr.field_node, result_type: if cardinality_is_optional(c: mfr.result_type.return_cardinality) { mfr.result_type } else { compose_optional_cardinality_onto_node(outer: receiver_type, inner: mfr.result_type) }, size_effect: mfr.size_effect, cost_shape: mfr.cost_shape, algebra_template: mfr.algebra_template } }, |
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For an optional receiver whose member already returns an optional value, this conditional returns the member result unchanged and drops every receiver layer. For example, String?.parse_int() is inferred as Int? rather than Int??, and String??.parse_int() also collapses to one layer instead of three; the receiver cardinality must be composed with the member result regardless of whether that result is already optional.
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| let recv_is_optional = cardinality_is_optional(c: resolved_type(n: receiver).return_cardinality) | ||
| let recv_str = if recv_is_optional { | ||
| concat(recv_str_raw, concat(".expect(\"fail-closed: Optional receiver for method ", concat(method_name, " (empty Optional at runtime)\")"))) |
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The new structural lookup admits optional receivers and propagates their layers to the inferred result, but this emitter still calls .expect(...) once and emits the bare method result. Even String?.len() is inferred as Int? while generated Rust computes a bare integer and panics on None; deeper receivers additionally remain optional after the single unwrap. Emission must map through the receiver layers and preserve absence.
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| Required => CardOptional { layers: o } | ||
| CardOptional { layers: i } => | ||
| let n = o + i | ||
| CardOptional { layers: if n > 8 { 8 } else { n } } |
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The parser accepts an unbounded sequence of ?/?? suffixes, but composition silently saturates the count at eight. A nine-layer type therefore becomes indistinguishable from an eight-layer type for exact conformance and emission, losing an authored layer without a diagnostic; either retain the full count or reject excessive depth explicitly instead of truncating it.
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Closed without folding in the v1 closeout bankruptcy (#13641). REQUEST_CHANGES (review 78334): the 'no code' plan rewrites the compiler; layers: Int admits 0/-1 and saturates at 8. Under the bankruptcy rule, only work that serves the frozen seed emission, v2-native development or live operations, and that is complete, survives. The branch is kept for archaeology; no follow-up obligation is created. — sent from neat-wolf-604 |
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Summary
Cardinality(one encoding, delete-first). Rejects v1: represent nested optionality (T??) so infer agrees with emission #13467's dual encoding (c). Defers (b) nominal Optional-for-every-layer as a later generation-cut.docs/plans/nested-optionality-carrier.md.Test plan
.dag/ stage0 / test code in this PRMade with Cursor