feat: close the adapter's connection on quit (#518)

This change introduces a new optional method of HarlequinConnection
implementations in adapters, giving them an opportunity to cleanly close
the connection to the underlying database when the app exists.

The `close()` method is called in the `action_quit()` handler.

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+### Features
+
+-   A new `HarlequinConnection.close()` method can be implemented by adapters to gracefully close database connections when the application exits.
+
 ### Bug Fixes
 
 -   Wrong link on text_area_clipboard_error error message ([#509](https://github.com/tconbeer/harlequin/issues/509))

src/harlequin/adapter.py

@@ -149,6 +149,15 @@ def validate_sql(self, text: str) -> str:
         """
         raise NotImplementedError
 
+    def close(self) -> None:
+        """
+        Closes the connection, if necessary. This function is called when the app
+        quits.
+
+        Returns: None
+        """
+        return None
+
 
 class HarlequinAdapter(ABC):
     """

src/harlequin/app.py

@@ -648,6 +648,8 @@ async def action_quit(self) -> None:
             s3_tree=self.data_catalog.s3_tree,
             history=self.history,
         )
+        if self.connection:
+            self.connection.close()
         await super().action_quit()
 
     def action_show_help_screen(self) -> None: