Add ignored-parents option to design checker (#4758)

* Add ignored-parents option to design checker

This allows users to specify classes to ignore while counting parent
classes.

Partially closes #3057

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

3 files changed, 44 insertions, 0 deletions

diff --git a/tests/functional/t/too/too_many_ancestors_ignored_parents.py b/tests/functional/t/too/too_many_ancestors_ignored_parents.py
new file mode 100644
index 000000000..93598d941
--- /dev/null
+++ b/tests/functional/t/too/too_many_ancestors_ignored_parents.py
@@ -0,0 +1,40 @@
+# pylint: disable=missing-docstring, too-few-public-methods, invalid-name
+
+# Inheritance diagram:
+#       F
+#      /
+#  D  E
+#   \/
+#    B  C
+#     \/
+#      A
+#
+# Once `E` is pruned from the tree, we have:
+#  D
+#   \
+#    B  C
+#     \/
+#      A
+#
+# By setting `max-parents=2`, we're able to check that tree-pruning works
+# correctly; in the new diagram, `B` has only 1 parent, so it doesn't raise a
+# message, and `A` has 3, so it does raise a message with the specific number
+# of parents.
+
+class F:
+    """0 parents"""
+
+class E(F):
+    """1 parent"""
+
+class D:
+    """0 parents"""
+
+class B(D, E):
+    """3 parents"""
+
+class C:
+    """0 parents"""
+
+class A(B, C): # [too-many-ancestors]
+    """5 parents"""
diff --git a/tests/functional/t/too/too_many_ancestors_ignored_parents.rc b/tests/functional/t/too/too_many_ancestors_ignored_parents.rc
new file mode 100644
index 000000000..1d06dad25
--- /dev/null
+++ b/tests/functional/t/too/too_many_ancestors_ignored_parents.rc
@@ -0,0 +1,3 @@
+[testoptions]
+max-parents=2
+ignored-parents=functional.t.too.too_many_ancestors_ignored_parents.E
diff --git a/tests/functional/t/too/too_many_ancestors_ignored_parents.txt b/tests/functional/t/too/too_many_ancestors_ignored_parents.txt
new file mode 100644
index 000000000..e1eea426a
--- /dev/null
+++ b/tests/functional/t/too/too_many_ancestors_ignored_parents.txt
@@ -0,0 +1 @@
+too-many-ancestors:39:0:A:Too many ancestors (3/2)