Fix: resolve release notes for a prerelease tag

api/test/changelog.test.js

@@ -173,3 +173,13 @@ test('release notes are the section body without the link definitions', () => {
   assert.equal(notesFor(sample, 'v1.1.0'), notes);
   assert.equal(notesFor(sample, '9.9.9'), null);
 });
+
+/* A beta is tagged before its section is dated, so it has none of its own. With
+   no fallback the release page step fails after the image has published. */
+test('a prerelease falls back to its base version, then to Unreleased', () => {
+  assert.match(notesFor(sample, 'v1.2.0-beta.1'), /Widget for the doorbell\./);
+  assert.equal(notesFor(sample, 'v1.1.0-beta.1'), notesFor(sample, '1.1.0'));
+
+  const nothingPending = sample.replace('### Added\n\n- Widget for the doorbell.\n\n', '');
+  assert.equal(notesFor(nothingPending, 'v1.2.0-beta.1'), null);
+});

scripts/release-notes.js

@@ -11,10 +11,30 @@ const cl = require('./changelog.js');
 
 const ROOT = path.join(__dirname, '..');
 
+/** The section a tag describes.
+
+    A prerelease has no section of its own: the changelog is dated when the
+    stable version is cut. `v1.8.0-beta.1` reads the 1.8.0 section if it already
+    exists, and [Unreleased] otherwise, which is what it is a candidate for.
+
+    @param {string} markdown @param {string} version */
+function sectionFor(doc, version) {
+  const name = version.replace(/^v/, '');
+  const exact = doc.versions.find(v => v.name === name);
+  if (exact) return exact;
+  const parsed = cl.parseTagName(name);
+  if (!parsed || !parsed.prerelease) return null;
+  const base = `${parsed.major}.${parsed.minor}.${parsed.patch}`;
+  const stable = doc.versions.find(v => v.name === base);
+  if (stable) return stable;
+  const unreleased = cl.unreleased(doc);
+  return unreleased && unreleased.sections.length ? unreleased : null;
+}
+
 /** @param {string} markdown @param {string} version */
 function notesFor(markdown, version) {
   const doc = cl.parse(markdown);
-  const wanted = doc.versions.find(v => v.name === version.replace(/^v/, ''));
+  const wanted = sectionFor(doc, version);
   if (!wanted) return null;
   const next = doc.versions[doc.versions.indexOf(wanted) + 1];
   const end = next ? next.line - 1 : doc.lines.length;