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 and all my other projects via 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 repo branch if you need documentation for a specific RuboCop
release.
- Installation
- Basic Usage
- Configuration
- Disabling Cops within Source Code
- Formatters
- Compatibility
- Editor integration
- Guard integration
- Rake integration
- Extensions
- Team
- Logo
- Contributors
- Mailing List
- Changelog
- Copyright
RuboCop's installation is pretty standard:
$ gem install rubocop
If you'd rather install RuboCop using bundler
, don't require it in your Gemfile
:
gem 'rubocop', require: false
Running rubocop
with no arguments will check all Ruby source files
in the current directory:
$ rubocop
Alternatively you can pass rubocop
a list of files and directories to check:
$ rubocop app spec lib/something.rb
Here's RuboCop in action. Consider the following Ruby source code:
def badName
if something
test
end
end
Running 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. |
-F/--fail-fast |
Inspects in modification time order and stops after first file with offenses. |
-d/--debug |
Displays some extra debug output. |
-D/--display-cop-names |
Displays cop names 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. |
--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. |
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 stylistics 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 -l
The -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.
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 -R
or add the following directive to your .rubocop.yml
:
AllCops:
RunRailsCops: true
The 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: 99
Note: 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.
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.yml
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 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/DefaultScope:
Include:
- app/models/*.rb
Cops 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/DefaultScope:
Exclude:
- app/models/problematic.rb
In 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: false
Cops can customize their severity level. Allowed params are refactor
,
convention
, warning
, error
and fatal
.
Metrics/CyclomaticComplexity:
Severity: warning
If 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 all cops that
currently detect an offense in the code. Then you can start removing the
entries in the generated 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/StringLiterals
You can also disable all cops with
# rubocop:disable all
[...]
# rubocop:enable all
One or more cops can be disabled on a single line with an end-of-line comment.
for x in (0..19) # rubocop:disable Style/AvoidFor
You 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 $stdout
You 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 detected
The 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 detected
The 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: 00:00:02
Machine-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, 2
The 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 detected
Machine-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 vim
Machine-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 Total
Useful for CI environments. It will create an HTML report like this.
$ rubocop --format html -o rubocop.html
RuboCop supports the following Ruby implementations:
- MRI 1.9.3
- MRI 2.0
- MRI 2.1
- MRI 2.2
- 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 atom-lint package runs RuboCop and highlights the offenses in Atom.
You can also use the linter-rubocop plugin for Atom's linter.
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.
If 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.new
The 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
end
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-extension
Note: 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
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 MyCustomFormatter
Here'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 and all my other projects via 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) 2012-2014 Bozhidar Batsov. See LICENSE.txt for further details.