rune-langium / visual-editor/src / Dehydrated

Type Alias: Dehydrated<T>

type Dehydrated<T> = {
  $cstRange?: {
     end: number;
     offset: number;
  };
  $namespace?: string;
  $type: T["$type"];
} & { -readonly [K in Exclude<keyof T, LangiumRuntimeFields | "$type">]: DehydratedField<T[K]> };

Defined in: packages/core/dist/serializer/dehydrated.d.ts:66

Lossless editable wire model for a Langium AST node.

Strips runtime-only internals ($container, $cstNode, etc.) and converts every Reference<T> to { $refText: string }. All semantic fields are preserved and made mutable for in-place editing.

This is the canonical substrate for the Rune editable store.

KNOWN FOLLOW-UP (verified during rune-langium spec 021 Phase 2, 2026-07): this type has three real gaps, each independently confirmed against a concrete AST node before being worked around downstream — worth fixing here rather than re-discovering per call site:

1. Non-distributive over a union type parameter. Dehydrated<T extends AstNode> reads keyof T in its mapped-type body — invoking it directly on a union (e.g. Dehydrated<RosettaExpression>, ~48 interface members) does NOT distribute member-wise the way Dehydrated<X> | Dehydrated<Y> would; it collapses to the fields common to every member ($type/$namespace/$cstRange only), silently dropping everything else. This is already live-latent in this repo's own consumer: packages/codegen/src/emit/rosetta/ render-expression.ts's DehydratedExpression = Dehydrated< RosettaExpression> | RosettaExpression has the identical collapse — it only "works" there because the consuming code immediately casts to an internal loosely-typed shape and never relies on the collapsed type's fields. Fix: make this type distributive (T extends AstNode ? {...} : never), or require every union-typed call site to build its own distributed alias (the workaround packages/codegen/src/import/constraint-translator.ts currently uses).
2. Array<Reference&lt;X&gt;> fields are never dehydrated.DehydratedField<F>'s reference-shape branch only matches a BARE Reference<X>; its array branch only matches Array<AstNode>. A field typed Array<Reference&lt;X&gt;> (e.g. the grammar's ChoiceOperation.attributes, and 7 other fields — every synonym node's sources, RosettaCorpus.corpusList, RosettaReport. eligibilityRules, two superSources fields) matches neither branch and passes through unchanged — a REAL resolved Reference[], not {$refText}[], unlike every other reference-shaped field on the same node.
3. Every field becomes a REQUIRED key of type V | undefined, never an optional key. The enclosing mapped type (-readonly [K in Exclude<keyof T, ...>]: DehydratedField&lt;F&gt;) is a non-homomorphic key remap, which drops the ? modifier — even for fields optional on the original interface (Condition.definition?, Data.superType?, RosettaEnumeration.parent?, etc.). A caller's conditional-spread idiom (...(x !== undefined && { x }), which OMITS the key) no longer type-checks against the resulting type, even though it is runtime-safe.

See packages/codegen/src/import/constraint-translator.ts and synonym-builder.ts for the current per-call-site workarounds (narrow, documented Omit<Dehydrated&lt;T&gt;, field> & { field: corrected } intersections) — none of this file's callers currently depend on the gaps above being present, so fixing them here should be additive.

Type Parameters

Type Parameter
T extends AstNode

Type Declaration

Name	Type	Defined in
$cstRange?	{ end: number; offset: number; }	packages/core/dist/serializer/dehydrated.d.ts:69
$cstRange.end	number	packages/core/dist/serializer/dehydrated.d.ts:71
$cstRange.offset	number	packages/core/dist/serializer/dehydrated.d.ts:70
$namespace?	string	packages/core/dist/serializer/dehydrated.d.ts:68
$type	T["$type"]	packages/core/dist/serializer/dehydrated.d.ts:67