Simplify how the ObjectLoader is used

The `ObjectLoader.prototype.load` method has a fast-path, which avoids any lookup/parsing if the entire PDF document is already loaded.
However, we still need to create an `ObjectLoader`-instance which seems unnecessary in that case.

Hence we introduce a *static* `ObjectLoader.load` method, which will help avoid creating `ObjectLoader`-instances needlessly and also (slightly) shortens the call-sites.
To ensure that the new method will be used, we extend the `no-restricted-syntax` ESLint rule to "forbid" direct usage of `new ObjectLoader()`.

Author: Snuffleupagus

eslint.config.mjs

@@ -303,6 +303,11 @@ export default [
           selector: "NewExpression[callee.name='Name']",
           message: "Use `Name.get()` rather than `new Name()`.",
         },
+        {
+          selector: "NewExpression[callee.name='ObjectLoader']",
+          message:
+            "Use `ObjectLoader.load()` rather than `new ObjectLoader()`.",
+        },
         {
           selector: "NewExpression[callee.name='Ref']",
           message: "Use `Ref.get()` rather than `new Ref()`.",

src/core/annotation.js

@@ -1158,15 +1158,12 @@ class Annotation {
     }
   }
 
-  loadResources(keys, appearance) {
-    return appearance.dict.getAsync("Resources").then(resources => {
-      if (!resources) {
-        return undefined;
-      }
-
-      const objectLoader = new ObjectLoader(resources, keys, resources.xref);
-      return objectLoader.load().then(() => resources);
-    });
+  async loadResources(keys, appearance) {
+    const resources = await appearance.dict.getAsync("Resources");
+    if (resources) {
+      await ObjectLoader.load(resources, keys, resources.xref);
+    }
+    return resources;
   }
 
   async getOperatorList(evaluator, task, intent, annotationStorage) {

src/core/document.js

@@ -417,8 +417,7 @@ class Page {
     // TODO: add async `_getInheritableProperty` and remove this.
     await (this.resourcesPromise ??= this.pdfManager.ensure(this, "resources"));
 
-    const objectLoader = new ObjectLoader(this.resources, keys, this.xref);
-    await objectLoader.load();
+    await ObjectLoader.load(this.resources, keys, this.xref);
   }
 
   async #getMergedResources(streamDict, keys) {
@@ -430,8 +429,7 @@ class Page {
     if (!(localResources instanceof Dict && localResources.size)) {
       return this.resources;
     }
-    const objectLoader = new ObjectLoader(localResources, keys, this.xref);
-    await objectLoader.load();
+    await ObjectLoader.load(localResources, keys, this.xref);
 
     return Dict.merge({
       xref: this.xref,
@@ -1254,8 +1252,7 @@ class PDFDocument {
     if (!(resources instanceof Dict)) {
       return;
     }
-    const objectLoader = new ObjectLoader(resources, ["Font"], this.xref);
-    await objectLoader.load();
+    await ObjectLoader.load(resources, ["Font"], this.xref);
 
     const fontRes = resources.get("Font");
     if (!(fontRes instanceof Dict)) {

src/core/object_loader.js

@@ -54,7 +54,7 @@ function addChildren(node, nodesToVisit) {
  * entire PDF document object graph to be traversed.
  */
 class ObjectLoader {
-  refSet = null;
+  refSet = new RefSet();
 
   constructor(dict, keys, xref) {
     this.dict = dict;
@@ -63,13 +63,7 @@ class ObjectLoader {
   }
 
   async load() {
-    // Don't walk the graph if all the data is already loaded.
-    if (this.xref.stream.isDataLoaded) {
-      return;
-    }
-
     const { keys, dict } = this;
-    this.refSet = new RefSet();
     // Setup the initial nodes to visit.
     const nodesToVisit = [];
     for (const key of keys) {
@@ -144,6 +138,16 @@ class ObjectLoader {
       await this.#walk(nodesToRevisit);
     }
   }
+
+  static async load(obj, keys, xref) {
+    // Don't walk the graph if all the data is already loaded.
+    if (xref.stream.isDataLoaded) {
+      return;
+    }
+    // eslint-disable-next-line no-restricted-syntax
+    const objLoader = new ObjectLoader(obj, keys, xref);
+    await objLoader.load();
+  }
 }
 
 export { ObjectLoader };