doc,tools: get altDocs versions from CHANGELOG.md

Parse `CHANGELOG.md` for versions of Node.js used by the documentation
feature `View another version` so that we don't have to manually update
the list when we cut a new version or transition a release to LTS.

PR-URL: https://github.com/nodejs/node/pull/27661
Reviewed-By: Rich Trott <rtrott@gmail.com>

2 files changed, 50 insertions, 16 deletions

diff --git a/tools/doc/html.js b/tools/doc/html.js
index efdc8b0d47..318feefe34 100644
--- a/tools/doc/html.js
+++ b/tools/doc/html.js
@@ -23,6 +23,7 @@
 
 const common = require('./common.js');
 const fs = require('fs');
+const getVersions = require('./versions.js');
 const unified = require('unified');
 const find = require('unist-util-find');
 const visit = require('unist-util-visit');
@@ -62,7 +63,7 @@ const gtocHTML = unified()
 const templatePath = path.join(docPath, 'template.html');
 const template = fs.readFileSync(templatePath, 'utf8');
 
-function toHTML({ input, content, filename, nodeVersion }, cb) {
+async function toHTML({ input, content, filename, nodeVersion }, cb) {
   filename = path.basename(filename, '.md');
 
   const id = filename.replace(/\W+/g, '-');
@@ -80,7 +81,7 @@ function toHTML({ input, content, filename, nodeVersion }, cb) {
   const docCreated = input.match(
     /<!--\s*introduced_in\s*=\s*v([0-9]+)\.([0-9]+)\.[0-9]+\s*-->/);
   if (docCreated) {
-    HTML = HTML.replace('__ALTDOCS__', altDocs(filename, docCreated));
+    HTML = HTML.replace('__ALTDOCS__', await altDocs(filename, docCreated));
   } else {
     console.error(`Failed to add alternative version links to ${filename}`);
     HTML = HTML.replace('__ALTDOCS__', '');
@@ -390,22 +391,10 @@ function getId(text, idCounters) {
   return text;
 }
 
-function altDocs(filename, docCreated) {
+async function altDocs(filename, docCreated) {
   const [, docCreatedMajor, docCreatedMinor] = docCreated.map(Number);
   const host = 'https://nodejs.org';
-  const versions = [
-    { num: '12.x' },
-    { num: '11.x' },
-    { num: '10.x', lts: true },
-    { num: '9.x' },
-    { num: '8.x', lts: true },
-    { num: '7.x' },
-    { num: '6.x' },
-    { num: '5.x' },
-    { num: '4.x' },
-    { num: '0.12.x' },
-    { num: '0.10.x' },
-  ];
+  const versions = await getVersions.versions();
 
   const getHref = (versionNum) =>
     `${host}/docs/latest-v${versionNum}/api/${filename}.html`;
diff --git a/tools/doc/versions.js b/tools/doc/versions.js
new file mode 100644
index 0000000000..854329bd9a
--- /dev/null
+++ b/tools/doc/versions.js
@@ -0,0 +1,45 @@
+'use strict';
+
+let _versions;
+
+const getUrl = (url) => {
+  return new Promise((resolve, reject) => {
+    const https = require('https');
+    const request = https.get(url, (response) => {
+      if (response.statusCode !== 200) {
+        reject(new Error(
+          `Failed to get ${url}, status code ${response.statusCode}`));
+      }
+      response.setEncoding('utf8');
+      let body = '';
+      response.on('data', (data) => body += data);
+      response.on('end', () => resolve(body));
+    });
+    request.on('error', (err) => reject(err));
+  });
+};
+
+module.exports = {
+  async versions() {
+    if (_versions) {
+      return _versions;
+    }
+
+    // The CHANGELOG.md on release branches may not reference newer semver
+    // majors of Node.js so fetch and parse the version from the master branch.
+    const githubContentUrl = 'https://raw.githubusercontent.com/nodejs/node/';
+    const changelog = await getUrl(`${githubContentUrl}/master/CHANGELOG.md`);
+    const ltsRE = /Long Term Support/i;
+    const versionRE = /\* \[Node\.js ([0-9.]+)\][^-—]+[-—]\s*(.*)\n/g;
+    _versions = [];
+    let match;
+    while ((match = versionRE.exec(changelog)) != null) {
+      const entry = { num: `${match[1]}.x` };
+      if (ltsRE.test(match[2])) {
+        entry.lts = true;
+      }
+      _versions.push(entry);
+    }
+    return _versions;
+  }
+};