bbatsov/rubocop

= Autocorrect
:page-aliases: auto_correct.adoc

In autocorrect mode, RuboCop will try to automatically fix offenses:

[source,sh]
----
$ rubocop -A
# or
$ rubocop --autocorrect-all
----

There are a couple of things to keep in mind about autocorrect:

- For some offenses, it is not possible to implement automatic correction.
- Some automatic corrections that _are_ possible have not been implemented yet.
- Some automatic corrections might change (slightly) the semantics of the code,
meaning they'd produce code that's mostly equivalent to the original code, but
not 100% equivalent. We call such autocorrect behavior "unsafe".

TIP: You should always run your test suite after using the autocorrect functionality.

== Safe autocorrect

[source,sh]
----
$ rubocop -a
# or
$ rubocop --autocorrect
----

In RuboCop 0.60, we began to annotate cops as `Safe` or not safe. The definition of
safety is that the cop doesn't generate false positives. On top of that there's `SafeAutoCorrect`
that might be set to `false` in cases where only the autocorrect performed by a cop
is unsafe, but that the offense detection logic is safe. To sum it up:

* Safe (`true/false`) - indicates whether the cop can yield false positives (by
design) or not.
* SafeAutoCorrect (`true/false`) - indicates whether the autocorrect a cop
does is safe (equivalent) by design. If a cop is unsafe its autocorrect automatically
becomes unsafe as well.

If a cop or its autocorrect is annotated as "not safe", it will be omitted when using `--autocorrect`.

NOTE: Currently there might still be cops that aren't marked as unsafe or
with unsafe autocorrect.  Eventually, the safety of each cop will be specified
in the default configuration.

=== Example of Unsafe Cop

[source,ruby]
----
class Miner
  def dig(how_deep)
    # ...
  end
end


Miner.new.dig(42) # => Style/SingleArgumentDig
                  # => Use Miner.new[] instead of dig
----

This is the wrong diagnostic; this (contrived) use of `dig` is not an issue,
and there might not be an alternative. This cop is marked as `Safe: false`.

[source,ruby]
----
# example.rb:
str = 'hello' # => Missing magic comment `# frozen_string_literal: true`
str << 'world'

# autocorrects to:
# frozen_string_literal: true

str = 'hello'
str << 'world' # => now fails because `str` is frozen

# must be manually corrected to:
# frozen_string_literal: true

str = +'hello' # => We want an unfrozen string literal here...
str << 'world' # => ok
----

This diagnostic is valid since the magic comment is indeed missing (thus `Safe: true`),
but the autocorrection is not; some string literals need to be prefixed with `+` to avoid
having them frozen.

To run all autocorrections (safe and unsafe):

[source,sh]
----
$ rubocop -A
# or
$ rubocop --autocorrect-all
----

It is recommended to be even more vigilant when using this option and review carefully the changes.

== Generating comments

[source,sh]
----
$ rubocop --autocorrect --disable-uncorrectable
----

or

[source,sh]
----
$ rubocop --autocorrect-all --disable-uncorrectable
----

You can add the flag `--disable-uncorrectable`, which will generate
`# rubocop:todo` comments in the code to stop the reporting of offenses that
could not be corrected automatically.