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 the use of output safety calls like html_safe, raw, and safe_concat. These methods do not escape content. They simply return a SafeBuffer containing the content as is. Instead, use safe_join to join content and escape it and concat to concatenate content and escape it, ensuring its safety.

Example:

user_content = "hi"

# bad
"
#{user_content}
".html_safe
# => ActiveSupport::SafeBuffer "
hi
"

# good
content_tag(:p, user_content)
# => ActiveSupport::SafeBuffer "
<b>hi</b>
"

# bad
out = ""
out << "
#{user_content}
"
out << "
#{user_content}
"
out.html_safe
# => ActiveSupport::SafeBuffer "
hi
hi
"

# good
out = []
out << content_tag(:li, user_content)
out << content_tag(:li, user_content)
safe_join(out)
# => ActiveSupport::SafeBuffer
#    "
<b>hi</b>
<b>hi</b>
"

# bad
out = "
trusted content
".html_safe
out.safe_concat(user_content)
# => ActiveSupport::SafeBuffer "
trusted_content
hi"

# good
out = "
trusted content
".html_safe
out.concat(user_content)
# => ActiveSupport::SafeBuffer
#    "
trusted_content
<b>hi</b>"

# safe, though maybe not good style
out = "trusted content"
result = out.concat(user_content)
# => String "trusted contenthi"
# because when rendered in ERB the String will be escaped:
# <%= result %>
# => trusted content<b>hi</b>

# bad
(user_content + " " + content_tag(:span, user_content)).html_safe
# => ActiveSupport::SafeBuffer "hi <span><b>hi</b></span>"

# good
safe_join([user_content, " ", content_tag(:span, user_content)])
# => ActiveSupport::SafeBuffer
#    "<b>hi</b> <span>&lt;b&gt;hi&lt;/b&gt;</span>"

This cop checks for the use of strings as keys in hashes. The use of symbols is preferred instead.

Example:

# bad
{ 'one' => 1, 'two' => 2, 'three' => 3 }

# good
{ one: 1, two: 2, three: 3 }

This cop checks for the use of strings as keys in hashes. The use of symbols is preferred instead.

Example:

# bad
{ 'one' => 1, 'two' => 2, 'three' => 3 }

# good
{ one: 1, two: 2, three: 3 }

This cop checks for the use of strings as keys in hashes. The use of symbols is preferred instead.

Example:

# bad
{ 'one' => 1, 'two' => 2, 'three' => 3 }

# good
{ one: 1, two: 2, three: 3 }

This cop checks for the use of strings as keys in hashes. The use of symbols is preferred instead.

Example:

# bad
{ 'one' => 1, 'two' => 2, 'three' => 3 }

# good
{ one: 1, two: 2, three: 3 }

This cop checks for the use of strings as keys in hashes. The use of symbols is preferred instead.

Example:

# bad
{ 'one' => 1, 'two' => 2, 'three' => 3 }

# good
{ one: 1, two: 2, three: 3 }

This cop checks for the use of strings as keys in hashes. The use of symbols is preferred instead.

Example:

# bad
{ 'one' => 1, 'two' => 2, 'three' => 3 }

# good
{ one: 1, two: 2, three: 3 }