Add configuration option ``exclude-too-few-public-methods`` (#5191)

Allow excluding classes based on their ancestors from the ``too-few-public-methods`` checker.

Closes #3370

Signed-off-by: Mike Fiedler <miketheman@gmail.com>

Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

10 files changed, 75 insertions, 1 deletions

diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 881d53db6..28b2e332c 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -562,3 +562,5 @@ contributors:
 * Youngsoo Sung: contributor
 
 * Arianna Yang: contributor
+
+* Mike Fiedler (miketheman): contributor
diff --git a/ChangeLog b/ChangeLog
index 541e6543f..9f60f43d1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -107,6 +107,11 @@ Release date: TBA
 * Fix ``missing-function-docstring`` not being able to check ``__init__`` and other
   magic methods even if the ``no-docstring-rgx`` setting was set to do so
 
+* Added configuration option ``exclude-too-few-public-methods`` to allow excluding
+  classes from the ``min-public-methods`` checker.
+
+  Closes #3370
+
 
 What's New in Pylint 2.11.2?
 ============================
diff --git a/doc/whatsnew/2.12.rst b/doc/whatsnew/2.12.rst
index 0573ddc50..52b5ba595 100644
--- a/doc/whatsnew/2.12.rst
+++ b/doc/whatsnew/2.12.rst
@@ -43,6 +43,11 @@ New checkers
 
   Closes #4774
 
+* Added configuration option ``exclude-too-few-public-methods`` to allow excluding
+  classes from the ``min-public-methods`` checker.
+
+  Closes #3370
+
 
 Removed checkers
 ================
diff --git a/pylint/checkers/design_analysis.py b/pylint/checkers/design_analysis.py
index 3b5056a9e..8486aa89e 100644
--- a/pylint/checkers/design_analysis.py
+++ b/pylint/checkers/design_analysis.py
@@ -402,6 +402,16 @@ class MisdesignChecker(BaseChecker):
                 "statement (see R0916).",
             },
         ),
+        (
+            "exclude-too-few-public-methods",
+            {
+                "default": [],
+                "type": "regexp_csv",
+                "metavar": "<pattern>[,<pattern>...]",
+                "help": "List of regular expressions of class ancestor names "
+                "to ignore when counting public methods (see R0903)",
+            },
+        ),
     )
 
     def __init__(self, linter=None):
@@ -416,6 +426,9 @@ class MisdesignChecker(BaseChecker):
         self._returns = []
         self._branches = defaultdict(int)
         self._stmts = []
+        self._exclude_too_few_public_methods = utils.get_global_option(
+            self, "exclude-too-few-public-methods", default=[]
+        )
 
     def _inc_all_stmts(self, amount):
         for i, _ in enumerate(self._stmts):
@@ -472,6 +485,15 @@ class MisdesignChecker(BaseChecker):
                 args=(my_methods, self.config.max_public_methods),
             )
 
+        # Stop here if the class is excluded via configuration.
+        if node.type == "class" and self._exclude_too_few_public_methods:
+            for ancestor in node.ancestors():
+                if any(
+                    pattern.match(ancestor.qname())
+                    for pattern in self._exclude_too_few_public_methods
+                ):
+                    return
+
         # Stop here for exception, metaclass, interface classes and other
         # classes for which we don't need to count the methods.
         if node.type != "class" or _is_exempt_from_public_methods(node):
diff --git a/pylint/utils/utils.py b/pylint/utils/utils.py
index 8243bc322..25b0ad3f1 100644
--- a/pylint/utils/utils.py
+++ b/pylint/utils/utils.py
@@ -59,7 +59,7 @@ GLOBAL_OPTION_PATTERN = Literal[
     "ignored-argument-names",
     "mixin-class-rgx",
 ]
-GLOBAL_OPTION_PATTERN_LIST = Literal["ignore-paths"]
+GLOBAL_OPTION_PATTERN_LIST = Literal["exclude-too-few-public-methods", "ignore-paths"]
 GLOBAL_OPTION_TUPLE_INT = Literal["py-version"]
 GLOBAL_OPTION_NAMES = Union[
     GLOBAL_OPTION_BOOL,
diff --git a/pylintrc b/pylintrc
index 7669da6e8..8df15f713 100644
--- a/pylintrc
+++ b/pylintrc
@@ -350,6 +350,9 @@ min-public-methods=2
 # Maximum number of public methods for a class (see R0904).
 max-public-methods=25
 
+# List of regular expressions of class ancestor names to
+# ignore when counting public methods (see R0903).
+exclude-too-few-public-methods=
 
 [CLASSES]
 
diff --git a/tests/checkers/unittest_design.py b/tests/checkers/unittest_design.py
index 5c6f38816..441793a2e 100644
--- a/tests/checkers/unittest_design.py
+++ b/tests/checkers/unittest_design.py
@@ -11,6 +11,7 @@ import astroid
 
 from pylint.checkers import design_analysis
 from pylint.testutils import CheckerTestCase, set_config
+from pylint.utils.utils import get_global_option
 
 
 class TestDesignChecker(CheckerTestCase):
@@ -42,3 +43,20 @@ class TestDesignChecker(CheckerTestCase):
         )
         with self.assertNoMessages():
             self.checker.visit_classdef(node)
+
+    @set_config(exclude_too_few_public_methods="toml.*")
+    def test_exclude_too_few_methods_with_value(self) -> None:
+        """Test exclude-too-few-public-methods option with value"""
+        options = get_global_option(self.checker, "exclude-too-few-public-methods")
+
+        assert any(i.match("toml") for i in options)
+        assert any(i.match("toml.*") for i in options)
+        assert any(i.match("toml.TomlEncoder") for i in options)
+
+    def test_ignore_paths_with_no_value(self) -> None:
+        """Test exclude-too-few-public-methods option with no value.
+        Compare against actual list to see if validator works."""
+        options = get_global_option(self.checker, "exclude-too-few-public-methods")
+
+        # pylint: disable-next=use-implicit-booleaness-not-comparison
+        assert options == []
diff --git a/tests/functional/t/too/too_few_public_methods_excluded.py b/tests/functional/t/too/too_few_public_methods_excluded.py
new file mode 100644
index 000000000..35ba873ee
--- /dev/null
+++ b/tests/functional/t/too/too_few_public_methods_excluded.py
@@ -0,0 +1,14 @@
+# pylint: disable=missing-docstring
+from json import JSONEncoder
+
+class Control: # [too-few-public-methods]
+    ...
+
+
+class MyJsonEncoder(JSONEncoder):
+    ...
+
+class InheritedInModule(Control):
+    """This class inherits from a class that doesn't have enough mehods,
+    and its parent is excluded via config, so it doesn't raise."""
+    ...
diff --git a/tests/functional/t/too/too_few_public_methods_excluded.rc b/tests/functional/t/too/too_few_public_methods_excluded.rc
new file mode 100644
index 000000000..00c025832
--- /dev/null
+++ b/tests/functional/t/too/too_few_public_methods_excluded.rc
@@ -0,0 +1,4 @@
+[testoptions]
+min-public-methods=10  # to combat inherited methods
+
+exclude-too-few-public-methods=json.*,^.*Control$
diff --git a/tests/functional/t/too/too_few_public_methods_excluded.txt b/tests/functional/t/too/too_few_public_methods_excluded.txt
new file mode 100644
index 000000000..c88cde25f
--- /dev/null
+++ b/tests/functional/t/too/too_few_public_methods_excluded.txt
@@ -0,0 +1 @@
+too-few-public-methods:4:0:Control:Too few public methods (0/10):HIGH