Adds WPS241 which forbids to have too many subjects in match stat…

…ements (#3214)

Co-authored-by: sobolevn <[email protected]>

CHANGELOG.md

@@ -101,6 +101,7 @@ Semantic versioning in our case means:
 - Adds a new rule to check problematic function params, #1343
 - Adds a new rule to detect duplicate conditions in `if`s and `elif`s, #2241
 - Adds a new rule to detect duplicate `case` pattens in `match`, #3206
+- Adds a new rule to find too many `match` subjects, #3201
 - Adds a new rule to find too complex `except` with too many exceptions
 - Adds a new rule to find too many `PEP695` type params
 - Adds a new rule to find useless ternary expressions, #1706

tests/fixtures/noqa/noqa.py

@@ -631,6 +631,11 @@ def many_raises_function(parameter):  # noqa: WPS238
     my_print('except')
 
 
+match inst1, inst2, inst3, inst4, inst5, inst6, inst7, inst8:  # noqa: WPS241
+    case 1:
+        my_print('except')
+
+
 my_print("""
 text
 """)  # noqa: WPS462

tests/test_checker/test_noqa.py

@@ -92,6 +92,7 @@
         'WPS238': 1,
         'WPS239': 1,
         'WPS240': 0,  # only triggers on 3.12+
+        'WPS241': 1,
         'WPS300': 1,
         'WPS301': 1,
         'WPS302': 0,  # disabled since 1.0.0

tests/test_visitors/test_ast/test_compares/test_conditionals.py

@@ -7,11 +7,6 @@
     WrongConditionalVisitor,
 )
 
-create_variable = """
-variable = 1
-{0}
-"""
-
 if_statement = 'if {0}: ...'
 ternary = 'ternary = 0 if {0} else 1'
 
@@ -83,9 +78,7 @@ def test_valid_conditional(
     mode,
 ):
     """Testing that conditionals work well."""
-    tree = parse_ast_tree(
-        mode(create_variable.format(code.format(comparators))),
-    )
+    tree = parse_ast_tree(mode(code.format(comparators)))
 
     visitor = WrongConditionalVisitor(default_options, tree=tree)
     visitor.run()
@@ -102,7 +95,6 @@ def test_valid_conditional(
         set_comprehension,
         dict_comprehension,
         gen_comprehension,
-        match_statement,
     ],
 )
 @pytest.mark.parametrize(
@@ -120,7 +112,9 @@ def test_valid_conditional(
         '{test : "1"}',
         '{"set"}',
         '("tuple",)',
-        '["list"]',
+        '[]',
+        '[variable]',
+        '(1, var)',
         'variable or False',
         'variable and False',
         'variable or True',
@@ -139,11 +133,85 @@ def test_constant_condition(
     mode,
 ):
     """Testing that violations are when using invalid conditional."""
+    tree = parse_ast_tree(mode(code.format(comparators)))
+
+    visitor = WrongConditionalVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [ConstantConditionViolation])
+
+
+@pytest.mark.parametrize(
+    'comparators',
+    [
+        'True',
+        'False',
+        'None',
+        '4',
+        '-4.8',
+        '--0.0',
+        '"test"',
+        "b'bytes'",
+        '("string in brackets")',
+        '{1 : "1"}',
+        '{"set"}',
+        '("tuple",)',
+        '[]',
+        '[1, 2]',
+        '(1, 2)',
+        'variable or False',
+        'variable and False',
+        'variable or True',
+        'variable and True',
+        '(unique := True)',
+        '(unique := -1)',
+        '...',
+    ],
+)
+def test_constant_condition_in_match(
+    assert_errors,
+    parse_ast_tree,
+    comparators,
+    default_options,
+):
+    """Testing that violations are when using invalid conditional in PM."""
     tree = parse_ast_tree(
-        mode(create_variable.format(code.format(comparators))),
+        match_statement.format(comparators),
     )
 
     visitor = WrongConditionalVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [ConstantConditionViolation])
+
+
+@pytest.mark.parametrize(
+    'comparators',
+    [
+        'variable',
+        '(x := y)',
+        '-number',
+        '[x, y]',
+        '{test : "1"}',
+        '{test}',
+        '(x, y)',
+        '{**keys, "data": None}',
+        'variable or other',
+        'variable and other',
+    ],
+)
+def test_regular_condition_in_match(
+    assert_errors,
+    parse_ast_tree,
+    comparators,
+    default_options,
+):
+    """Testing correct conditional in PM."""
+    tree = parse_ast_tree(
+        match_statement.format(comparators),
+    )
+
+    visitor = WrongConditionalVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [])

tests/test_visitors/test_ast/test_complexity/test_pm/test_match_subjects.py

@@ -0,0 +1,90 @@
+import pytest
+
+from wemake_python_styleguide.violations.complexity import (
+    TooManyMatchSubjectsViolation,
+)
+from wemake_python_styleguide.visitors.ast.complexity.pm import (
+    MatchSubjectsVisitor,
+)
+
+match_call_expr = """
+match some_call():
+    case 1: ...
+"""
+
+match_case_long_tuple = """
+match some_call['a']:
+    case (a, b, c, d, e, f, g, h, i): ...
+"""
+
+match_subjects8 = """
+match a1, b2, c3, d4, e5, f6, g7, h8:
+    case 1: ...
+"""
+
+match_subjects7 = """
+match a1, b2, c3, d4, e5, f6, g7:
+    case 1: ...
+"""
+
+
+def test_match_subjects_wrong_count(
+    assert_errors,
+    assert_error_text,
+    parse_ast_tree,
+    default_options,
+):
+    """Testing that default settings raise a warning."""
+    tree = parse_ast_tree(match_subjects8)
+
+    visitor = MatchSubjectsVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [TooManyMatchSubjectsViolation])
+    assert_error_text(visitor, '8', baseline=default_options.max_match_subjects)
+
+
+@pytest.mark.parametrize(
+    'code',
+    [
+        match_subjects7,
+        match_call_expr,
+        match_case_long_tuple,
+    ],
+)
+def test_match_subjects_correct_count(
+    assert_errors,
+    parse_ast_tree,
+    code,
+    default_options,
+):
+    """Testing that default settings do not raise a warning."""
+    tree = parse_ast_tree(code)
+
+    visitor = MatchSubjectsVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [])
+
+
+@pytest.mark.parametrize(
+    'code',
+    [
+        match_subjects8,
+        match_subjects7,
+    ],
+)
+def test_match_subjects_configured_count(
+    assert_errors,
+    parse_ast_tree,
+    code,
+    options,
+):
+    """Testing that settings can reflect the change."""
+    tree = parse_ast_tree(code)
+
+    option_values = options(max_match_subjects=1)
+    visitor = MatchSubjectsVisitor(option_values, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [TooManyMatchSubjectsViolation])

wemake_python_styleguide/logic/tree/compares.py

@@ -2,10 +2,9 @@
 import types
 from collections import defaultdict
 from collections.abc import Mapping
-from typing import Final, TypeAlias
+from typing import Final, TypeAlias, final
 
 import attr
-from typing_extensions import final
 
 from wemake_python_styleguide.logic import source
 

wemake_python_styleguide/logic/tree/pattern_matching.py

@@ -2,7 +2,11 @@
 from collections.abc import Iterable
 
 from wemake_python_styleguide.logic.nodes import get_parent
+from wemake_python_styleguide.logic.tree import (
+    operators,
+)
 from wemake_python_styleguide.logic.walk import get_subnodes_by_type
+from wemake_python_styleguide.logic.walrus import get_assigned_expr
 
 
 def get_explicit_as_names(
@@ -21,3 +25,23 @@ def get_explicit_as_names(
             and match_as.name
         ):
             yield match_as
+
+
+def is_constant_subject(condition: ast.AST | list[ast.expr]) -> bool:
+    """Detect constant subjects for `ast.Match` nodes."""
+    if isinstance(condition, list):
+        return all(is_constant_subject(node) for node in condition)
+    node = operators.unwrap_unary_node(get_assigned_expr(condition))
+    if isinstance(node, ast.Constant):
+        return True
+    if isinstance(node, ast.Tuple | ast.List | ast.Set):
+        return is_constant_subject(node.elts)
+    if isinstance(node, ast.Dict):
+        return (
+            not any(dict_key is None for dict_key in node.keys)
+            and is_constant_subject([
+                dict_key for dict_key in node.keys if dict_key is not None
+            ])
+            and is_constant_subject(node.values)
+        )
+    return False

wemake_python_styleguide/options/config.py

@@ -153,6 +153,9 @@ class of violations that are forbidden to ignore inline, defaults to
 - ``max-type-params`` - maximum number of PEP695 type parameters,
     defaults to
     :str:`wemake_python_styleguide.options.defaults.MAX_TYPE_PARAMS`
+- ``max-match-subjects`` - maximum number of subjects in a match statement,
+    defaults to
+    :str:`wemake_python_styleguide.options.defaults.MAX_MATCH_SUBJECTS`
 
 .. rubric:: Formatter options
 
@@ -423,6 +426,11 @@ class Configuration:
             defaults.MAX_TYPE_PARAMS,
             'Maximum number of PEP695 type parameters.',
         ),
+        _Option(
+            '--max-match-subjects',
+            defaults.MAX_MATCH_SUBJECTS,
+            'Maximum number of subjects in a match statement.',
+        ),
         # Formatter:
         _Option(
             '--show-violation-links',

wemake_python_styleguide/options/defaults.py

@@ -138,7 +138,10 @@
 MAX_TUPLE_UNPACK_LENGTH: Final = 4  # guessed
 
 #: Maximum number of PEP695 type parameters.
-MAX_TYPE_PARAMS: Final = 6  # guessed
+MAX_TYPE_PARAMS: Final = 6  # 7-1, guessed
+
+#: Maximum number of subjects in a ``match`` statement.
+MAX_MATCH_SUBJECTS: Final = 7  # 7 +- 0, guessed
 
 # ==========
 # Formatter:

wemake_python_styleguide/options/validation.py

@@ -98,6 +98,7 @@ class _ValidatedOptions:
     max_import_from_members: int = attr.ib(validator=[_min_max(min=1)])
     max_tuple_unpack_length: int = attr.ib(validator=[_min_max(min=1)])
     max_type_params: int = attr.ib(validator=[_min_max(min=1)])
+    max_match_subjects: int = attr.ib(validator=[_min_max(min=1)])
     show_violation_links: bool
     exps_for_one_empty_line: int
 

wemake_python_styleguide/presets/topics/complexity.py

@@ -12,6 +12,7 @@
     nested,
     offset,
     overuses,
+    pm,
 )
 
 #: Used to store all complexity related visitors to be later passed to checker:
@@ -36,4 +37,5 @@
     access.AccessVisitor,
     calls.CallChainsVisitor,
     annotations.AnnotationComplexityVisitor,
+    pm.MatchSubjectsVisitor,
 )

wemake_python_styleguide/types.py

@@ -231,3 +231,6 @@ def show_violation_links(self) -> bool: ...
 
     @property
     def exps_for_one_empty_line(self) -> int: ...
+
+    @property
+    def max_match_subjects(self) -> int: ...