Support EnforcedStyleForEmptyBraces for SpaceBeforeBlockBraces cop

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### New features
 
+* [#4464](https://github.com/bbatsov/rubocop/pull/4464): Add `EnforcedStyleForEmptyBraces` parameter to `Layout/SpaceBeforeBlockBraces` cop. ([@palkan][])
 * [#4453](https://github.com/bbatsov/rubocop/pull/4453): New cop `Style/RedundantConditional` checks for conditionals that return true/false. ([@petehamilton][])
 * [#4448](https://github.com/bbatsov/rubocop/pull/4448): Add new `TapFormatter`. ([@cyberdelia][])
 * Add new `Style/HeredocDelimiters` cop. ([@drenmi][])

config/default.yml

@@ -490,6 +490,9 @@ Layout/SpaceBeforeBlockBraces:
   SupportedStyles:
     - space
     - no_space
+  SupportedStylesForEmptyBraces:
+    - space
+    - no_space
 
 Layout/SpaceBeforeFirstArg:
   # When `true`, allows most uses of extra spacing if the intent is to align

lib/rubocop/cop/layout/space_before_block_braces.rb

@@ -19,6 +19,9 @@ module Layout
       class SpaceBeforeBlockBraces < Cop
         include ConfigurableEnforcedStyle
 
+        MISSING_MSG = 'Space missing to the left of {.'.freeze
+        DETECTED_MSG = 'Space detected to the left of {.'.freeze
+
         def self.autocorrect_incompatible_with
           [Style::SymbolProc]
         end
@@ -31,30 +34,61 @@ def on_block(node)
           used_style =
             space_plus_brace.source.start_with?('{') ? :no_space : :space
 
+          if empty_braces?(node.loc)
+            check_empty(left_brace, space_plus_brace, used_style)
+          else
+            check_non_empty(left_brace, space_plus_brace, used_style)
+          end
+        end
+
+        private
+
+        def check_empty(left_brace, space_plus_brace, used_style)
+          return if style_for_empty_braces == used_style
+
+          config_to_allow_offenses['EnforcedStyleForEmptyBraces'] =
+            used_style.to_s
+
+          if style_for_empty_braces == :space
+            add_offense(left_brace, left_brace, MISSING_MSG)
+          else
+            space = range_between(space_plus_brace.begin_pos,
+                                  left_brace.begin_pos)
+            add_offense(space, space, DETECTED_MSG)
+          end
+        end
+
+        def check_non_empty(left_brace, space_plus_brace, used_style)
           case used_style
           when style  then correct_style_detected
           when :space then space_detected(left_brace, space_plus_brace)
           else             space_missing(left_brace)
           end
         end
 
-        private
-
         def space_missing(left_brace)
-          add_offense(left_brace, left_brace,
-                      'Space missing to the left of {.') do
+          add_offense(left_brace, left_brace, MISSING_MSG) do
             opposite_style_detected
           end
         end
 
         def space_detected(left_brace, space_plus_brace)
           space = range_between(space_plus_brace.begin_pos,
                                 left_brace.begin_pos)
-          add_offense(space, space, 'Space detected to the left of {.') do
+          add_offense(space, space, DETECTED_MSG) do
             opposite_style_detected
           end
         end
 
+        def style_for_empty_braces
+          case cop_config['EnforcedStyleForEmptyBraces']
+          when 'space'    then :space
+          when 'no_space' then :no_space
+          when nil then style
+          else raise 'Unknown EnforcedStyleForEmptyBraces selected!'
+          end
+        end
+
         def autocorrect(range)
           lambda do |corrector|
             case range.source
@@ -63,6 +97,10 @@ def autocorrect(range)
             end
           end
         end
+
+        def empty_braces?(loc)
+          loc.begin.end_pos == loc.end.begin_pos
+        end
       end
     end
   end

manual/cops_layout.md

@@ -2062,6 +2062,7 @@ Attribute | Value
 --- | ---
 EnforcedStyle | space
 SupportedStyles | space, no_space
+SupportedStylesForEmptyBraces | space, no_space
 
 ## Layout/SpaceBeforeComma
 

spec/rubocop/cop/layout/space_before_block_braces_spec.rb

@@ -71,4 +71,65 @@
       expect_no_offenses('each{ puts }')
     end
   end
+
+  context 'with space before empty braces not allowed' do
+    let(:cop_config) do
+      {
+        'EnforcedStyle' => 'space',
+        'EnforcedStyleForEmptyBraces' => 'no_space'
+      }
+    end
+
+    it 'accepts empty braces without outer space' do
+      expect_no_offenses('->{}')
+    end
+
+    it 'registers an offense for empty braces' do
+      inspect_source('-> {}')
+      expect(cop.messages).to eq(['Space detected to the left of {.'])
+      expect(cop.highlights).to eq([' '])
+      expect(cop.config_to_allow_offenses)
+        .to eq('EnforcedStyleForEmptyBraces' => 'space')
+    end
+
+    it 'auto-corrects unwanted space' do
+      new_source = autocorrect_source('-> {}')
+      expect(new_source).to eq('->{}')
+    end
+  end
+
+  context 'with space before empty braces allowed' do
+    let(:cop_config) do
+      {
+        'EnforcedStyle' => 'no_space',
+        'EnforcedStyleForEmptyBraces' => 'space'
+      }
+    end
+
+    it 'accepts empty braces with outer space' do
+      expect_no_offenses('-> {}')
+    end
+
+    it 'registers an offense for empty braces' do
+      inspect_source('->{}')
+      expect(cop.messages).to eq(['Space missing to the left of {.'])
+      expect(cop.highlights).to eq(['{'])
+      expect(cop.config_to_allow_offenses)
+        .to eq('EnforcedStyleForEmptyBraces' => 'no_space')
+    end
+
+    it 'auto-corrects missing space' do
+      new_source = autocorrect_source('->{}')
+      expect(new_source).to eq('-> {}')
+    end
+  end
+
+  context 'with invalid value for EnforcedStyleForEmptyBraces' do
+    let(:cop_config) { { 'EnforcedStyleForEmptyBraces' => 'unknown' } }
+
+    it 'fails with an error' do
+      expect { inspect_source('each {}') }
+        .to raise_error('Unknown EnforcedStyleForEmptyBraces selected!')
+    end
+  end
 end