Role models are important.
-- Officer Alex J. Murphy / RoboCop
RuboCop is a Ruby static code analyzer. Out of the box it will enforce many of the guidelines outlined in the community Ruby Style Guide.
Most aspects of its behavior can be tweaked via various configuration options.
Apart from reporting problems in your code, RuboCop can also automatically fix some of the problems for you.
You can support my work on RuboCop via Salt and Gratipay.
This documentation tracks the master branch of RuboCop. Some of
the features and settings discussed here might not be available in
older releases (including the current stable release). Please, consult
the relevant git tag (e.g. v0.30.0) if you need documentation for a
specific RuboCop release.
- Installation
- Basic Usage
- Configuration
- Disabling Cops within Source Code
- Formatters
- Compatibility
- Editor integration
- Git pre-commit hook integration
- Guard integration
- Rake integration
- Exit codes
- Caching
- Extensions
- Team
- Logo
- Contributors
- Mailing List
- Changelog
- Copyright
RuboCop's installation is pretty standard:
$ gem install rubocopIf you'd rather install RuboCop using bundler, don't require it in your Gemfile:
gem 'rubocop', require: falseRuboCop's development is moving at a very rapid pace and there are
often backward-incompatible changes between minor releases (since we
haven't reached version 1.0 yet). To prevent an unwanted RuboCop update you
might want to use a conservative version locking in your Gemfile:
gem 'rubocop', '~> 0.38.0', require: falseRunning rubocop with no arguments will check all Ruby source files
in the current directory:
$ rubocopAlternatively you can pass rubocop a list of files and directories to check:
$ rubocop app spec lib/something.rbHere's RuboCop in action. Consider the following Ruby source code:
def badName
if something
test
end
endRunning RuboCop on it (assuming it's in a file named test.rb) would produce the following report:
Inspecting 1 file
W
Offenses:
test.rb:1:5: C: Use snake_case for method names.
def badName
^^^^^^^
test.rb:2:3: C: Use a guard clause instead of wrapping the code inside a conditional expression.
if something
^^
test.rb:2:3: C: Favor modifier if usage when having a single-line body. Another good alternative is the usage of control flow &&/||.
if something
^^
test.rb:4:5: W: end at 4, 4 is not aligned with if at 2, 2
end
^^^
1 file inspected, 4 offenses detected
For more details check the available command-line options:
$ rubocop -h| Command flag | Description |
|---|---|
-v/--version |
Displays the current version and exits. |
-V/--verbose-version |
Displays the current version plus the version of Parser and Ruby. |
-L/--list-target-files |
List all files RuboCop will inspect. |
-F/--fail-fast |
Inspects in modification time order and stops after first file with offenses. |
-C/--cache |
Store and reuse results for faster operation. |
-d/--debug |
Displays some extra debug output. |
-D/--display-cop-names |
Displays cop names in offense messages. |
-E/--extra-details |
Displays extra details in offense messages. |
-c/--config |
Run with specified config file. |
-f/--format |
Choose a formatter. |
-o/--out |
Write output to a file instead of STDOUT. |
-r/--require |
Require Ruby file (see Loading Extensions). |
-R/--rails |
Run extra Rails cops. |
-l/--lint |
Run only lint cops. |
-a/--auto-correct |
Auto-correct certain offenses. Note: Experimental - use with caution. |
--only |
Run only the specified cop(s) and/or cops in the specified departments. |
--except |
Run all cops enabled by configuration except the specified cop(s) and/or departments. |
--auto-gen-config |
Generate a configuration file acting as a TODO list. |
--no-offense-counts |
Don't show offense counts in config file generated by --auto-gen-config |
--exclude-limit |
Limit how many individual files --auto-gen-config can list in Exclude parameters, default is 15. |
--show-cops |
Shows available cops and their configuration. |
--fail-level |
Minimum severity for exit with error code. Full severity name or upper case initial can be given. Normally, auto-corrected offenses are ignored. Use A or autocorrect if you'd like them to trigger failure. |
-s/--stdin |
Pipe source from STDIN. This is useful for editor integration. |
--[no-]color |
Force color output on or off. |
In RuboCop lingo the various checks performed on the code are called cops. There are several cop departments.
You can also load custom cops.
Most of the cops in RuboCop are so called style cops that check for stylistic problems in your code. Almost all of the them are based on the Ruby Style Guide. Many of the style cops have configurations options allowing them to support different popular coding conventions.
Lint cops check for possible errors and very bad practices in your
code. RuboCop implements in a portable way all built-in MRI lint
checks (ruby -wc) and adds a lot of extra lint checks of its
own. You can run only the lint cops like this:
$ rubocop -lThe -l/--lint option can be used together with --only to run all the
enabled lint cops plus a selection of other cops.
Disabling any of the lint cops is generally a bad idea.
Metrics cops deal with properties of the source code that can be measured,
such as class length, method length, etc. Generally speaking, they have a
configuration parameter called Max and when running
rubocop --auto-gen-config, this parameter will be set to the highest value
found for the inspected code.
Performance cops catch Ruby idioms which are known to be slower than another equivalent (and equally readable) idiom.
Rails cops are specific to the Ruby on Rails framework. Unlike style and lint cops they are not used by default and you have to request them specifically:
$ rubocop -Ror add the following directive to your .rubocop.yml:
Rails:
Enabled: trueThe behavior of RuboCop can be controlled via the .rubocop.yml configuration file. It makes it possible to enable/disable certain cops (checks) and to alter their behavior if they accept any parameters. The file can be placed either in your home directory or in some project directory.
RuboCop will start looking for the configuration file in the directory where the inspected file is and continue its way up to the root directory.
The file has the following format:
inherit_from: ../.rubocop.yml
Style/Encoding:
Enabled: false
Metrics/LineLength:
Max: 99Note: Qualifying cop name with its type, e.g., Style, is recommended,
but not necessary as long as the cop name is unique across all types.
RuboCop supports inheriting configuration from one or more supplemental configuration files at runtime.
The optional inherit_from directive is used to include configuration
from one or more files. This makes it possible to have the common
project settings in the .rubocop.yml file at the project root, and
then only the deviations from those rules in the subdirectories. The
files can be given with absolute paths or paths relative to the file
where they are referenced. The settings after an inherit_from
directive override any settings in the file(s) inherited from. When
multiple files are included, the first file in the list has the lowest
precedence and the last one has the highest. The format for multiple
inheritance is:
inherit_from:
- ../.rubocop.yml
- ../conf/.rubocop.ymlThe optional inherit_from directive can contain a full url to a remote
file. This makes it possible to have common project settings stored on a http
server and shared between many projects.
The remote config file is cached locally and is only updated if:
- The file does not exist.
- The file has not been updated in the last 24 hours.
- The remote copy has a newer modification time than the local copy.
You can inherit from both remote and local files in the same config and the same inheritance rules apply to remote URLs and inheriting from local files where the first file in the list has the lowest precedence and the last one has the highest. The format for multiple inheritance using URLs is:
inherit_from:
- http://www.example.com/rubocop.yml
- ../.rubocop.ymlThe optional inherit_gem directive is used to include configuration from
one or more gems external to the current project. This makes it possible to
inherit a shared dependency's RuboCop configuration that can be used from
multiple disparate projects.
Configurations inherited in this way will be essentially prepended to the
inherit_from directive, such that the inherit_gem configurations will be
loaded first, then the inherit_from relative file paths will be loaded
(overriding the configurations from the gems), and finally the remaining
directives in the configuration file will supersede any of the inherited
configurations. This means the configurations inherited from one or more gems
have the lowest precedence of inheritance.
The directive should be formatted as a YAML Hash using the gem name as the key and the relative path within the gem as the value:
inherit_gem:
my-shared-gem: .rubocop.yml
cucumber: conf/rubocop.ymlNote: If the shared dependency is declared using a Bundler
Gemfile and the gem was installed using bundle install, it would be
necessary to also invoke RuboCop using Bundler in order to find the
dependency's installation path at runtime:
$ bundle exec rubocop <options...>
The file
config/default.yml
under the RuboCop home directory contains the default settings that
all configurations inherit from. Project and personal .rubocop.yml
files need only make settings that are different from the default
ones. If there is no .rubocop.yml file in the project or home
directory, config/default.yml will be used.
RuboCop checks all files found by a recursive search starting from the
directory it is run in, or directories given as command line
arguments. However, it only recognizes files ending with .rb or
extensionless files with a #!.*ruby declaration as Ruby files.
Hidden directories (i.e., directories whose names start with a dot)
are not searched by default. If you'd like it to check files that are
not included by default, you'll need to pass them in on the command
line, or to add entries for them under AllCops/Include. Files and
directories can also be ignored through AllCops/Exclude.
Here is an example that might be used for a Rails project:
AllCops:
Include:
- '**/Rakefile'
- '**/config.ru'
Exclude:
- 'db/**/*'
- 'config/**/*'
- 'script/**/*'
- !ruby/regexp /old_and_unused\.rb$/
# other configuration
# ...Files and directories are specified relative to the .rubocop.yml file.
Note: Patterns that are just a file name, e.g. Rakefile, will match
that file name in any directory, but this pattern style is deprecated. The
correct way to match the file in any directory, including the current, is
**/Rakefile.
Note: The pattern config/** will match any file recursively under
config, but this pattern style is deprecated and should be replaced by
config/**/*.
Note: The Include and Exclude parameters are special. They are
valid for the directory tree starting where they are defined. They are not
shadowed by the setting of Include and Exclude in other .rubocop.yml
files in subdirectories. This is different from all other parameters, who
follow RuboCop's general principle that configuration for an inspected file
is taken from the nearest .rubocop.yml, searching upwards.
Cops can be run only on specific sets of files when that's needed (for
instance you might want to run some Rails model checks only on files whose
paths match app/models/*.rb). All cops support the
Include param.
Rails/HasAndBelongsToMany:
Include:
- app/models/*.rbCops can also exclude only specific sets of files when that's needed (for
instance you might want to run some cop only on a specific file). All cops support the
Exclude param.
Rails/HasAndBelongsToMany:
Exclude:
- app/models/problematic.rbIn addition to Include and Exclude, the following parameters are available
for every cop.
Specific cops can be disabled by setting Enabled to false for that specific cop.
Metrics/LineLength:
Enabled: falseMost cops are enabled by default. Some cops, configured in config/disabled.yml, are disabled by default. The cop enabling process can be altered by setting DisabledByDefault to true.
AllCops:
DisabledByDefault: trueAll cops are then disabled by default, and only cops appearing in user configuration files are enabled. Enabled: true does not have to be set for cops in user configuration. They will be enabled anyway.
Each cop has a default severity level based on which department it belongs
to. The level is warning for Lint and convention for all the others.
Cops can customize their severity level. Allowed params are refactor,
convention, warning, error and fatal.
There is one exception from the general rule above and that is Lint/Syntax, a
special cop that checks for syntax errors before the other cops are invoked. It
can not be disabled and its severity (fatal) can not be changed in
configuration.
Metrics/CyclomaticComplexity:
Severity: warningIndividual cops can be embellished with extra details in offense messages:
Metrics/LineLength:
Details: >-
If lines are too short, text becomes hard to read because you must
constantly jump from one line to the next while reading. If lines are too
long, the line jumping becomes too hard because you "lose the line" while
going back to the start of the next line. 80 characters is a good
compromise.Cops that support the --auto-correct option can have that support
disabled. For example:
Style/PerlBackrefs:
AutoCorrect: falseSome checks are dependent on the version of the Ruby interpreter which the inspected code must run on. For example, using Ruby 2.0+ keyword arguments rather than an options hash can help make your code shorter and more expressive... unless it must run on Ruby 1.9.
Let RuboCop know the oldest version of Ruby which your project supports with:
AllCops:
TargetRubyVersion: 1.9If you have a code base with an overwhelming amount of offenses, it can
be a good idea to use rubocop --auto-gen-config and add an
inherit_from: .rubocop_todo.yml in your .rubocop.yml. The generated
file .rubocop_todo.yml contains configuration to disable cops that
currently detect an offense in the code by excluding the offending
files, or disabling the cop altogether once a file count limit has been
reached.
By adding the option --exclude-limit COUNT, e.g., rubocop --auto-gen-config --exclude-limit 5, you can change how many files are
excluded before the cop is entirely disabled. The default COUNT is 15.
Then you can start removing the entries in the generated
.rubocop_todo.yml file one by one as you work through all the offenses
in the code.
One or more individual cops can be disabled locally in a section of a file by adding a comment such as
# rubocop:disable Metrics/LineLength, Style/StringLiterals
[...]
# rubocop:enable Metrics/LineLength, Style/StringLiteralsYou can also disable all cops with
# rubocop:disable all
[...]
# rubocop:enable allOne or more cops can be disabled on a single line with an end-of-line comment.
for x in (0..19) # rubocop:disable Style/AvoidForYou can change the output format of RuboCop by specifying formatters with the -f/--format option.
RuboCop ships with several built-in formatters, and also you can create your custom formatter.
Additionally the output can be redirected to a file instead of $stdout with the -o/--out option.
Some of the built-in formatters produce machine-parsable output and they are considered public APIs. The rest of the formatters are for humans, so parsing their outputs is discouraged.
You can enable multiple formatters at the same time by specifying -f/--format multiple times.
The -o/--out option applies to the previously specified -f/--format,
or the default progress format if no -f/--format is specified before the -o/--out option.
# Simple format to $stdout.
$ rubocop --format simple
# Progress (default) format to the file result.txt.
$ rubocop --out result.txt
# Both progress and offense count formats to $stdout.
# The offense count formatter outputs only the final summary,
# so you'll mostly see the outputs from the progress formatter,
# and at the end the offense count summary will be outputted.
$ rubocop --format progress --format offenses
# Progress format to $stdout, and JSON format to the file rubocop.json.
$ rubocop --format progress --format json --out rubocop.json
# ~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~
# | |_______________|
# $stdout
# Progress format to result.txt, and simple format to $stdout.
$ rubocop --output result.txt --format simple
# ~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~
# | |
# default format $stdoutYou can also load custom formatters.
The default progress formatter outputs a character for each inspected file,
and at the end it displays all detected offenses in the clang format.
A . represents a clean file, and each of the capital letters means
the severest offense (convention, warning, error or fatal) found in a file.
$ rubocop
Inspecting 26 files
..W.C....C..CWCW.C...WC.CC
Offenses:
lib/foo.rb:6:5: C: Missing top-level class documentation comment.
class Foo
^^^^^
...
26 files inspected, 46 offenses detectedThe clang formatter displays the offenses in a manner similar to clang:
$ rubocop test.rb
Inspecting 1 file
W
Offenses:
test.rb:1:5: C: Use snake_case for method names.
def badName
^^^^^^^
test.rb:2:3: C: Use a guard clause instead of wrapping the code inside a conditional expression.
if something
^^
test.rb:2:3: C: Favor modifier if usage when having a single-line body. Another good alternative is the usage of control flow &&/||.
if something
^^
test.rb:4:5: W: end at 4, 4 is not aligned with if at 2, 2
end
^^^
1 file inspected, 4 offenses detectedThe fuubar style formatter displays a progress bar
and shows details of offenses in the clang format as soon as they are detected.
This is inspired by the Fuubar formatter for RSpec.
$ rubocop --format fuubar
lib/foo.rb.rb:1:1: C: Use snake_case for methods and variables.
def badName
^^^^^^^
lib/bar.rb:13:14: W: File.exists? is deprecated in favor of File.exist?.
File.exists?(path)
^^^^^^^
22/53 files |======== 43 ========> | ETA: 00:00:02Machine-parsable
The emacs formatter displays the offenses in a format suitable for consumption by Emacs (and possibly other tools).
$ rubocop --format emacs test.rb
/Users/bozhidar/projects/test.rb:1:1: C: Use snake_case for methods and variables.
/Users/bozhidar/projects/test.rb:2:3: C: Favor modifier if/unless usage when you have a single-line body. Another good alternative is the usage of control flow &&/||.
/Users/bozhidar/projects/test.rb:4:5: W: end at 4, 4 is not aligned with if at 2, 2The name of the formatter says it all :-)
$ rubocop --format simple test.rb
== test.rb ==
C: 1: 5: Use snake_case for method names.
C: 2: 3: Use a guard clause instead of wrapping the code inside a conditional expression.
C: 2: 3: Favor modifier if usage when having a single-line body. Another good alternative is the usage of control flow &&/||.
W: 4: 5: end at 4, 4 is not aligned with if at 2, 2
1 file inspected, 4 offenses detectedMachine-parsable
Sometimes you might want to just open all files with offenses in your favorite editor. This formatter outputs just the names of the files with offenses in them and makes it possible to do something like:
$ rubocop --format files | xargs vimMachine-parsable
You can get RuboCop's inspection result in JSON format by passing --format json option in command line.
The JSON structure is like the following example:
{
"metadata": {
"rubocop_version": "0.9.0",
"ruby_engine": "ruby",
"ruby_version": "2.0.0",
"ruby_patchlevel": "195",
"ruby_platform": "x86_64-darwin12.3.0"
},
"files": [{
"path": "lib/foo.rb",
"offenses": []
}, {
"path": "lib/bar.rb",
"offenses": [{
"severity": "convention",
"message": "Line is too long. [81/80]",
"cop_name": "LineLength",
"corrected": true,
"location": {
"line": 546,
"column": 80,
"length": 4
}
}, {
"severity": "warning",
"message": "Unreachable code detected.",
"cop_name": "UnreachableCode",
"corrected": false,
"location": {
"line": 15,
"column": 9,
"length": 10
}
}
]
}
],
"summary": {
"offense_count": 2,
"target_file_count": 2,
"inspected_file_count": 2
}
}Sometimes when first applying RuboCop to a codebase, it's nice to be able to see where most of your style cleanup is going to be spent.
With this in mind, you can use the offense count formatter to outline the offended cops and the number of offenses found for each by running:
$ rubocop --format offenses
87 Documentation
12 DotPosition
8 AvoidGlobalVars
7 EmptyLines
6 AssignmentInCondition
4 Blocks
4 CommentAnnotation
3 BlockAlignment
1 IndentationWidth
1 AvoidPerlBackrefs
1 ColonMethodCall
--
134 TotalSimilar to the Offense Count formatter, but lists the files which need the most attention:
$ rubocop --format worst
89 this/file/is/really/bad.rb
2 much/better.rb
--
91 TotalUseful for CI environments. It will create an HTML report like this.
$ rubocop --format html -o rubocop.htmlRuboCop supports the following Ruby implementations:
- MRI 1.9.3
- MRI 2.0
- MRI 2.1
- MRI 2.2
- MRI 2.3
- JRuby in 1.9 mode
- Rubinius 2.0+
rubocop.el is a simple Emacs interface for RuboCop. It allows you to run RuboCop inside Emacs and quickly jump between problems in your code.
flycheck > 0.9 also supports RuboCop and uses it by default when available.
The vim-rubocop plugin runs RuboCop and displays the results in Vim.
There's also a RuboCop checker in syntastic.
If you're a ST user you might find the Sublime RuboCop plugin useful.
The brackets-rubocop extension displays RuboCop results in Brackets. It can be installed via the extension manager in Brackets.
The textmate2-rubocop bundle displays formatted RuboCop results in a new window. Installation instructions can be found here.
The linter-rubocop plugin for Atom's linter runs RuboCop and highlights the offenses in Atom.
The lt-rubocop plugin provides LightTable integration.
The rubocop-for-rubymine plugin provides basic RuboCop integration for RubyMine/IntelliJ IDEA.
Here's one great opportunity to contribute to RuboCop - implement RuboCop integration for your favorite editor.
overcommit is a fully configurable and
extendable Git commit hook manager. To use RuboCop with overcommit, add the
following to your .overcommit.yml file:
PreCommit:
RuboCop:
enabled: trueIf you're fond of Guard you might like guard-rubocop. It allows you to automatically check Ruby code style with RuboCop when files are modified.
To use RuboCop in your Rakefile add the following:
require 'rubocop/rake_task'
RuboCop::RakeTask.newIf you run rake -T, the following two RuboCop tasks should show up:
rake rubocop # Run RuboCop
rake rubocop:auto_correct # Auto-correct RuboCop offensesThe above will use default values
require 'rubocop/rake_task'
desc 'Run RuboCop on the lib directory'
RuboCop::RakeTask.new(:rubocop) do |task|
task.patterns = ['lib/**/*.rb']
# only show the files with failures
task.formatters = ['files']
# don't abort rake on failure
task.fail_on_error = false
endRuboCop exits with the following status codes:
- 0 if no offenses are found, or if the severity of all offenses are less than
--fail-level. (By default, if you use--auto-correct, offenses which are auto-corrected do not cause RuboCop to fail.) - 1 if one or more offenses equal or greater to
--fail-levelare found. (By default, this is any offense which is not auto-corrected.) - 2 if RuboCop terminates abnormally due to invalid configuration, invalid CLI options, or an internal error.
Large projects containing hundreds or even thousands of files can take a really long time to inspect, but RuboCop has functionality to mitigate this problem. There's a caching mechanism that stores information about offenses found in inspected files.
Later runs will be able to retrieve this information and present the stored information instead of inspecting the file again. This will be done if the cache for the file is still valid, which it is if there are no changes in:
- the contents of the inspected file
- RuboCop configuration for the file
- the options given to
rubocop, with some exceptions that have no bearing on which offenses are reported - the Ruby version used to invoke
rubocop - version of the
rubocopprogram (or to be precise, anything in the source code of the invokedrubocopprogram)
The caching functionality is enabled if the configuration parameter
AllCops: UseCache is true, which it is by default. The command
line option --cache false can be used to turn off caching, thus
overriding the configuration parameter. If AllCops: UseCache is set
to false in the local .rubocop.yml, then it's --cache true that
overrides the setting.
By default, the cache is stored in in a subdirectory of the temporary
directory, /tmp/rubocop_cache/ on Unix-like systems. The
configuration parameter AllCops: CacheRootDirectory can be used to
set it to a different path. One reason to use this option could be
that there's a network disk where users on different machines want to
have a common RuboCop cache. Another could be that a Continuous
Integration system allows directories, but not a temporary directory,
to be saved between runs.
Each time a file has changed, its offenses will be stored under a new
key in the cache. This means that the cache will continue to grow
until we do something to stop it. The configuration parameter
AllCops: MaxFilesInCache sets a limit, and when the number of files
in the cache exceeds that limit, the oldest files will be automatically
removed from the cache.
It's possible to extend RuboCop with custom cops and formatters.
Besides the --require command line option you can also specify ruby
files that should be loaded with the optional require directive in the
.rubocop.yml file:
require:
- ../my/custom/file.rb
- rubocop-extensionNote: The paths are directly passed to Kernel.require. If your
extension file is not in $LOAD_PATH, you need to specify the path as
relative path prefixed with ./ explicitly, or absolute path.
You can configure the custom cops in your .rubocop.yml just like any
other cop.
- rubocop-rspec - RSpec-specific analysis
- rubocop-cask - Analysis for Homebrew-Cask files.
You can customize RuboCop's output format with custom formatters.
To implement a custom formatter, you need to subclass
RuboCop::Formatter::BaseFormatter and override some methods,
or implement all formatter API methods by duck typing.
Please see the documents below for more formatter API details.
You can tell RuboCop to use your custom formatter with a combination of
--format and --require option.
For example, when you have defined MyCustomFormatter in
./path/to/my_custom_formatter.rb, you would type this command:
$ rubocop --require ./path/to/my_custom_formatter --format MyCustomFormatterHere's a list of RuboCop's core developers:
RuboCop's logo was created by Dimiter Petrov. You can find the logo in various formats here.
The logo is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
Here's a list of all the people who have contributed to the development of RuboCop.
I'm extremely grateful to each and every one of them!
If you'd like to contribute to RuboCop, please take the time to go through our short contribution guidelines.
Converting more of the Ruby Style Guide into RuboCop cops is our top priority right now. Writing a new cop is a great way to dive into RuboCop!
Of course, bug reports and suggestions for improvements are always welcome. GitHub pull requests are even better! :-)
You can also support my work on RuboCop via Salt and Gratipay.
If you're interested in everything regarding RuboCop's development, consider joining its Google Group.
If you're into IRC you can visit the #rubocop channel on Freenode.
RuboCop's changelog is available here.
Copyright (c) 2012-2016 Bozhidar Batsov. See LICENSE.txt for further details.