Limit empty lines in functions or methods body (#2487)

* add class and test for restrict all empty lines in func body

* add test case: function with comments

* add configuration param

* fix baseline for formatting violation

* self.generic_visit(node) in visitor

* rename WrongEmptyLinesCountVisitorViolation -> WrongEmptyLinesCountViolation

* 0 available empty lines case

* update CHANGELOG

* Fix tests

* Fix algorithm for calculating expression lines

* Update tests/test_visitors/test_ast/test_classes/test_wrong_empty_lines_count.py

fix typo

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Update wemake_python_styleguide/options/config.py

fix typo

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Update wemake_python_styleguide/options/defaults.py

fix typo

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Update wemake_python_styleguide/violations/best_practices.py

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Update wemake_python_styleguide/violations/best_practices.py

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Copying set by method

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Optimize visitor

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Update wemake_python_styleguide/visitors/ast/function_empty_lines.py

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>

* Fix typos and parse_ast_tree argument

* change visitor to BaseTokenVisitor

* test option

* test cases with docstring and comments

* fix error template

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

* expanded documentation

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

* test valid configuration with allow zero empty lines

Co-authored-by: Łukasz Skarżyński <skarzynski_lukasz@protonmail.com>
Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

CHANGELOG.md

@@ -25,6 +25,8 @@ Semantic versioning in our case means:
 - Adds `__init_subclass__` in the beginning of accepted methods
   order as per WPS338 #2411
 
+- Adds `WrongEmptyLinesCountViolation` #2486
+
 ### Bugfixes
 
 - Fixes `WPS226` false positives on `|` use in `SomeType | AnotherType`

tests/test_checker/test_noqa.py

@@ -303,6 +303,7 @@
     'WPS613': 1,
     'WPS614': 1,
     'WPS615': 2,
+    'WPS473': 0,
 })
 
 # Violations which may be tweaked by `i_control_code` option:

tests/test_visitors/test_ast/test_classes/test_wrong_empty_lines_count.py

@@ -0,0 +1,197 @@
+"""Test method contain only allowed empty lines count."""
+import pytest
+
+from wemake_python_styleguide.violations.best_practices import (
+    WrongEmptyLinesCountViolation,
+)
+from wemake_python_styleguide.visitors.ast.function_empty_lines import (
+    WrongEmptyLinesCountVisitor,
+)
+
+class_with_wrong_method = """
+class WrongClass(object):
+
+    def wrong_method(self):
+        foo()
+
+        bar()
+
+        baz()
+
+        lighter()
+"""
+
+class_with_valid_method = """
+class WrongClass(object):
+
+    def wrong_method(self):
+        foo()
+        bar()
+        baz()
+"""
+
+wrong_function = """
+def func():
+    foo()
+
+    a = 1 + 4
+
+    bar()
+
+    baz()
+"""
+
+wrong_function_with_loop = """
+def func():
+    for x in range(10):
+
+        requests.get(
+
+
+            'https://github.com/wemake-services/wemake-python-styleguide'
+        )
+"""
+
+allow_function = """
+def func():
+    foo()
+    if name == 'Moonflower':
+        print('Love')
+
+    baz()
+"""
+
+allow_function_with_comments = """
+def test_func():
+   # This function
+   #
+   # has lots
+   #
+   # of empty
+   #
+   # lines
+   #
+   # in comments
+   return 0
+"""
+
+function_with_docstring = """
+def test_func():
+   \"""
+   Its docstring
+
+   has many new lines
+
+   but this is
+
+   totally fine
+
+   we don't raise a violation for this
+   \"""
+   return
+"""
+
+function_with_docstring_and_comments = """
+def test_func():
+   \"""
+   Its docstring
+
+   has many new lines
+
+   but this is
+
+   totally fine
+
+   we don't raise a violation for this
+   \"""
+   # This function
+   #
+   # has lots
+   #
+   # of empty
+   #
+   # lines
+   #
+   # in comments
+   return 0
+"""
+
+
+@pytest.mark.parametrize('input_', [
+    class_with_wrong_method,
+    wrong_function,
+    wrong_function_with_loop,
+])
+def test_wrong(
+    input_,
+    default_options,
+    assert_errors,
+    parse_tokens,
+    mode,
+):
+    """Testing wrong cases."""
+    file_tokens = parse_tokens(mode(input_))
+
+    visitor = WrongEmptyLinesCountVisitor(
+        default_options, file_tokens=file_tokens,
+    )
+    visitor.run()
+
+    assert_errors(visitor, [WrongEmptyLinesCountViolation])
+
+
+@pytest.mark.parametrize('input_', [
+    class_with_valid_method,
+    allow_function,
+    allow_function_with_comments,
+    function_with_docstring,
+    function_with_docstring_and_comments,
+])
+def test_success(
+    input_,
+    parse_tokens,
+    default_options,
+    assert_errors,
+    mode,
+):
+    """Testing available cases."""
+    file_tokens = parse_tokens(mode(input_))
+
+    visitor = WrongEmptyLinesCountVisitor(
+        default_options, file_tokens=file_tokens,
+    )
+    visitor.run()
+
+    assert_errors(visitor, [])
+
+
+def test_zero_option(
+    parse_tokens,
+    default_options,
+    assert_errors,
+    options,
+    mode,
+):
+    """Test zero configuration."""
+    file_tokens = parse_tokens(mode(allow_function))
+    visitor = WrongEmptyLinesCountVisitor(
+        options(exps_for_one_empty_line=0), file_tokens=file_tokens,
+    )
+    visitor.run()
+    assert_errors(visitor, [WrongEmptyLinesCountViolation])
+
+
+def test_zero_option_with_valid_method(
+    parse_tokens,
+    default_options,
+    assert_errors,
+    options,
+    mode,
+):
+    """Test zero configuration with valid method."""
+    file_tokens = parse_tokens(mode(class_with_valid_method))
+    visitor = WrongEmptyLinesCountVisitor(
+        options(exps_for_one_empty_line=0), file_tokens=file_tokens,
+    )
+    visitor.run()
+    assert_errors(visitor, [])

wemake_python_styleguide/options/config.py

@@ -59,6 +59,9 @@
 - ``forbidden-inline-ignore`` - list of codes of violations or
     class of violations that are forbidden to ignore inline, defaults to
     :str:`wemake_python_styleguide.options.defaults.FORBIDDEN_INLINE_IGNORE`
+- ``exps-for-one-empty-line`` - number of expressions in
+    function or method body for available empty line (without code)
+    :str:`wemake_python_styleguide.options.defaults.EXPS_FOR_ONE_EMPTY_LINE`
 
 
 .. rubric:: Complexity options
@@ -262,6 +265,11 @@ class Configuration(object):
             type=String,
             comma_separated_list=True,
         ),
+        _Option(
+            '--exps-for-one-empty-line',
+            defaults.EXPS_FOR_ONE_EMPTY_LINE,
+            'Count of expressions for one empty line in a function body.',
+        ),
 
         # Complexity:
 

wemake_python_styleguide/options/defaults.py

@@ -46,6 +46,9 @@
 #: Violation codes that are forbidden to use.
 FORBIDDEN_INLINE_IGNORE: Final = ()
 
+#: Count of available expressions for one empty line in function or method body.
+EXPS_FOR_ONE_EMPTY_LINE: Final = 2
+
 # ===========
 # Complexity:
 # ===========

wemake_python_styleguide/options/validation.py

@@ -98,6 +98,7 @@ class _ValidatedOptions(object):
     max_import_from_members: int = attr.ib(validator=[_min_max(min=1)])
     max_tuple_unpack_length: int = attr.ib(validator=[_min_max(min=1)])
     show_violation_links: bool
+    exps_for_one_empty_line: int
 
 
 def validate_options(options: ConfigurationOptions) -> _ValidatedOptions:

wemake_python_styleguide/presets/types/tree.py

@@ -11,6 +11,7 @@
     conditions,
     decorators,
     exceptions,
+    function_empty_lines,
     functions,
     imports,
     iterables,
@@ -107,6 +108,8 @@
 
     redundancy.RedundantEnumerateVisitor,
 
+    function_empty_lines.WrongEmptyLinesCountVisitor,
+
     # Modules:
     modules.EmptyModuleContentsVisitor,
     modules.MagicModuleFunctionsVisitor,

wemake_python_styleguide/types.py

@@ -273,3 +273,7 @@ def max_tuple_unpack_length(self) -> int:
     @property
     def show_violation_links(self) -> bool:
         ...
+
+    @property
+    def exps_for_one_empty_line(self) -> int:
+        ...

wemake_python_styleguide/violations/best_practices.py

@@ -89,6 +89,7 @@
    KwargsUnpackingInClassDefinitionViolation
    ConsecutiveSlicesViolation
    GettingElementByUnpackingViolation
+   WrongEmptyLinesCountViolation
 
 Best practices
 --------------
@@ -166,6 +167,7 @@
 .. autoclass:: KwargsUnpackingInClassDefinitionViolation
 .. autoclass:: ConsecutiveSlicesViolation
 .. autoclass:: GettingElementByUnpackingViolation
+.. autoclass:: WrongEmptyLinesCountViolation
 
 """
 
@@ -2770,3 +2772,48 @@ class GettingElementByUnpackingViolation(ASTViolation):
         'Found unpacking used to get a single element from a collection'
     )
     code = 472
+
+
+@final
+class WrongEmptyLinesCountViolation(TokenizeViolation):
+    """
+    Limit empty lines in functions or methods body.
+
+    Reasoning:
+        It's not holistic to have functions or methods that contain many
+        empty lines, and it makes sense to divide the method into several
+        ones.
+
+    Solution:
+        Limit count of empty lines of the function or method body
+        By default, we allow 1 empty line for 2 non-empty lines.
+
+    Example::
+
+        # Correct:
+        def func(name):
+            foo()
+            if name == 'Moonflower':
+                print('Love')
+            baz()
+
+        # Wrong:
+        def func(name):
+            foo()
+
+            if name == 'Moonflower':
+                print('Love')
+
+            baz()
+
+    Configuration:
+        This rule is configurable with ``--exps-for-one-empty-line``.
+        Default:
+        :str:`wemake_python_styleguide.options.defaults.EXPS_FOR_ONE_EMPTY_LINE`
+
+    .. versionadded:: 0.17.0
+
+    """
+
+    error_template = 'Found too many empty lines in `def`: {0}'
+    code = 473