fix: _print output respects relativeURLs=true (#2638)

tests/print-relative-urls.test.mjs

@@ -0,0 +1,57 @@
+// Regression guard for google/docsy#2638: the `_print` output format did not
+// respect `relativeURLs = true`, so printable pages emitted absolute (root-
+// relative) asset URLs while the rest of the site emitted relative ones. This
+// broke offline/local viewing of `_print/*` (missing CSS, JS, and images) and
+// local HTML-to-PDF conversion.
+//
+// Mechanism: Hugo only runs its relativeURLs search-and-replace pass on output
+// formats classified as HTML (`isHTML: true`). The print format had `isHTML`
+// left unset as a workaround for gohugoio/hugo#14381 (relative *alias*
+// generation). That workaround is no longer needed: the print format sets
+// `permalinkable: false`, and Hugo only generates the aliases #14381 concerned
+// when both `isHTML` and `permalinkable` are true — so enabling `isHTML` never
+// exercises that path here.
+//
+// TDD trace: red with `isHTML` unset on the print format, green with
+// `isHTML: true` (theme/hugo.yaml). Verified on hugo-extended@0.161.1
+// (theme min is 0.160.1).
+
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { buildSite } from './lib/build-site.mjs';
+
+test('print output respects relativeURLs=true (no absolute asset URLs)', () => {
+  const r = buildSite('print-relative-urls', {
+    extraConfig: [
+      'relativeURLs: true',
+      'outputs:',
+      '  section: [HTML, print]',
+      '',
+    ].join('\n'),
+    files: {
+      'content/docs/_index.md': '---\ntitle: Docs\n---\n\nSection landing.\n',
+      'content/docs/page-one.md':
+        '---\ntitle: Page One\n---\n\nContent of page one.\n',
+    },
+  });
+  assert.equal(r.status, 0, `hugo build failed:\n${r.stdout}${r.stderr}`);
+
+  const html = r.publicFile('_print/docs/index.html');
+
+  // The bug: assets referenced with a leading-slash (absolute) URL. With the
+  // fix these are rewritten relative to the print page, like the rest of the
+  // site. The site CSS/JS are Hugo resource RelPermalinks — the same code path
+  // that carries processed-image URLs — so this guards the image symptom too.
+  assert.doesNotMatch(
+    html,
+    /(?:src|href)="\/[^"/][^"]*\.(?:css|js)"/,
+    'print page must not emit absolute (leading-slash) asset URLs',
+  );
+
+  // Positive check: the main stylesheet is referenced with a page-relative URL.
+  assert.match(
+    html,
+    /href="(?:\.\.\/)+scss\/main\.min\.[0-9a-f]+\.css"/,
+    'print page must reference the site CSS with a relative URL',
+  );
+});

theme/hugo.yaml

@@ -15,9 +15,7 @@ outputFormats:
     notAlternative: true
   print:
     baseName: index
-    # FIXME: leave isHTML unset (i.e. false) until we get a Hugo fix for
-    # https://github.com/gohugoio/hugo/issues/14381
-    # isHTML: true
+    isHTML: true
     mediaType: text/html
     path: _print
     permalinkable: false