Brakeman reports on several cases of remote code execution, in which a user is able to control and execute code in ways unintended by application authors.

The obvious form of this is the use of eval with user input.

However, Brakeman also reports on dangerous uses of send, constantize, and other methods which allow creation of arbitrary objects or calling of arbitrary methods.

Injection is #1 on the 2013 OWASP Top Ten web security risks. SQL injection is when a user is able to manipulate a value which is used unsafely inside a SQL query. This can lead to data leaks, data loss, elevation of privilege, and other unpleasant outcomes.

Brakeman focuses on ActiveRecord methods dealing with building SQL statements.

A basic (Rails 2.x) example looks like this:

User.first(:conditions => "username = '#{params[:username]}'")

Brakeman would produce a warning like this:

Possible SQL injection near line 30: User.first(:conditions => ("username = '#{params[:username]}'"))

The safe way to do this query is to use a parameterized query:

User.first(:conditions => ["username = ?", params[:username]])

Brakeman also understands the new Rails 3.x way of doing things (and local variables and concatenation):

username = params[:user][:name].downcase
password = params[:user][:password]

User.first.where("username = '" + username + "' AND password = '" + password + "'")

This results in this kind of warning:

Possible SQL injection near line 37:
User.first.where((((("username = '" + params[:user][:name].downcase) + "' AND password = '") + params[:user][:password]) + "'"))

See the Ruby Security Guide for more information and Rails-SQLi.org for many examples of SQL injection in Rails.

Unvalidated redirects and forwards are #10 on the OWASP Top Ten.

Redirects which rely on user-supplied values can be used to "spoof" websites or hide malicious links in otherwise harmless-looking URLs. They can also allow access to restricted areas of a site if the destination is not validated.

Brakeman will raise warnings whenever redirect_to appears to be used with a user-supplied value that may allow them to change the :host option.

For example,

redirect_to params.merge(:action => :home)

will create a warning like

Possible unprotected redirect near line 46: redirect_to(params)

This is because params could contain :host => 'evilsite.com' which would redirect away from your site and to a malicious site.

If the first argument to redirect_to is a hash, then adding :only_path => true will limit the redirect to the current host. Another option is to specify the host explicitly.

redirect_to params.merge(:only_path => true)

redirect_to params.merge(:host => 'myhost.com')

If the first argument is a string, then it is possible to parse the string and extract the path:

redirect_to URI.parse(some_url).path

If the URL does not contain a protocol (e.g., http://), then you will probably get unexpected results, as redirect_to will prepend the current host name and a protocol.

Brakeman reports on several cases of remote code execution, in which a user is able to control and execute code in ways unintended by application authors.

The obvious form of this is the use of eval with user input.

However, Brakeman also reports on dangerous uses of send, constantize, and other methods which allow creation of arbitrary objects or calling of arbitrary methods.

Unvalidated redirects and forwards are #10 on the OWASP Top Ten.

Redirects which rely on user-supplied values can be used to "spoof" websites or hide malicious links in otherwise harmless-looking URLs. They can also allow access to restricted areas of a site if the destination is not validated.

Brakeman will raise warnings whenever redirect_to appears to be used with a user-supplied value that may allow them to change the :host option.

For example,

redirect_to params.merge(:action => :home)

will create a warning like

Possible unprotected redirect near line 46: redirect_to(params)

This is because params could contain :host => 'evilsite.com' which would redirect away from your site and to a malicious site.

If the first argument to redirect_to is a hash, then adding :only_path => true will limit the redirect to the current host. Another option is to specify the host explicitly.

redirect_to params.merge(:only_path => true)

redirect_to params.merge(:host => 'myhost.com')

If the first argument is a string, then it is possible to parse the string and extract the path:

redirect_to URI.parse(some_url).path

If the URL does not contain a protocol (e.g., http://), then you will probably get unexpected results, as redirect_to will prepend the current host name and a protocol.

Unvalidated redirects and forwards are #10 on the OWASP Top Ten.

Redirects which rely on user-supplied values can be used to "spoof" websites or hide malicious links in otherwise harmless-looking URLs. They can also allow access to restricted areas of a site if the destination is not validated.

Brakeman will raise warnings whenever redirect_to appears to be used with a user-supplied value that may allow them to change the :host option.

For example,

redirect_to params.merge(:action => :home)

will create a warning like

Possible unprotected redirect near line 46: redirect_to(params)

This is because params could contain :host => 'evilsite.com' which would redirect away from your site and to a malicious site.

If the first argument to redirect_to is a hash, then adding :only_path => true will limit the redirect to the current host. Another option is to specify the host explicitly.

redirect_to params.merge(:only_path => true)

redirect_to params.merge(:host => 'myhost.com')

If the first argument is a string, then it is possible to parse the string and extract the path:

redirect_to URI.parse(some_url).path

If the URL does not contain a protocol (e.g., http://), then you will probably get unexpected results, as redirect_to will prepend the current host name and a protocol.

Using unfiltered user data to select a Class or Method to be dynamically sent is dangerous.

It is much safer to whitelist the desired target or method.

Unsafe use of method:

method = params[:method]
@result = User.send(method.to_sym)

Safe:

method = params[:method] == 1 ? :method_a : :method_b
@result = User.send(method, *args)

Unsafe use of target:

table = params[:table]
model = table.classify.constantize
@result = model.send(:method)

Safe:

target = params[:target] == 1 ? Account : User
@result = target.send(:method, *args)

Including user data in the arguments passed to an Object#send is safe, as long as the method can properly handle potentially bad data.

Safe:

args = params["args"] || []
@result = User.send(:method, *args)

Brakeman reports on several cases of remote code execution, in which a user is able to control and execute code in ways unintended by application authors.

The obvious form of this is the use of eval with user input.

However, Brakeman also reports on dangerous uses of send, constantize, and other methods which allow creation of arbitrary objects or calling of arbitrary methods.

This cop checks if the length a class exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

This cop tries to produce a complexity score that's a measure of the complexity the reader experiences when looking at a method. For that reason it considers when nodes as something that doesn't add as much complexity as an if or a &&. Except if it's one of those special case/when constructs where there's no expression after case. Then the cop treats it as an if/elsif/elsif... and lets all the when nodes count. In contrast to the CyclomaticComplexity cop, this cop considers else nodes as adding complexity.

Example:

def my_method                   # 1
  if cond                       # 1
    case var                    # 2 (0.8 + 4 * 0.2, rounded)
    when 1 then func_one
    when 2 then func_two
    when 3 then func_three
    when 4..10 then func_other
    end
  else                          # 1
    do_something until a && b   # 2
  end                           # ===
end                             # 7 complexity points

This cop checks if the length of a method exceeds some maximum value. Comment lines can optionally be ignored. The maximum allowed length is configurable.

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks that the cyclomatic complexity of methods is not higher than the configured maximum. The cyclomatic complexity is the number of linearly independent paths through a method. The algorithm counts decision points and adds one.

An if statement (or unless or ?:) increases the complexity by one. An else branch does not, since it doesn't add a decision point. The && operator (or keyword and) can be converted to a nested if statement, and ||/or is shorthand for a sequence of ifs, so they also add one. Loops can be said to have an exit condition, so they add one.

This cop checks that the ABC size of methods is not higher than the configured maximum. The ABC size is based on assignments, branches (method calls), and conditions. See http://c2.com/cgi/wiki?AbcMetric

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

This cop checks for excessive nesting of conditional and looping constructs.

You can configure if blocks are considered using the CountBlocks option. When set to false (the default) blocks are not counted towards the nesting level. Set to true to count blocks as well.

The maximum level of nesting allowed is configurable.

This cop checks for unused block arguments.

Example:

# bad

do_something do |used, unused|
  puts used
end

do_something do |bar|
  puts :foo
end

define_method(:foo) do |bar|
  puts :baz
end

Example:

#good

do_something do |used, _unused|
  puts used
end

do_something do
  puts :foo
end

define_method(:foo) do |_bar|
  puts :baz
end

This cop checks that the closing brace in an array literal is either on the same line as the last array element, or a new line.

When using the symmetrical (default) style:

If an array's opening brace is on the same line as the first element of the array, then the closing brace should be on the same line as the last element of the array.

If an array's opening brace is on the line above the first element of the array, then the closing brace should be on the line below the last element of the array.

When using the new_line style:

The closing brace of a multi-line array literal must be on the line after the last element of the array.

When using the same_line style:

The closing brace of a multi-line array literal must be on the same line as the last element of the array.

Example: EnforcedStyle: symmetrical (default)

# bad
  [ :a,
    :b
  ]

  # bad
  [
    :a,
    :b ]

  # good
  [ :a,
    :b ]

  # good
  [
    :a,
    :b
  ]

Example: EnforcedStyle: new_line

# bad
  [
    :a,
    :b ]

  # bad
  [ :a,
    :b ]

  # good
  [ :a,
    :b
  ]

  # good
  [
    :a,
    :b
  ]

Example: EnforcedStyle: same_line

# bad
  [ :a,
    :b
  ]

  # bad
  [
    :a,
    :b
  ]

  # good
  [
    :a,
    :b ]

  # good
  [ :a,
    :b ]

This cop checks for unused method arguments.

Example:

# bad

def some_method(used, unused, _unused_but_allowed)
  puts used
end

Example:

# good

def some_method(used, _unused, _unused_but_allowed)
  puts used
end

This cop checks for unused block arguments.

Example:

# bad

do_something do |used, unused|
  puts used
end

do_something do |bar|
  puts :foo
end

define_method(:foo) do |bar|
  puts :baz
end

Example:

#good

do_something do |used, _unused|
  puts used
end

do_something do
  puts :foo
end

define_method(:foo) do |_bar|
  puts :baz
end

This cop checks for :true and :false symbols. In most cases it would be a typo.

Example:

# bad
:true

# good
true

Example:

# bad
:false

# good
false

This cop checks for unused block arguments.

Example:

# bad

do_something do |used, unused|
  puts used
end

do_something do |bar|
  puts :foo
end

define_method(:foo) do |bar|
  puts :baz
end

Example:

#good

do_something do |used, _unused|
  puts used
end

do_something do
  puts :foo
end

define_method(:foo) do |_bar|
  puts :baz
end

This cop checks that the closing brace in an array literal is either on the same line as the last array element, or a new line.

When using the symmetrical (default) style:

If an array's opening brace is on the same line as the first element of the array, then the closing brace should be on the same line as the last element of the array.

If an array's opening brace is on the line above the first element of the array, then the closing brace should be on the line below the last element of the array.

When using the new_line style:

The closing brace of a multi-line array literal must be on the line after the last element of the array.

When using the same_line style:

The closing brace of a multi-line array literal must be on the same line as the last element of the array.

Example: EnforcedStyle: symmetrical (default)

# bad
  [ :a,
    :b
  ]

  # bad
  [
    :a,
    :b ]

  # good
  [ :a,
    :b ]

  # good
  [
    :a,
    :b
  ]

Example: EnforcedStyle: new_line

# bad
  [
    :a,
    :b ]

  # bad
  [ :a,
    :b ]

  # good
  [ :a,
    :b
  ]

  # good
  [
    :a,
    :b
  ]

Example: EnforcedStyle: same_line

# bad
  [ :a,
    :b
  ]

  # bad
  [
    :a,
    :b
  ]

  # good
  [
    :a,
    :b ]

  # good
  [ :a,
    :b ]

This cop checks for unused block arguments.

Example:

# bad

do_something do |used, unused|
  puts used
end

do_something do |bar|
  puts :foo
end

define_method(:foo) do |bar|
  puts :baz
end

Example:

#good

do_something do |used, _unused|
  puts used
end

do_something do
  puts :foo
end

define_method(:foo) do |_bar|
  puts :baz
end

This cop looks for uses of the for keyword, or each method. The preferred alternative is set in the EnforcedStyle configuration parameter. An each call with a block on a single line is always allowed, however.

If the else branch of a conditional consists solely of an if node, it can be combined with the else to become an elsif. This helps to keep the nesting level from getting too deep.

Example:

# bad
if condition_a
  action_a
else
  if condition_b
    action_b
  else
    action_c
  end
end

# good
if condition_a
  action_a
elsif condition_b
  action_b
else
  action_c
end

Checks for if and unless statements that would fit on one line if written as a modifier if/unless. The maximum line length is configured in the Metrics/LineLength cop.

Example:

# bad
if condition
  do_stuff(bar)
end

unless qux.empty?
  Foo.do_something
end

# good
do_stuff(bar) if condition
Foo.do_something unless qux.empty?

This cop enforces the consistent usage of %-literal delimiters.

Specify the 'default' key to set all preferred delimiters at once. You can continue to specify individual preferred delimiters to override the default.

Example:

# Style/PercentLiteralDelimiters:
#   PreferredDelimiters:
#     default: '[]'
#     '%i':    '()'

# good
%w[alpha beta] + %i(gamma delta)

# bad
%W(alpha #{beta})

# bad
%I(alpha beta)

This cop looks for unless expressions with else clauses.

Example:

# bad
unless foo_bar.nil?
  # do something...
else
  # do a different thing...
end

# good
if foo_bar.present?
  # do something...
else
  # do a different thing...
end

This cop enforces the consistent usage of %-literal delimiters.

Specify the 'default' key to set all preferred delimiters at once. You can continue to specify individual preferred delimiters to override the default.

Example:

# Style/PercentLiteralDelimiters:
#   PreferredDelimiters:
#     default: '[]'
#     '%i':    '()'

# good
%w[alpha beta] + %i(gamma delta)

# bad
%W(alpha #{beta})

# bad
%I(alpha beta)

This cop can check for array literals made up of word-like strings, that are not using the %w() syntax.

Alternatively, it can check for uses of the %w() syntax, in projects which do not want to include that syntax.

Configuration option: MinSize If set, arrays with fewer elements than this value will not trigger the cop. For example, a MinSize of 3 will not enforce a style on an array of 2 or fewer elements.

Example: EnforcedStyle: percent (default)

# good
%w[foo bar baz]

# bad
['foo', 'bar', 'baz']

Example: EnforcedStyle: brackets

# good
['foo', 'bar', 'baz']

# bad
%w[foo bar baz]

Checks for if and unless statements that would fit on one line if written as a modifier if/unless. The maximum line length is configured in the Metrics/LineLength cop.

Example:

# bad
if condition
  do_stuff(bar)
end

unless qux.empty?
  Foo.do_something
end

# good
do_stuff(bar) if condition
Foo.do_something unless qux.empty?

Checks for uses of if with a negated condition. Only ifs without else are considered. There are three different styles:

- both
- prefix
- postfix

Example: EnforcedStyle: both (default)

# enforces `unless` for `prefix` and `postfix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# bad

bar if !foo

# good

bar unless foo

Example: EnforcedStyle: prefix

# enforces `unless` for just `prefix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# good

bar if !foo

Example: EnforcedStyle: postfix

# enforces `unless` for just `postfix` conditionals

# bad

bar if !foo

# good

bar unless foo

# good

if !foo
  bar
end

Checks for uses of if with a negated condition. Only ifs without else are considered. There are three different styles:

- both
- prefix
- postfix

Example: EnforcedStyle: both (default)

# enforces `unless` for `prefix` and `postfix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# bad

bar if !foo

# good

bar unless foo

Example: EnforcedStyle: prefix

# enforces `unless` for just `prefix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# good

bar if !foo

Example: EnforcedStyle: postfix

# enforces `unless` for just `postfix` conditionals

# bad

bar if !foo

# good

bar unless foo

# good

if !foo
  bar
end

Use next to skip iteration instead of a condition at the end.

Example: EnforcedStyle: skipmodifierifs (default)

# bad
[1, 2].each do |a|
  if a == 1
    puts a
  end
end

# good
[1, 2].each do |a|
  next unless a == 1
  puts a
end

# good
[1, 2].each do |o|
  puts o unless o == 1
end

Example: EnforcedStyle: always

# With `always` all conditions at the end of an iteration needs to be
# replaced by next - with `skip_modifier_ifs` the modifier if like
# this one are ignored: `[1, 2].each { |a| return 'yes' if a == 1 }`

# bad
[1, 2].each do |o|
  puts o unless o == 1
end

# bad
[1, 2].each do |a|
  if a == 1
    puts a
  end
end

# good
[1, 2].each do |a|
  next unless a == 1
  puts a
end

This cop checks for unused method arguments.

Example:

# bad

def some_method(used, unused, _unused_but_allowed)
  puts used
end

Example:

# good

def some_method(used, _unused, _unused_but_allowed)
  puts used
end

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

This cop looks for uses of the for keyword, or each method. The preferred alternative is set in the EnforcedStyle configuration parameter. An each call with a block on a single line is always allowed, however.

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

Checks for if and unless statements that would fit on one line if written as a modifier if/unless. The maximum line length is configured in the Metrics/LineLength cop.

Example:

# bad
if condition
  do_stuff(bar)
end

unless qux.empty?
  Foo.do_something
end

# good
do_stuff(bar) if condition
Foo.do_something unless qux.empty?

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok

This cop checks for every useless assignment to local variable in every scope. The basic idea for this cop was from the warning of ruby -cw:

assigned but unused variable - foo

Currently this cop has advanced logic that detects unreferenced reassignments and properly handles varied cases such as branch, loop, rescue, ensure, etc.

Example:

# bad

def some_method
  some_var = 1
  do_something
end

Example:

# good

def some_method
  some_var = 1
  do_something(some_var)
end

Checks for if and unless statements that would fit on one line if written as a modifier if/unless. The maximum line length is configured in the Metrics/LineLength cop.

Example:

# bad
if condition
  do_stuff(bar)
end

unless qux.empty?
  Foo.do_something
end

# good
do_stuff(bar) if condition
Foo.do_something unless qux.empty?

Checks for uses of if with a negated condition. Only ifs without else are considered. There are three different styles:

- both
- prefix
- postfix

Example: EnforcedStyle: both (default)

# enforces `unless` for `prefix` and `postfix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# bad

bar if !foo

# good

bar unless foo

Example: EnforcedStyle: prefix

# enforces `unless` for just `prefix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# good

bar if !foo

Example: EnforcedStyle: postfix

# enforces `unless` for just `postfix` conditionals

# bad

bar if !foo

# good

bar unless foo

# good

if !foo
  bar
end

Checks for uses of if with a negated condition. Only ifs without else are considered. There are three different styles:

- both
- prefix
- postfix

Example: EnforcedStyle: both (default)

# enforces `unless` for `prefix` and `postfix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# bad

bar if !foo

# good

bar unless foo

Example: EnforcedStyle: prefix

# enforces `unless` for just `prefix` conditionals

# bad

if !foo
  bar
end

# good

unless foo
  bar
end

# good

bar if !foo

Example: EnforcedStyle: postfix

# enforces `unless` for just `postfix` conditionals

# bad

bar if !foo

# good

bar unless foo

# good

if !foo
  bar
end

This cop checks for braces around the last parameter in a method call if the last parameter is a hash. It supports braces, no_braces and context_dependent styles.

Example: EnforcedStyle: braces

# The `braces` style enforces braces around all method
# parameters that are hashes.

# bad
some_method(x, y, a: 1, b: 2)

# good
some_method(x, y, {a: 1, b: 2})

Example: EnforcedStyle: no_braces (default)

# The `no_braces` style checks that the last parameter doesn't
# have braces around it.

# bad
some_method(x, y, {a: 1, b: 2})

# good
some_method(x, y, a: 1, b: 2)

Example: EnforcedStyle: context_dependent

# The `context_dependent` style checks that the last parameter
# doesn't have braces around it, but requires braces if the
# second to last parameter is also a hash literal.

# bad
some_method(x, y, {a: 1, b: 2})
some_method(x, y, {a: 1, b: 2}, a: 1, b: 2)

# good
some_method(x, y, a: 1, b: 2)
some_method(x, y, {a: 1, b: 2}, {a: 1, b: 2})

Use a guard clause instead of wrapping the code inside a conditional expression

Example:

# bad
def test
  if something
    work
  end
end

# good
def test
  return unless something
  work
end

# also good
def test
  work if something
end

# bad
if something
  raise 'exception'
else
  ok
end

# good
raise 'exception' if something
ok