Cannot understand what generates warning while serving

Hello, I am getting the following log when running bundle exec jekyll serve --trace --watch, but I have no idea what generates it. Is it Jekyll? Is it a plugin? Is it Ruby?

Configuration file: /Users/tommi/tommi.space/_config.yml
            Source: /Users/tommi/tommi.space
       Destination: /Users/tommi/tommi.space/_site
 Incremental build: disabled. Enable with --incremental
      Generating...
[jekyll-webmention_io] Webmentions won’t be gathered when running `jekyll serve`.
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
       Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
[jekyll-webmention_io] Webmentions lookups are not run when running `jekyll serve`.
[jekyll-webmention_io] A WebmentionIO.js source file will not be generated during `jekyll serve`.
Jekyll-Graph: To generate the tree graph, please either add and enable the 'jekyll-namespaces' plugin  or disable the tree in the jekyll-graph config
         AutoPages: Disabled/Not configured in site.config.
        Pagination: Complete, processed 2 pagination page(s)
       Jekyll Feed: Generating feed for poetry
       Jekyll Feed: Generating feed for notes
       Jekyll Feed: Generating feed for posts
           Warning: Empty `slug` generated for ''.
           Warning: Empty `slug` generated for ''.

Build Process Summary:

| PHASE      |    TIME |
+------------+---------+
| RESET      |  0.0002 |
| READ       |  0.5662 |
| GENERATE   |  3.0381 |
| RENDER     | 21.6354 |
| CLEANUP    |  0.0303 |
| WRITE      |  0.5037 |
+------------+---------+
| TOTAL TIME | 25.7739 |


Site Render Stats:

| Filename                                                           | Count |     Bytes |   Time |
+--------------------------------------------------------------------+-------+-----------+--------+
| _layouts/wrapper.html                                              |   332 | 16807.68K |  8.832 |
| _includes/head.html                                                |   348 |  4135.10K |  8.626 |
| _layouts/jam.html                                                  |   227 |  3369.48K |  1.280 |
| feeds/all.xml                                                      |     1 |  1970.87K |  0.586 |
| _includes/nav.html                                                 |   332 |   233.15K |  0.462 |
| _includes/anchor-parser.html                                       |   298 |  1487.35K |  0.362 |
| _layouts/vuoto.html                                                |    13 |   154.60K |  0.300 |
| _layouts/post.html                                                 |    60 |   947.73K |  0.221 |
| _includes/post-tags.html                                           |   291 |    69.11K |  0.179 |
| _includes/share.html                                               |   291 |  2007.55K |  0.173 |
| _includes/toc.html                                                 |   112 |    64.39K |  0.170 |
| sitemap.xml                                                        |     1 |    35.22K |  0.115 |
| pages/tags.html                                                    |     1 |    80.10K |  0.114 |
| .html                                                              |    14 |   129.18K |  0.077 |
| pages/whole-jam.html                                               |     1 |   138.91K |  0.073 |
| feeds/italiano.xml                                                 |     1 |   725.27K |  0.073 |
| _includes/goto.html                                                |   287 |   160.33K |  0.069 |
| _includes/footer.html                                              |   332 |  4452.85K |  0.053 |
| pages/test.html                                                    |     1 |    40.14K |  0.037 |
| pages/Everyone.html                                                |     1 |    16.44K |  0.034 |
| _includes/backlinks.html                                           |   291 |   108.37K |  0.033 |
| feeds/jam.xml                                                      |     1 |    24.97K |  0.032 |
| jekyll-redirect-from-0.16.0/lib/jekyll-redirect-from/redirect.html |   614 |   283.08K |  0.032 |
| feeds/zibaldone.xml                                                |     1 |   179.36K |  0.031 |
| feeds/poetry.xml                                                   |     1 |    14.99K |  0.030 |
| _notes/public/Apps.html                                            |     1 |    55.06K |  0.022 |
| _notes/public/Website development.md                               |     1 |    21.60K |  0.021 |
| _notes/public/Books.html                                           |     1 |    80.49K |  0.021 |
| _notes/public/People.html                                          |     1 |    10.84K |  0.019 |
| _notes/public/Internet Awesomeness.html                            |     1 |    37.44K |  0.019 |
| _notes/public/Tutto.html                                           |     1 |    48.38K |  0.018 |
| pages/404.html                                                     |     1 |    10.78K |  0.017 |
| pages/Everyone-it.html                                             |     1 |     7.99K |  0.015 |
| pages/index.html                                                   |     1 |    11.78K |  0.015 |
| _notes/public/La Marmellata.html                                   |     1 |    10.05K |  0.013 |
| _includes/webmentions.html                                         |   291 |    25.58K |  0.012 |
| _includes/stuff.html                                               |     2 |    23.37K |  0.012 |
| _notes/public/Quotes.html                                          |     1 |    25.31K |  0.011 |
| _includes/comments.html                                            |   291 |    60.40K |  0.011 |
| _includes/date-it.html                                             |   104 |     2.00K |  0.011 |
| feeds/internet-awesomeness.xml                                     |     1 |    38.03K |  0.009 |
| _layouts/sconnesso.html                                            |     4 |    77.41K |  0.009 |
| _notes/public/Watchlog.md                                          |     1 |    52.55K |  0.008 |
| pages/stuff-it.html                                                |     1 |    12.85K |  0.008 |
| _includes/date-entry-it.html                                       |    76 |     1.47K |  0.008 |
| _notes/public/Parole.html                                          |     1 |    15.28K |  0.006 |
| _includes/jam-graph.html                                           |   227 |   171.10K |  0.006 |
| _includes/tags.html                                                |    17 |    25.83K |  0.006 |
| pages/stuff.html                                                   |     1 |    11.18K |  0.005 |
| _notes/public/Missing digital tools.md                             |     1 |     3.58K |  0.005 |
+--------------------------------------------------------------------+-------+-----------+--------+
| TOTAL (for 50 files)                                               |  4881 | 38476.55K | 22.298 |

                    done in 25.799 seconds.
 Auto-regeneration: enabled for '/Users/tommi/tommi.space'
LiveReload address: http://127.0.0.1:35729
    Server address: http://127.0.0.1:4000/
  Server running... press ctrl-c to stop.

Its a plugin.
The only way to find out which plugin exactly, is by taking out every single one, including those inside _plugins folder, and adding them back, one-by-one and building your site after each re-introduction.
Do not serve until you’ve found the offending plugin as regeneration won’t load new Ruby code.

1 Like

I don’t know what WebMentions is.

But for the deprecation warnings, that looks like in Jekyll itself

bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb

Though the error happens after the Webmentions line starts.

[jekyll-webmention_io] Webmentions won’t be gathered when running `jekyll serve`.
             Deprecation: Document#title is now a key in the #data hash.
       Deprecation: Called by ["/Users/tommi/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/bundler/gems/jekyll-d46bef774a8f/lib/jekyll/document.rb:411:in `method_missing'"].
 

Suggesting that Webmentions is interactive with Jekyll and a method is missing.

Upgrade to new Webmentions and new Jekyll.

I’ve submitted a patch to fix the deprecation warning.
@xplosionmind If you’re using Jekyll 4, you may edit your Gemfile to use the patch directly in your site to easily find the offending plugin.

# Gemfile

gem "jekyll", github: "jekyll/jekyll", ref: "refs/pull/8960/head"

UPDATE: The patch has been merged and will be available from v4.3.0 onwards