feat: Build cached anchor/alias node list for faster alias resolving

src/doc/Document.ts

@@ -433,7 +433,8 @@ export class Document<
       keep: !json,
       mapAsMap: mapAsMap === true,
       mapKeyWarned: false,
-      maxAliasCount: typeof maxAliasCount === 'number' ? maxAliasCount : 100
+      maxAliasCount: typeof maxAliasCount === 'number' ? maxAliasCount : 100,
+      anchorAndAliasNodes: []
     }
     const res = toJS(this.contents, jsonArg ?? '', ctx)
     if (typeof onAnchor === 'function')

src/nodes/Alias.ts

@@ -52,7 +52,17 @@ export class Alias extends NodeBase {
   toJSON(_arg?: unknown, ctx?: ToJSContext): unknown {
     if (!ctx) return { source: this.source }
     const { anchors, doc, maxAliasCount } = ctx
-    const source = this.resolve(doc)
+
+    let source: Scalar | YAMLMap | YAMLSeq | undefined = undefined
+    if (ctx.anchorAndAliasNodes) {
+      for (const node of ctx.anchorAndAliasNodes) {
+        if (node === this) break
+        if (node.anchor === this.source) source = node
+      }
+    } else {
+      source = this.resolve(doc)
+    }
+
     if (!source) {
       const msg = `Unresolved alias (the anchor must be set before the alias): ${this.source}`
       throw new ReferenceError(msg)

src/nodes/toJS.ts

@@ -1,6 +1,10 @@
 import type { Document } from '../doc/Document.ts'
-import { hasAnchor } from './identity.ts'
+import { hasAnchor, isAlias } from './identity.ts'
 import type { Node } from './Node.ts'
+import type { Alias } from './Alias.ts'
+import type { Scalar } from './Scalar.ts'
+import type { YAMLMap } from './YAMLMap.ts'
+import type { YAMLSeq } from './YAMLSeq.ts'
 
 export interface AnchorData {
   aliasCount: number
@@ -10,6 +14,8 @@ export interface AnchorData {
 
 export interface ToJSContext {
   anchors: Map<Node, AnchorData>
+  /** Cached anchor and allias nodes in the order they occurred in the document */
+  anchorAndAliasNodes?: (Alias | Scalar | YAMLMap | YAMLSeq)[]
   doc: Document<Node, boolean>
   keep: boolean
   mapAsMap: boolean
@@ -33,13 +39,24 @@ export function toJS(value: any, arg: string | null, ctx?: ToJSContext): any {
   if (Array.isArray(value)) return value.map((v, i) => toJS(v, String(i), ctx))
   if (value && typeof value.toJSON === 'function') {
     // eslint-disable-next-line @typescript-eslint/no-unsafe-call
-    if (!ctx || !hasAnchor(value)) return value.toJSON(arg, ctx)
+    if (!ctx) return value.toJSON(arg, ctx)
+
+    if (!hasAnchor(value)) {
+      if (ctx.anchorAndAliasNodes && isAlias(value))
+        ctx.anchorAndAliasNodes.push(value)
+      // eslint-disable-next-line @typescript-eslint/no-unsafe-call
+      return value.toJSON(arg, ctx)
+    }
+
     const data: AnchorData = { aliasCount: 0, count: 1, res: undefined }
     ctx.anchors.set(value, data)
     ctx.onCreate = res => {
       data.res = res
       delete ctx.onCreate
     }
+
+    if (ctx.anchorAndAliasNodes) ctx.anchorAndAliasNodes.push(value)
+
     const res = value.toJSON(arg, ctx)
     if (ctx.onCreate) ctx.onCreate(res)
     return res