Closes #602

CHANGELOG.md

@@ -39,6 +39,8 @@ big cudos to the developers of this wonderful tool.
 - Forces to write `isinstance(some, (A, B))`
   instead of `isinstance(some, A) or isinstance(some, B)`
 - Forbids to use `isinstance(some (A,))`
+- Forces to merge `a == b or a == c` into `a in {b, c}` and
+  to merge `a != b and a != c` into `a not in {b, c}`
 
 ### Bugfixes
 

tests/fixtures/noqa.py

@@ -288,6 +288,8 @@ def some_function():
 for index in [1, 2]:  # noqa: Z335
     print(index)
 
+print(one == 'a' or one == 'b')  # noqa: Z336
+
 try:
     anti_z444 = 1
 except BaseException:  # noqa: Z424

tests/test_checker/test_noqa.py

@@ -110,6 +110,7 @@ def test_noqa_fixture_disabled(absolute_path, all_violations):
         'Z333': 1,
         'Z334': 1,
         'Z335': 1,
+        'Z336': 1,
 
         'Z400': 0,
         'Z401': 0,

tests/test_visitors/test_ast/test_conditions/test_implicit_complex_compare.py

@@ -6,7 +6,7 @@
     ImplicitComplexCompareViolation,
 )
 from wemake_python_styleguide.visitors.ast.conditions import (
-    BooleanConditionVisitor,
+    ImplicitBoolPatternsVisitor,
 )
 
 # Wrong:
@@ -87,7 +87,7 @@ def test_implicit_complex_compare(
     """Testing implicit complex compare."""
     tree = parse_ast_tree(code.format(*comparators))
 
-    visitor = BooleanConditionVisitor(default_options, tree=tree)
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [ImplicitComplexCompareViolation])
@@ -126,7 +126,7 @@ def test_implicit_complex_compare_reversed(
     """Testing implicit complex compare."""
     tree = parse_ast_tree(code.format(*comparators))
 
-    visitor = BooleanConditionVisitor(default_options, tree=tree)
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [ImplicitComplexCompareViolation])
@@ -166,7 +166,7 @@ def test_compare_wrong_values(
     """Testing implicit complex compare."""
     tree = parse_ast_tree(code.format(*comparators))
 
-    visitor = BooleanConditionVisitor(default_options, tree=tree)
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [])
@@ -206,7 +206,7 @@ def test_regular_compare(
     """Testing implicit complex compare."""
     tree = parse_ast_tree(code.format(*comparators))
 
-    visitor = BooleanConditionVisitor(default_options, tree=tree)
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [])
@@ -228,7 +228,7 @@ def test_regular_short_compare(
     """Testing implicit complex compare."""
     tree = parse_ast_tree(code)
 
-    visitor = BooleanConditionVisitor(default_options, tree=tree)
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [])

tests/test_visitors/test_ast/test_conditions/test_implicit_in.py

@@ -0,0 +1,104 @@
+# -*- coding: utf-8 -*-
+
+import pytest
+
+from wemake_python_styleguide.violations.consistency import (
+    ImplicitInConditionViolation,
+)
+from wemake_python_styleguide.visitors.ast.conditions import (
+    ImplicitBoolPatternsVisitor,
+)
+
+# Correct:
+
+eq_and = '{0} == some1 and {1} == some2'
+noteq_or = '{0} != some1 or {1} != some2'
+
+# Wrong:
+
+eq_or = '{0} == some1 or {1} == some2'
+noteq_and = '{0} != some1 and {1} != some2'
+
+
+@pytest.mark.parametrize('code', [
+    eq_and,
+    noteq_or,
+    eq_or,
+    noteq_and,
+])
+@pytest.mark.parametrize('first, second', [
+    ('first', 'second'),
+    ('one.attr', 'one'),
+    ('first', 'first()'),
+    ('value.method()', 'value.method'),
+    ('value.method(1)', 'value.method(2)'),
+])
+def test_different_in_values(
+    code,
+    first,
+    second,
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Testing regular conditions."""
+    tree = parse_ast_tree(code.format(first, second))
+
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [])
+
+
+@pytest.mark.parametrize('code', [
+    eq_and,
+    noteq_or,
+])
+@pytest.mark.parametrize('first, second', [
+    ('first', 'first'),
+    ('one.attr', 'one.attr'),
+    ('first()', 'first()'),
+    ('value.method(1)', 'value.method(2)'),
+])
+def test_safe_patterns_in_values(
+    code,
+    first,
+    second,
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Testing safe in patterns."""
+    tree = parse_ast_tree(code.format(first, second))
+
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [])
+
+
+@pytest.mark.parametrize('code', [
+    eq_or,
+    noteq_and,
+])
+@pytest.mark.parametrize('first, second', [
+    ('first', 'first'),
+    ('one.attr', 'one.attr'),
+    ('first()', 'first()'),
+    ('value.method(1)', 'value.method(1)'),
+])
+def test_wrong_patterns_in_values(
+    code,
+    first,
+    second,
+    assert_errors,
+    parse_ast_tree,
+    default_options,
+):
+    """Testing safe in patterns."""
+    tree = parse_ast_tree(code.format(first, second))
+
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [ImplicitInConditionViolation])

tests/test_visitors/test_ast/test_conditions/test_implicit_ternary.py

@@ -6,7 +6,7 @@
     ImplicitTernaryViolation,
 )
 from wemake_python_styleguide.visitors.ast.conditions import (
-    BooleanConditionVisitor,
+    ImplicitBoolPatternsVisitor,
 )
 
 # Correct:
@@ -49,7 +49,7 @@ def test_implicit_ternary(
     """Testing implicit ternary."""
     tree = parse_ast_tree(code.format(first, second))
 
-    visitor = BooleanConditionVisitor(default_options, tree=tree)
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [ImplicitTernaryViolation])
@@ -85,7 +85,7 @@ def test_regular_compare_not_ternary(
     """Testing regular compares and not ternaries."""
     tree = parse_ast_tree(code.format(first, second))
 
-    visitor = BooleanConditionVisitor(default_options, tree=tree)
+    visitor = ImplicitBoolPatternsVisitor(default_options, tree=tree)
     visitor.run()
 
     assert_errors(visitor, [])

tests/test_visitors/test_ast/test_conditions/test_same_element.py

@@ -5,9 +5,6 @@
 from wemake_python_styleguide.violations.best_practices import (
     SameElementsInConditionViolation,
 )
-from wemake_python_styleguide.violations.consistency import (
-    ImplicitTernaryViolation,
-)
 from wemake_python_styleguide.visitors.ast.conditions import (
     BooleanConditionVisitor,
 )
@@ -84,7 +81,4 @@ def test_duplicate_element_and_ternary(
     visitor = BooleanConditionVisitor(default_options, tree=tree)
     visitor.run()
 
-    assert_errors(visitor, [
-        ImplicitTernaryViolation,
-        SameElementsInConditionViolation,
-    ])
+    assert_errors(visitor, [SameElementsInConditionViolation])

wemake_python_styleguide/presets/general.py

@@ -65,6 +65,7 @@
 
     conditions.IfStatementVisitor,
     conditions.BooleanConditionVisitor,
+    conditions.ImplicitBoolPatternsVisitor,
 
     # Classes:
     classes.WrongClassVisitor,

wemake_python_styleguide/violations/consistency.py

@@ -61,6 +61,7 @@
    ImplicitComplexCompareViolation
    ReversedComplexCompareViolation
    IncorectLoopIterTypeViolation
+   ImplicitInConditionViolation
 
 Consistency checks
 ------------------
@@ -101,6 +102,7 @@
 .. autoclass:: ImplicitComplexCompareViolation
 .. autoclass:: ReversedComplexCompareViolation
 .. autoclass:: IncorectLoopIterTypeViolation
+.. autoclass:: ImplicitInConditionViolation
 
 """
 
@@ -1372,3 +1374,35 @@ class IncorectLoopIterTypeViolation(ASTViolation):
 
     code = 335
     error_template = 'Found incorrect `for` loop iter type'
+
+
+@final
+class ImplicitInConditionViolation(ASTViolation):
+    """
+    Forbids to use multiple equality compare with the same variable name.
+
+    Reasoning:
+        Using double+ equality compare with ``or``
+        or double+ non-equality compare with ``and``
+        indicates that you have implicit ``in`` or ``not in`` condition.
+        It is just hidden from you.
+
+    Solution:
+        Refactor compares to use ``in`` or ``not in`` clauses.
+
+    Example::
+
+        # Correct:
+        print(some in {'first', 'second'})
+        print(some not in {'first', 'second'})
+
+        # Wrong:
+        print(some == 'first' or some == 'second')
+        print(some != 'first' and some != 'second')
+
+    .. versionadded:: 0.10.0
+
+    """
+
+    code = 336
+    error_template = 'Found implicit `in` condition'