feat: add SimplifiableIfMatchViolation for single-case matches

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

Author: SoulSniper1212

tests/test_visitors/test_ast/test_conditions/test_simplified_match_conditions.py

@@ -1,6 +1,7 @@
 import pytest
 
 from wemake_python_styleguide.violations.consistency import (
+    SimplifiableIfMatchViolation,
     SimplifiableMatchViolation,
 )
 from wemake_python_styleguide.visitors.ast.conditions import (
@@ -187,3 +188,111 @@ def test_not_simplifiable_match_templates(
     visitor = SimplifiableMatchVisitor(default_options, tree=tree)
     visitor.run()
     assert_errors(visitor, [])
+
+
+# New tests for single-case matches:
+
+# Wrong (single case):
+single_case_match = """
+match x:
+    case {0}:
+        do_something()
+"""
+
+single_case_with_as_binding_match = """
+match x:
+    case {0} as y:
+        do_something()
+"""
+
+# Correct (not single case or has guards):
+multi_case_match = """
+match x:
+    case 1:
+        do_something()
+    case 2:
+        do_something_else()
+"""
+
+single_case_with_guard = """
+match x:
+    case y if y > 0:
+        do_something()
+"""
+
+wildcard_case = """
+match x:
+    case _:
+        do_something()
+"""
+
+pattern_with_complex_structure = """
+match x:
+    case [a, b]:
+        do_something()
+"""
+
+pattern_with_class_args = """
+match x:
+    case SomeClass(a):
+        do_something()
+"""
+
+
+@pytest.mark.parametrize(
+    'code',
+    [
+        '1',
+        'True',
+        'None',
+        '"string"',
+        'ns.CONST',
+        'State.ACCEPTED',
+    ],
+)
+def test_single_case_match(
+    code,
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Test that single-case matches raise a violation."""
+    tree = parse_ast_tree(single_case_match.format(code))
+    visitor = SimplifiableMatchVisitor(default_options, tree=tree)
+    visitor.run()
+    assert_errors(visitor, [SimplifiableIfMatchViolation])
+
+
+def test_single_case_with_as_binding(
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Test that single-case matches with as-binding raise a violation."""
+    tree = parse_ast_tree(single_case_with_as_binding_match.format('1'))
+    visitor = SimplifiableMatchVisitor(default_options, tree=tree)
+    visitor.run()
+    assert_errors(visitor, [SimplifiableIfMatchViolation])
+
+
+@pytest.mark.parametrize(
+    'template',
+    [
+        multi_case_match,
+        single_case_with_guard,
+        wildcard_case,
+        pattern_with_complex_structure,
+        pattern_with_class_args,
+    ],
+)
+def test_not_single_case_match(
+    template,
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Test that non-single-case matches do not raise the single-case violation."""
+    tree = parse_ast_tree(template)
+    visitor = SimplifiableMatchVisitor(default_options, tree=tree)
+    visitor.run()
+    assert_errors(visitor, [])

wemake_python_styleguide/violations/consistency.py

@@ -2460,3 +2460,43 @@ class SimplifiableMatchViolation(ASTViolation):
         'Found simplifiable `match` statement that can be just `if`'
     )
     code = 365
+
+
+@final
+class SimplifiableIfMatchViolation(ASTViolation):
+    """
+    Single-case ``match`` statements can be simplified to ``if`` statements.
+
+    Reasoning:
+        Using ``match`` for a single case is unnecessarily complex compared to a 
+        simple ``if`` condition. The intent is clear, and using ``if`` reduces 
+        nesting and cognitive load.
+
+    Solution:
+        Replace single-case ``match ... case`` statements with ``if``.
+
+    When is this violation is raised?
+        - When there is exactly one ``case`` statement
+        - When the pattern is simple (literal, constant, enum, etc.)
+        - When no guard (``if`` ...) is used
+        - When no wildcard pattern is used
+
+    Example::
+
+        # Correct:
+        if x == 1:
+            do_something()
+
+        # Wrong:
+        match x:
+            case 1:
+                do_something()
+
+    .. versionadded:: 1.10.0
+
+    """
+
+    error_template = (
+        'Found single-case `match` statement that can be simplified to `if`'
+    )
+    code = 366

wemake_python_styleguide/visitors/ast/conditions.py

@@ -208,7 +208,18 @@ def visit_Match(self, node: ast.Match) -> None:
 
     def _check_simplifiable_match(self, node: ast.Match) -> None:
         cases = node.cases
-        if len(cases) == 2:
+        
+        # Check for single-case matches with no guard
+        if len(cases) == 1:
+            case = cases[0]
+            # Check if there's no guard condition
+            if case.guard is None:
+                # Check if the pattern is simple (literal, constant, enum, etc.)
+                if pattern_matching.is_simple_pattern(case.pattern):
+                    self.add_violation(consistency.SimplifiableIfMatchViolation(node))
+        
+        # Check for two-case matches with wildcard (existing logic)
+        elif len(cases) == 2:
             first, second = cases
 
             if not pattern_matching.is_wildcard_pattern(second):