Allow extensionless document in a strict site (#7950)

Merge pull request 7950

features/collections.feature

@@ -624,3 +624,36 @@ Feature: Collections
     Then I should get a zero exit status
     And the _site directory should exist
     And I should see "I have no front matter." in "_site/methods/extensionless_static_file"
+
+  Scenario: Rendered collection with an extensionless document
+    Given I have fixture collections
+    And I have a "_config.yml" file with content:
+    """
+    collections:
+      methods:
+        output: true
+    """
+    When I run jekyll build
+    Then I should get a zero exit status
+    And the _site directory should exist
+    And I should see "I have no file extension but I should still be a part of the collection." in "_site/methods/collection/entries"
+
+  Scenario: Rendered collection with an extensionless document in a strict site
+    Given I have fixture collections
+    And I have a _posts directory
+    And I have an "_posts/2019-12-26-extensioned.md" file that contains "Hello!"
+    And I have an "_posts/2019-12-26-extensionless" file that contains "Aloha!"
+    And I have an "index.md" page that contains "{{ site.posts | map: 'title' }}"
+    And I have a "_config.yml" file with content:
+    """
+    strict_front_matter: true
+    collections:
+      methods:
+        output: true
+    """
+    When I run jekyll build
+    Then I should get a zero exit status
+    And the _site directory should exist
+    And I should see "I have no file extension but I should still be a part of the collection." in "_site/methods/collection/entries"
+    And I should see "Extensioned" in "_site/index.html"
+    But I should not see "Extensionless" in "_site/index.html"

lib/jekyll/document.rb

@@ -498,6 +498,7 @@ module Jekyll
       end
     end
 
+    # rubocop:disable Metrics/AbcSize
     def populate_title
       if relative_path =~ DATE_FILENAME_MATCHER
         date, slug, ext = Regexp.last_match.captures
@@ -505,6 +506,10 @@ module Jekyll
       elsif relative_path =~ DATELESS_FILENAME_MATCHER
         slug, ext = Regexp.last_match.captures
       end
+      # `slug` will be nil for documents without an extension since the regex patterns
+      # above tests for an extension as well.
+      # In such cases, assign `basename_without_ext` as the slug.
+      slug ||= basename_without_ext
 
       # slugs shouldn't end with a period
       # `String#gsub!` removes all trailing periods (in comparison to `String#chomp!`)
@@ -516,6 +521,7 @@ module Jekyll
       data["slug"]  ||= slug
       data["ext"]   ||= ext
     end
+    # rubocop:enable Metrics/AbcSize
 
     def modify_date(date)
       if !data["date"] || data["date"].to_i == site.time.to_i