enso/app/gui2/shared/ast/tree.ts

import type { DeepReadonly } from 'vue'
import type {
  Identifier,
  IdentifierOrOperatorIdentifier,
  IdentifierOrOperatorIdentifierToken,
  IdentifierToken,
  Module,
  NodeChild,
  Owned,
  RawNodeChild,
  SpanMap,
  SyncTokenId,
  TypeOrConstructorIdentifier,
} from '.'
import {
  MutableModule,
  ROOT_ID,
  Token,
  asOwned,
  escapeTextLiteral,
  isIdentifier,
  isToken,
  isTokenChild,
  isTokenId,
  newExternalId,
  parentId,
} from '.'
import { assert, assertDefined, assertEqual, bail } from '../util/assert'
import type { Result } from '../util/data/result'
import { Err, Ok } from '../util/data/result'
import type { SourceRangeEdit } from '../util/data/text'
import { allKeys } from '../util/types'
import type { ExternalId, VisualizationMetadata } from '../yjsModel'
import { visMetadataEquals } from '../yjsModel'
import * as RawAst from './generated/ast'
import {
  applyTextEditsToAst,
  parse,
  parseBlock,
  print,
  printAst,
  printBlock,
  printDocumented,
  syncToCode,
} from './parse'

declare const brandAstId: unique symbol
export type AstId = string & { [brandAstId]: never }

/** @internal */
export interface MetadataFields {
  externalId: ExternalId
}
export interface NodeMetadataFields {
  position?: { x: number; y: number } | undefined
  visualization?: VisualizationMetadata | undefined
  colorOverride?: string | undefined
}
const nodeMetadataKeys = allKeys<NodeMetadataFields>({
  position: null,
  visualization: null,
  colorOverride: null,
})
export type NodeMetadata = FixedMapView<NodeMetadataFields>
export type MutableNodeMetadata = FixedMap<NodeMetadataFields>
export function asNodeMetadata(map: Map<string, unknown>): NodeMetadata {
  return map as unknown as NodeMetadata
}
/** @internal */
interface RawAstFields {
  id: AstId
  type: string
  parent: AstId | undefined
  metadata: FixedMap<MetadataFields>
}
export interface AstFields extends RawAstFields, LegalFieldContent {}
const astFieldKeys = allKeys<RawAstFields>({
  id: null,
  type: null,
  parent: null,
  metadata: null,
})
export abstract class Ast {
  readonly module: Module
  /** @internal */
  readonly fields: FixedMapView<AstFields>

  get id(): AstId {
    return this.fields.get('id')
  }

  get externalId(): ExternalId {
    const id = this.fields.get('metadata').get('externalId')
    assert(id != null)
    return id
  }

  get nodeMetadata(): NodeMetadata {
    const metadata = this.fields.get('metadata')
    return metadata as FixedMapView<NodeMetadataFields>
  }

  /** Returns a JSON-compatible object containing all metadata properties. */
  serializeMetadata(): MetadataFields & NodeMetadataFields {
    return this.fields.get('metadata').toJSON() as any
  }

  typeName(): string {
    return this.fields.get('type')
  }

  /**
   * Return whether `this` and `other` are the same object, possibly in different modules.
   */
  is<T extends Ast>(other: T): boolean {
    return this.id === other.id
  }

  innerExpression(): Ast {
    return this.wrappedExpression()?.innerExpression() ?? this
  }

  wrappedExpression(): Ast | undefined {
    return undefined
  }

  wrappingExpression(): Ast | undefined {
    const parent = this.parent()
    return parent?.wrappedExpression()?.is(this) ? parent : undefined
  }

  wrappingExpressionRoot(): Ast {
    return this.wrappingExpression()?.wrappingExpressionRoot() ?? this
  }

  documentingAncestor(): Documented | undefined {
    return this.wrappingExpression()?.documentingAncestor()
  }

  code(): string {
    return print(this).code
  }

  visitRecursive(visit: (node: Ast | Token) => void): void {
    visit(this)
    for (const child of this.children()) {
      if (isToken(child)) {
        visit(child)
      } else {
        child.visitRecursive(visit)
      }
    }
  }

  visitRecursiveAst(visit: (ast: Ast) => void | boolean): void {
    if (visit(this) === false) return
    for (const child of this.children()) {
      if (!isToken(child)) child.visitRecursiveAst(visit)
    }
  }

  printSubtree(
    info: SpanMap,
    offset: number,
    parentIndent: string | undefined,
    verbatim?: boolean,
  ): string {
    return printAst(this, info, offset, parentIndent, verbatim)
  }

  /** Returns child subtrees, without information about the whitespace between them. */
  *children(): IterableIterator<Ast | Token> {
    for (const child of this.concreteChildren()) {
      if (isTokenId(child.node)) {
        yield this.module.getToken(child.node)
      } else {
        const node = this.module.get(child.node)
        if (node) yield node
      }
    }
  }

  get parentId(): AstId | undefined {
    const parentId = this.fields.get('parent')
    if (parentId !== ROOT_ID) return parentId
  }

  parent(): Ast | undefined {
    return this.module.get(this.parentId)
  }

  static parseBlock(source: string, inModule?: MutableModule) {
    return parseBlock(source, inModule)
  }

  static parse(source: string, module?: MutableModule) {
    return parse(source, module)
  }

  ////////////////////

  protected constructor(module: Module, fields: FixedMapView<AstFields>) {
    this.module = module
    this.fields = fields
  }

  /** @internal
   *  Returns child subtrees, including information about the whitespace between them.
   */
  abstract concreteChildren(verbatim?: boolean): IterableIterator<RawNodeChild>
}
export interface MutableAst {}
export abstract class MutableAst extends Ast {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields>

  setExternalId(id: ExternalId) {
    this.fields.get('metadata').set('externalId', id)
  }

  mutableNodeMetadata(): MutableNodeMetadata {
    const metadata = this.fields.get('metadata')
    return metadata as FixedMap<NodeMetadataFields>
  }

  setNodeMetadata(nodeMeta: NodeMetadataFields) {
    const metadata = this.fields.get('metadata') as unknown as Map<string, unknown>
    for (const [key, value] of Object.entries(nodeMeta)) {
      if (!nodeMetadataKeys.has(key)) continue
      if (value === undefined) {
        metadata.delete(key)
      } else {
        metadata.set(key, value)
      }
    }
  }

  /** Modify the parent of this node to refer to a new object instead. Return the object, which now has no parent. */
  replace<T extends MutableAst>(replacement: Owned<T>): Owned<typeof this> {
    const parentId = this.fields.get('parent')
    if (parentId) {
      const parent = this.module.get(parentId)
      parent.replaceChild(this.id, replacement)
      this.fields.set('parent', undefined)
    }
    return asOwned(this)
  }

  /** Change the value of the object referred to by the `target` ID. (The initial ID of `replacement` will be ignored.)
   *  Returns the old value, with a new (unreferenced) ID.
   */
  replaceValue<T extends MutableAst>(replacement: Owned<T>): Owned<typeof this> {
    const replacement_ = this.module.copyIfForeign(replacement)
    const old = this.replace(replacement_)
    replacement_.fields.set('metadata', old.fields.get('metadata').clone())
    old.setExternalId(newExternalId())
    return old
  }

  replaceValueChecked<T extends MutableAst>(replacement: Owned<T>): Owned<typeof this> {
    const parentId = this.fields.get('parent')
    assertDefined(parentId)
    return this.replaceValue(replacement)
  }

  /** Replace the parent of this object with a reference to a new placeholder object.
   *  Returns the object, now parentless, and the placeholder. */
  takeToReplace(): Removed<this> {
    if (parentId(this)) {
      const placeholder = Wildcard.new(this.module)
      const node = this.replace(placeholder)
      return { node, placeholder }
    } else {
      return { node: asOwned(this), placeholder: undefined }
    }
  }

  /** Replace the parent of this object with a reference to a new placeholder object.
   *  Returns the object, now parentless. */
  take(): Owned<this> {
    return this.replace(Wildcard.new(this.module))
  }

  takeIfParented(): Owned<typeof this> {
    const parent = parentId(this)
    if (parent) {
      const parentAst = this.module.get(parent)
      const placeholder = Wildcard.new(this.module)
      parentAst.replaceChild(this.id, placeholder)
      this.fields.set('parent', undefined)
    }
    return asOwned(this)
  }

  /** Replace the value assigned to the given ID with a placeholder.
   *  Returns the removed value, with a new unreferenced ID.
   **/
  takeValue(): Removed<typeof this> {
    const placeholder = Wildcard.new(this.module)
    const node = this.replaceValue(placeholder)
    return { node, placeholder }
  }

  /** Take this node from the tree, and replace it with the result of applying the given function to it.
   *
   *  Note that this is a modification of the *parent* node. Any `Ast` objects or `AstId`s that pointed to the old value
   *  will still point to the old value.
   */
  update<T extends MutableAst>(f: (x: Owned<typeof this>) => Owned<T>): T {
    const taken = this.takeToReplace()
    assertDefined(taken.placeholder, 'To replace an `Ast`, it must have a parent.')
    const replacement = f(taken.node)
    taken.placeholder.replace(replacement)
    return replacement
  }

  /** Take this node from the tree, and replace it with the result of applying the given function to it; transfer the
   *  metadata from this node to the replacement.
   *
   *  Note that this is a modification of the *parent* node. Any `Ast` objects or `AstId`s that pointed to the old value
   *  will still point to the old value.
   */
  updateValue<T extends MutableAst>(f: (x: Owned<typeof this>) => Owned<T>): T {
    const taken = this.takeValue()
    assertDefined(taken.placeholder, 'To replace an `Ast`, it must have a parent.')
    const replacement = f(taken.node)
    taken.placeholder.replaceValue(replacement)
    return replacement
  }

  mutableParent(): MutableAst | undefined {
    const parentId = this.fields.get('parent')
    if (parentId === 'ROOT_ID') return
    return this.module.get(parentId)
  }

  /** Modify this tree to represent the given code, while minimizing changes from the current set of `Ast`s. */
  syncToCode(code: string, metadataSource?: Module) {
    syncToCode(this, code, metadataSource)
  }

  /** Update the AST according to changes to its corresponding source code. */
  applyTextEdits(textEdits: SourceRangeEdit[], metadataSource?: Module) {
    applyTextEditsToAst(this, textEdits, metadataSource ?? this.module)
  }

  getOrInitDocumentation(): MutableDocumented {
    const existing = this.documentingAncestor()
    if (existing) return this.module.getVersion(existing)
    return this.module
      .getVersion(this.wrappingExpressionRoot())
      .updateValue((ast) => Documented.new('', ast))
  }

  ///////////////////

  /** @internal */
  importReferences(module: Module) {
    if (module === this.module) return
    for (const child of this.concreteChildren()) {
      if (!isTokenId(child.node)) {
        const childInForeignModule = module.get(child.node)
        assert(childInForeignModule !== undefined)
        const importedChild = this.module.copy(childInForeignModule)
        importedChild.fields.set('parent', undefined)
        this.replaceChild(child.node, asOwned(importedChild))
      }
    }
  }

  /** @internal */
  replaceChild<T extends MutableAst>(target: AstId, replacement: Owned<T>) {
    const replacementId = this.claimChild(replacement)
    const changes = rewriteRefs(this, (id) => (id === target ? replacementId : undefined))
    assertEqual(changes, 1)
  }

  protected claimChild<T extends MutableAst>(child: Owned<T>): AstId
  protected claimChild<T extends MutableAst>(child: Owned<T> | undefined): AstId | undefined
  protected claimChild<T extends MutableAst>(child: Owned<T> | undefined): AstId | undefined {
    return child ? claimChild(this.module, child, this.id) : undefined
  }
}

/** Values that may be found in fields of `Ast` subtypes. */
type FieldData<T extends TreeRefs = RawRefs> =
  | NonArrayFieldData<T>
  | NonArrayFieldData<T>[]
  | (T['ast'] | T['token'])[]

// Logically `FieldData<T>[]` could be a type of `FieldData`, but the type needs to be non-recursive so that it can be
// used with `DeepReadonly`.
type NonArrayFieldData<T extends TreeRefs> = T['ast'] | T['token'] | undefined | StructuralField<T>

/** Objects that do not directly contain `AstId`s or `SyncTokenId`s, but may have `NodeChild` fields. */
type StructuralField<T extends TreeRefs = RawRefs> =
  | MultiSegmentAppSegment<T>
  | Line<T>
  | OpenCloseTokens<T>
  | NameSpecification<T>
  | TextElement<T>
  | ArgumentDefinition<T>
  | VectorElement<T>

/** Type whose fields are all suitable for storage as `Ast` fields. */
interface FieldObject<T extends TreeRefs> {
  [field: string]: FieldData<T>
}

/** Returns the fields of an `Ast` subtype that are not part of `AstFields`. */
function* fieldDataEntries<Fields>(map: FixedMapView<Fields>) {
  for (const entry of map.entries()) {
    // All fields that are not from `AstFields` are `FieldData`.
    if (!astFieldKeys.has(entry[0])) yield entry as [string, DeepReadonly<FieldData>]
  }
}

function idRewriter(
  f: (id: AstId) => AstId | undefined,
): (field: DeepReadonly<FieldData>) => FieldData | undefined {
  return (field: DeepReadonly<FieldData>) => {
    if (typeof field !== 'object') return
    if (!('node' in field)) return
    if (isTokenId(field.node)) return
    const newId = f(field.node)
    if (!newId) return
    return { whitespace: field.whitespace, node: newId }
  }
}

/** Apply the given function to each `AstId` in the fields of `ast`. For each value that it returns an output, that
 *  output will be substituted for the input ID.
 */
export function rewriteRefs(ast: MutableAst, f: (id: AstId) => AstId | undefined) {
  let fieldsChanged = 0
  for (const [key, value] of fieldDataEntries(ast.fields)) {
    const newValue = rewriteFieldRefs(value, idRewriter(f))
    if (newValue !== undefined) {
      ast.fields.set(key as any, newValue)
      fieldsChanged += 1
    }
  }
  return fieldsChanged
}

/** Copy all fields except the `Ast` base fields from `ast2` to `ast1`. A reference-rewriting function will be applied
 *  to `AstId`s in copied fields; see {@link rewriteRefs}.
 */
export function syncFields(ast1: MutableAst, ast2: Ast, f: (id: AstId) => AstId | undefined) {
  for (const [key, value] of fieldDataEntries(ast2.fields)) {
    const newValue = mapRefs(value, idRewriter(f))
    if (!fieldEqual(ast1.fields.get(key as any), newValue)) ast1.fields.set(key as any, newValue)
  }
}

export function syncNodeMetadata(target: MutableNodeMetadata, source: NodeMetadata) {
  const oldPos = target.get('position')
  const newPos = source.get('position')
  if (oldPos?.x !== newPos?.x || oldPos?.y !== newPos?.y) target.set('position', newPos)
  const newVis = source.get('visualization')
  if (!visMetadataEquals(target.get('visualization'), newVis)) target.set('visualization', newVis)
}

function rewriteFieldRefs<T extends TreeRefs, U extends TreeRefs>(
  field: DeepReadonly<FieldData<T>>,
  f: (t: DeepReadonly<FieldData<T>>) => FieldData<U> | undefined,
): FieldData<U> {
  const newValue = f(field)
  if (newValue) return newValue
  if (typeof field !== 'object') return
  // `Array.isArray` doesn't work with `DeepReadonly`, but we just need a narrowing that distinguishes it from all
  // `StructuralField` types.
  if ('forEach' in field) {
    const newValues = new Map<number, FieldData<U>>()
    field.forEach((subfield, i) => {
      const newValue = rewriteFieldRefs(subfield, f)
      if (newValue !== undefined) newValues.set(i, newValue)
    })
    if (newValues.size) return Array.from(field, (oldValue, i) => newValues.get(i) ?? oldValue)
  } else {
    const fieldObject = field satisfies DeepReadonly<StructuralField>
    const newValues = new Map<string, FieldData<U>>()
    for (const [key, value] of Object.entries(fieldObject)) {
      const newValue = rewriteFieldRefs(value, f)
      if (newValue !== undefined) newValues.set(key, newValue)
    }
    if (newValues.size)
      return Object.fromEntries(
        Object.entries(fieldObject).map(([key, oldValue]) => [key, newValues.get(key) ?? oldValue]),
      )
  }
}

type MapRef<T extends TreeRefs, U extends TreeRefs> = (t: FieldData<T>) => FieldData<U> | undefined

// This operation can transform any `FieldData` type parameterized by some `TreeRefs` into the same type parameterized
// by another `TreeRefs`, but it is not possible to express that generalization to TypeScript as such.
function mapRefs<T extends TreeRefs, U extends TreeRefs>(
  field: ImportFields<T>,
  f: MapRef<T, U>,
): ImportFields<U>
function mapRefs<T extends TreeRefs, U extends TreeRefs>(
  field: TextToken<T>,
  f: MapRef<T, U>,
): TextToken<U>
function mapRefs<T extends TreeRefs, U extends TreeRefs>(
  field: TextElement<T>,
  f: MapRef<T, U>,
): TextElement<U>
function mapRefs<T extends TreeRefs, U extends TreeRefs>(
  field: ArgumentDefinition<T>,
  f: MapRef<T, U>,
): ArgumentDefinition<U>
function mapRefs<T extends TreeRefs, U extends TreeRefs>(
  field: VectorElement<T>,
  f: MapRef<T, U>,
): VectorElement<U>
function mapRefs<T extends TreeRefs, U extends TreeRefs>(
  field: FieldData<T>,
  f: MapRef<T, U>,
): FieldData<U>
function mapRefs<T extends TreeRefs, U extends TreeRefs>(
  field: FieldData<T>,
  f: MapRef<T, U>,
): FieldData<U> {
  return rewriteFieldRefs(field, f) ?? field
}

function fieldEqual(field1: FieldData, field2: FieldData): boolean {
  if (typeof field1 !== 'object') return field1 === field2
  if (typeof field2 !== 'object') return false
  if ('node' in field1 && 'node' in field2) {
    if (field1['whitespace'] !== field2['whitespace']) return false
    if (isTokenId(field1.node) && isTokenId(field2.node))
      return Token.equal(field1.node, field2.node)
    else return field1.node === field2.node
  } else if ('node' in field1 || 'node' in field2) {
    return false
  } else if (Array.isArray(field1) && Array.isArray(field2)) {
    return (
      field1.length === field2.length && field1.every((value1, i) => fieldEqual(value1, field2[i]))
    )
  } else if (Array.isArray(field1) || Array.isArray(field2)) {
    return false
  } else {
    const fieldObject1 = field1 satisfies StructuralField
    const fieldObject2 = field2 satisfies StructuralField
    const keys = new Set<string>()
    for (const key of Object.keys(fieldObject1)) keys.add(key)
    for (const key of Object.keys(fieldObject2)) keys.add(key)
    for (const key of keys)
      if (!fieldEqual((fieldObject1 as any)[key], (fieldObject2 as any)[key])) return false
    return true
  }
}

function applyMixins(derivedCtor: any, constructors: any[]) {
  constructors.forEach((baseCtor) => {
    Object.getOwnPropertyNames(baseCtor.prototype).forEach((name) => {
      Object.defineProperty(
        derivedCtor.prototype,
        name,
        Object.getOwnPropertyDescriptor(baseCtor.prototype, name) || Object.create(null),
      )
    })
  })
}

interface AppFields {
  function: NodeChild<AstId>
  parens: OpenCloseTokens | undefined
  nameSpecification: NameSpecification | undefined
  argument: NodeChild<AstId>
}
interface OpenCloseTokens<T extends TreeRefs = RawRefs> {
  open: T['token']
  close: T['token']
}
interface NameSpecification<T extends TreeRefs = RawRefs> {
  name: T['token']
  equals: T['token']
}
export class App extends Ast {
  declare fields: FixedMap<AstFields & AppFields>
  constructor(module: Module, fields: FixedMapView<AstFields & AppFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableApp> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableApp) return parsed
  }

  static concrete(
    module: MutableModule,
    func: NodeChild<Owned>,
    parens: OpenCloseTokens | undefined,
    nameSpecification: NameSpecification | undefined,
    argument: NodeChild<Owned>,
  ) {
    const base = module.baseObject('App')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      function: concreteChild(module, func, id_),
      parens,
      nameSpecification,
      argument: concreteChild(module, argument, id_),
    })
    return asOwned(new MutableApp(module, fields))
  }

  static new(
    module: MutableModule,
    func: Owned,
    argumentName: StrictIdentLike | undefined,
    argument: Owned,
  ) {
    return App.concrete(
      module,
      autospaced(func),
      undefined,
      nameSpecification(argumentName),
      autospaced(argument),
    )
  }

  static positional(func: Owned, argument: Owned, module?: MutableModule): Owned<MutableApp> {
    return App.new(module ?? MutableModule.Transient(), func, undefined, argument)
  }

  static PositionalSequence(func: Owned, args: Owned[]): Owned {
    return args.reduce(
      (expression, argument) => App.new(func.module, expression, undefined, argument),
      func,
    )
  }

  get function(): Ast {
    return this.module.get(this.fields.get('function').node)
  }
  get argumentName(): Token | undefined {
    return this.module.getToken(this.fields.get('nameSpecification')?.name.node)
  }
  get argument(): Ast {
    return this.module.get(this.fields.get('argument').node)
  }

  *concreteChildren(verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { function: function_, parens, nameSpecification, argument } = getAll(this.fields)
    yield ensureUnspaced(function_, verbatim)
    const useParens = !!(parens && (nameSpecification || verbatim))
    const spacedEquals = useParens && !!nameSpecification?.equals.whitespace
    if (useParens) yield ensureSpaced(parens.open, verbatim)
    if (nameSpecification) {
      yield useParens ?
        preferUnspaced(nameSpecification.name)
      : ensureSpaced(nameSpecification.name, verbatim)
      yield ensureSpacedOnlyIf(nameSpecification.equals, spacedEquals, verbatim)
    }
    yield ensureSpacedOnlyIf(argument, !nameSpecification || spacedEquals, verbatim)
    if (useParens) yield preferUnspaced(parens.close)
  }

  printSubtree(
    info: SpanMap,
    offset: number,
    parentIndent: string | undefined,
    verbatim?: boolean,
  ): string {
    const verbatim_ =
      verbatim ?? (this.function instanceof Invalid || this.argument instanceof Invalid)
    return super.printSubtree(info, offset, parentIndent, verbatim_)
  }
}
function ensureSpacedOnlyIf<T>(
  child: NodeChild<T>,
  condition: boolean,
  verbatim: boolean | undefined,
): ConcreteChild<T> {
  return condition ? ensureSpaced(child, verbatim) : ensureUnspaced(child, verbatim)
}

type ConcreteChild<T> = { whitespace: string; node: T }
function isConcrete<T>(child: NodeChild<T>): child is ConcreteChild<T> {
  return child.whitespace !== undefined
}
function tryAsConcrete<T>(child: NodeChild<T>): ConcreteChild<T> | undefined {
  return isConcrete(child) ? child : undefined
}
function ensureSpaced<T>(child: NodeChild<T>, verbatim: boolean | undefined): ConcreteChild<T> {
  const concreteInput = tryAsConcrete(child)
  if (verbatim && concreteInput) return concreteInput
  return concreteInput?.whitespace ? concreteInput : { ...child, whitespace: ' ' }
}
function ensureUnspaced<T>(child: NodeChild<T>, verbatim: boolean | undefined): ConcreteChild<T> {
  const concreteInput = tryAsConcrete(child)
  if (verbatim && concreteInput) return concreteInput
  return concreteInput?.whitespace === '' ? concreteInput : { ...child, whitespace: '' }
}
function preferSpacedIf<T>(child: NodeChild<T>, condition: boolean): ConcreteChild<T> {
  return condition ? preferSpaced(child) : preferUnspaced(child)
}
function preferUnspaced<T>(child: NodeChild<T>): ConcreteChild<T> {
  return tryAsConcrete(child) ?? { ...child, whitespace: '' }
}
function preferSpaced<T>(child: NodeChild<T>): ConcreteChild<T> {
  return tryAsConcrete(child) ?? { ...child, whitespace: ' ' }
}
export class MutableApp extends App implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & AppFields>

  setFunction<T extends MutableAst>(value: Owned<T>) {
    setNode(this.fields, 'function', this.claimChild(value))
  }
  setArgumentName(name: StrictIdentLike | undefined) {
    this.fields.set('nameSpecification', nameSpecification(name))
  }
  setArgument<T extends MutableAst>(value: Owned<T>) {
    setNode(this.fields, 'argument', this.claimChild(value))
  }
}
export interface MutableApp extends App, MutableAst {
  get function(): MutableAst
  get argument(): MutableAst
}
applyMixins(MutableApp, [MutableAst])

interface UnaryOprAppFields {
  operator: NodeChild<SyncTokenId>
  argument: NodeChild<AstId> | undefined
}
export class UnaryOprApp extends Ast {
  declare fields: FixedMapView<AstFields & UnaryOprAppFields>
  constructor(module: Module, fields: FixedMapView<AstFields & UnaryOprAppFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableUnaryOprApp> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableUnaryOprApp) return parsed
  }

  static concrete(
    module: MutableModule,
    operator: NodeChild<Token>,
    argument: NodeChild<Owned> | undefined,
  ) {
    const base = module.baseObject('UnaryOprApp')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      operator,
      argument: concreteChild(module, argument, id_),
    })
    return asOwned(new MutableUnaryOprApp(module, fields))
  }

  static new(module: MutableModule, operator: Token, argument: Owned | undefined) {
    return this.concrete(module, unspaced(operator), argument ? autospaced(argument) : undefined)
  }

  get operator(): Token {
    return this.module.getToken(this.fields.get('operator').node)
  }
  get argument(): Ast | undefined {
    return this.module.get(this.fields.get('argument')?.node)
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { operator, argument } = getAll(this.fields)
    yield operator
    if (argument) yield argument
  }
}
export class MutableUnaryOprApp extends UnaryOprApp implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & UnaryOprAppFields>

  setOperator(value: Token) {
    this.fields.set('operator', unspaced(value))
  }
  setArgument<T extends MutableAst>(argument: Owned<T> | undefined) {
    setNode(this.fields, 'argument', this.claimChild(argument))
  }
}
export interface MutableUnaryOprApp extends UnaryOprApp, MutableAst {
  get argument(): MutableAst | undefined
}
applyMixins(MutableUnaryOprApp, [MutableAst])

interface AutoscopedIdentifierFields {
  operator: NodeChild<SyncTokenId>
  identifier: NodeChild<SyncTokenId>
}
export class AutoscopedIdentifier extends Ast {
  declare fields: FixedMapView<AstFields & AutoscopedIdentifierFields>
  constructor(module: Module, fields: FixedMapView<AstFields & AutoscopedIdentifierFields>) {
    super(module, fields)
  }

  static tryParse(
    source: string,
    module?: MutableModule,
  ): Owned<MutableAutoscopedIdentifier> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableAutoscopedIdentifier) return parsed
  }

  static concrete(module: MutableModule, operator: NodeChild<Token>, identifier: NodeChild<Token>) {
    const base = module.baseObject('AutoscopedIdentifier')
    const fields = composeFieldData(base, {
      operator,
      identifier,
    })
    return asOwned(new MutableAutoscopedIdentifier(module, fields))
  }

  static new(
    identifier: TypeOrConstructorIdentifier,
    module?: MutableModule,
  ): Owned<MutableAutoscopedIdentifier> {
    const module_ = module || MutableModule.Transient()
    const operator = Token.new('..')
    const ident = Token.new(identifier, RawAst.Token.Type.Ident)
    return this.concrete(module_, unspaced(operator), unspaced(ident))
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { operator, identifier } = getAll(this.fields)
    yield operator
    yield identifier
  }
}
export class MutableAutoscopedIdentifier extends AutoscopedIdentifier implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & AutoscopedIdentifierFields>

  setIdentifier(value: TypeOrConstructorIdentifier) {
    const token = Token.new(value, RawAst.Token.Type.Ident)
    this.fields.set('identifier', unspaced(token))
  }
}
export interface MutableAutoscopedIdentifier extends AutoscopedIdentifier, MutableAst {}
applyMixins(MutableAutoscopedIdentifier, [MutableAst])

interface NegationAppFields {
  operator: NodeChild<SyncTokenId>
  argument: NodeChild<AstId>
}
export class NegationApp extends Ast {
  declare fields: FixedMapView<AstFields & NegationAppFields>
  constructor(module: Module, fields: FixedMapView<AstFields & NegationAppFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableNegationApp> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableNegationApp) return parsed
  }

  static concrete(module: MutableModule, operator: NodeChild<Token>, argument: NodeChild<Owned>) {
    const base = module.baseObject('NegationApp')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      operator,
      argument: concreteChild(module, argument, id_),
    })
    return asOwned(new MutableNegationApp(module, fields))
  }

  static new(module: MutableModule, operator: Token, argument: Owned) {
    return this.concrete(module, unspaced(operator), autospaced(argument))
  }

  get operator(): Token {
    return this.module.getToken(this.fields.get('operator').node)
  }
  get argument(): Ast {
    return this.module.get(this.fields.get('argument').node)
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { operator, argument } = getAll(this.fields)
    yield operator
    if (argument) yield argument
  }
}
export class MutableNegationApp extends NegationApp implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & NegationAppFields>

  setArgument<T extends MutableAst>(value: Owned<T>) {
    setNode(this.fields, 'argument', this.claimChild(value))
  }
}
export interface MutableNegationApp extends NegationApp, MutableAst {
  get argument(): MutableAst
}
applyMixins(MutableNegationApp, [MutableAst])

interface OprAppFields {
  lhs: NodeChild<AstId> | undefined
  operators: NodeChild<SyncTokenId>[]
  rhs: NodeChild<AstId> | undefined
}
export class OprApp extends Ast {
  declare fields: FixedMapView<AstFields & OprAppFields>
  constructor(module: Module, fields: FixedMapView<AstFields & OprAppFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableOprApp> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableOprApp) return parsed
  }

  static concrete(
    module: MutableModule,
    lhs: NodeChild<Owned> | undefined,
    operators: NodeChild<Token>[],
    rhs: NodeChild<Owned> | undefined,
  ) {
    const base = module.baseObject('OprApp')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      lhs: concreteChild(module, lhs, id_),
      operators,
      rhs: concreteChild(module, rhs, id_),
    })
    return asOwned(new MutableOprApp(module, fields))
  }

  static new(
    module: MutableModule,
    lhs: Owned | undefined,
    operator: Token | string,
    rhs: Owned | undefined,
  ) {
    const operatorToken =
      operator instanceof Token ? operator : Token.new(operator, RawAst.Token.Type.Operator)
    return OprApp.concrete(module, unspaced(lhs), [autospaced(operatorToken)], autospaced(rhs))
  }

  get lhs(): Ast | undefined {
    return this.module.get(this.fields.get('lhs')?.node)
  }
  get operator(): Result<Token, NodeChild<Token>[]> {
    const operators = this.fields.get('operators')
    const operators_ = operators.map((child) => ({
      ...child,
      node: this.module.getToken(child.node),
    }))
    const [opr] = operators_
    return opr ? Ok(opr.node) : Err(operators_)
  }
  get rhs(): Ast | undefined {
    return this.module.get(this.fields.get('rhs')?.node)
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { lhs, operators, rhs } = getAll(this.fields)
    if (lhs) yield lhs
    yield* operators
    if (rhs) yield rhs
  }
}
export class MutableOprApp extends OprApp implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & OprAppFields>

  setLhs<T extends MutableAst>(value: Owned<T>) {
    setNode(this.fields, 'lhs', this.claimChild(value))
  }
  setOperator(value: Token) {
    this.fields.set('operators', [unspaced(value)])
  }
  setRhs<T extends MutableAst>(value: Owned<T>) {
    setNode(this.fields, 'rhs', this.claimChild(value))
  }
}
export interface MutableOprApp extends OprApp, MutableAst {
  get lhs(): MutableAst | undefined
  get rhs(): MutableAst | undefined
}
applyMixins(MutableOprApp, [MutableAst])

interface PropertyAccessFields {
  lhs: NodeChild<AstId> | undefined
  operator: NodeChild<SyncTokenId>
  rhs: NodeChild<AstId>
}
export class PropertyAccess extends Ast {
  declare fields: FixedMapView<AstFields & PropertyAccessFields>
  constructor(module: Module, fields: FixedMapView<AstFields & PropertyAccessFields>) {
    super(module, fields)
  }

  static tryParse(
    source: string,
    module?: MutableModule,
  ): Owned<MutablePropertyAccess> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutablePropertyAccess) return parsed
  }

  static new(module: MutableModule, lhs: Owned, rhs: IdentLike, style?: { spaced?: boolean }) {
    const dot = Token.new('.', RawAst.Token.Type.Operator)
    const whitespace = style?.spaced ? ' ' : ''
    return this.concrete(
      module,
      unspaced(lhs),
      { whitespace, node: dot },
      { whitespace, node: Ident.newAllowingOperators(module, toIdent(rhs)) },
    )
  }

  static Sequence(
    segments: [StrictIdentLike, ...StrictIdentLike[]],
    module: MutableModule,
  ): Owned<MutablePropertyAccess> | Owned<MutableIdent>
  static Sequence(
    segments: [StrictIdentLike, ...StrictIdentLike[], IdentLike],
    module: MutableModule,
  ): Owned<MutablePropertyAccess> | Owned<MutableIdent>
  static Sequence(
    segments: IdentLike[],
    module: MutableModule,
  ): Owned<MutablePropertyAccess> | Owned<MutableIdent> | undefined
  static Sequence(
    segments: IdentLike[],
    module: MutableModule,
  ): Owned<MutablePropertyAccess> | Owned<MutableIdent> | undefined {
    let path: Owned<MutablePropertyAccess> | Owned<MutableIdent> | undefined
    let operatorInNonFinalSegment = false
    segments.forEach((s, i) => {
      const t = toIdent(s)
      if (i !== segments.length - 1 && !isIdentifier(t.code())) operatorInNonFinalSegment = true
      path = path ? this.new(module, path, t) : Ident.newAllowingOperators(module, t)
    })
    if (!operatorInNonFinalSegment) return path
  }

  static concrete(
    module: MutableModule,
    lhs: NodeChild<Owned> | undefined,
    operator: NodeChild<Token>,
    rhs: NodeChild<Owned<MutableIdent>>,
  ) {
    const base = module.baseObject('PropertyAccess')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      lhs: concreteChild(module, lhs, id_),
      operator,
      rhs: concreteChild(module, rhs, id_),
    })
    return asOwned(new MutablePropertyAccess(module, fields))
  }

  get lhs(): Ast | undefined {
    return this.module.get(this.fields.get('lhs')?.node)
  }
  get operator(): Token {
    return this.module.getToken(this.fields.get('operator').node)
  }
  get rhs(): IdentifierOrOperatorIdentifierToken {
    const ast = this.module.get(this.fields.get('rhs').node)
    assert(ast instanceof Ident)
    return ast.token as IdentifierOrOperatorIdentifierToken
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { lhs, operator, rhs } = getAll(this.fields)
    if (lhs) yield lhs
    yield operator
    yield rhs
  }
}
export class MutablePropertyAccess extends PropertyAccess implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & PropertyAccessFields>

  setLhs<T extends MutableAst>(value: Owned<T> | undefined) {
    setNode(this.fields, 'lhs', this.claimChild(value))
  }
  setRhs(ident: IdentLike) {
    const node = this.claimChild(Ident.newAllowingOperators(this.module, ident))
    const old = this.fields.get('rhs')
    this.fields.set('rhs', old ? { ...old, node } : unspaced(node))
  }
}
export interface MutablePropertyAccess extends PropertyAccess, MutableAst {
  get lhs(): MutableAst | undefined
}
applyMixins(MutablePropertyAccess, [MutableAst])

/** Unroll the provided chain of `PropertyAccess` nodes, returning the first non-access as `subject` and the accesses
 *  from left-to-right. */
export function accessChain(ast: Ast): { subject: Ast; accessChain: PropertyAccess[] } {
  const accessChain = new Array<PropertyAccess>()
  while (ast instanceof PropertyAccess && ast.lhs) {
    accessChain.push(ast)
    ast = ast.lhs
  }
  accessChain.reverse()
  return { subject: ast, accessChain }
}

interface GenericFields {
  children: RawNodeChild[]
}
export class Generic extends Ast {
  declare fields: FixedMapView<AstFields & GenericFields>
  constructor(module: Module, fields: FixedMapView<AstFields & GenericFields>) {
    super(module, fields)
  }

  static concrete(module: MutableModule, children: (NodeChild<Owned> | NodeChild<Token>)[]) {
    const base = module.baseObject('Generic')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      children: children.map((child) => concreteChild(module, child, id_)),
    })
    return asOwned(new MutableGeneric(module, fields))
  }

  concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    return this.fields.get('children')[Symbol.iterator]()
  }
}
export class MutableGeneric extends Generic implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & GenericFields>
}
export interface MutableGeneric extends Generic, MutableAst {}
applyMixins(MutableGeneric, [MutableAst])

interface MultiSegmentAppSegment<T extends TreeRefs = RawRefs> {
  header: T['token']
  body: T['ast'] | undefined
}
function multiSegmentAppSegment<T extends MutableAst>(
  header: string,
  body: Owned<T>,
): MultiSegmentAppSegment<OwnedRefs>
function multiSegmentAppSegment<T extends MutableAst>(
  header: string,
  body: Owned<T> | undefined,
): MultiSegmentAppSegment<OwnedRefs> | undefined
function multiSegmentAppSegment<T extends MutableAst>(
  header: string,
  body: Owned<T> | undefined,
): MultiSegmentAppSegment<OwnedRefs> | undefined {
  return {
    header: autospaced(Token.new(header, RawAst.Token.Type.Ident)),
    body: spaced(body ? (body as any) : undefined),
  }
}

function multiSegmentAppSegmentToRaw(
  module: MutableModule,
  msas: MultiSegmentAppSegment<OwnedRefs> | undefined,
  parent: AstId,
): MultiSegmentAppSegment | undefined {
  if (!msas) return undefined
  return {
    ...msas,
    body: concreteChild(module, msas.body, parent),
  }
}
interface ImportFields<T extends TreeRefs = RawRefs> extends FieldObject<T> {
  polyglot: MultiSegmentAppSegment<T> | undefined
  from: MultiSegmentAppSegment<T> | undefined
  import: MultiSegmentAppSegment<T>
  all: T['token'] | undefined
  as: MultiSegmentAppSegment<T> | undefined
  hiding: MultiSegmentAppSegment<T> | undefined
}

export class Import extends Ast {
  declare fields: FixedMapView<AstFields & ImportFields>
  constructor(module: Module, fields: FixedMapView<AstFields & ImportFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableImport> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableImport) return parsed
  }

  get polyglot(): Ast | undefined {
    return this.module.get(this.fields.get('polyglot')?.body?.node)
  }
  get from(): Ast | undefined {
    return this.module.get(this.fields.get('from')?.body?.node)
  }
  get import_(): Ast | undefined {
    return this.module.get(this.fields.get('import').body?.node)
  }
  get all(): Token | undefined {
    return this.module.getToken(this.fields.get('all')?.node)
  }
  get as(): Ast | undefined {
    return this.module.get(this.fields.get('as')?.body?.node)
  }
  get hiding(): Ast | undefined {
    return this.module.get(this.fields.get('hiding')?.body?.node)
  }

  static concrete(
    module: MutableModule,
    polyglot: MultiSegmentAppSegment<OwnedRefs> | undefined,
    from: MultiSegmentAppSegment<OwnedRefs> | undefined,
    import_: MultiSegmentAppSegment<OwnedRefs>,
    all: NodeChild<Token> | undefined,
    as: MultiSegmentAppSegment<OwnedRefs> | undefined,
    hiding: MultiSegmentAppSegment<OwnedRefs> | undefined,
  ) {
    const base = module.baseObject('Import')
    const id_ = base.get('id')
    const ownedFields: ImportFields<OwnedRefs> = {
      polyglot,
      from,
      import: import_,
      all,
      as,
      hiding,
    }
    const rawFields = mapRefs(ownedFields, ownedToRaw(module, id_))
    const fields = composeFieldData(base, rawFields)
    return asOwned(new MutableImport(module, fields))
  }

  static Qualified(path: IdentLike[], module: MutableModule): Owned<MutableImport> | undefined {
    const path_ = PropertyAccess.Sequence(path, module)
    if (!path_) return
    return MutableImport.concrete(
      module,
      undefined,
      undefined,
      multiSegmentAppSegment('import', path_),
      undefined,
      undefined,
      undefined,
    )
  }

  static Unqualified(
    path: IdentLike[],
    name: IdentLike,
    module: MutableModule,
  ): Owned<MutableImport> | undefined {
    const path_ = PropertyAccess.Sequence(path, module)
    if (!path_) return
    const name_ = Ident.newAllowingOperators(module, name)
    return MutableImport.concrete(
      module,
      undefined,
      multiSegmentAppSegment('from', path_),
      multiSegmentAppSegment('import', name_),
      undefined,
      undefined,
      undefined,
    )
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const segment = (segment: MultiSegmentAppSegment | undefined) => {
      const parts = []
      if (segment) parts.push(segment.header)
      if (segment?.body) parts.push(segment.body)
      return parts
    }
    const { polyglot, from, import: import_, all, as, hiding } = getAll(this.fields)
    yield* segment(polyglot)
    yield* segment(from)
    yield* segment(import_)
    if (all) yield all
    yield* segment(as)
    yield* segment(hiding)
  }
}
export class MutableImport extends Import implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & ImportFields>

  private toRaw(msas: MultiSegmentAppSegment<OwnedRefs>): MultiSegmentAppSegment
  private toRaw(
    msas: MultiSegmentAppSegment<OwnedRefs> | undefined,
  ): MultiSegmentAppSegment | undefined
  private toRaw(
    msas: MultiSegmentAppSegment<OwnedRefs> | undefined,
  ): MultiSegmentAppSegment | undefined {
    return multiSegmentAppSegmentToRaw(this.module, msas, this.id)
  }

  setPolyglot<T extends MutableAst>(value: Owned<T> | undefined) {
    this.fields.set(
      'polyglot',
      value ? this.toRaw(multiSegmentAppSegment('polyglot', value)) : undefined,
    )
  }
  setFrom<T extends MutableAst>(value: Owned<T> | undefined) {
    this.fields.set('from', value ? this.toRaw(multiSegmentAppSegment('from', value)) : value)
  }
  setImport<T extends MutableAst>(value: Owned<T>) {
    this.fields.set('import', this.toRaw(multiSegmentAppSegment('import', value)))
  }
  setAll(value: Token | undefined) {
    this.fields.set('all', spaced(value))
  }
  setAs<T extends MutableAst>(value: Owned<T> | undefined) {
    this.fields.set('as', this.toRaw(multiSegmentAppSegment('as', value)))
  }
  setHiding<T extends MutableAst>(value: Owned<T> | undefined) {
    this.fields.set('hiding', this.toRaw(multiSegmentAppSegment('hiding', value)))
  }
}
export interface MutableImport extends Import, MutableAst {
  get polyglot(): MutableAst | undefined
  get from(): MutableAst | undefined
  get import_(): MutableAst | undefined
  get as(): MutableAst | undefined
  get hiding(): MutableAst | undefined
}
applyMixins(MutableImport, [MutableAst])

interface TreeRefs {
  token: any
  ast: any
}
type RefMap<T extends TreeRefs, U extends TreeRefs> = (
  field: FieldData<T>,
) => FieldData<U> | undefined
type RawRefs = {
  token: NodeChild<SyncTokenId>
  ast: NodeChild<AstId>
}
export type OwnedRefs = {
  token: NodeChild<Token>
  ast: NodeChild<Owned>
}
type ConcreteRefs = {
  token: NodeChild<Token>
  ast: NodeChild<Ast>
}
function ownedToRaw(module: MutableModule, parentId: AstId): RefMap<OwnedRefs, RawRefs> {
  return (child: FieldData<OwnedRefs>) => {
    if (typeof child !== 'object') return
    if (!('node' in child)) return
    if (isToken(child.node)) return
    return { ...child, node: claimChild(module, child.node, parentId) }
  }
}
function rawToConcrete(module: Module): RefMap<RawRefs, ConcreteRefs> {
  return (child: FieldData) => {
    if (typeof child !== 'object') return
    if (!('node' in child)) return
    if (isTokenId(child.node)) return { ...child, node: module.getToken(child.node) }
    else return { ...child, node: module.get(child.node) }
  }
}

function concreteToOwned(module: MutableModule): RefMap<ConcreteRefs, OwnedRefs> {
  return (child: FieldData<ConcreteRefs>) => {
    if (typeof child !== 'object') return
    if (!('node' in child)) return
    if (isTokenChild(child)) return child
    else return { ...child, node: module.copy(child.node) }
  }
}

export interface TextToken<T extends TreeRefs = RawRefs> {
  type: 'token'
  readonly token: T['token']
  readonly interpreted?: string | undefined
}
export interface TextSplice<T extends TreeRefs = RawRefs> {
  type: 'splice'
  readonly open: T['token']
  readonly expression: T['ast'] | undefined
  readonly close: T['token']
}

export type TextElement<T extends TreeRefs = RawRefs> = TextToken<T> | TextSplice<T>

function textElementValue(element: TextElement<ConcreteRefs>): string {
  switch (element.type) {
    case 'token': {
      if (element.interpreted != null) return element.interpreted
      // The logical newline is not necessarily the same as the concrete token, e.g. the token could be a CRLF.
      if (element.token.node.tokenType_ === RawAst.Token.Type.TextNewline) return '\n'
      // The token is an invalid escape-sequence or a text-section; return it verbatim.
      return element.token.node.code()
    }
    case 'splice': {
      let s = ''
      s += element.open.node.code()
      if (element.expression) {
        s += element.expression.whitespace ?? ''
        s += element.expression.node.code()
      }
      s += element.close.whitespace ?? ''
      s += element.close.node.code()
      return s
    }
  }
}

function rawTextElementValue(raw: TextElement, module: Module): string {
  return textElementValue(mapRefs(raw, rawToConcrete(module)))
}

function uninterpolatedText(elements: DeepReadonly<TextElement[]>, module: Module): string {
  return elements.reduce((s, e) => s + rawTextElementValue(e, module), '')
}

function fieldConcreteChildren(field: FieldData) {
  const children = new Array<RawNodeChild>()
  rewriteFieldRefs(field, (subfield: FieldData) => {
    if (typeof subfield === 'object' && 'node' in subfield) children.push(subfield)
  })
  return children
}

interface TextLiteralFields {
  open: NodeChild<SyncTokenId> | undefined
  newline: NodeChild<SyncTokenId> | undefined
  elements: TextElement[]
  close: NodeChild<SyncTokenId> | undefined
}
export class TextLiteral extends Ast {
  declare fields: FixedMapView<AstFields & TextLiteralFields>
  constructor(module: Module, fields: FixedMapView<AstFields & TextLiteralFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableTextLiteral> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableTextLiteral) return parsed
  }

  static concrete(
    module: MutableModule,
    open: NodeChild<Token> | undefined,
    newline: NodeChild<Token> | undefined,
    elements: TextElement<OwnedRefs>[],
    close: NodeChild<Token> | undefined,
  ) {
    const base = module.baseObject('TextLiteral')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      open,
      newline,
      elements: elements.map((e) => mapRefs(e, ownedToRaw(module, id_))),
      close,
    })
    return asOwned(new MutableTextLiteral(module, fields))
  }

  static new(rawText: string, module?: MutableModule): Owned<MutableTextLiteral> {
    const escaped = escapeTextLiteral(rawText)
    const parsed = parse(`'${escaped}'`, module)
    if (!(parsed instanceof MutableTextLiteral)) {
      console.error(`Failed to escape string for interpolated text`, rawText, escaped, parsed)
      const safeText = rawText.replaceAll(/[^-+A-Za-z0-9_. ]/g, '')
      return TextLiteral.new(safeText, module)
    }
    return parsed
  }

  /**
   * Return the literal value of the string with all escape sequences applied, but without
   * evaluating any interpolated expressions.
   */
  get rawTextContent(): string {
    return uninterpolatedText(this.fields.get('elements'), this.module)
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { open, newline, elements, close } = getAll(this.fields)
    if (open) yield open
    if (newline) yield newline
    for (const e of elements) yield* fieldConcreteChildren(e)
    if (close) yield close
  }

  boundaryTokenCode(): string | undefined {
    return (this.open || this.close)?.code()
  }

  isInterpolated(): boolean {
    const token = this.boundaryTokenCode()
    return token === "'" || token === "'''"
  }

  get open(): Token | undefined {
    return this.module.getToken(this.fields.get('open')?.node)
  }

  get close(): Token | undefined {
    return this.module.getToken(this.fields.get('close')?.node)
  }

  get elements(): TextElement<ConcreteRefs>[] {
    return this.fields.get('elements').map((e) => mapRefs(e, rawToConcrete(this.module)))
  }
}
export class MutableTextLiteral extends TextLiteral implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & TextLiteralFields>

  setBoundaries(code: string) {
    this.fields.set('open', unspaced(Token.new(code)))
    this.fields.set('close', unspaced(Token.new(code)))
  }

  setElements(elements: TextElement<OwnedRefs>[]) {
    this.fields.set(
      'elements',
      elements.map((e) => mapRefs(e, ownedToRaw(this.module, this.id))),
    )
  }

  /**
   * Set literal value of the string. The code representation of assigned text will be automatically
   * transformed to use escape sequences when necessary.
   */
  setRawTextContent(rawText: string) {
    let boundary = this.boundaryTokenCode()
    const isInterpolated = this.isInterpolated()
    const mustBecomeInterpolated = !isInterpolated && (!boundary || rawText.match(/["\n\r]/))
    if (mustBecomeInterpolated) {
      boundary = "'"
      this.setBoundaries(boundary)
    }
    const literalContents =
      isInterpolated || mustBecomeInterpolated ? escapeTextLiteral(rawText) : rawText
    const parsed = parse(`${boundary}${literalContents}${boundary}`)
    assert(parsed instanceof TextLiteral)
    const elements = parsed.elements.map((e) => mapRefs(e, concreteToOwned(this.module)))
    this.setElements(elements)
  }
}
export interface MutableTextLiteral extends TextLiteral, MutableAst {}
applyMixins(MutableTextLiteral, [MutableAst])

interface DocumentedFields {
  open: NodeChild<SyncTokenId>
  elements: TextToken[]
  newlines: NodeChild<SyncTokenId>[]
  expression: NodeChild<AstId> | undefined
}
export class Documented extends Ast {
  declare fields: FixedMapView<AstFields & DocumentedFields>
  constructor(module: Module, fields: FixedMapView<AstFields & DocumentedFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableDocumented> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableDocumented) return parsed
  }

  static new(text: string, expression: Owned) {
    return this.concrete(
      expression.module,
      undefined,
      textToUninterpolatedElements(text),
      undefined,
      autospaced(expression),
    )
  }

  static concrete(
    module: MutableModule,
    open: NodeChild<Token> | undefined,
    elements: TextToken<OwnedRefs>[],
    newlines: NodeChild<Token>[] | undefined,
    expression: NodeChild<Owned> | undefined,
  ) {
    const base = module.baseObject('Documented')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      open: open ?? unspaced(Token.new('##', RawAst.Token.Type.Operator)),
      elements: elements.map((e) => mapRefs(e, ownedToRaw(module, id_))),
      newlines: newlines ?? [unspaced(Token.new('\n', RawAst.Token.Type.Newline))],
      expression: concreteChild(module, expression, id_),
    })
    return asOwned(new MutableDocumented(module, fields))
  }

  get expression(): Ast | undefined {
    return this.module.get(this.fields.get('expression')?.node)
  }

  /** Return the string value of the documentation. */
  documentation(): string {
    const raw = uninterpolatedText(this.fields.get('elements'), this.module)
    return raw.startsWith(' ') ? raw.slice(1) : raw
  }

  wrappedExpression(): Ast | undefined {
    return this.expression
  }

  documentingAncestor(): Documented | undefined {
    return this
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { open, elements, newlines, expression } = getAll(this.fields)
    yield open
    for (const { token } of elements) yield token
    yield* newlines
    if (expression) yield expression
  }

  printSubtree(
    info: SpanMap,
    offset: number,
    parentIndent: string | undefined,
    verbatim?: boolean,
  ): string {
    return printDocumented(this, info, offset, parentIndent, verbatim)
  }
}
export class MutableDocumented extends Documented implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & DocumentedFields>

  setDocumentationText(text: string) {
    this.fields.set(
      'elements',
      textToUninterpolatedElements(text).map((owned) =>
        mapRefs(owned, ownedToRaw(this.module, this.id)),
      ),
    )
  }

  setExpression<T extends MutableAst>(value: Owned<T> | undefined) {
    this.fields.set('expression', unspaced(this.claimChild(value)))
  }
}
export interface MutableDocumented extends Documented, MutableAst {
  get expression(): MutableAst | undefined
}
applyMixins(MutableDocumented, [MutableAst])

function textToUninterpolatedElements(text: string): TextToken<OwnedRefs>[] {
  const elements = new Array<TextToken<OwnedRefs>>()
  text.split('\n').forEach((line, i) => {
    if (i)
      elements.push({
        type: 'token',
        token: unspaced(Token.new('\n', RawAst.Token.Type.TextNewline)),
      })
    elements.push({
      type: 'token',
      token: autospaced(Token.new(line, RawAst.Token.Type.TextSection)),
    })
  })
  return elements
}

interface InvalidFields {
  expression: NodeChild<AstId>
}
export class Invalid extends Ast {
  declare fields: FixedMapView<AstFields & InvalidFields>
  constructor(module: Module, fields: FixedMapView<AstFields & InvalidFields>) {
    super(module, fields)
  }

  static concrete(module: MutableModule, expression: NodeChild<Owned>) {
    const base = module.baseObject('Invalid')
    return asOwned(new MutableInvalid(module, invalidFields(module, base, expression)))
  }

  get expression(): Ast {
    return this.module.get(this.fields.get('expression').node)
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    yield this.fields.get('expression')
  }

  printSubtree(
    info: SpanMap,
    offset: number,
    parentIndent: string | undefined,
    _verbatim?: boolean,
  ): string {
    return super.printSubtree(info, offset, parentIndent, true)
  }
}
export function invalidFields(
  module: MutableModule,
  base: FixedMap<AstFields>,
  expression: NodeChild<Owned>,
): FixedMap<AstFields & InvalidFields> {
  const id_ = base.get('id')
  return composeFieldData(base, { expression: concreteChild(module, expression, id_) })
}
export class MutableInvalid extends Invalid implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & InvalidFields>
}
export interface MutableInvalid extends Invalid, MutableAst {
  /** The `expression` getter is intentionally not narrowed to provide mutable access:
   *  It makes more sense to `.replace` the `Invalid` node. */
}
applyMixins(MutableInvalid, [MutableAst])

interface GroupFields {
  open: NodeChild<SyncTokenId> | undefined
  expression: NodeChild<AstId> | undefined
  close: NodeChild<SyncTokenId> | undefined
}
export class Group extends Ast {
  declare fields: FixedMapView<AstFields & GroupFields>
  constructor(module: Module, fields: FixedMapView<AstFields & GroupFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableGroup> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableGroup) return parsed
  }

  static concrete(
    module: MutableModule,
    open: NodeChild<Token> | undefined,
    expression: NodeChild<Owned> | undefined,
    close: NodeChild<Token> | undefined,
  ) {
    const base = module.baseObject('Group')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      open,
      expression: concreteChild(module, expression, id_),
      close,
    })
    return asOwned(new MutableGroup(module, fields))
  }

  static new(module: MutableModule, expression: Owned) {
    const open = unspaced(Token.new('(', RawAst.Token.Type.OpenSymbol))
    const close = unspaced(Token.new(')', RawAst.Token.Type.CloseSymbol))
    return this.concrete(module, open, unspaced(expression), close)
  }

  get expression(): Ast | undefined {
    return this.module.get(this.fields.get('expression')?.node)
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { open, expression, close } = getAll(this.fields)
    if (open) yield open
    if (expression) yield expression
    if (close) yield close
  }
}
export class MutableGroup extends Group implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & GroupFields>

  setExpression<T extends MutableAst>(value: Owned<T> | undefined) {
    this.fields.set('expression', unspaced(this.claimChild(value)))
  }
}
export interface MutableGroup extends Group, MutableAst {
  get expression(): MutableAst | undefined
}
applyMixins(MutableGroup, [MutableAst])

interface NumericLiteralFields {
  tokens: NodeChild<SyncTokenId>[]
}
export class NumericLiteral extends Ast {
  declare fields: FixedMapView<AstFields & NumericLiteralFields>
  constructor(module: Module, fields: FixedMapView<AstFields & NumericLiteralFields>) {
    super(module, fields)
  }

  static tryParse(
    source: string,
    module?: MutableModule,
  ): Owned<MutableNumericLiteral> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableNumericLiteral) return parsed
  }

  static concrete(module: MutableModule, tokens: NodeChild<Token>[]) {
    const base = module.baseObject('NumericLiteral')
    const fields = composeFieldData(base, { tokens })
    return asOwned(new MutableNumericLiteral(module, fields))
  }

  concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    return this.fields.get('tokens')[Symbol.iterator]()
  }
}
export class MutableNumericLiteral extends NumericLiteral implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & NumericLiteralFields>
}
export interface MutableNumericLiteral extends NumericLiteral, MutableAst {}
applyMixins(MutableNumericLiteral, [MutableAst])

/** The actual contents of an `ArgumentDefinition` are complex, but probably of more interest to the compiler than the
 *  GUI. We just need to represent them faithfully and create the simple cases. */
type ArgumentDefinition<T extends TreeRefs = RawRefs> = (T['ast'] | T['token'])[]

interface FunctionFields {
  name: NodeChild<AstId>
  argumentDefinitions: ArgumentDefinition[]
  equals: NodeChild<SyncTokenId>
  body: NodeChild<AstId> | undefined
}
export class Function extends Ast {
  declare fields: FixedMapView<AstFields & FunctionFields>
  constructor(module: Module, fields: FixedMapView<AstFields & FunctionFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableFunction> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableFunction) return parsed
  }

  get name(): Ast {
    return this.module.get(this.fields.get('name').node)
  }
  get body(): Ast | undefined {
    return this.module.get(this.fields.get('body')?.node)
  }
  get argumentDefinitions(): ArgumentDefinition<ConcreteRefs>[] {
    return this.fields
      .get('argumentDefinitions')
      .map((raw) => raw.map((part) => this.module.getConcrete(part)))
  }

  static concrete(
    module: MutableModule,
    name: NodeChild<Owned>,
    argumentDefinitions: ArgumentDefinition<OwnedRefs>[],
    equals: NodeChild<Token>,
    body: NodeChild<Owned> | undefined,
  ) {
    const base = module.baseObject('Function')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      name: concreteChild(module, name, id_),
      argumentDefinitions: argumentDefinitions.map((def) => mapRefs(def, ownedToRaw(module, id_))),
      equals,
      body: concreteChild(module, body, id_),
    })
    return asOwned(new MutableFunction(module, fields))
  }

  static new(
    module: MutableModule,
    name: IdentLike,
    argumentDefinitions: ArgumentDefinition<OwnedRefs>[],
    body: Owned,
  ): Owned<MutableFunction> {
    // Note that a function name may not be an operator if the function is not in the body of a type definition, but we
    // can't easily enforce that because we don't currently make a syntactic distinction between top-level functions and
    // type methods.
    return MutableFunction.concrete(
      module,
      unspaced(Ident.newAllowingOperators(module, name)),
      argumentDefinitions,
      spaced(makeEquals()),
      autospaced(body),
    )
  }

  /** Construct a function with simple (name-only) arguments and a body block. */
  static fromStatements(
    module: MutableModule,
    name: IdentLike,
    argumentNames: StrictIdentLike[],
    statements: Owned[],
  ): Owned<MutableFunction> {
    const statements_: OwnedBlockLine[] = statements.map((statement) => ({
      expression: unspaced(statement),
    }))
    const argumentDefinitions = argumentNames.map((name) => [spaced(Ident.new(module, name))])
    const body = BodyBlock.new(statements_, module)
    return MutableFunction.new(module, name, argumentDefinitions, body)
  }

  *bodyExpressions(): IterableIterator<Ast> {
    const body = this.body
    if (body instanceof BodyBlock) {
      yield* body.statements()
    } else if (body) {
      yield body
    }
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { name, argumentDefinitions, equals, body } = getAll(this.fields)
    yield name
    for (const def of argumentDefinitions) yield* def
    yield { whitespace: equals.whitespace ?? ' ', node: this.module.getToken(equals.node) }
    if (body) yield preferSpacedIf(body, this.module.tryGet(body.node) instanceof BodyBlock)
  }
}
export class MutableFunction extends Function implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & FunctionFields>

  setName<T extends MutableAst>(value: Owned<T>) {
    this.fields.set('name', unspaced(this.claimChild(value)))
  }
  setBody<T extends MutableAst>(value: Owned<T> | undefined) {
    this.fields.set('body', unspaced(this.claimChild(value)))
  }
  setArgumentDefinitions(defs: ArgumentDefinition<OwnedRefs>[]) {
    this.fields.set(
      'argumentDefinitions',
      defs.map((def) => mapRefs(def, ownedToRaw(this.module, this.id))),
    )
  }

  /** Returns the body, after converting it to a block if it was empty or an inline expression. */
  bodyAsBlock(): MutableBodyBlock {
    const oldBody = this.body
    if (oldBody instanceof MutableBodyBlock) return oldBody
    const newBody = BodyBlock.new([], this.module)
    if (oldBody) newBody.push(oldBody.take())
    return newBody
  }
}
export interface MutableFunction extends Function, MutableAst {
  get name(): MutableAst
  get body(): MutableAst | undefined
}
applyMixins(MutableFunction, [MutableAst])

interface AssignmentFields {
  pattern: NodeChild<AstId>
  equals: NodeChild<SyncTokenId>
  expression: NodeChild<AstId>
}
export class Assignment extends Ast {
  declare fields: FixedMapView<AstFields & AssignmentFields>
  constructor(module: Module, fields: FixedMapView<AstFields & AssignmentFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableAssignment> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableAssignment) return parsed
  }

  static concrete(
    module: MutableModule,
    pattern: NodeChild<Owned>,
    equals: NodeChild<Token>,
    expression: NodeChild<Owned>,
  ) {
    const base = module.baseObject('Assignment')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      pattern: concreteChild(module, pattern, id_),
      equals,
      expression: concreteChild(module, expression, id_),
    })
    return asOwned(new MutableAssignment(module, fields))
  }

  static new(module: MutableModule, ident: StrictIdentLike, expression: Owned) {
    return Assignment.concrete(
      module,
      unspaced(Ident.new(module, ident)),
      spaced(makeEquals()),
      spaced(expression),
    )
  }

  get pattern(): Ast {
    return this.module.get(this.fields.get('pattern').node)
  }
  get expression(): Ast {
    return this.module.get(this.fields.get('expression').node)
  }

  *concreteChildren(verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { pattern, equals, expression } = getAll(this.fields)
    yield ensureUnspaced(pattern, verbatim)
    yield ensureSpacedOnlyIf(equals, expression.whitespace !== '', verbatim)
    yield preferSpaced(expression)
  }
}
export class MutableAssignment extends Assignment implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & AssignmentFields>

  setPattern<T extends MutableAst>(value: Owned<T>) {
    this.fields.set('pattern', unspaced(this.claimChild(value)))
  }
  setExpression<T extends MutableAst>(value: Owned<T>) {
    setNode(this.fields, 'expression', this.claimChild(value))
  }
}
export interface MutableAssignment extends Assignment, MutableAst {
  get pattern(): MutableAst
  get expression(): MutableAst
}
applyMixins(MutableAssignment, [MutableAst])

interface BodyBlockFields {
  lines: RawBlockLine[]
}
export class BodyBlock extends Ast {
  declare fields: FixedMapView<AstFields & BodyBlockFields>
  constructor(module: Module, fields: FixedMapView<AstFields & BodyBlockFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableBodyBlock> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableBodyBlock) return parsed
  }

  static concrete(module: MutableModule, lines: OwnedBlockLine[]) {
    const base = module.baseObject('BodyBlock')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      lines: lines.map((line) => lineToRaw(line, module, id_)),
    })
    return asOwned(new MutableBodyBlock(module, fields))
  }

  static new(lines: OwnedBlockLine[], module: MutableModule) {
    return BodyBlock.concrete(module, lines)
  }

  get lines(): BlockLine[] {
    return this.fields.get('lines').map((line) => lineFromRaw(line, this.module))
  }

  *statements(): IterableIterator<Ast> {
    for (const line of this.lines) {
      if (line.expression) yield line.expression.node
    }
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    for (const line of this.fields.get('lines')) {
      yield preferUnspaced(line.newline)
      if (line.expression) yield line.expression
    }
  }

  printSubtree(
    info: SpanMap,
    offset: number,
    parentIndent: string | undefined,
    verbatim?: boolean,
  ): string {
    return printBlock(this, info, offset, parentIndent, verbatim)
  }
}
export class MutableBodyBlock extends BodyBlock implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & BodyBlockFields>

  updateLines(map: (lines: OwnedBlockLine[]) => OwnedBlockLine[]) {
    return this.setLines(map(this.takeLines()))
  }
  takeLines(): OwnedBlockLine[] {
    return this.fields.get('lines').map((line) => ownedLineFromRaw(line, this.module))
  }
  setLines(lines: OwnedBlockLine[]) {
    this.fields.set(
      'lines',
      lines.map((line) => lineToRaw(line, this.module, this.id)),
    )
  }

  /** Insert the given statement(s) starting at the specified line index. */
  insert(index: number, ...statements: (Owned | undefined)[]) {
    const before = this.fields.get('lines').slice(0, index)
    const insertions = statements.map((statement) => ({
      newline: unspaced(Token.new('\n', RawAst.Token.Type.Newline)),
      expression: statement && unspaced(this.claimChild(statement)),
    }))
    const after = this.fields.get('lines').slice(index)
    this.fields.set('lines', [...before, ...insertions, ...after])
  }

  push(statement: Owned) {
    const oldLines = this.fields.get('lines')
    const newLine = {
      newline: unspaced(Token.new('\n', RawAst.Token.Type.Newline)),
      expression: unspaced(this.claimChild(statement)),
    }
    this.fields.set('lines', [...oldLines, newLine])
  }

  filter(keep: (ast: MutableAst) => boolean) {
    const oldLines = this.fields.get('lines')
    const filteredLines = oldLines.filter((line) => {
      if (!line.expression) return true
      return keep(this.module.get(line.expression.node))
    })
    this.fields.set('lines', filteredLines)
  }
}
export interface MutableBodyBlock extends BodyBlock, MutableAst {
  statements(): IterableIterator<MutableAst>
}
applyMixins(MutableBodyBlock, [MutableAst])

interface RawLine<T extends TreeRefs> {
  newline: T['token']
  expression: T['ast'] | undefined
}

interface Line<T extends TreeRefs> {
  newline?: T['token'] | undefined
  expression: T['ast'] | undefined
}

type RawBlockLine = RawLine<RawRefs>
export type BlockLine = Line<ConcreteRefs>
export type OwnedBlockLine = Line<OwnedRefs>

function lineFromRaw(raw: RawBlockLine, module: Module): BlockLine {
  const expression = raw.expression ? module.get(raw.expression.node) : undefined
  return {
    newline: { ...raw.newline, node: module.getToken(raw.newline.node) },
    expression:
      expression ?
        {
          whitespace: raw.expression?.whitespace,
          node: expression,
        }
      : undefined,
  }
}

function ownedLineFromRaw(raw: RawBlockLine, module: MutableModule): OwnedBlockLine {
  const expression = raw.expression ? module.get(raw.expression.node).takeIfParented() : undefined
  return {
    newline: { ...raw.newline, node: module.getToken(raw.newline.node) },
    expression:
      expression ?
        {
          whitespace: raw.expression?.whitespace,
          node: expression,
        }
      : undefined,
  }
}

function lineToRaw(line: OwnedBlockLine, module: MutableModule, block: AstId): RawBlockLine {
  return {
    newline: line.newline ?? unspaced(Token.new('\n', RawAst.Token.Type.Newline)),
    expression:
      line.expression ?
        {
          whitespace: line.expression?.whitespace,
          node: claimChild(module, line.expression.node, block),
        }
      : undefined,
  }
}

interface IdentFields {
  token: NodeChild<SyncTokenId>
}
export class Ident extends Ast {
  declare fields: FixedMapView<AstFields & IdentFields>
  constructor(module: Module, fields: FixedMapView<AstFields & IdentFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableIdent> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableIdent) return parsed
  }

  get token(): IdentifierToken {
    return this.module.getToken(this.fields.get('token').node) as IdentifierToken
  }

  static concrete(module: MutableModule, token: NodeChild<Token>) {
    const base = module.baseObject('Ident')
    const fields = composeFieldData(base, { token })
    return asOwned(new MutableIdent(module, fields))
  }

  static new(module: MutableModule, ident: StrictIdentLike) {
    return Ident.concrete(module, unspaced(toIdentStrict(ident)))
  }

  /** @internal */
  static newAllowingOperators(module: MutableModule, ident: IdentLike) {
    return Ident.concrete(module, unspaced(toIdent(ident)))
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    yield this.fields.get('token')
  }

  code(): Identifier {
    return this.token.code() as Identifier
  }
}
export class MutableIdent extends Ident implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & IdentFields>

  setToken(ident: IdentLike) {
    this.fields.set('token', unspaced(toIdent(ident)))
  }

  code(): Identifier {
    return this.token.code()
  }
}
export interface MutableIdent extends Ident, MutableAst {}
applyMixins(MutableIdent, [MutableAst])

interface WildcardFields {
  token: NodeChild<SyncTokenId>
}
export class Wildcard extends Ast {
  declare fields: FixedMapView<AstFields & WildcardFields>
  constructor(module: Module, fields: FixedMapView<AstFields & WildcardFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableWildcard> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableWildcard) return parsed
  }

  get token(): Token {
    return this.module.getToken(this.fields.get('token').node)
  }

  static concrete(module: MutableModule, token: NodeChild<Token>) {
    const base = module.baseObject('Wildcard')
    const fields = composeFieldData(base, { token })
    return asOwned(new MutableWildcard(module, fields))
  }

  static new(module?: MutableModule) {
    const token = Token.new('_', RawAst.Token.Type.Wildcard)
    return this.concrete(module ?? MutableModule.Transient(), unspaced(token))
  }

  *concreteChildren(_verbatim?: boolean): IterableIterator<RawNodeChild> {
    yield this.fields.get('token')
  }
}

export class MutableWildcard extends Wildcard implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & WildcardFields>
}
export interface MutableWildcard extends Wildcard, MutableAst {}
applyMixins(MutableWildcard, [MutableAst])

type AbstractVectorElement<T extends TreeRefs> = {
  delimiter?: T['token']
  value: T['ast'] | undefined
}
function delimitVectorElement(element: AbstractVectorElement<OwnedRefs>): VectorElement<OwnedRefs> {
  return {
    ...element,
    delimiter: element.delimiter ?? unspaced(Token.new(',', RawAst.Token.Type.Operator)),
  }
}
type VectorElement<T extends TreeRefs> = { delimiter: T['token']; value: T['ast'] | undefined }
interface VectorFields {
  open: NodeChild<Token>
  elements: VectorElement<RawRefs>[]
  close: NodeChild<Token>
}
export class Vector extends Ast {
  declare fields: FixedMapView<AstFields & VectorFields>
  constructor(module: Module, fields: FixedMapView<AstFields & VectorFields>) {
    super(module, fields)
  }

  static tryParse(source: string, module?: MutableModule): Owned<MutableVector> | undefined {
    const parsed = parse(source, module)
    if (parsed instanceof MutableVector) return parsed
  }

  static concrete(
    module: MutableModule,
    open: NodeChild<Token> | undefined,
    elements: AbstractVectorElement<OwnedRefs>[],
    close: NodeChild<Token> | undefined,
  ) {
    const base = module.baseObject('Vector')
    const id_ = base.get('id')
    const fields = composeFieldData(base, {
      open: open ?? unspaced(Token.new('[', RawAst.Token.Type.OpenSymbol)),
      elements: elements.map(delimitVectorElement).map((e) => mapRefs(e, ownedToRaw(module, id_))),
      close: close ?? unspaced(Token.new(']', RawAst.Token.Type.CloseSymbol)),
    })
    return asOwned(new MutableVector(module, fields))
  }

  static new(module: MutableModule, elements: Owned[]) {
    return this.concrete(
      module,
      undefined,
      elements.map((value) => ({ value: autospaced(value) })),
      undefined,
    )
  }

  static tryBuild<T>(
    inputs: Iterable<T>,
    elementBuilder: (input: T, module: MutableModule) => Owned,
    edit?: MutableModule,
  ): Owned<MutableVector>
  static tryBuild<T>(
    inputs: Iterable<T>,
    elementBuilder: (input: T, module: MutableModule) => Owned | undefined,
    edit?: MutableModule,
  ): Owned<MutableVector> | undefined
  static tryBuild<T>(
    inputs: Iterable<T>,
    valueBuilder: (input: T, module: MutableModule) => Owned | undefined,
    edit?: MutableModule,
  ): Owned<MutableVector> | undefined {
    const module = edit ?? MutableModule.Transient()
    const elements = new Array<AbstractVectorElement<OwnedRefs>>()
    for (const input of inputs) {
      const value = valueBuilder(input, module)
      if (!value) return
      elements.push({ value: autospaced(value) })
    }
    return Vector.concrete(module, undefined, elements, undefined)
  }

  static build<T>(
    inputs: Iterable<T>,
    elementBuilder: (input: T, module: MutableModule) => Owned,
    edit?: MutableModule,
  ): Owned<MutableVector> {
    return Vector.tryBuild(inputs, elementBuilder, edit)
  }

  *concreteChildren(verbatim?: boolean): IterableIterator<RawNodeChild> {
    const { open, elements, close } = getAll(this.fields)
    yield ensureUnspaced(open, verbatim)
    let isFirst = true
    for (const { delimiter, value } of elements) {
      if (isFirst && value) {
        yield preferUnspaced(value)
      } else {
        yield preferUnspaced(delimiter)
        if (value) yield preferSpaced(value)
      }
      isFirst = false
    }
    yield preferUnspaced(close)
  }

  *values(): IterableIterator<Ast> {
    for (const element of this.fields.get('elements'))
      if (element.value) yield this.module.get(element.value.node)
  }
}
export class MutableVector extends Vector implements MutableAst {
  declare readonly module: MutableModule
  declare readonly fields: FixedMap<AstFields & VectorFields>

  push(value: Owned) {
    const elements = this.fields.get('elements')
    const element = mapRefs(
      delimitVectorElement({ value: autospaced(value) }),
      ownedToRaw(this.module, this.id),
    )
    this.fields.set('elements', [...elements, element])
  }

  keep(predicate: (ast: Ast) => boolean) {
    const elements = this.fields.get('elements')
    const filtered = elements.filter(
      (element) => element.value && predicate(this.module.get(element.value.node)),
    )
    this.fields.set('elements', filtered)
  }
}
export interface MutableVector extends Vector, MutableAst {
  values(): IterableIterator<MutableAst>
}
applyMixins(MutableVector, [MutableAst])

export type Mutable<T extends Ast = Ast> =
  T extends App ? MutableApp
  : T extends Assignment ? MutableAssignment
  : T extends BodyBlock ? MutableBodyBlock
  : T extends Documented ? MutableDocumented
  : T extends Function ? MutableFunction
  : T extends Generic ? MutableGeneric
  : T extends Group ? MutableGroup
  : T extends Ident ? MutableIdent
  : T extends Import ? MutableImport
  : T extends Invalid ? MutableInvalid
  : T extends NegationApp ? MutableNegationApp
  : T extends NumericLiteral ? MutableNumericLiteral
  : T extends OprApp ? MutableOprApp
  : T extends PropertyAccess ? MutablePropertyAccess
  : T extends TextLiteral ? MutableTextLiteral
  : T extends UnaryOprApp ? MutableUnaryOprApp
  : T extends Vector ? MutableVector
  : T extends Wildcard ? MutableWildcard
  : MutableAst

export function materializeMutable(module: MutableModule, fields: FixedMap<AstFields>): MutableAst {
  const type = fields.get('type')
  const fieldsForType = fields as FixedMap<any>
  switch (type) {
    case 'App':
      return new MutableApp(module, fieldsForType)
    case 'Assignment':
      return new MutableAssignment(module, fieldsForType)
    case 'BodyBlock':
      return new MutableBodyBlock(module, fieldsForType)
    case 'Documented':
      return new MutableDocumented(module, fieldsForType)
    case 'Function':
      return new MutableFunction(module, fieldsForType)
    case 'Generic':
      return new MutableGeneric(module, fieldsForType)
    case 'Group':
      return new MutableGroup(module, fieldsForType)
    case 'Ident':
      return new MutableIdent(module, fieldsForType)
    case 'Import':
      return new MutableImport(module, fieldsForType)
    case 'Invalid':
      return new MutableInvalid(module, fieldsForType)
    case 'NegationApp':
      return new MutableNegationApp(module, fieldsForType)
    case 'NumericLiteral':
      return new MutableNumericLiteral(module, fieldsForType)
    case 'OprApp':
      return new MutableOprApp(module, fieldsForType)
    case 'PropertyAccess':
      return new MutablePropertyAccess(module, fieldsForType)
    case 'TextLiteral':
      return new MutableTextLiteral(module, fieldsForType)
    case 'UnaryOprApp':
      return new MutableUnaryOprApp(module, fieldsForType)
    case 'AutoscopedIdentifier':
      return new MutableAutoscopedIdentifier(module, fieldsForType)
    case 'Vector':
      return new MutableVector(module, fieldsForType)
    case 'Wildcard':
      return new MutableWildcard(module, fieldsForType)
  }
  bail(`Invalid type: ${type}`)
}

export function materialize(module: Module, fields: FixedMapView<AstFields>): Ast {
  const type = fields.get('type')
  const fields_ = fields as FixedMapView<any>
  switch (type) {
    case 'App':
      return new App(module, fields_)
    case 'Assignment':
      return new Assignment(module, fields_)
    case 'BodyBlock':
      return new BodyBlock(module, fields_)
    case 'Documented':
      return new Documented(module, fields_)
    case 'Function':
      return new Function(module, fields_)
    case 'Generic':
      return new Generic(module, fields_)
    case 'Group':
      return new Group(module, fields_)
    case 'Ident':
      return new Ident(module, fields_)
    case 'Import':
      return new Import(module, fields_)
    case 'Invalid':
      return new Invalid(module, fields_)
    case 'NegationApp':
      return new NegationApp(module, fields_)
    case 'NumericLiteral':
      return new NumericLiteral(module, fields_)
    case 'OprApp':
      return new OprApp(module, fields_)
    case 'PropertyAccess':
      return new PropertyAccess(module, fields_)
    case 'TextLiteral':
      return new TextLiteral(module, fields_)
    case 'UnaryOprApp':
      return new UnaryOprApp(module, fields_)
    case 'AutoscopedIdentifier':
      return new AutoscopedIdentifier(module, fields_)
    case 'Vector':
      return new Vector(module, fields_)
    case 'Wildcard':
      return new Wildcard(module, fields_)
  }
  bail(`Invalid type: ${type}`)
}

export interface FixedMapView<Fields> {
  get<Key extends string & keyof Fields>(key: Key): DeepReadonly<Fields[Key]>
  /** @internal Unsafe. The caller must ensure the yielded values are not modified. */
  entries(): IterableIterator<readonly [string, unknown]>
  clone(): FixedMap<Fields>
  has(key: string): boolean
  toJSON(): object
}

export interface FixedMap<Fields> extends FixedMapView<Fields> {
  set<Key extends string & keyof Fields>(key: Key, value: Fields[Key]): void
}

type DeepReadonlyFields<T> = {
  [K in keyof T]: DeepReadonly<T[K]>
}

function getAll<Fields extends object>(map: FixedMapView<Fields>): DeepReadonlyFields<Fields> {
  return Object.fromEntries(map.entries()) as DeepReadonlyFields<Fields>
}

declare const brandLegalFieldContent: unique symbol
/** Used to add a constraint to all `AstFields`s subtypes ensuring that they were produced by `composeFieldData`, which
 *  enforces a requirement that the provided fields extend `FieldObject`.
 */
interface LegalFieldContent {
  [brandLegalFieldContent]: never
}

/** Modifies the input `map`. Returns the same object with an extended type. */
export function setAll<Fields1, Fields2 extends Record<string, any>>(
  map: FixedMap<Fields1>,
  fields: Fields2,
): FixedMap<Fields1 & Fields2> {
  const map_ = map as FixedMap<Fields1 & Fields2>
  for (const [k, v] of Object.entries(fields)) {
    const k_ = k as string & (keyof Fields1 | keyof Fields2)
    map_.set(k_, v as any)
  }
  return map_
}

/** Modifies the input `map`. Returns the same object with an extended type. The added fields are required to have only
 *  types extending `FieldData`; the returned object is branded as `LegalFieldContent`. */
export function composeFieldData<Fields1, Fields2 extends FieldObject<RawRefs>>(
  map: FixedMap<Fields1>,
  fields: Fields2,
): FixedMap<Fields1 & Fields2 & LegalFieldContent> {
  return setAll(map, fields) as FixedMap<Fields1 & Fields2 & LegalFieldContent>
}

function claimChild<T extends MutableAst>(
  module: MutableModule,
  child: Owned<T>,
  parent: AstId,
): AstId {
  if (child.module === module) assertEqual(child.fields.get('parent'), undefined)
  const child_ = module.copyIfForeign(child)
  child_.fields.set('parent', parent)
  return child_.id
}

function concreteChild(
  module: MutableModule,
  child: NodeChild<Owned>,
  parent: AstId,
): NodeChild<AstId>
function concreteChild(
  module: MutableModule,
  child: NodeChild<Owned> | undefined,
  parent: AstId,
): NodeChild<AstId> | undefined
function concreteChild(
  module: MutableModule,
  child: NodeChild<Owned | Token>,
  parent: AstId,
): NodeChild<AstId> | NodeChild<Token>
function concreteChild(
  module: MutableModule,
  child: NodeChild<Owned | Token> | undefined,
  parent: AstId,
): NodeChild<AstId> | NodeChild<Token> | undefined
function concreteChild(
  module: MutableModule,
  child: NodeChild<Owned | Token> | undefined,
  parent: AstId,
): NodeChild<AstId> | NodeChild<Token> | undefined {
  if (!child) return undefined
  if (isTokenId(child.node)) return child as NodeChild<Token>
  return { ...child, node: claimChild(module, child.node, parent) }
}

type StrictIdentLike = Identifier | IdentifierToken
function toIdentStrict(ident: StrictIdentLike): IdentifierToken
function toIdentStrict(ident: StrictIdentLike | undefined): IdentifierToken | undefined
function toIdentStrict(ident: StrictIdentLike | undefined): IdentifierToken | undefined {
  return (
    ident ?
      isToken(ident) ? ident
      : (Token.new(ident, RawAst.Token.Type.Ident) as IdentifierToken)
    : undefined
  )
}

type IdentLike = IdentifierOrOperatorIdentifier | IdentifierOrOperatorIdentifierToken
function toIdent(ident: IdentLike): IdentifierOrOperatorIdentifierToken
function toIdent(ident: IdentLike | undefined): IdentifierOrOperatorIdentifierToken | undefined
function toIdent(ident: IdentLike | undefined): IdentifierOrOperatorIdentifierToken | undefined {
  return (
    ident ?
      isToken(ident) ? ident
      : (Token.new(ident, RawAst.Token.Type.Ident) as IdentifierOrOperatorIdentifierToken)
    : undefined
  )
}

function makeEquals(): Token {
  return Token.new('=', RawAst.Token.Type.Operator)
}

function nameSpecification(
  name: StrictIdentLike | undefined,
): { name: NodeChild<Token>; equals: NodeChild<Token> } | undefined {
  return name && { name: autospaced(toIdentStrict(name)), equals: unspaced(makeEquals()) }
}

type KeysOfFieldType<Fields, T> = {
  [K in keyof Fields]: Fields[K] extends T ? K : never
}[keyof Fields]
function setNode<Fields, Key extends string & KeysOfFieldType<Fields, NodeChild<AstId>>>(
  map: FixedMap<Fields>,
  key: Key,
  node: AstId,
): void
function setNode<
  Fields,
  Key extends string & KeysOfFieldType<Fields, NodeChild<AstId> | undefined>,
>(map: FixedMap<Fields>, key: Key, node: AstId | undefined): void
function setNode<
  Fields,
  Key extends string & KeysOfFieldType<Fields, NodeChild<AstId> | undefined>,
>(map: FixedMap<Fields>, key: Key, node: AstId | undefined): void {
  // The signature correctly only allows this function to be called if `Fields[Key] instanceof NodeChild<SyncId>`,
  // but it doesn't prove that property to TSC, so we have to cast here.
  const old = map.get(key as string & keyof Fields) as DeepReadonly<NodeChild<AstId>>
  const updated = old ? { ...old, node } : autospaced(node)
  map.set(key, updated as Fields[Key])
}

function spaced<T extends object | string>(node: T): NodeChild<T>
function spaced<T extends object | string>(node: T | undefined): NodeChild<T> | undefined
function spaced<T extends object | string>(node: T | undefined): NodeChild<T> | undefined {
  if (node === undefined) return node
  return { whitespace: ' ', node }
}

function unspaced<T extends object | string>(node: T): NodeChild<T>
function unspaced<T extends object | string>(node: T | undefined): NodeChild<T> | undefined
function unspaced<T extends object | string>(node: T | undefined): NodeChild<T> | undefined {
  if (node === undefined) return node
  return { whitespace: '', node }
}

export function autospaced<T extends object | string>(node: T): NodeChild<T>
export function autospaced<T extends object | string>(node: T | undefined): NodeChild<T> | undefined
export function autospaced<T extends object | string>(
  node: T | undefined,
): NodeChild<T> | undefined {
  if (node === undefined) return node
  return { whitespace: undefined, node }
}

export interface Removed<T extends MutableAst> {
  node: Owned<T>
  placeholder: MutableWildcard | undefined
}