A sane Rubocop config

rubocop.yml

AllCops:
  RunRailsCops: true
  DisplayCopNames: true
  DisplayStyleGuide: false
  ExtraDetails: false
  UseCache: false
  Exclude:
    - bin/**/*
    - db/schema.rb
    - db/seeds.rb
    - vendor/bundle/**/*

# Indent private/protected/public as deep as method definitions.
Style/AccessModifierIndentation:
  EnforcedStyle: indent

# Align the key beginning and hash-rockets of multi-line hashes.
Style/AlignHash:
  EnforcedHashRocketStyle: table
  EnforcedColonStyle: table
  EnforcedLastArgumentHashStyle: always_inspect

# Align multi-line method calls to next indented level.
Style/AlignParameters:
  EnforcedStyle: with_fixed_indentation

# Ban `and` / `or` keywords everywhere.
Style/AndOr:
  EnforcedStyle: always

# Enforce %() over %Q().
Style/BarePercentLiterals:
  EnforcedStyle: bare_percent

# Enforce braces on single-line blocks and do..end around for multi-line blocks.
Style/BlockDelimiters:
  EnforcedStyle: line_count_based
  ProceduralMethods:
    # Calls which use method return value instead of block return value.
    - benchmark
    - bm
    - bmbm
    - create
    - each_with_object
    - measure
    - new
    - realtime
    - tap
    - with_object
  FunctionalMethods:
    # Calls with return values which don't appear to be used.
    - let
    - let!
    - subject
    - watch
  IgnoredMethods:
    # Methods which cannot be categorised based on their usage alone.
    - lambda
    - proc
    - it

# Require braces if second-to-last parameter is also a hash literal.
Style/BracesAroundHashParameters:
  EnforcedStyle: context_dependent

# Indent each `when` additional level inside case..end block.
Style/CaseIndentation:
  IndentWhenRelativeTo: case
  IndentOneStep: true

# Ban compact (e.g. `class Foo::Bar`) class/module definition style.
Style/ClassAndModuleChildren:
  EnforcedStyle: nested

# Prefer `is_a?` over `kind_of?`.
Style/ClassCheck:
  EnforcedStyle: is_a?

# TODO: https://github.com/bbatsov/rubocop/issues/1758
Style/ClosingParenthesisIndentation:
  Enabled: true

# Align with the style guide (but `reduce` is dumb).
Style/CollectionMethods:
  PreferredMethods:
    collect: 'map'
    collect!: 'map!'
    inject: 'inject'
    detect: 'find'
    find_all: 'select'

# Use `..` for single-line, and %x on multi-line commands.
Style/CommandLiteral:
  EnforcedStyle: mixed
  AllowInnerBackticks: false

# Enforce formatting of special comments.
Style/CommentAnnotation:
  Keywords:
    - FIXME
    - HACK
    - NOTE
    - OPTIMIZE
    - REVIEW
    - TODO

# General license is more than sufficient.
Style/Copyright:
  Enabled: false

# Don't require top-level class documentation.
Style/Documentation:
  Enabled: false

# Multi-line method chaining should be done with leading dots.
Style/DotPosition:
  EnforcedStyle: leading

# An explicit true/false return value is not an unreasonable expectation.
Style/DoubleNegation:
  Enabled: false

# Warn on empty else or else statements with nil.
Style/EmptyElse:
  EnforcedStyle: both

# Require empty lines only between multi-line method definitions.
Style/EmptyLineBetweenDefs:
  AllowAdjacentOneLineDefs: true

# No empty lines between block interior.
Style/EmptyLinesAroundBlockBody:
  EnforcedStyle: no_empty_lines

# No empty lines between class interior.
Style/EmptyLinesAroundClassBody:
  EnforcedStyle: no_empty_lines

# No empty lines between module interior.
Style/EmptyLinesAroundModuleBody:
  EnforcedStyle: no_empty_lines

# Require `# coding: utf-8` at beginning of each ruby file.
Style/Encoding:
  EnforcedStyle: always

# Loosens rules surrounding extra spacing intended for alignment.
Style/ExtraSpacing:
  AllowForAlignment: true
  Exclude:
    - app/views/**/*

# Ignore executable ruby script files.
Style/FileName:
  IgnoreExecutableScripts: true

# Indent first parameter for multi-line calls, require
# parentheses if any other arguments are also method calls.
Style/FirstParameterIndentation:
  EnforcedStyle: special_for_inner_method_call_in_parentheses

# Prefer `each` over `for` loops.
Style/For:
  EnforcedStyle: each

# Enforce `% foo` style for string formatting.
Style/FormatString:
  EnforcedStyle: format

# Ban global variables except the standard built-ins.
Style/GlobalVars:
  Enabled: true

# Prefer guard clauses for single-line `if` / `end` blocks.
Style/GuardClause:
  MinBodyLength: 1

# Prefer key-value pairs over hash-rockets and ban mixed styles.
Style/HashSyntax:
  EnforcedStyle: ruby19_no_mixed_keys
  UseHashRocketsWithSymbolValues: false

# Annoying rule.
Style/IfUnlessModifier:
  Enabled: false

# All method + modifier keywords should be indented the same.
Style/IndentationConsistency:
  EnforcedStyle: normal

Style/IndentationWidth:
  # Number of spaces for each indentation level.
  Width: 2

# Indent multi-line hash key-value pairs the same, regardless of context.
Style/IndentHash:
  EnforcedStyle: consistent

# Ban `lambda.(x, y)` syntactic sugar.
Style/LambdaCall:
  EnforcedStyle: call

# Use `next` to skip iteration instead of conditional at end.
Style/Next:
  EnforcedStyle: skip_modifier_ifs

# Allow various forms of `.nil?` checks, as `===` behavior CAN be important.
Style/NonNilCheck:
  IncludeSemanticChanges: false

# Always equire parantheses around method argument definitions.
Style/MethodDefParentheses:
  EnforcedStyle: require_parentheses

# Use snake_case for method definitions, since it's a nearly universal best
# practice to only use CamelCase in Ruby for certain constants.
Style/MethodName:
  EnforcedStyle: snake_case

# Enforce right-hand operand alignment of binary operations.
Style/MultilineOperationIndentation:
  EnforcedStyle: indented

# Require `_` in between each 3-digit group beyond 4-digits in length.
Style/NumericLiterals:
  MinDigits: 5

# Sometimes you need these, and they don't have identical behavior.
Style/OptionHash:
  Enabled: false

# Too handy to enable.
Style/ParallelAssignment:
  Enabled: false

# Allow safe assignment in conditions.
Style/ParenthesesAroundCondition:
  AllowSafeAssignment: true

# `{}` for strings, `[]` for arrays, `()` for everything else.
Style/PercentLiteralDelimiters:
  PreferredDelimiters:
    '%':  '{}'
    '%i': '[]'
    '%I': '[]'
    '%q': '{}'
    '%Q': '{}'
    '%r': '()'
    '%s': '()'
    '%w': '[]'
    '%W': '[]'
    '%x': '()'

# Use `%Q` only when necessary.
Style/PercentQLiterals:
  EnforcedStyle: lower_case_q

# Prefer `.foo?` over `.is_foo?`.
Style/PredicateName:
  NamePrefixBlacklist:
    - can_
    - has_
    - have_
    - is_
    - will_
  NameWhitelist:
    - is_a?

# Prefer `raise Exception, msg` over `raise Exception.new(msg)`.
Style/RaiseArgs:
  EnforcedStyle: exploded

# Prefer `return [x, y]` over `return x, y`.
Style/RedundantReturn:
  AllowMultipleReturnValues: false

# Prefer `/../` for regular expressions (and disallow inner slashes in `/../`).
Style/RegexpLiteral:
  EnforcedStyle: slashes
  AllowInnerSlashes: false

# Disallow multiple expressions on the same line.
Style/Semicolon:
  AllowAsExpressionSeparator: false

# This is garbage, considering there's a lack of prominent Ruby literature that
# effectively justifies the contrived nature of this semantic preference.
Style/SignalException:
  Enabled: false

# Variable names should always be expressive, and not be dictated simply because
# common method calls more prominently feature short-hand in the Ruby universe.
Style/SingleLineBlockParams:
  Enabled: false

# Disallow all single-line methods.
Style/SingleLineMethods:
  AllowIfMethodIsEmpty: false

# TODO: Not helpful for aligning similar, sequential method calls.
Style/SingleSpaceBeforeFirstArg:
  Enabled: false

# Require parentheses around short-hand lambda arguments.
Style/StabbyLambdaParentheses:
  EnforcedStyle: require_parentheses

# Prefer single-quotes when possible.
Style/StringLiterals:
  EnforcedStyle: single_quotes

# Prefer single-quotes when possible.
Style/StringLiteralsInInterpolation:
  EnforcedStyle: single_quotes

# No space between `|` and parameters in block definition.
Style/SpaceAroundBlockParameters:
  EnforcedStyleInsidePipes: no_space

# Require spaces around `=` sign when defining parameter defaults.
Style/SpaceAroundEqualsInParameterDefault:
  EnforcedStyle: space

# This just makes alignment a nightmare for conditional waterfall operations.
Style/SpaceAroundOperators:
  Enabled: false

# Require space between method call and block definition braces.
Style/SpaceBeforeBlockBraces:
  EnforcedStyle: space

# Require spaces inside block definition braces
Style/SpaceInsideBlockBraces:
  EnforcedStyle: space
  EnforcedStyleForEmptyBraces: space
  SpaceBeforeBlockParameters: true

# Require spaces inside hash definition braces, except for empty hashes.
Style/SpaceInsideHashLiteralBraces:
  EnforcedStyle: space
  EnforcedStyleForEmptyBraces: no_space

# Ban spaces inside string interpolation braces.
Style/SpaceInsideStringInterpolation:
  EnforcedStyle: no_space

# Prefer `.map(&:to_s)` over `.map { |i| i.to_s }`.
Style/SymbolProc:
  Enabled: true

# Require final newline at end of each Ruby file.
Style/TrailingBlankLines:
  EnforcedStyle: final_newline

# The precedent of including a trailing comma in lists is only for convenience
# of reading file diffs and shouldn't dictate the general style of any language.
Style/TrailingComma:
  EnforcedStyleForMultiline: no_comma

# Warn when defining methods which could use built-in `attr_*` declarations.
Style/TrivialAccessors:
  AllowDSLWriters: true
  AllowPredicates: false
  ExactNameMatch: true

# See Style/MethodName for more information.
Style/VariableName:
  EnforcedStyle: snake_case

# Warns when `while` loops could be single-line `while` / `until` loops.
Style/WhileUntilModifier:
  MaxLineLength: 80

# Prefer `%w[]` for array literals of word-like strings.
Style/WordArray:
  Enabled: true

##################### Metrics ##################################

# Enforces a reasonable maximum Assignment/Branch/Condition magnitude
# that will allow for organic development and timely warnings.
Metrics/AbcSize:
  Max: 16

# Warn when block nesting exceeds 3 levels.
Metrics/BlockNesting:
  Max: 3

# These values are rather contrived and have been reasonably adjusted to
# reflect the broader application of length metrics in the real world.
Metrics/ClassLength:
  CountComments: false
  Max: 120

# See Metrics/ClassLength for more information.
Metrics/ModuleLength:
  CountComments: false
  Max: 120

# Enforce a maximum CyclomaticComplexity magnitude.
Metrics/CyclomaticComplexity:
  Max: 7

# The archaic practice of 80-character line lengths is hilariously insufficient.
Metrics/LineLength:
  Max: 100
  AllowURI: true

# See Metrics/ClassLength for more information.
Metrics/MethodLength:
  CountComments: false
  Max: 15

# Use keyword arguments if parameter list length exceeds 5 declarations.
Metrics/ParameterLists:
  CountKeywordArgs: false
  Max: 5

# Sets maximum score for the ease of reading a method.
Metrics/PerceivedComplexity:
  Max: 7

##################### Lint ##################################

# Allow safe assignment in conditions.
Lint/AssignmentInCondition:
  AllowSafeAssignment: true

# Align `end` with `keyword`.
Lint/EndAlignment:
  AlignWith: keyword

# Align with current level of modifier keyword indentation.
Lint/DefEndAlignment:
  AlignWith: start_of_line

# Checks for unused block arguments.
Lint/UnusedBlockArgument:
  IgnoreEmptyBlocks: true

# Checks for unused method arguments.
Lint/UnusedMethodArgument:
  AllowUnusedKeywordArguments: false
  IgnoreEmptyMethods: true

##################### Rails ##################################

# Enforce `_action` over `_filter`.
Rails/ActionFilter:
  EnforcedStyle: action

# Allow calls which are overridden to reflect current timezone.
Rails/Date:
  EnforcedStyle: flexible

# See Rails/Date for more information
Rails/TimeZone:
  EnforcedStyle: flexible