Special treat when the first line ends with a dot [ci skip]

tool/sync_default_gems.rb

@@ -449,7 +449,11 @@ module SyncDefaultGems
     log.delete!("\r")
     log << "\n" if !log.end_with?("\n")
     repo_url = "https://github.com/#{repo}"
-    subject, log = log.split(/\n(?:[ \t]*(?:\n|\z))/, 2)
+
+    # Split the subject from the log message according to git conventions.
+    # SPECIAL TREAT: when the first line ends with a dot `.` (which is not
+    # obeying the conventions too), takes only that line.
+    subject, log = log.split(/\A.+\.\K\n(?=\S)|\n(?:[ \t]*(?:\n|\z))/, 2)
     conv = proc do |s|
       mod = true if s.gsub!(/\b(?:(?i:fix(?:e[sd])?|close[sd]?|resolve[sd]?) +)\K#(?=\d+\b)|\bGH-#?(?=\d+\b)|\(\K#(?=\d+\))/) {
         "#{repo_url}/pull/"

tool/test/test_sync_default_gems.rb

@@ -73,6 +73,15 @@ module Test_SyncDefaultGems
       ]
       assert_message_filter(expected, trailers, [expected, "", trailers].join("\n"))
     end
+
+    def test_dot_ending_subject
+      expected = [
+        "subject with a dot.",
+        "",
+        "- next body line",
+      ]
+      assert_message_filter(expected, nil, [expected[0], expected[2], ""].join("\n"))
+    end
   end
 
   class TestSyncWithCommits < Test::Unit::TestCase