Fix some outstanding bugs in the docs linter.

scripts/_lint-docs/lint-http-link.js

@@ -28,9 +28,9 @@ function checkKnownCorrectRequestFail(href, headers, status, body) {
 
 /**
  * Returns `undefined` if no error, a string if an error does occur.
- * @param {(message?: string)} callback
+ * @param {(message?: string) => void} callback
  */
-function checkHttp(href, callback) {
+function checkHttpInner(href, callback) {
 	// Prefer https: > http: where possible, but allow http: when https: is inaccessible.
 
 	const url = new URL(href)
@@ -67,6 +67,39 @@ function checkHttp(href, callback) {
 	})
 }
 
+// Kill the remaining duplication by using a global cache.
+const urlCache = new Map()
+
+/**
+ * Returns `undefined` if no error, a string if an error does occur.
+ * @param {(message?: string) => void} callback
+ */
+function checkHttp(href, callback) {
+	if (href.includes("#")) {
+		process.exitCode = 1
+		callback(`Expected href to be sanitized of hashes, but found ${href}`)
+	}
+
+	if (urlCache.has(href)) {
+		const message = urlCache.get(href)
+		if (Array.isArray(message)) {
+			message.push(callback)
+		} else {
+			process.nextTick(callback, message)
+		}
+	} else {
+		const queue = []
+		urlCache.set(href, queue)
+		checkHttpInner(href, (message) => {
+			urlCache.set(href, message)
+			process.nextTick(callback, message)
+			for (const callback of queue) {
+				process.nextTick(callback, message)
+			}
+		})
+	}
+}
+
 module.exports = {
 	checkHttp,
 }

scripts/_lint-docs/task-queue.js

@@ -9,7 +9,7 @@ let running = 0
 function runTask(task, callback) {
 	process.nextTick(task, (...args) => {
 		process.nextTick(callback, ...args)
-		if (running === maxConcurrency) {
+		if (running === maxConcurrency && queue.length !== 0) {
 			const [nextTask, nextCallback] = queue.splice(0, 2)
 			runTask(nextTask, nextCallback)
 		}
@@ -22,6 +22,14 @@ function runTask(task, callback) {
  * @param {(...args: A) => void} callback
  */
 function submitTask(task, callback) {
+	if (typeof task !== "function") {
+		throw new TypeError("`task` must be a function")
+	}
+
+	if (typeof callback !== "function") {
+		throw new TypeError("`callback` must be a function")
+	}
+
 	if (running < maxConcurrency) {
 		running++
 		runTask(task, callback)