Add always_braces to Style/BlockDelimiters

This style always prefers braces over do...end. Similar to double
quotes, some developers don't want to bother with changing the style
when adding or removing a line or debate, whether a blocks like

```ruby
date = Timecop.freeze(1.year.ago) { format_date(Time.now) }
customer = Timecop.freeze(1.year.ago) { create(:customer) }
```

are functional or procedual.

I didn't add a always_do_end style, as I don't think that someone wants
to enforce this in all situation (chaining, ...).

Sponsored by @BillFront

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### New features
 
+* [#6973](https://github.com/rubocop-hq/rubocop/pull/6973): Add `always_braces` to `Style/BlockDelimiter`. ([@iGEL][])
 * [#6841](https://github.com/rubocop-hq/rubocop/issues/6841): Node patterns can now match children in any order using `<>`. ([@marcandre][])
 * [#6928](https://github.com/rubocop-hq/rubocop/pull/6928): Add `--init` option for generate `.rubocop.yml` file in the current directory. ([@koic][])
 * Add new `Layout/HeredocArgumentClosingParenthesis` cop. ([@maxh][])

config/default.yml

@@ -2663,6 +2663,8 @@ Style/BlockDelimiters:
     # return value is being chained with another method (in which case braces
     # are enforced).
     - braces_for_chaining
+    # The `always_braces` style always enforces braces.
+    - always_braces
   ProceduralMethods:
     # Methods that are known to be procedural in nature but look functional from
     # their usage, e.g.

lib/rubocop/cop/style/block_delimiters.rb

@@ -95,10 +95,24 @@ module Style
       #     word.flip.flop
       #   }.join("-")
       #
+      # @example EnforcedStyle: always_braces
+      #   # bad
+      #   words.each do |word|
+      #     word.flip.flop
+      #   end
+      #
+      #   # good
+      #   words.each { |word|
+      #     word.flip.flop
+      #   }
+      #
       class BlockDelimiters < Cop
         include ConfigurableEnforcedStyle
         include IgnoredMethods
 
+        ALWAYS_BRACES_MESSAGE = 'Prefer `{...}` over `do...end` for blocks.'
+                                .freeze
+
         def on_send(node)
           return unless node.arguments?
           return if node.parenthesized? || node.operator_method?
@@ -166,6 +180,7 @@ def message(node)
           when :line_count_based    then line_count_based_message(node)
           when :semantic            then semantic_message(node)
           when :braces_for_chaining then braces_for_chaining_message(node)
+          when :always_braces       then ALWAYS_BRACES_MESSAGE
           end
         end
 
@@ -229,6 +244,7 @@ def proper_block_style?(node)
           when :line_count_based    then line_count_based_block_style?(node)
           when :semantic            then semantic_block_style?(node)
           when :braces_for_chaining then braces_for_chaining_style?(node)
+          when :always_braces       then braces_style?(node)
           end
         end
 
@@ -257,6 +273,10 @@ def braces_for_chaining_style?(node)
                          end
         end
 
+        def braces_style?(node)
+          node.loc.begin.source == '{'
+        end
+
         def return_value_chaining?(node)
           node.parent && node.parent.send_type? && node.parent.dot?
         end

manual/cops_style.md

@@ -460,12 +460,25 @@ words.each { |word|
   word.flip.flop
 }.join("-")
 ```
+#### EnforcedStyle: always_braces
+
+```ruby
+# bad
+words.each do |word|
+  word.flip.flop
+end
+
+# good
+words.each { |word|
+  word.flip.flop
+}
+```
 
 ### Configurable attributes
 
 Name | Default value | Configurable values
 --- | --- | ---
-EnforcedStyle | `line_count_based` | `line_count_based`, `semantic`, `braces_for_chaining`
+EnforcedStyle | `line_count_based` | `line_count_based`, `semantic`, `braces_for_chaining`, `always_braces`
 ProceduralMethods | `benchmark`, `bm`, `bmbm`, `create`, `each_with_object`, `measure`, `new`, `realtime`, `tap`, `with_object` | Array
 FunctionalMethods | `let`, `let!`, `subject`, `watch` | Array
 IgnoredMethods | `lambda`, `proc`, `it` | Array

spec/rubocop/cop/style/block_delimiters_spec.rb

@@ -507,4 +507,97 @@
       end
     end
   end
+
+  context 'always braces' do
+    cop_config = {
+      'EnforcedStyle' => 'always_braces',
+      'IgnoredMethods' => %w[proc]
+    }
+
+    let(:cop_config) { cop_config }
+
+    it 'registers an offense for a single line block with do-end' do
+      expect_offense(<<-RUBY.strip_indent)
+        each do |x| end
+             ^^ Prefer `{...}` over `do...end` for blocks.
+      RUBY
+    end
+
+    it 'accepts a single line block with braces' do
+      expect_no_offenses('each { |x| }')
+    end
+
+    it 'registers an offence for a multi-line block with do-end' do
+      expect_offense(<<-RUBY.strip_indent)
+        each do |x|
+             ^^ Prefer `{...}` over `do...end` for blocks.
+        end
+      RUBY
+    end
+
+    it 'auto-corrects do and end for single line blocks to { and }' do
+      new_source = autocorrect_source('block do |x| end')
+      expect(new_source).to eq('block { |x| }')
+    end
+
+    it 'does not auto-correct do-end if {} would change the meaning' do
+      src = "s.subspec 'Subspec' do |sp| end"
+      new_source = autocorrect_source(src)
+      expect(new_source).to eq(src)
+    end
+
+    it 'accepts a multi-line block that needs braces to be valid ruby' do
+      expect_no_offenses(<<-RUBY.strip_indent)
+        puts [1, 2, 3].map { |n|
+          n * n
+        }, 1
+      RUBY
+    end
+
+    it 'registers an offense for multi-line chained do-end blocks' do
+      expect_offense(<<-RUBY.strip_indent)
+        each do |x|
+             ^^ Prefer `{...}` over `do...end` for blocks.
+        end.map(&:to_s)
+      RUBY
+    end
+
+    it 'auto-corrects do-end for chained blocks' do
+      src = <<-RUBY.strip_indent
+        each do |x|
+        end.map(&:to_s)
+      RUBY
+      new_source = autocorrect_source(src)
+      expect(new_source).to eq(<<-RUBY.strip_indent)
+        each { |x|
+        }.map(&:to_s)
+      RUBY
+    end
+
+    it 'accepts a multi-line functional block with do-end if it is ' \
+       'an ignored method' do
+      expect_no_offenses(<<-RUBY.strip_indent)
+        foo = proc do
+          puts 42
+        end
+      RUBY
+    end
+
+    context 'when there are braces around a multi-line block' do
+      it 'registers an offense in the simple case' do
+        expect_offense(<<-RUBY.strip_indent)
+          each do |x|
+               ^^ Prefer `{...}` over `do...end` for blocks.
+          end
+        RUBY
+      end
+
+      it 'allows when the block is being chained' do
+        expect_no_offenses(<<-RUBY.strip_indent)
+          each { |x|
+          }.map(&:to_sym)
+        RUBY
+      end
+    end
+  end
 end