ifmeorg/ifme

Checks for non-atomic file operation. And then replace it with a nearly equivalent and atomic method.

These can cause problems that are difficult to reproduce, especially in cases of frequent file operations in parallel, such as test runs with parallel_rspec.

For examples: creating a directory if there is none, has the following problems

An exception occurs when the directory didn't exist at the time of exist?, but someone else created it before mkdir was executed.

Subsequent processes are executed without the directory that should be there when the directory existed at the time of exist?, but someone else deleted it shortly afterwards.

Safety:

This cop is unsafe, because autocorrection change to atomic processing. The atomic processing of the replacement destination is not guaranteed to be strictly equivalent to that before the replacement.

Example:

# bad - race condition with another process may result in an error in `mkdir`
unless Dir.exist?(path)
  FileUtils.mkdir(path)
end

# good - atomic and idempotent creation
FileUtils.mkdir_p(path)

# bad - race condition with another process may result in an error in `remove`
if File.exist?(path)
  FileUtils.remove(path)
end

# good - atomic and idempotent removal
FileUtils.rm_f(path)

This cop is used to identify usages of all.each and change them to use all.find_each instead.

Example:

# bad
User.all.each

# good
User.all.find_each

Checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

NOTE: When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Two modes are supported: 1. aggressive style checks and corrects all occurrences of + where either the left or right side of + is a string literal. 2. conservative style on the other hand, checks and corrects only if left side (receiver of + method call) is a string literal. This is useful when the receiver is some expression that returns string like Pathname instead of a string literal.

Safety:

This cop is unsafe in aggressive mode, as it cannot be guaranteed that the receiver is actually a string, which can result in a false positive.

Example: Mode: aggressive (default)

# bad
email_with_name = user.name + ' <' + user.email + '>'
Pathname.new('/') + 'test'

# good
email_with_name = "#{user.name} <#{user.email}>"
email_with_name = format('%s <%s>', user.name, user.email)
"#{Pathname.new('/')}test"

# accepted, line-end concatenation
name = 'First' +
  'Last'

Example: Mode: conservative

# bad
'Hello' + user.name

# good
"Hello #{user.name}"
user.name + '!!'
Pathname.new('/') + 'test'

Checks if return or return nil is used in predicate method definitions.

Safety:

Autocorrection is marked as unsafe because the change of the return value from nil to false could potentially lead to incompatibility issues.

Example:

# bad
def foo?
  return if condition

  do_something?
end

# bad
def foo?
  return nil if condition

  do_something?
end

# good
def foo?
  return false if condition

  do_something?
end

Example: AllowedMethods: ['foo?']

# good
def foo?
  return if condition

  do_something?
end

Example: AllowedPatterns: [/foo/]

# good
def foo?
  return if condition

  do_something?
end

Checks for places where string concatenation can be replaced with string interpolation.

The cop can autocorrect simple cases but will skip autocorrecting more complex cases where the resulting code would be harder to read. In those cases, it might be useful to extract statements to local variables or methods which you can then interpolate in a string.

NOTE: When concatenation between two strings is broken over multiple lines, this cop does not register an offense; instead, Style/LineEndConcatenation will pick up the offense if enabled.

Two modes are supported: 1. aggressive style checks and corrects all occurrences of + where either the left or right side of + is a string literal. 2. conservative style on the other hand, checks and corrects only if left side (receiver of + method call) is a string literal. This is useful when the receiver is some expression that returns string like Pathname instead of a string literal.

Safety:

This cop is unsafe in aggressive mode, as it cannot be guaranteed that the receiver is actually a string, which can result in a false positive.

Example: Mode: aggressive (default)

# bad
email_with_name = user.name + ' <' + user.email + '>'
Pathname.new('/') + 'test'

# good
email_with_name = "#{user.name} <#{user.email}>"
email_with_name = format('%s <%s>', user.name, user.email)
"#{Pathname.new('/')}test"

# accepted, line-end concatenation
name = 'First' +
  'Last'

Example: Mode: conservative

# bad
'Hello' + user.name

# good
"Hello #{user.name}"
user.name + '!!'
Pathname.new('/') + 'test'

Checks for places where keyword arguments can be used instead of boolean arguments when defining methods. respond_to_missing? method is allowed by default. These are customizable with AllowedMethods option.

Safety:

This cop is unsafe because changing a method signature will implicitly change behavior.

Example:

# bad
def some_method(bar = false)
  puts bar
end

# bad - common hack before keyword args were introduced
def some_method(options = {})
  bar = options.fetch(:bar, false)
  puts bar
end

# good
def some_method(bar: false)
  puts bar
end

Example: AllowedMethods: ['some_method']

# good
def some_method(bar = false)
  puts bar
end

Looks for places where an subset of an Enumerable (array, range, set, etc.; see note below) is calculated based on a Regexp match, and suggests grep or grep_v instead.

NOTE: Hashes do not behave as you may expect with grep, which means that hash.grep is not equivalent to hash.select. Although RuboCop is limited by static analysis, this cop attempts to avoid registering an offense when the receiver is a hash (hash literal, Hash.new, Hash#[], or to_h/to_hash).

NOTE: grep and grep_v were optimized when used without a block in Ruby 3.0, but may be slower in previous versions. See https://bugs.ruby-lang.org/issues/17030

Safety:

Autocorrection is marked as unsafe because MatchData will not be created by grep, but may have previously been relied upon after the match? or =~ call.

Additionally, the cop cannot guarantee that the receiver of select or reject is actually an array by static analysis, so the correction may not be actually equivalent.

Example:

# bad (select or find_all)
array.select { |x| x.match? /regexp/ }
array.select { |x| /regexp/.match?(x) }
array.select { |x| x =~ /regexp/ }
array.select { |x| /regexp/ =~ x }

# bad (reject)
array.reject { |x| x.match? /regexp/ }
array.reject { |x| /regexp/.match?(x) }
array.reject { |x| x =~ /regexp/ }
array.reject { |x| /regexp/ =~ x }

# good
array.grep(regexp)
array.grep_v(regexp)