Wrong category link when post is contained in multiple listings

[kasbah]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

Category links go to the wrong location when there are multiple listings.

We have this issue on https://topos.institute

Minimal reproduction: https://github.com/ToposInstitute/quarto-category-link-bug-repro

Steps to reproduce

git clone https://github.com/ToposInstitute/quarto-category-link-bug-repro.git
cd quarto-category-link-bug-repro
quarto preview

• http://localhost:5142/
• Go to "Post one"
• Click on the "Alpha" category

Actual behavior

Goes to http://localhost:5142/index.html#category=alpha which does not filter by category

Expected behavior

Goes to http://localhost:5142/blog/index.html#category=alpha

LLM diagnosis:

Root cause

src/resources/formats/html/quarto.js defines findNearestParentListing:

const findNearestParentListing = (href, listingHrefs) => {
  if (!href || !listingHrefs) return undefined;
  const relativeParts = href.substring(1).split("/");
  while (relativeParts.length > 0) {
    const path = relativeParts.join("/");           // "blog/post-one/", "blog/post-one", "blog", ""
    for (const listingHref of listingHrefs) {
      if (listingHref.startsWith(path)) return listingHref; // listingHref is "/blog/index.html"
    }
    relativeParts.pop();
  }
  return undefined;
};

listingHrefs entries always begin with / (e.g. /blog/index.html,
/index.html); path is built without a leading slash. So
"/blog/index.html".startsWith("blog/post-one/") is false, and so are all
later iterations until path === "", which matches every listing. The
function therefore returns listingHrefs[0] — whatever happens to be first.

In this repro /index.html ends up first in listings.json, so all post
categories link to the home page.

Suggested fix

Compare against a leading slash, or use a "longest-directory-prefix" match:

const findNearestParentListing = (href, listingHrefs) => {
  if (!href || !listingHrefs?.length) return undefined;
  const postDir = href.replace(/[^/]+$/, "");        // "/blog/post-one/"
  let best, bestLen = -1;
  for (const listingHref of listingHrefs) {
    const listingDir = listingHref.replace(/[^/]+$/, ""); // "/blog/"
    if (postDir.startsWith(listingDir) && listingDir.length > bestLen) {
      best = listingHref;
      bestLen = listingDir.length;
    }
  }
  return best;
};

Your environment

NixOS
Quarto 1.10.3 pre-release

Quarto check output

Quarto 1.10.3
[✓] Checking environment information...
      Quarto cache location: /home/kaspar/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.8.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.4.5: OK
      Typst version 0.14.2: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.10.3
      Path: /nix/store/0nyh651yyjjd03l8mhdj1csrj4c7jnd4-quarto-1.10.3/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chrome Headless Shell: (not installed)
      VeraPDF: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /nix/store/ig6nbiwhs9zp54vzaj2ry00pzcs88lbx-texlive-combined-2025/bin
      Version: undefined

[✓] Checking Chrome Headless....................OK
      Chrome:  (not detected)

[✓] Checking basic markdown render....OK

[✓] Checking R installation...........OK
      Version: 4.5.3
      Path: /nix/store/fcw23ybidpqhmpb9vy0mw1056kwrshj3-R-4.5.3/lib/R
      LibPaths:
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      knitr: 1.51
      rmarkdown: 2.30

[✓] Checking Knitr engine render......OK

[✓] Checking Python 3 installation....OK
      Version: 3.13.12
      Path: /run/current-system/sw/bin/python3
      Jupyter: (None)

      Jupyter is not available in this Python installation.
      Install with python3 -m pip install jupyter

[✓] Checking Julia installation...

[mcanouil]

Thanks.
Please avoid posting unverified LLM output as diagnosis.

The bug is real, but the mechanism in your post is wrong:

• findNearestParentListing does not return listingHrefs[0].
  Loop guard is while (relativeParts.length > 0), so path === "" only happens when input href is / itself.
  For /blog/post-one/index.html the loop pops down to [] and exits, returning undefined.
• Wrong listing actually comes from the fallback: when findNearestParentListing returns undefined, the code matches document.referrer against listingHrefs, then defaults to listingHrefs[0].
  In your repro the referrer is /index.html (you click through from the home preview), so that branch wins.
  Hence /index.html#category=alpha.
• Suggested fix (longest-directory-prefix with replace(/[^/]+$/, "")) seems correct.