feat: add check for simplifiable match with sequence or mapping patterns

Signed-off-by: SoulSniper1212 <[email protected]>

Author: SoulSniper1212

.gitignore

@@ -212,3 +212,6 @@ fabric.properties
 # Used for testing:
 ex.py
 setup.py
+
+# CodeRabbit logs:
+logs/

tests/test_visitors/test_ast/test_conditions/test_simplified_match_with_sequence_or_mapping.py

@@ -0,0 +1,165 @@
+import pytest
+
+from wemake_python_styleguide.violations.consistency import (
+    SimplifiableMatchWithSequenceOrMappingViolation,
+)
+from wemake_python_styleguide.visitors.ast.conditions import (
+    SimplifiableMatchWithSequenceOrMappingVisitor,
+)
+
+# Wrong: Simple sequence patterns
+simple_list_match = """
+match data:
+    case [1, 2]:
+        handle_pair()
+    case _:
+        ignore()
+"""
+
+simple_nested_list_match = """
+match data:
+    case [[1, 2], [3, 4]]:
+        handle_nested()
+    case _:
+        ignore()
+"""
+
+simple_tuple_match = """
+match data:
+    case (1, "a"):
+        handle_tuple()
+    case _:
+        ignore()
+"""
+
+simple_dict_match = """
+match data:
+    case {"key": "value"}:
+        handle_dict()
+    case _:
+        ignore()
+"""
+
+simple_nested_dict_match = """
+match data:
+    case {"outer": {"inner": 42}}:
+        handle_nested_dict()
+    case _:
+        ignore()
+"""
+
+mixed_list_dict_match = """
+match data:
+    case [{"key": "value"}, 42]:
+        handle_mixed()
+    case _:
+        ignore()
+"""
+
+# Correct: Complex patterns that should not be simplified
+complex_with_binding = """
+match data:
+    case [x, y]:
+        handle_with_binding(x, y)
+    case _:
+        ignore()
+"""
+
+with_star_pattern = """
+match data:
+    case [first, *rest]:
+        handle_with_rest(first, rest)
+    case _:
+        ignore()
+"""
+
+with_rest_name = """
+match data:
+    case {"key": value, **rest}:
+        handle_with_rest(value, rest)
+    case _:
+        ignore()
+"""
+
+with_guard = """
+match data:
+    case [1, 2] if condition > 0:
+        handle_guarded()
+    case _:
+        ignore()
+"""
+
+complex_match = """
+match data:
+    case SomeClass(x):
+        handle_class()
+    case _:
+        ignore()
+"""
+
+no_wildcard = """
+match data:
+    case [1, 2]:
+        handle_first()
+    case [3, 4]:
+        handle_second()
+"""
+
+more_than_two_cases = """
+match data:
+    case [1, 2]:
+        handle_first()
+    case [3, 4]:
+        handle_second()
+    case _:
+        handle_default()
+"""
+
+
+@pytest.mark.parametrize(
+    'code',
+    [
+        simple_list_match,
+        simple_nested_list_match,
+        simple_tuple_match,
+        simple_dict_match,
+        simple_nested_dict_match,
+        mixed_list_dict_match,
+    ],
+)
+def test_simplifiable_sequence_or_mapping_match(
+    code,
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Test that simple sequence and mapping matches raise a violation."""
+    tree = parse_ast_tree(code)
+    visitor = SimplifiableMatchWithSequenceOrMappingVisitor(default_options, tree=tree)
+    visitor.run()
+    assert_errors(visitor, [SimplifiableMatchWithSequenceOrMappingViolation])
+
+
+@pytest.mark.parametrize(
+    'template',
+    [
+        complex_with_binding,
+        with_star_pattern,
+        with_rest_name,
+        with_guard,
+        complex_match,
+        no_wildcard,
+        more_than_two_cases,
+    ],
+)
+def test_not_simplifiable_sequence_or_mapping_match(
+    template,
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Test that complex or non-simplifiable matches do not raise violations."""
+    tree = parse_ast_tree(template)
+    visitor = SimplifiableMatchWithSequenceOrMappingVisitor(default_options, tree=tree)
+    visitor.run()
+    assert_errors(visitor, [])

wemake_python_styleguide/logic/tree/pattern_matching.py

@@ -102,3 +102,96 @@ def is_irrefutable_binding(pattern: ast.pattern) -> bool:
         and pattern.pattern is None
         and pattern.name is not None
     )
+
+
+def is_simple_sequence_or_mapping_pattern(pattern: ast.pattern) -> bool:
+    """
+    Checks if a pattern is a simple sequence or mapping without
+    variable bindings.
+
+    Supports:
+    - Simple lists: ``[1, 2]``, ``["a", "b"]``, ``[const.A, const.B]``
+    - Simple tuples: ``(1, 2)``, ``("a", "b")``
+    - Simple dicts: ``{"key": "value"}``, ``{1: 2}``
+    - No variable bindings (like ``[x, y]``) or starred patterns
+      (like ``[first, *rest]``)
+    - No guards allowed
+    """
+    # Check for simple list or tuple patterns
+    if isinstance(pattern, ast.MatchSequence):
+        # Check that there are no starred patterns (*rest)
+        if not _has_star_pattern(pattern):
+            # Check that all elements are simple patterns (not binding vars)
+            return all(
+                _is_simple_pattern_element(element)
+                for element in pattern.patterns
+            )
+
+    # Check for simple dict patterns
+    elif isinstance(pattern, ast.MatchMapping):
+        # Check that all keys are simple (not variables) and all
+        # values are simple patterns
+        if any(
+            key is None or not _is_simple_key_pattern(key)
+            for key in pattern.keys
+        ):
+            return False
+        if pattern.patterns and any(
+            not _is_simple_pattern_element(value) for value in pattern.patterns
+        ):
+            return False
+        # If rest name is present (has variable binding), it's not simple
+        return pattern.rest is None
+
+    return False
+
+
+def _has_star_pattern(pattern: ast.MatchSequence) -> bool:
+    """Check if the sequence pattern contains starred patterns."""
+    # ast.MatchStar has been added in Python 3.10 for starred patterns
+    for sub_pattern in pattern.patterns:
+        if isinstance(sub_pattern, ast.MatchStar):
+            return True
+    return False
+
+
+def _is_simple_pattern_element(pattern: ast.pattern) -> bool:
+    """Check if a pattern element is simple (not binding variables)."""
+    # Handle simple value patterns (literals, constants, attributes)
+    if isinstance(pattern, ast.MatchValue):
+        return isinstance(
+            pattern.value, (ast.Constant, ast.Name, ast.Attribute)
+        )
+
+    # Handle simple singleton patterns (True, False, None)
+    if isinstance(pattern, ast.MatchSingleton):
+        return True
+
+    # Handle simple nested patterns
+    if isinstance(pattern, (ast.MatchSequence, ast.MatchMapping)):
+        return is_simple_sequence_or_mapping_pattern(pattern)
+
+    # Handle Union patterns (| operator)
+    if isinstance(pattern, ast.MatchOr):
+        return all(_is_simple_pattern_element(sub) for sub in pattern.patterns)
+
+    # Handle MatchAs patterns - not simple if it's binding a variable
+    if isinstance(pattern, ast.MatchAs):
+        # If pattern.name is not None, it's a binding (not simple)
+        if pattern.name is not None:
+            return False
+        # If pattern.name is None but pattern.pattern is not None, 
+        # check if the inner pattern is simple
+        if pattern.pattern is not None:
+            return _is_simple_pattern_element(pattern.pattern)
+        # This case should not happen in valid Python ASTs
+        return False
+
+    # Other pattern types are not simple (like MatchClass with constructors)
+    return False
+
+
+def _is_simple_key_pattern(key: ast.expr) -> bool:
+    """Check if a mapping key is simple (not a variable)."""
+    # Keys should be constants or attributes, not variable names
+    return isinstance(key, (ast.Constant, ast.Name, ast.Attribute))

wemake_python_styleguide/presets/types/tree.py

@@ -71,6 +71,7 @@
     conditions.MatchVisitor,
     conditions.ChainedIsVisitor,
     conditions.SimplifiableMatchVisitor,
+    conditions.SimplifiableMatchWithSequenceOrMappingVisitor,
     conditions.LeakingForLoopVisitor,
     iterables.IterableUnpackingVisitor,
     blocks.AfterBlockVariablesVisitor,

wemake_python_styleguide/violations/consistency.py

@@ -2460,3 +2460,54 @@ class SimplifiableMatchViolation(ASTViolation):
         'Found simplifiable `match` statement that can be just `if`'
     )
     code = 365
+
+
+@final
+class SimplifiableMatchWithSequenceOrMappingViolation(ASTViolation):
+    """
+    Some ``match`` statements with simple sequences or mappings can be.
+
+    Reasoning:
+        Using ``match`` for exact structural comparisons of simple literals
+        (like lists or dicts) is unnecessarily verbose. While match excels
+        at deconstruction, using it to check for an exact list or dict value
+        is better expressed with a direct equality comparison (``==``),
+        which is more readable and performant.
+
+    Solution:
+        Replace ``match`` statements that check for simple sequences or
+        mappings (with no deconstruction) with ``if`` statements using ``==``.
+
+    When is this violation is raised?
+        - When there are exactly two ``case`` statements
+        - When the first case uses a simple sequence or mapping pattern
+        - When the second case is a wildcard: ``case _:``
+        - When the pattern contains only literals/contants (no
+      variable bindings)
+        - When there are no guards or starred patterns
+
+
+    Example::
+
+        # Correct:
+        if data == [1, 2]:
+            handle_pair()
+        else:
+            ignore()
+
+        # Wrong:
+        match data:
+            case [1, 2]:
+                handle_pair()
+            case _:
+                ignore()
+
+    .. versionadded:: 1.5.0
+
+    """
+
+    error_template = (
+        'Found simplifiable `match` statement with sequence or mapping '
+        'that can be just `if`'
+    )
+    code = 366

wemake_python_styleguide/visitors/ast/conditions.py

@@ -220,6 +220,34 @@ def _check_simplifiable_match(self, node: ast.Match) -> None:
                 self.add_violation(consistency.SimplifiableMatchViolation(node))
 
 
+@final
+class SimplifiableMatchWithSequenceOrMappingVisitor(BaseNodeVisitor):
+    """Checks for match statements with simple sequences and mappings."""
+
+    def visit_Match(self, node: ast.Match) -> None:
+        """Checks match statements with simple sequences and mappings."""
+        self._check_simplifiable_match_seq_or_map(node)
+        self.generic_visit(node)
+
+    def _check_simplifiable_match_seq_or_map(self, node: ast.Match) -> None:
+        cases = node.cases
+        if len(cases) == 2:
+            first, second = cases
+
+            if not pattern_matching.is_wildcard_pattern(second):
+                return
+
+            # Check if the first pattern is a simple sequence or mapping pattern
+            # without variable bindings AND no guard is present
+            if (
+                pattern_matching.is_simple_sequence_or_mapping_pattern(
+                    first.pattern
+                )
+                and first.guard is None  # No guard clause
+            ):
+                self.add_violation(consistency.SimplifiableMatchWithSequenceOrMappingViolation(node))
+
+
 @final
 class LeakingForLoopVisitor(BaseNodeVisitor):
     """Finds 'for' loops directly inside class or module bodies."""