Test bad parsing of duplicate line

netutils/config/parser.py

@@ -621,7 +621,14 @@ def _update_same_line_children_configs(self) -> None:
         new_config_lines: t.List[ConfigLine] = []
         for line in self.config_lines:
             if line in self.same_line_children:
-                previous_line = new_config_lines[-1]
+                try:
+                    previous_line = new_config_lines[-1]
+                except IndexError as error:
+                    raise IndexError(
+                        f"This error is likely from a duplicate line detected at the line `{line.config_line}`, "
+                        "see https://netutils.readthedocs.io/en/latest/dev/dev_config/#duplicate-line-detection "
+                        f"for more details.\nOriginal Error: {error}"
+                    )
                 previous_config_line = previous_line.config_line
                 current_parents = previous_line.parents + (previous_config_line,)
                 line = ConfigLine(line.config_line, current_parents)

tests/unit/test_parser.py

@@ -55,6 +55,44 @@ def test_find_children_w_parents(
     assert "\n".join(os_parser(device_cfg).find_children_w_parents(**kwargs)) == received_data
 
 
+def test_bad_parsing_of_duplicate_line():
+    """This is a test to show an issue, this should raise and Index error, but the issue is the
+    Parents calculation is off, here is an example of what it returns:
+    [
+
+       ConfigLine(config_line='logging host one.two.three.one', parents=()),
+       ConfigLine(config_line='logging host one.two.three.two', parents=('logging host one.two.three.one',)),
+       ConfigLine(config_line='logging host one.two.three.two', parents=('logging host one.two.three.one', 'logging host one.two.three.two')),
+       ConfigLine(config_line='logging host one.two.three.four', parents=())
+    ]
+    We see that the parents of `parents=('logging host one.two.three.one',` shows up, which is wrong.
+    The key behaviour I have seen, is when there is 3 dots e.g. `.` in the config, so `logging host 10.1.1` would work
+    but not `logging host 10.1.1.1`.
+    When this tests pass, everything should be good, but the underlying code to be checked in is `_update_same_line_children_configs` method.
+    ."""
+    logging = (
+        "!\n"
+        "logging host one.two.three.one\n"
+        "logging host one.two.three.two\n"
+        "logging host one.two.three.two\n"
+        "logging host one.two.three.four\n"
+    )
+    with pytest.raises(IndexError, match=r".*This error is from likely a duplicate line detected.*"):
+        compliance.parser_map["cisco_ios"](logging).config_lines  # pylint: disable=expression-not-assigned
+    logging = (
+        "!\n"
+        "logging host 10.1.1.1\n"
+        "logging host 10.1.1.2\n"
+        "logging host 10.1.1.2\n"
+        "logging host 10.1.1.4\n"
+        "!\n"
+        "!\n"
+        "!\n"
+    )
+    with pytest.raises(IndexError, match=r".*This error is from likely a duplicate line detected.*"):
+        compliance.parser_map["cisco_ios"](logging).config_lines  # pylint: disable=expression-not-assigned
+
+
 def test_incorrect_banner_ios():
     banner_cfg = (
         "aaa new-model\n"
@@ -68,3 +106,14 @@ def test_incorrect_banner_ios():
     )
     with pytest.raises(ValueError):
         compliance.parser_map["cisco_ios"](banner_cfg).config_lines  # pylint: disable=expression-not-assigned
+
+
+def test_duplicate_line():
+    logging = (
+        "!\n"
+        "snmp-server community <<REPLACED>> RO SNMP_ACL_RO\n"
+        "snmp-server community <<REPLACED>> RO SNMP_ACL_RO\n"
+        "snmp-server community <<REPLACED>> RW SNMP_ACL_RW\n"
+    )
+    with pytest.raises(IndexError, match=r".*This error is likely from a duplicate line detected.*"):
+        compliance.parser_map["cisco_ios"](logging).config_lines  # pylint: disable=expression-not-assigned