From 0723cced1bfe6d471cf37d88397feb1d8f6b8d3c Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Thu, 12 Aug 2021 17:26:48 +0900
Subject: [PATCH] [Fix #10004] Fix a false positive for `Style/RedundantBegin`

Fixes #10004.

This PR fixes a false positive for `Style/RedundantBegin`
when using one-liner with semicolon.
---
 ...alse_positive_for_style_redundant_begin.md |  1 +
 lib/rubocop/cop/style/redundant_begin.rb      | 25 ++++++++++
 .../rubocop/cop/style/redundant_begin_spec.rb | 47 +++++++++++++++++++
 3 files changed, 73 insertions(+)
 create mode 100644 changelog/fix_false_positive_for_style_redundant_begin.md

diff --git a/changelog/fix_false_positive_for_style_redundant_begin.md b/changelog/fix_false_positive_for_style_redundant_begin.md
new file mode 100644
index 00000000000..c3822bc9351
--- /dev/null
+++ b/changelog/fix_false_positive_for_style_redundant_begin.md
@@ -0,0 +1 @@
+* [#10004](https://github.com/rubocop/rubocop/issues/10004): Fix a false positive for `Style/RedundantBegin` when using one-liner with semicolon. ([@koic][])
diff --git a/lib/rubocop/cop/style/redundant_begin.rb b/lib/rubocop/cop/style/redundant_begin.rb
index c0eaccc1f28..4f07b8b024b 100644
--- a/lib/rubocop/cop/style/redundant_begin.rb
+++ b/lib/rubocop/cop/style/redundant_begin.rb
@@ -84,6 +84,7 @@ def on_block(node)
 
         def on_kwbegin(node)
           return if empty_begin?(node) ||
+                    begin_block_has_multiline_statements?(node) ||
                     contain_rescue_or_ensure?(node) ||
                     valid_context_using_only_begin?(node)
 
@@ -102,6 +103,9 @@ def register_offense(node)
               corrector.remove(offense_range)
             end
 
+            if use_modifier_form_after_multiline_begin_block?(node)
+              correct_modifier_form_after_multiline_begin_block(corrector, node)
+            end
             corrector.remove(node.loc.end)
           end
         end
@@ -127,10 +131,31 @@ def restore_removed_comments(corrector, offense_range, node, first_child)
           corrector.insert_before(node.parent, comments) unless comments.blank?
         end
 
+        def use_modifier_form_after_multiline_begin_block?(node)
+          return unless (parent = node.parent)
+
+          node.multiline? && parent.if_type? && parent.modifier_form?
+        end
+
+        def correct_modifier_form_after_multiline_begin_block(corrector, node)
+          condition_range = condition_range(node.parent)
+
+          corrector.insert_after(node.children.first, " #{condition_range.source}")
+          corrector.remove(range_by_whole_lines(condition_range, include_final_newline: true))
+        end
+
+        def condition_range(node)
+          range_between(node.loc.keyword.begin_pos, node.condition.source_range.end_pos)
+        end
+
         def empty_begin?(node)
           node.children.empty?
         end
 
+        def begin_block_has_multiline_statements?(node)
+          node.children.count >= 2
+        end
+
         def contain_rescue_or_ensure?(node)
           first_child = node.children.first
 
diff --git a/spec/rubocop/cop/style/redundant_begin_spec.rb b/spec/rubocop/cop/style/redundant_begin_spec.rb
index b875420a85a..8d504659a91 100644
--- a/spec/rubocop/cop/style/redundant_begin_spec.rb
+++ b/spec/rubocop/cop/style/redundant_begin_spec.rb
@@ -415,4 +415,51 @@ def a_method
       end
     RUBY
   end
+
+  it 'accepts when one-liner `begin` block has multiple statements with modifier condition' do
+    expect_no_offenses(<<~RUBY)
+      begin foo; bar; end unless condition
+    RUBY
+  end
+
+  it 'accepts when multi-line `begin` block has multiple statements with modifier condition' do
+    expect_no_offenses(<<~RUBY)
+      begin
+        foo; bar
+      end unless condition
+    RUBY
+  end
+
+  it 'reports an offense when one-liner `begin` block has single statement with modifier condition' do
+    expect_offense(<<~RUBY)
+      begin foo end unless condition
+      ^^^^^ Redundant `begin` block detected.
+    RUBY
+
+    expect_correction(" foo  unless condition\n")
+  end
+
+  it 'reports an offense when multi-line `begin` block has single statement with modifier condition' do
+    expect_offense(<<~RUBY)
+      begin
+      ^^^^^ Redundant `begin` block detected.
+        foo
+      end unless condition
+    RUBY
+
+    expect_correction("\n  foo unless condition\n")
+  end
+
+  it 'reports an offense when multi-line `begin` block has single statement and it is inside condition' do
+    expect_offense(<<~RUBY)
+      unless condition
+        begin
+        ^^^^^ Redundant `begin` block detected.
+          foo
+        end
+      end
+    RUBY
+
+    expect_correction("unless condition\n  \n    foo\n  \nend\n")
+  end
 end