Perf: offload reject fetch & parse into a worker thread

Build/lib/rules/base.ts

@@ -189,19 +189,32 @@ export class FileOutput {
     return this;
   }
 
+  private addDomainsetLine(line: string) {
+    const otherPoundSign = line.lastIndexOf('#');
+
+    if (otherPoundSign > 0) {
+      line = line.slice(0, otherPoundSign).trimEnd();
+    }
+
+    if (line[0] === '.') {
+      this.addDomainSuffix(line);
+    } else {
+      this.domainTrie.add(line);
+    }
+  }
+
   private async addFromDomainsetPromise(source: MaybePromise<AsyncIterable<string> | Iterable<string> | string[]>) {
-    for await (let line of await source) {
-      const otherPoundSign = line.lastIndexOf('#');
-
-      if (otherPoundSign > 0) {
-        line = line.slice(0, otherPoundSign).trimEnd();
-      }
-
-      if (line[0] === '.') {
-        this.addDomainSuffix(line);
-      } else {
-        this.domainTrie.add(line);
+    const resolved = await source;
+    // `for await` over a plain array still yields to the microtask queue once
+    // per element; the parsed remote lists are hundreds of thousands of lines
+    if (Array.isArray(resolved)) {
+      for (let i = 0, len = resolved.length; i < len; i++) {
+        this.addDomainsetLine(resolved[i]);
       }
+      return;
+    }
+    for await (const line of resolved) {
+      this.addDomainsetLine(line);
     }
   }