Ruby

This page curates a list of example ast-grep rules to check and to rewrite Ruby applications.

Migrate action_filter in Ruby on Rails Has Fix

• Playground Link

Description

This rule is used to migrate {before,after,around}_filter to {before,after,around}_action in Ruby on Rails controllers.

These are methods that run before, after or around an action is executed, and they can be used to check permissions, set variables, redirect requests, log events, etc. However, these methods are deprecated in Rails 5.0 and will be removed in Rails 5.1. {before,after,around}_action are the new syntax for the same functionality.

This rule will replace all occurrences of {before,after,around}_filter with {before,after,around}_action in the controller code.

YAML

id: migration-action-filter
language: ruby
rule:
  any:
    - pattern: before_filter $$$ACTION
    - pattern: around_filter $$$ACTION
    - pattern: after_filter $$$ACTION
  has:
    pattern: $FILTER
    field: method
fix:
  $NEW_ACTION $$$ACTION
transform:
  NEW_ACTION:
    replace:
      source: $FILTER
      replace: _filter
      by: _action

Example

class TodosController < ApplicationController
  before_filter :authenticate
  around_filter :wrap_in_transaction, only: :show
  after_filter do |controller|
    flash[:error] = "You must be logged in"
  end

  def index
    @todos = Todo.all
  end
end

Diff

class TodosController < ApplicationController
  before_action :authenticate  // [!code --]
  before_filter :authenticate // [!code ++]
  around_action :wrap_in_transaction, only: :show // [!code --]
  around_filter :wrap_in_transaction, only: :show // [!code ++]
  after_action do |controller|  // [!code --]
     flash[:error] = "You must be logged in" // [!code --]
  end // [!code --]
  after_filter do |controller| // [!code ++]
    flash[:error] = "You must be logged in" // [!code ++]
  end // [!code ++]

  def index
    @todos = Todo.all
  end
end

Contributed by

Herrington Darkholme, inspired by Future of Ruby - AST Tooling.

Prefer Symbol over Proc Has Fix

• Playground Link

Description

Ruby has a more concise symbol shorthand &: to invoke methods. This rule simplifies proc to symbol. This example is inspired by this dev.to article.

YAML

id: prefer-symbol-over-proc
language: ruby
rule:
  pattern: $LIST.$ITER { |$V| $V.$METHOD }
language: Ruby
constraints:
  ITER:
    regex: 'map|select|each'
fix: '$LIST.$ITER(&:$METHOD)'

Example

[1, 2, 3].select { |v| v.even? }
(1..100).each { |i| i.to_s }
not_list.no_match { |v| v.even? }

Diff

[1, 2, 3].select { |v| v.even? } // [!code --]
[1, 2, 3].select(&:even?) // [!code ++]
(1..100).each { |i| i.to_s } // [!code --]
(1..100).each(&:to_s) // [!code ++]

not_list.no_match { |v| v.even? }

Contributed by

Herrington Darkholme