Enable basic autocorrection for Style/Semicolon.

When a semicolon is found between expressions, it is replaced with a newline. In order to avoid adding multiple newlines, when the semicolons are making a single-line method, autocorrection is disabled in favour of the autocorrection from `Style/SingleLineMethods`.

changelog/change_enable_basic_autocorrection_for.md

@@ -0,0 +1 @@
+* [#9979](https://github.com/rubocop/rubocop/pull/9979): Enable basic autocorrection for `Style/Semicolon`. ([@dvandersluis][])

lib/rubocop/cop/style/semicolon.rb

@@ -32,6 +32,10 @@ class Semicolon < Base
 
         MSG = 'Do not use semicolons to terminate expressions.'
 
+        def self.autocorrect_incompatible_with
+          [Style::SingleLineMethods]
+        end
+
         def on_new_investigation
           return if processed_source.blank?
 
@@ -50,7 +54,7 @@ def on_begin(node)
             # potential offense
             next unless expr_on_line.size > 1
 
-            find_semicolon_positions(line) { |pos| register_semicolon(line, pos, false) }
+            find_semicolon_positions(line) { |pos| register_semicolon(line, pos, true) }
           end
         end
 
@@ -60,7 +64,7 @@ def check_for_line_terminator_or_opener
           # Make the obvious check first
           return unless processed_source.raw_source.include?(';')
 
-          each_semicolon { |line, column| register_semicolon(line, column, true) }
+          each_semicolon { |line, column| register_semicolon(line, column, false) }
         end
 
         def each_semicolon
@@ -74,12 +78,15 @@ def tokens_for_lines
           processed_source.tokens.group_by(&:line)
         end
 
-        def register_semicolon(line, column, autocorrect)
+        def register_semicolon(line, column, after_expression)
           range = source_range(processed_source.buffer, line, column)
-          # Don't attempt to autocorrect if semicolon is separating statements
-          # on the same line
+
           add_offense(range) do |corrector|
-            corrector.remove(range) if autocorrect
+            if after_expression
+              corrector.replace(range, "\n")
+            else
+              corrector.remove(range)
+            end
           end
         end
 

spec/rubocop/cli/autocorrect_spec.rb

@@ -902,7 +902,10 @@ def func
       end
 
       def func
-        x; y; rescue StandardError; z
+        x
+        y
+      rescue StandardError
+        z
       end
 
       def method
@@ -1285,7 +1288,8 @@ def func2() do_1; do_2; end
     exit_status = cli.run(
       %w[--auto-correct-all --format offenses --only] << %w[
         SingleLineMethods Semicolon EmptyLineBetweenDefs
-        DefWithParentheses TrailingWhitespace
+        DefWithParentheses TrailingWhitespace TrailingBodyOnMethodDefinition
+        DefEndAlignment IndentationConsistency
       ].join(',')
     )
     expect(exit_status).to eq(0)
@@ -1302,13 +1306,16 @@ def func2
     RUBY
     expect($stdout.string).to eq(<<~RESULT)
 
-      6   Layout/TrailingWhitespace
+      4   Layout/TrailingWhitespace
       3   Style/Semicolon
+      2   Layout/IndentationConsistency
       2   Style/SingleLineMethods
+      1   Layout/DefEndAlignment
       1   Layout/EmptyLineBetweenDefs
       1   Style/DefWithParentheses
+      1   Style/TrailingBodyOnMethodDefinition
       --
-      13  Total
+      15  Total
 
     RESULT
   end
@@ -1529,16 +1536,11 @@ def self.some_method(foo, bar: 1)
         log.debug(foo)
       end
     RUBY
-    corrected = <<~RUBY
-      func a do b end
-      Signal.trap('TERM') { system(cmd); exit }
-      def self.some_method(foo, bar: 1)
-        log.debug(foo)
-      end
-    RUBY
     create_file('.rubocop.yml', <<~YAML)
       AllCops:
         TargetRubyVersion: 2.5
+      Style/Semicolon:
+        AutoCorrect: false
     YAML
     create_file('example.rb', src)
     exit_status = cli.run(
@@ -1547,7 +1549,7 @@ def self.some_method(foo, bar: 1)
     )
     expect(exit_status).to eq(1)
     expect($stderr.string).to eq('')
-    expect(File.read('example.rb')).to eq(corrected)
+    expect(File.read('example.rb')).to eq(src)
     expect($stdout.string).to eq(<<~RESULT)
       == example.rb ==
       C:  1:  8: Style/BlockDelimiters: Prefer {...} over do...end for single-line blocks.
@@ -2162,4 +2164,32 @@ def my_func
       }
     RUBY
   end
+
+  it 'avoids adding extra spaces when both `Style/Semicolon` and `Style/SingleLineMethods`' \
+     'both apply' do
+    source_file = Pathname('example.rb')
+    create_file(source_file, <<~RUBY)
+      def foo(a) x(1); y(2); z(3); end
+    RUBY
+
+    create_file('.rubocop.yml', <<~YAML)
+      Style/Semicolon:
+        AllowAsExpressionSeparator: false
+    YAML
+
+    status = cli.run(
+      %w[--auto-correct --only] << %w[
+        Semicolon SingleLineMethods TrailingBodyOnMethodDefinition
+        DefEndAlignment TrailingWhitespace IndentationConsistency
+      ].join(',')
+    )
+    expect(status).to eq(0)
+    expect(source_file.read).to eq(<<~RUBY)
+      def foo(a)
+        x(1)
+        y(2)
+        z(3)
+      end
+    RUBY
+  end
 end

spec/rubocop/cop/style/semicolon_spec.rb

@@ -20,7 +20,10 @@
                            ^ Do not use semicolons to terminate expressions.
     RUBY
 
-    expect_no_corrections
+    expect_correction(<<~RUBY)
+      puts "this is a test"
+       puts "So is this"
+    RUBY
   end
 
   it 'registers an offense for one line method with two statements' do
@@ -31,7 +34,12 @@ def foo(a) x(1); y(2); z(3); end
                      ^ Do not use semicolons to terminate expressions.
     RUBY
 
-    expect_no_corrections
+    expect_correction(<<~RUBY)
+      def foo(a) x(1)
+       y(2)
+       z(3)
+       end
+    RUBY
   end
 
   it 'accepts semicolon before end if so configured' do