Improve debugging output for passphrase validation failures

src/borg/crypto/key.py

@@ -371,6 +371,8 @@ def detect(cls, repository, manifest_data):
                     passphrase = Passphrase.getpass(prompt)
                     if key.load(target, passphrase):
                         break
+                    else:
+                        Passphrase.display_debug_info(passphrase)
                 else:
                     raise PasswordRetriesExceeded
         else:

src/borg/helpers/passphrase.py

@@ -118,6 +118,11 @@ def verification(cls, passphrase):
             print(
                 "Your passphrase (UTF-8 encoding in hex): %s" % bin_to_hex(passphrase.encode("utf-8")), file=sys.stderr
             )
+            print(
+                "It is recommended to keep the UTF-8 encoding in hex together with the passphrase at a safe place. "
+                "In case you should ever run into passphrase issues, it could sometimes help debugging them.\n",
+                file=sys.stderr,
+            )
             try:
                 passphrase.encode("ascii")
             except UnicodeEncodeError:
@@ -129,12 +134,16 @@ def verification(cls, passphrase):
 
     @staticmethod
     def display_debug_info(passphrase):
-        print(
-            "Incorrect passphrase (UTF-8 encoding in hex): %s" % bin_to_hex(passphrase.encode("utf-8")), file=sys.stderr
-        )
+        print("Incorrect passphrase!", file=sys.stderr)
+        print(f'Passphrase used (between double-quotes): "{passphrase}"', file=sys.stderr)
+        print(f'Same, UTF-8 encoded, in hex: {bin_to_hex(passphrase.encode("utf-8"))}', file=sys.stderr)
+        print("Relevant Environment Variables:", file=sys.stderr)
         for env_var in ["BORG_PASSPHRASE", "BORG_PASSCOMMAND", "BORG_PASSPHRASE_FD"]:
             env_var_value = os.environ.get(env_var)
-            print(f"{env_var} = {env_var_value}", file=sys.stderr)
+            if env_var_value is not None:
+                print(f'{env_var} = "{env_var_value}"', file=sys.stderr)
+            else:
+                print(f"# {env_var} is not set", file=sys.stderr)
 
     @classmethod
     def new(cls, allow_empty=False):

src/borg/testsuite/helpers_test.py

@@ -1417,11 +1417,12 @@ def test_passphrase_wrong(self, capsys, monkeypatch):
             raise PassphraseWrong("wrong_passphrase")
 
         out, err = capsys.readouterr()
-        assert "Incorrect passphrase (UTF-8 encoding in hex)" in err
+        assert "Incorrect passphrase!" in err
+        assert 'Passphrase used (between double-quotes): "wrong_passphrase"' in err
         assert "77726f6e675f70617373706872617365" in err
-        assert "BORG_PASSPHRASE = wrong_passphrase" in err
-        assert "BORG_PASSCOMMAND = echo wrong_passphrase" in err
-        assert "BORG_PASSPHRASE_FD = 123" in err
+        assert "BORG_PASSPHRASE" in err
+        assert "BORG_PASSCOMMAND" in err
+        assert "BORG_PASSPHRASE_FD" in err
 
         assert str(exc_info.value) == (
             "passphrase supplied in BORG_PASSPHRASE, by BORG_PASSCOMMAND or via BORG_PASSPHRASE_FD is incorrect."
@@ -1457,11 +1458,12 @@ def test_display_debug_info(self, capsys, monkeypatch):
         Passphrase.display_debug_info(passphrase)
 
         out, err = capsys.readouterr()
-        assert "Incorrect passphrase (UTF-8 encoding in hex)" in err
+        assert "Incorrect passphrase!" in err
+        assert 'Passphrase used (between double-quotes): "debug_test"' in err
         assert "64656275675f74657374" in err  # UTF-8 hex encoding of 'debug_test'
-        assert "BORG_PASSPHRASE = debug_env_passphrase" in err
-        assert "BORG_PASSCOMMAND = command" in err
-        assert "BORG_PASSPHRASE_FD = fd_value" in err
+        assert "BORG_PASSPHRASE" in err
+        assert "BORG_PASSCOMMAND" in err
+        assert "BORG_PASSPHRASE_FD" in err
 
 
 @pytest.mark.parametrize(