add comparison output, refactor main, bump python version

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

flupdt/flake_diff.py

@@ -7,8 +7,8 @@ from flupdt.common import bash_wrapper
 
 
 def compare_derivations(
-    path_to_flake: str, path_to_pre_drv: str, path_to_post_drv: str
-) -> list[str]:
+    path_to_flake: str, path_to_pre_drv: str, path_to_post_drv: str, *, soft_failure: bool = True
+) -> str:
     """Gets all derivations present in a flake.
 
     :param path_to_flake: path to flake to be checked
@@ -19,12 +19,15 @@ def compare_derivations(
     if nvd_path is None:
         status_msg = "nvd is not available in the PATH, please verify that it is installed"
         raise RuntimeError(status_msg)
-    diff_output =  bash_wrapper(
+    stdout, stderr, returncode = bash_wrapper(
         f"{nvd_path} diff {path_to_pre_drv} {path_to_post_drv}", path=path_to_flake
     )
 
-    logging.debug(diff_output[0])
-    logging.debug(diff_output[1])
-    logging.debug(diff_output[2])
+    if returncode != 0:
+        log_func = logging.error
+        if soft_failure:
+            log_func = logging.warning
+        logging.warning(f"diff failed for {path_to_pre_drv} and {path_to_post_drv}")
+        log_func(stderr)
 
-    return diff_output
+    return stdout