detect broken links

src/build.ts

@@ -365,9 +365,37 @@ export async function build(
   }
   effects.logger.log("");
 
+  // Check links. TODO Have this break the build, and move this check earlier?
+  const [validLinks, brokenLinks] = validateLinks(outputs);
+  if (brokenLinks.length) {
+    effects.logger.warn(`${yellow("Warning: ")}${brokenLinks.length} broken link${brokenLinks.length === 1 ? "" : "s"} (${validLinks.length + brokenLinks.length} validated)`); // prettier-ignore
+    for (const [path, link] of brokenLinks) effects.logger.log(`${faint("↳")} ${path} ${faint("→")} ${red(link)}`);
+  } else if (validLinks.length) {
+    effects.logger.log(`${green(`${validLinks.length}`)} link${validLinks.length === 1 ? "" : "s"} validated`);
+  }
+
   Telemetry.record({event: "build", step: "finish", pageCount});
 }
 
+type Link = [path: string, target: string];
+
+function validateLinks(outputs: Map<string, {resolvers: Resolvers}>): [valid: Link[], broken: Link[]] {
+  const validTargets = new Set<string>(outputs.keys()); // e.g., "/this/page#hash";
+  for (const [path, {resolvers}] of outputs) {
+    for (const anchor of resolvers.anchors) {
+      validTargets.add(`${path}#${encodeURIComponent(anchor)}`);
+    }
+  }
+  const valid: Link[] = [];
+  const broken: Link[] = [];
+  for (const [path, {resolvers}] of outputs) {
+    for (const target of resolvers.localLinks) {
+      (validTargets.has(target) ? valid : broken).push([path, target]);
+    }
+  }
+  return [valid, broken];
+}
+
 function applyHash(path: string, hash: string): string {
   const ext = extname(path);
   let name = basename(path, ext);

src/html.ts

@@ -3,7 +3,7 @@ import he from "he";
 import hljs from "highlight.js";
 import type {DOMWindow} from "jsdom";
 import {JSDOM, VirtualConsole} from "jsdom";
-import {isAssetPath, relativePath, resolveLocalPath} from "./path.js";
+import {isAssetPath, parseRelativeUrl, relativePath, resolveLocalPath, resolvePath} from "./path.js";
 
 const ASSET_ATTRIBUTES: readonly [selector: string, src: string][] = [
   ["a[href][download]", "href"],
@@ -41,6 +41,8 @@ export function parseHtml(html: string): DOMWindow {
 
 interface Assets {
   files: Set<string>;
+  anchors: Set<string>;
+  localLinks: Set<string>;
   localImports: Set<string>;
   globalImports: Set<string>;
   staticImports: Set<string>;
@@ -49,6 +51,8 @@ interface Assets {
 export function findAssets(html: string, path: string): Assets {
   const {document} = parseHtml(html);
   const files = new Set<string>();
+  const anchors = new Set<string>();
+  const localLinks = new Set<string>();
   const localImports = new Set<string>();
   const globalImports = new Set<string>();
   const staticImports = new Set<string>();
@@ -99,7 +103,20 @@ export function findAssets(html: string, path: string): Assets {
     }
   }
 
-  return {files, localImports, globalImports, staticImports};
+  for (const element of document.querySelectorAll<HTMLElement>("[id],[name]")) {
+    if (isExternal(element)) continue;
+    anchors.add(element.getAttribute("id") ?? element.getAttribute("name")!);
+  }
+
+  for (const a of document.querySelectorAll<HTMLAnchorElement>("a[href]")) {
+    if (isExternal(a) || a.hasAttribute("download")) continue;
+    const href = a.getAttribute("href")!;
+    if (/^\w+:/.test(href)) continue; // URL
+    const {pathname, search, hash} = parseRelativeUrl(href);
+    localLinks.add(resolvePath(path, pathname).replace(/\.html$/i, "").replace(/\/$/, "/index") + search + hash); // prettier-ignore
+  }
+
+  return {files, localImports, globalImports, staticImports, localLinks, anchors};
 }
 
 export function rewriteHtmlPaths(html: string, path: string): string {

src/path.ts

@@ -32,7 +32,7 @@ export function resolvePath(root: string, source: string, target: string): strin
 export function resolvePath(root: string, source: string, target?: string): string {
   if (target === undefined) (target = source), (source = root), (root = ".");
   const path = join(root, target === "" ? source : target.startsWith("/") ? "." : dirname(source), target);
-  return path.startsWith("../") ? path : `/${path}`;
+  return path.startsWith("../") ? path : join("/", path);
 }
 
 /**

src/resolvers.ts

@@ -19,6 +19,8 @@ export interface Resolvers {
   hash: string;
   assets: Set<string>; // like files, but not registered for FileAttachment
   files: Set<string>;
+  anchors: Set<string>;
+  localLinks: Set<string>;
   localImports: Set<string>;
   globalImports: Set<string>;
   staticImports: Set<string>;
@@ -88,6 +90,8 @@ export async function getResolvers(page: MarkdownPage, config: ResolversConfig):
   const assets = new Set<string>();
   const files = new Set<string>();
   const fileMethods = new Set<string>();
+  const anchors = new Set<string>();
+  const localLinks = new Set<string>();
   const localImports = new Set<string>();
   const globalImports = new Set<string>(defaultImports);
   const staticImports = new Set<string>(defaultImports);
@@ -98,6 +102,8 @@ export async function getResolvers(page: MarkdownPage, config: ResolversConfig):
     if (!html) continue;
     const info = findAssets(html, path);
     for (const f of info.files) assets.add(f);
+    for (const a of info.anchors) anchors.add(a);
+    for (const l of info.localLinks) localLinks.add(l);
     for (const i of info.localImports) localImports.add(i);
     for (const i of info.globalImports) globalImports.add(i);
     for (const i of info.staticImports) staticImports.add(i);
@@ -151,6 +157,8 @@ export async function getResolvers(page: MarkdownPage, config: ResolversConfig):
     path,
     hash: hash.digest("hex"),
     assets,
+    anchors,
+    localLinks,
     ...(await resolveResolvers(
       {
         files,
@@ -172,6 +180,8 @@ export async function getModuleResolvers(path: string, config: Omit<ResolversCon
     path,
     hash: getModuleHash(root, path),
     assets: new Set(),
+    anchors: new Set(),
+    localLinks: new Set(),
     ...(await resolveResolvers({localImports: [path], staticImports: [path]}, {path, ...config}))
   };
 }
@@ -193,7 +203,7 @@ async function resolveResolvers(
     stylesheets?: Iterable<string> | null;
   },
   {root, path, normalizePath, loaders}: ResolversConfig
-): Promise<Omit<Resolvers, "path" | "hash" | "assets">> {
+): Promise<Omit<Resolvers, "path" | "hash" | "assets" | "anchors" | "localLinks">> {
   const files = new Set<string>(initialFiles);
   const fileMethods = new Set<string>(initialFileMethods);
   const localImports = new Set<string>(initialLocalImports);

test/html-test.ts

@@ -100,6 +100,26 @@ describe("findAssets(html, path)", () => {
     const html = '<script src="test.js" type="other">';
     assert.deepStrictEqual(findAssets(html, "foo").files, new Set(["./test.js"]));
   });
+  it("finds anchors by [id] or [name]", () => {
+    const html = '<a id="id1">foo</a> <a name="id2">bar</a>';
+    assert.deepStrictEqual(findAssets(html, "foo").anchors, new Set(["id1", "id2"]));
+  });
+  it("finds local links by a[href]", () => {
+    const html = '<a href="#anchor">a</a> <a href="other#baz">b</a> <a href="?test">self</a>';
+    assert.deepStrictEqual(findAssets(html, "foo").localLinks, new Set(["/foo#anchor", "/other#baz", "/foo?test"]));
+  });
+  it("finds relative links", () => {
+    const html = '<a href="./test">a</a>';
+    assert.deepStrictEqual(findAssets(html, "foo/bar").localLinks, new Set(["/foo/test"]));
+  });
+  it("finds links that go up", () => {
+    const html = '<a href="../test">a</a>';
+    assert.deepStrictEqual(findAssets(html, "foo/bar").localLinks, new Set(["/test"]));
+  });
+  it("finds links that go above the root", () => {
+    const html = '<a href="../test">a</a>';
+    assert.deepStrictEqual(findAssets(html, "foo").localLinks, new Set(["../test"]));
+  });
 });
 
 describe("rewriteHtml(html, resolve)", () => {

test/path-test.ts

@@ -4,13 +4,16 @@ import {isPathImport, parseRelativeUrl, relativePath, resolveLocalPath, resolveP
 describe("resolvePath(source, target)", () => {
   it("returns the path to the specified target within the source root", () => {
     assert.strictEqual(resolvePath("foo", "baz"), "/baz");
+    assert.strictEqual(resolvePath("foo", "./"), "/");
     assert.strictEqual(resolvePath("./foo", "./baz"), "/baz");
     assert.strictEqual(resolvePath("/foo", "baz"), "/baz");
     assert.strictEqual(resolvePath("/foo", "./baz"), "/baz");
     assert.strictEqual(resolvePath("foo/bar", "baz"), "/foo/baz");
+    assert.strictEqual(resolvePath("foo/bar", "./"), "/foo/");
     assert.strictEqual(resolvePath("./foo/bar", "./baz"), "/foo/baz");
     assert.strictEqual(resolvePath("/foo/bar", "baz"), "/foo/baz");
     assert.strictEqual(resolvePath("/foo/bar", "./baz"), "/foo/baz");
+    assert.strictEqual(resolvePath("/foo/bar", "../"), "/");
   });
   it("allows paths outside the root", () => {
     assert.strictEqual(resolvePath("foo", "../baz"), "../baz");