Allow disabling import of theme configuration (#8131)

Merge pull request 8131

docs/_docs/configuration/options.md

@@ -72,6 +72,24 @@ class="flag">flags</code> (specified on the command-line) that control them.
         <p><code class="flag">--disable-disk-cache</code></p>
       </td>
     </tr>
+    <tr class="setting">
+      <td>
+        <p class="name">
+          <strong>Ignore theme configuration</strong>
+          <span class="version-badge" title="Introduced in v4.1.0">4.1.0</span>
+        </p>
+        <p class="description">
+          Jekyll 4.0 started allowing themes to bundle a <code>_config.yml</code>
+          to simplify theme-onboarding for new users.
+          In the unfortunate situation that importing a bundled theme configuration
+          messes up the merged site-configuration, the user can configure Jekyll
+          to not import the theme-config entirely.
+        </p>
+      </td>
+      <td class="align-center">
+        <p><code class="option">ignore_theme_config: BOOL</code></p>
+      </td>
+    </tr>
     <tr class="setting">
       <td>
         <p class="name"><strong>Exclude</strong></p>

features/theme_configuration.feature

@@ -11,6 +11,17 @@ Feature: Bundling Config file with Theme gems
     And the _site directory should exist
     And I should see "aero" in "_site/index.html"
 
+  Scenario: Disabling import of theme configuration entirely
+    Given I have a configuration file with:
+      | key                 | value      |
+      | theme               | test-theme |
+      | ignore_theme_config | true       |
+    And I have an "index.md" page that contains "{{ site.test_theme.skin }}"
+    When I run jekyll build
+    Then I should get a zero exit status
+    And the _site directory should exist
+    And I should not see "aero" in "_site/index.html"
+
   Scenario: A pre-configured theme with valid config file overriding Jekyll defaults
     Given I have a configuration file with "theme" set to "test-theme"
     And I have an "index.md" page that contains "{{ site.baseurl }}"

lib/jekyll/site.rb

@@ -432,6 +432,8 @@ module Jekyll
     private
 
     def load_theme_configuration(config)
+      return config if config["ignore_theme_config"] == true
+
       theme_config_file = in_theme_dir("_config.yml")
       return config unless File.exist?(theme_config_file)