[Fix rubocop#7705] Fix problem of one_line_conditional cop with elsif.

One line conditionals with elsif branches are now transformed into
multiline versions. Before this change, they were broken and autocorrect
produced code that resulted in a syntax error. See Issue rubocop#7705 for more
details.

CHANGELOG.md

@@ -15,6 +15,7 @@
 
 ### Bug fixes
 
+* [#7705](https://github.com/rubocop-hq/rubocop/issues/7705): Fix problem of one_line_conditional cop with elsif conditionals. ([@Lykos][])
 * [#7644](https://github.com/rubocop-hq/rubocop/issues/7644): Fix patterns with named wildcards in unions. ([@marcandre][])
 * [#7639](https://github.com/rubocop-hq/rubocop/pull/7639): Fix logical operator edge case in `omit_parentheses` style of `Style/MethodCallWithArgsParentheses`. ([@gsamokovarov][])
 * [#7661](https://github.com/rubocop-hq/rubocop/pull/7661): Fix to return correct info from multi-line regexp. ([@Tietew][])
@@ -4357,3 +4358,4 @@
 [@masarakki]: https://github.com/masarakki
 [@djudd]: https://github.com/djudd
 [@jemmaissroff]: https://github.com/jemmaissroff
+[@Lykos]: https://github.com/Lykos

lib/rubocop/cop/style/one_line_conditional.rb

@@ -25,11 +25,13 @@ module Style
       class OneLineConditional < Cop
         include OnNormalIfUnless
 
-        MSG = 'Favor the ternary operator (`?:`) ' \
-              'over `%<keyword>s/then/else/end` constructs.'
+        MSG_USE_TERNARY = 'Favor the ternary operator (`?:`) ' \
+                          'over `%<keyword>s/then/else/end` constructs.'
+        MSG_USE_MULTILINE = 'Use multiple lines for ' \
+                            '`if/then/elsif/then/else/end` constructs.'
 
         def on_normal_if_unless(node)
-          return unless node.single_line? && node.else_branch
+          return unless node.single_line? && node.else_branch && !node.elsif?
 
           add_offense(node)
         end
@@ -43,21 +45,55 @@ def autocorrect(node)
         private
 
         def message(node)
-          format(MSG, keyword: node.keyword)
+          if node.elsif_conditional?
+            MSG_USE_MULTILINE
+          else
+            format(MSG_USE_TERNARY, keyword: node.keyword)
+          end
         end
 
         def replacement(node)
-          return to_ternary(node) unless node.parent
+          return to_ternary_or_multiline(node) unless node.parent
 
           if %i[and or].include?(node.parent.type)
-            return "(#{to_ternary(node)})"
+            return "(#{to_ternary_or_multiline(node)})"
           end
 
           if node.parent.send_type? && node.parent.operator_method?
-            return "(#{to_ternary(node)})"
+            return "(#{to_ternary_or_multiline(node)})"
           end
 
-          to_ternary(node)
+          to_ternary_or_multiline(node)
+        end
+
+        def to_ternary_or_multiline(node)
+          node.elsif_conditional? ? to_multiline(node) : to_ternary(node)
+        end
+
+        def to_multiline(node)
+          indentation = ' ' * node.source_range.column
+          to_indented_multiline(node, indentation)
+        end
+
+        def to_indented_multiline(node, indentation)
+          if_branch = <<~RUBY
+            #{node.keyword} #{node.condition.source}
+            #{indentation}  #{node.if_branch.source}
+          RUBY
+          else_branch = else_branch_to_multiline(node.else_branch, indentation)
+          if_branch + else_branch
+        end
+
+        def else_branch_to_multiline(else_branch, indentation)
+          if else_branch.if_type? && else_branch.elsif?
+            to_indented_multiline(else_branch, indentation)
+          else
+            <<~RUBY.chomp
+              #{indentation}else
+              #{indentation}  #{else_branch.source}
+              #{indentation}end
+            RUBY
+          end
         end
 
         def to_ternary(node)

manual/cops_naming.md

@@ -350,7 +350,7 @@ This cop can be configured with the EnforcedStyleForLeadingUnderscores
 directive. It can be configured to allow for memoized instance variables
 prefixed with an underscore. Prefixing ivars with an underscore is a
 convention that is used to implicitly indicate that an ivar should not
-be set or referenced outside of the memoization method.
+be set or referencd outside of the memoization method.
 
 ### Examples
 

spec/rubocop/cop/style/one_line_conditional_spec.rb

@@ -12,6 +12,15 @@
     end
   end
 
+  shared_examples 'multiline offense' do
+    it 'registers an offense where multiline should be used' do
+      inspect_source(source)
+      expect(cop.messages)
+        .to eq(['Use multiple lines for ' \
+                '`if/then/elsif/then/else/end` constructs.'])
+    end
+  end
+
   shared_examples 'no offense' do
     it 'does not register an offense' do
       expect_no_offenses(source)
@@ -38,6 +47,40 @@
     end
   end
 
+  context 'one line if/then/elsif/then/else/end' do
+    let(:source) { 'if cond then run elsif elscond then elsrun else dont end' }
+
+    include_examples 'multiline offense'
+    include_examples 'autocorrect', <<~RUBY.chomp
+      if cond
+        run
+      elsif elscond
+        elsrun
+      else
+        dont
+      end
+    RUBY
+  end
+
+  context 'one line if/then/elsif/then/else/end with multiple elsifs' do
+    let(:source) do
+      'if c0 then r0 elsif c1 then r1 elsif c2 then r2 else r3 end'
+    end
+
+    include_examples 'multiline offense'
+    include_examples 'autocorrect', <<~RUBY.chomp
+      if c0
+        r0
+      elsif c1
+        r1
+      elsif c2
+        r2
+      else
+        r3
+      end
+    RUBY
+  end
+
   context 'one line if/then/else/end when `then` branch has no body' do
     let(:source) { 'if cond then else dont end' }