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/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;