Add link checker

Author: rvedotrc

.github/workflows/validate-links.yml

@@ -0,0 +1,25 @@
+---
+name: Validate links
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+
+jobs:
+  build:
+    name: Validate links
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: npm install
+        run: npm install
+      - name: Run the checker
+        run: node dist/validateLinks.js

.prettierignore

@@ -0,0 +1 @@
+/dist/

.tool-versions

@@ -0,0 +1 @@
+nodejs 23.11.0

dist/parse.js

@@ -0,0 +1,35 @@
+import mit from "markdown-it";
+export const parse = (content) => {
+    const parser = mit();
+    const tokens = parser.parse(content, {});
+    const parsedLinks = [];
+    const parsedImages = [];
+    const scan = (tokens) => {
+        tokens.forEach((token, index) => {
+            if (token.type === "link_open") {
+                const indexOfNextClose = tokens.findIndex((t2, i2) => i2 > index && t2.type === "link_close");
+                if (indexOfNextClose > index) {
+                    parsedLinks.push({
+                        target: token.attrGet("href"),
+                        content: tokens
+                            .slice(index + 1, indexOfNextClose)
+                            .map((t) => t.content)
+                            .join(""),
+                    });
+                }
+            }
+            if (token.type === "image")
+                parsedImages.push({
+                    src: token.attrGet("src"),
+                    alt: token.content,
+                });
+            if (token.children)
+                scan(token.children);
+        });
+    };
+    scan(tokens);
+    return {
+        links: parsedLinks,
+        images: parsedImages,
+    };
+};

dist/validateLinks.js

@@ -0,0 +1,87 @@
+import { exec } from "node:child_process";
+import { readFile, stat } from "node:fs/promises";
+import { parse } from "./parse.js";
+import path, { dirname, normalize } from "node:path/posix";
+import { isAbsolute } from "node:path";
+const findMarkdownFilesInGit = async () => {
+    return await new Promise((resolve, reject) => {
+        exec("git ls-files -z", (error, stdout, stderr) => {
+            if (error)
+                reject(error);
+            if (stderr)
+                reject(new Error(`git ls-files outputted on stderr: ${stderr}`));
+            else
+                resolve(stdout.split("\0").filter((s) => s.endsWith(".md")));
+        });
+    });
+};
+const findMarkdownFiles = async () => {
+    const ignorePattern = /^(README|LICENSE|contributing\/)/;
+    return (await findMarkdownFilesInGit()).filter((f) => !ignorePattern.test(f));
+};
+const scanForLinks = async (filenames) => {
+    return Promise.all(filenames.map(async (filename) => {
+        const content = await readFile(filename, "utf-8");
+        return { filename, ...parse(content) };
+    }));
+};
+const externalLinkPattern = /^\w+:/;
+const isExternalLink = (t) => externalLinkPattern.test(t);
+const main = async () => {
+    const markdownFilenames = await findMarkdownFiles();
+    const parsedFiles = await scanForLinks(markdownFilenames);
+    let errors = 0;
+    for (const parsedFile of parsedFiles) {
+        for (const img of parsedFile.images) {
+            if (!isExternalLink(img.src)) {
+                const resolved = path.join(dirname(parsedFile.filename), img.src);
+                const exists = await stat(resolved).then(() => true, () => false);
+                if (!exists) {
+                    console.log(`error BROKEN-INTERNAL-IMAGE ${parsedFile.filename}:0 Broken internal image reference ${img.src}`);
+                    ++errors;
+                }
+            }
+        }
+        for (const link of parsedFile.links) {
+            if (link.target.startsWith("#")) {
+                // Already checked by the linter
+                continue;
+            }
+            if (!isExternalLink(link.target)) {
+                const target = link.target.split("#")[0];
+                let resolved;
+                if (isAbsolute(target)) {
+                    resolved = normalize(`./${target}`);
+                }
+                else {
+                    resolved = normalize(path.join(dirname(parsedFile.filename), target));
+                }
+                const stats = await stat(resolved).catch(() => undefined);
+                if (stats?.isDirectory()) {
+                    const readmeExists = await stat(`${resolved}/README.md`).catch(() => undefined);
+                    if (readmeExists) {
+                        // console.log(
+                        //   `info LINK-TO-DIR-WITH-README ${parsedFile.filename}:0 Link to a directory, which has a README: ${target}`
+                        // );
+                    }
+                    else {
+                        console.log(`error LINK-TO-RAW-DIR ${parsedFile.filename}:0 Link to a directory, which has no README: ${target}`);
+                        ++errors;
+                    }
+                }
+                else if (stats === undefined) {
+                    console.log(`error BROKEN-INTERNAL-LINK ${parsedFile.filename}:0 Link target does not exist: ${target}`);
+                    ++errors;
+                }
+            }
+        }
+    }
+    if (errors > 0) {
+        console.error("Link validation found errors");
+        process.exit(1);
+    }
+};
+main().catch((error) => {
+    console.error(error);
+    process.exit(1);
+});

package-lock.json

@@ -2,5 +2,11 @@
   "dependencies": {
     "markdownlint-cli": "^0.44.0",
     "prettier": "^3.5.3"
+  },
+  "type": "module",
+  "devDependencies": {
+    "@types/markdown-it": "^14.1.2",
+    "@types/node": "^22.14.1",
+    "typescript": "^5.8.3"
   }
 }

package.json

@@ -0,0 +1,60 @@
+import mit from "markdown-it";
+import type { Token } from "markdown-it/index.js";
+
+export type ParsedLink = {
+  readonly target: string;
+  readonly content: string;
+};
+
+export type ParsedImage = {
+  readonly src: string;
+  readonly alt: string;
+};
+
+export type ParseResult = {
+  readonly links: readonly ParsedLink[];
+  readonly images: readonly ParsedImage[];
+};
+
+export const parse = (content: string): ParseResult => {
+  const parser = mit();
+  const tokens = parser.parse(content, {});
+
+  const parsedLinks: ParsedLink[] = [];
+  const parsedImages: ParsedImage[] = [];
+
+  const scan = (tokens: Token[]) => {
+    tokens.forEach((token, index) => {
+      if (token.type === "link_open") {
+        const indexOfNextClose = tokens.findIndex(
+          (t2, i2) => i2 > index && t2.type === "link_close",
+        );
+
+        if (indexOfNextClose > index) {
+          parsedLinks.push({
+            target: token.attrGet("href") as string,
+            content: tokens
+              .slice(index + 1, indexOfNextClose)
+              .map((t) => t.content)
+              .join(""),
+          });
+        }
+      }
+
+      if (token.type === "image")
+        parsedImages.push({
+          src: token.attrGet("src") as string,
+          alt: token.content,
+        });
+
+      if (token.children) scan(token.children);
+    });
+  };
+
+  scan(tokens);
+
+  return {
+    links: parsedLinks,
+    images: parsedImages,
+  };
+};