Add support, in Dict.merge, for merging of "sub"-dictionaries

This allows for merging of dictionaries one level deeper than previously. This could be useful e.g. for /Resources dictionaries, where you want to e.g. merge their respective /Font dictionaries (and other) together rather than picking just the first one.

src/core/document.js

@@ -114,7 +114,7 @@ class Page {
     if (value.length === 1 || !isDict(value[0])) {
       return value[0];
     }
-    return Dict.merge(this.xref, value);
+    return Dict.merge({ xref: this.xref, dictArray: value });
   }
 
   get content() {

src/core/evaluator.js

@@ -726,8 +726,10 @@ class PartialEvaluator {
     const tilingOpList = new OperatorList();
     // Merge the available resources, to prevent issues when the patternDict
     // is missing some /Resources entries (fixes issue6541.pdf).
-    const resourcesArray = [patternDict.get("Resources"), resources];
-    const patternResources = Dict.merge(this.xref, resourcesArray);
+    const patternResources = Dict.merge({
+      xref: this.xref,
+      dictArray: [patternDict.get("Resources"), resources],
+    });
 
     return this.getOperatorList({
       stream: pattern,

src/core/primitives.js

@@ -173,22 +173,61 @@ var Dict = (function DictClosure() {
 
   Dict.empty = new Dict(null);
 
-  Dict.merge = function (xref, dictArray) {
+  Dict.merge = function ({ xref, dictArray, mergeSubDicts = false }) {
     const mergedDict = new Dict(xref);
 
-    for (let i = 0, ii = dictArray.length; i < ii; i++) {
-      const dict = dictArray[i];
-      if (!isDict(dict)) {
-        continue;
-      }
-      for (const keyName in dict._map) {
-        if (mergedDict._map[keyName] !== undefined) {
+    if (!mergeSubDicts) {
+      for (const dict of dictArray) {
+        if (!(dict instanceof Dict)) {
           continue;
         }
-        mergedDict._map[keyName] = dict._map[keyName];
+        for (const [key, value] of Object.entries(dict._map)) {
+          if (mergedDict._map[key] === undefined) {
+            mergedDict._map[key] = value;
+          }
+        }
+      }
+      return mergedDict.size > 0 ? mergedDict : Dict.empty;
+    }
+    const properties = new Map();
+
+    for (const dict of dictArray) {
+      if (!(dict instanceof Dict)) {
+        continue;
+      }
+      for (const [key, value] of Object.entries(dict._map)) {
+        let property = properties.get(key);
+        if (property === undefined) {
+          property = [];
+          properties.set(key, property);
+        }
+        property.push(value);
       }
     }
-    return mergedDict;
+    for (const [name, values] of properties) {
+      if (values.length === 1 || !(values[0] instanceof Dict)) {
+        mergedDict._map[name] = values[0];
+        continue;
+      }
+      const subDict = new Dict(xref);
+
+      for (const dict of values) {
+        if (!(dict instanceof Dict)) {
+          continue;
+        }
+        for (const [key, value] of Object.entries(dict._map)) {
+          if (subDict._map[key] === undefined) {
+            subDict._map[key] = value;
+          }
+        }
+      }
+      if (subDict.size > 0) {
+        mergedDict._map[name] = subDict;
+      }
+    }
+    properties.clear();
+
+    return mergedDict.size > 0 ? mergedDict : Dict.empty;
   };
 
   return Dict;

src/shared/compatibility.js

@@ -390,4 +390,13 @@ if (
     }
     Object.values = require("core-js/es/object/values.js");
   })();
+
+  // Provides support for Object.entries in legacy browsers.
+  // Support: IE, Chrome<54
+  (function checkObjectEntries() {
+    if (Object.entries) {
+      return;
+    }
+    Object.entries = require("core-js/es/object/entries.js");
+  })();
 }