Annotate return types of abstract methods

src/sqlite3/connection.cr

@@ -12,11 +12,11 @@ class SQLite3::Connection < DB::Connection
     URI.unescape((uri.host || "") + uri.path)
   end
 
-  def build_prepared_statement(query)
+  def build_prepared_statement(query) : Statement
     Statement.new(self, query)
   end
 
-  def build_unprepared_statement(query)
+  def build_unprepared_statement(query) : Statement
     # sqlite3 does not support unprepared statement.
     # All statements once prepared should be released
     # when unneeded. Unprepared statement are not aim

src/sqlite3/driver.cr

@@ -1,5 +1,5 @@
 class SQLite3::Driver < DB::Driver
-  def build_connection(context : DB::ConnectionContext)
+  def build_connection(context : DB::ConnectionContext) : SQLite3::Connection
     SQLite3::Connection.new(context)
   end
 end

src/sqlite3/result_set.cr

@@ -9,7 +9,7 @@ class SQLite3::ResultSet < DB::ResultSet
   # Advances to the next row. Returns `true` if there's a next row,
   # `false` otherwise. Must be called at least once to advance to the first
   # row.
-  def move_next
+  def move_next : Bool
     @column_index = 0
 
     case step
@@ -79,11 +79,11 @@ class SQLite3::ResultSet < DB::ResultSet
     read(Int64?).try &.!=(0)
   end
 
-  def column_count
+  def column_count : Int32
     LibSQLite3.column_count(self)
   end
 
-  def column_name(index)
+  def column_name(index) : String
     String.new LibSQLite3.column_name(self, index)
   end