Raise when DB schema version comment is missing

lib/que/migrations.rb

@@ -48,14 +48,41 @@ def db_version
           # No table in the database at all.
           0
         elsif (d = result.first[:description]).nil?
-          # There's a table, it was just created before the migration system
-          # existed.
-          1
+          # The table exists but the version comment is missing
+          if _db_schema_matches_db_version_1?
+            1
+          else
+            _raise_db_version_comment_missing_error
+          end
         else
           d.to_i
         end
       end
 
+      # The que_jobs table could be missing the schema version comment either due to:
+      # - Being created before the migration system existed (matching DB version 1); or
+      # - A bug in Rails schema dump in some versions of Rails
+      # So to determine which is the case, here we check an aspect of the schema that's only like that if just the first migration has been applied
+      def _db_schema_matches_db_version_1?
+        result =
+          Que.execute <<-SQL
+            SELECT column_default AS default_priority
+            FROM information_schema.columns
+            WHERE (table_schema, table_name, column_name) = ('public', 'que_jobs', 'priority');
+          SQL
+        result.first[:default_priority] == '1'
+      end
+
+      def _raise_db_version_comment_missing_error
+        raise Error, <<~ERROR
+          Cannot determine Que DB schema version.
+
+          The que_jobs table is abnormally missing its comment recording the Que DB schema version. This is likely due to a bug in Rails schema dump in Rails 7 versions prior to 7.0.3, omitting comments - see https://github.com/que-rb/que/issues/363. Please determine the appropriate schema version from your migrations and record it manually by running the following SQL (replacing version as appropriate):
+
+          COMMENT ON TABLE que_jobs IS 'version';
+        ERROR
+      end
+
       def set_db_version(version)
         i = version.to_i
         Que.execute "COMMENT ON TABLE que_jobs IS '#{i}'" unless i.zero?

spec/que/migrations_spec.rb

@@ -63,25 +63,41 @@
     assert DB.table_exists?(:que_jobs)
   end
 
-  it "should be able to recognize a que_jobs table at version 0" do
+  it "should be able to honor the original behavior of Que.create!" do
     Que.migrate! version: 0
-    DB.create_table(:que_jobs){serial :id} # Dummy Table.
+    Que.create!
+    assert DB.table_exists?(:que_jobs)
     assert_equal 1, Que::Migrations.db_version
-    DB.drop_table(:que_jobs)
-    Que.migrate!(version: Que::Migrations::CURRENT_VERSION)
+
+    # Clean up.
+    Que::Migrations.migrate!(version: Que::Migrations::CURRENT_VERSION)
+    assert DB.table_exists?(:que_jobs)
   end
 
-  it "should be able to honor the original behavior of Que.create!" do
-    Que.migrate! version: 0
+  it "should be able to determine the db version when the que_jobs table was created prior to the existence of the migrations system" do
+    Que.migrate!(version: 0)
     Que.create!
-    assert DB.table_exists?(:que_jobs)
+    Que.execute("COMMENT ON TABLE que_jobs IS NULL") # Simulate migrations system not existing yet
     assert_equal 1, Que::Migrations.db_version
 
     # Clean up.
     Que::Migrations.migrate!(version: Que::Migrations::CURRENT_VERSION)
     assert DB.table_exists?(:que_jobs)
   end
 
+  it "should raise if the db version comment is missing abnormally due to a bug in Rails schema dump" do
+    Que::Migrations.migrate!(version: Que::Migrations::CURRENT_VERSION)
+    Que.execute("COMMENT ON TABLE que_jobs IS NULL") # Simulate bug in Rails schema dump
+
+    assert_raises_with_message(Que::Error, /^Cannot determine Que DB schema version./) do
+      Que::Migrations.migrate!(version: Que::Migrations::CURRENT_VERSION)
+    end
+
+    # Clean up.
+    Que.execute("COMMENT ON TABLE que_jobs IS '#{Que::Migrations::CURRENT_VERSION}'")
+    assert_equal Que::Migrations::CURRENT_VERSION, Que::Migrations.db_version
+  end
+
   it "down migrations should precisely undo what the up migrations did" do
     Que.migrate! version: 0
     versions = (1..Que::Migrations::CURRENT_VERSION).to_a