Refactor merge function to support optional parameter and update merge calls in emitDom for shallow merging

Author: Bashamega

src/build.ts

@@ -150,7 +150,7 @@ async function emitDom() {
         target.comment = descObject.__comment;
       }
     }
-    idl = merge(idl, descriptions);
+    idl = merge(idl, descriptions, {optional:true});
 
     return idl;
   }
@@ -179,7 +179,7 @@ async function emitDom() {
   };
 
   for (const w of widlStandardTypes) {
-    webidl = merge(webidl, w.browser, true);
+    webidl = merge(webidl, w.browser, {shallow: true});
   }
   for (const w of widlStandardTypes) {
     for (const partial of w.partialInterfaces) {
@@ -189,32 +189,32 @@ async function emitDom() {
         webidl.mixins!.mixin[partial.name];
       if (base) {
         if (base.exposed) resolveExposure(partial, base.exposed);
-        merge(base.constants, partial.constants, true);
-        merge(base.methods, partial.methods, true);
-        merge(base.properties, partial.properties, true);
+        merge(base.constants, partial.constants, {shallow: true});
+        merge(base.methods, partial.methods, {shallow: true});
+        merge(base.properties, partial.properties, {shallow: true});
       }
     }
     for (const partial of w.partialMixins) {
       const base = webidl.mixins!.mixin[partial.name];
       if (base) {
         if (base.exposed) resolveExposure(partial, base.exposed);
-        merge(base.constants, partial.constants, true);
-        merge(base.methods, partial.methods, true);
-        merge(base.properties, partial.properties, true);
+        merge(base.constants, partial.constants, {shallow: true});
+        merge(base.methods, partial.methods, {shallow: true});
+        merge(base.properties, partial.properties, {shallow: true});
       }
     }
     for (const partial of w.partialDictionaries) {
       const base = webidl.dictionaries!.dictionary[partial.name];
       if (base) {
-        merge(base.members, partial.members, true);
+        merge(base.members, partial.members, {shallow: true});
       }
     }
     for (const partial of w.partialNamespaces) {
       const base = webidl.namespaces?.find((n) => n.name === partial.name);
       if (base) {
         if (base.exposed) resolveExposure(partial, base.exposed);
-        merge(base.methods, partial.methods, true);
-        merge(base.properties, partial.properties, true);
+        merge(base.methods, partial.methods, {shallow: true});
+        merge(base.properties, partial.properties, {shallow: true});
       }
     }
     for (const include of w.includes) {

src/build/helpers.ts

@@ -118,7 +118,7 @@ export function exposesTo(o: { exposed?: string }, target: string[]): boolean {
   return o.exposed.split(" ").some((e) => target.includes(e));
 }
 
-export function merge<T>(target: T, src: T, shallow?: boolean): T {
+export function merge<T>(target: T, src: T, { shallow = false, optional = false }: { shallow?: boolean, optional?: boolean } = { }): T {
   if (typeof target !== "object" || typeof src !== "object") {
     return src;
   }
@@ -145,10 +145,10 @@ export function merge<T>(target: T, src: T, shallow?: boolean): T {
                 `Redundant merge value ${targetProp} in ${JSON.stringify(src)}`,
               );
             }
-            target[k] = merge(targetProp, srcProp, shallow);
+            target[k] = merge(targetProp, srcProp, { shallow, optional });
           }
         }
-      } else {
+      } else if (!optional || typeof src[k] !== "object") {
         target[k] = src[k];
       }
     }