[#91] Add nested interpolation cop

.rubocop.yml

@@ -8,3 +8,8 @@ inherit_mode:
 
 AllCops:
   TargetRubyVersion: 2.3
+
+# for checking cops with interpolation
+Lint/InterpolationCheck:
+  Exclude:
+    - 'spec/**/*.rb'

CHANGELOG.md

@@ -7,6 +7,7 @@ The format is described in [Contributing notes](CONTRIBUTING.md#changelog-entry-
 ### Added
 
 * Enable `rubocop-rails` cops for rails config. ([@ula][])
+* Add `Style/NestedInterpolation` cop. ([@r.dubrovsky][])
 
 ## 0.7.0 (2020-01-27)
 

config/base.yml

@@ -22,7 +22,6 @@ Layout/ArrayAlignmentExtended:
     - with_fixed_indentation
   IndentationWidth: ~
 
-
 Layout/HashAlignment:
   EnforcedLastArgumentHashStyle: always_ignore
 
@@ -64,5 +63,8 @@ Style/EmptyMethod:
 Style/FrozenStringLiteralComment:
   Enabled: false
 
+Style/NestedInterpolation:
+  Enabled: true
+
 Style/StringLiterals:
   EnforcedStyle: double_quotes

doc/STYLE_GUIDE.md

@@ -35,6 +35,19 @@ This is a small list of differences which we have when compared with community s
   Adopt a consistent string literal quoting style.
   <sup>[[link](#style-string-quotes)]</sup>
 
+* <a name="style-nested-interpolation"></a>
+  Avoid using nested interpolation.
+   <sup>[[link](#style-nested-interpolation)]</sup>
+
+```ruby
+# bad
+"Hello, #{user.blank? ? 'guest' : "dear #{user.name}"}"
+
+# good
+user_name = user.blank? ? 'guest' : "dear #{user.name}"
+"Hello, #{user_name}"
+```
+
 * <a name="style-hash-aligning"></a>
   If elements of a hash literal span more than one line, we're aligning them by keys.
   Also, the first hash key is aligned by an indentation level.

lib/datarockets/style.rb

@@ -4,6 +4,7 @@
 require "datarockets/style/version"
 
 require "datarockets/style/cop/layout/array_alignment_extended"
+require "datarockets/style/cop/style/nested_interpolation"
 
 module Datarockets
   # Datarickors sharable config

lib/datarockets/style/cop/style/nested_interpolation.rb

@@ -0,0 +1,29 @@
+module Datarockets
+  module Style
+    module Cop
+      module Style
+        # This cop checks nested interpolations
+        #
+        # @example
+        #
+        # # bad
+        # "Hello, #{user.blank? ? 'guest' : "dear #{user.name}"}"
+        #
+        # # good
+        # user_name = user.blank? ? 'guest' : "dear #{user.name}"
+        # "Hello, #{user_name}"
+        class NestedInterpolation < RuboCop::Cop::Cop
+          include RuboCop::Cop::Interpolation
+
+          MSG = "Redundant nested interpolation.".freeze
+
+          def on_interpolation(node)
+            node.each_descendant(:begin) do |descendant_node|
+              add_offense(descendant_node)
+            end
+          end
+        end
+      end
+    end
+  end
+end

manual/cops_layout.md

@@ -51,3 +51,24 @@ Name | Default value | Configurable values
 --- | --- | ---
 EnforcedStyle | `with_first_parameter` | `with_first_parameter`, `with_fixed_indentation`
 IndentationWidth | `<none>` | Integer
+
+# Style
+
+## Style/NestedInterpolation
+
+Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+--- | --- | --- | --- | ---
+Enabled | Yes | No | 0.8.0 | -
+
+This cop checks nested interpolations
+
+### Example
+
+```ruby
+# bad
+"Hello, #{user.blank? ? 'guest' : "dear #{user.name}"}"
+
+# good
+user_name = user.blank? ? 'guest' : "dear #{user.name}"
+"Hello, #{user_name}"
+```

spec/datarockets/style/cop/style/nested_interpolation_spec.rb

@@ -0,0 +1,39 @@
+RSpec.describe Datarockets::Style::Cop::Style::NestedInterpolation do
+  subject(:cop) { described_class.new }
+
+  it "accepts single interpolation" do
+    expect_no_offenses('"dear #{user.name}"')
+  end
+
+  it "accepts two single interpolation" do
+    expect_no_offenses('"Hello #{user1.name} and #{user2.name}"')
+  end
+
+  it 'registers an offense for "Hello, #{user.blank? ? guest : "dear #{user.name}"}"' do
+    expect_offense(<<~'RUBY')
+      "Hello, #{user.blank? ? 'guest' : "dear #{user.name}"}"
+                                              ^^^^^^^^^^^^ Redundant nested interpolation.
+    RUBY
+  end
+
+  it 'registers an offense for %|Hello, #{user.blank? ? guest : "dear #{user.name}"|' do
+    expect_offense(<<~'RUBY')
+      %|Hello, #{user.blank? ? 'guest' : "dear #{user.name}"}|
+                                               ^^^^^^^^^^^^ Redundant nested interpolation.
+    RUBY
+  end
+
+  it 'registers an offense for %Q(Hello, #{user.blank? ? guest : "dear #{user.name}")' do
+    expect_offense(<<~'RUBY')
+      %Q(Hello, #{user.blank? ? 'guest' : "dear #{user.name}"})
+                                                ^^^^^^^^^^^^ Redundant nested interpolation.
+    RUBY
+  end
+
+  it 'registers an offense for ["Hello, #{user.blank? ? guest : "dear #{user.name}"}"]' do
+    expect_offense(<<~'RUBY')
+      ["Hello, #{user.blank? ? 'guest' : "dear #{user.name}"}", 'foo']
+                                               ^^^^^^^^^^^^ Redundant nested interpolation.
+    RUBY
+  end
+end