From 118abeb6b086fa788964f3dfaee833f05e534b27 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Wed, 14 Jul 2021 10:06:10 +0900
Subject: [PATCH] Support Ruby 2.7's pattern matching for
 `Lint/DuplicateBranch`

This PR supports Ruby 2.7's pattern matching for `Lint/DuplicateBranch`.

And this PR uses rubocop/rubocop-ast#192 feature,
so it requires RuboCop AST 1.8.0 or higher.
---
 ..._doc_and_test_for_lint_duplicate_branch.md |  1 +
 lib/rubocop/cop/lint/duplicate_branch.rb      |  3 +-
 rubocop.gemspec                               |  2 +-
 .../rubocop/cop/lint/duplicate_branch_spec.rb | 32 ++++++++++++++++++-
 4 files changed, 35 insertions(+), 3 deletions(-)
 create mode 100644 changelog/new_add_pattern_matching_doc_and_test_for_lint_duplicate_branch.md

diff --git a/changelog/new_add_pattern_matching_doc_and_test_for_lint_duplicate_branch.md b/changelog/new_add_pattern_matching_doc_and_test_for_lint_duplicate_branch.md
new file mode 100644
index 00000000000..a6a6781ee09
--- /dev/null
+++ b/changelog/new_add_pattern_matching_doc_and_test_for_lint_duplicate_branch.md
@@ -0,0 +1 @@
+* [#9930](https://github.com/rubocop/rubocop/pull/9930): Support Ruby 2.7's pattern matching for `Lint/DuplicateBranch` cop. ([@koic][])
diff --git a/lib/rubocop/cop/lint/duplicate_branch.rb b/lib/rubocop/cop/lint/duplicate_branch.rb
index 32d68d0daac..587142b4b03 100644
--- a/lib/rubocop/cop/lint/duplicate_branch.rb
+++ b/lib/rubocop/cop/lint/duplicate_branch.rb
@@ -4,7 +4,7 @@ module RuboCop
   module Cop
     module Lint
       # This cop checks that there are no repeated bodies
-      # within `if/unless`, `case-when` and `rescue` constructs.
+      # within `if/unless`, `case-when`, `case-in` and `rescue` constructs.
       #
       # With `IgnoreLiteralBranches: true`, branches are not registered
       # as offenses if they return a basic literal value (string, symbol,
@@ -97,6 +97,7 @@ def on_branching_statement(node)
         end
         alias on_if on_branching_statement
         alias on_case on_branching_statement
+        alias on_case_match on_branching_statement
         alias on_rescue on_branching_statement
 
         private
diff --git a/rubocop.gemspec b/rubocop.gemspec
index 032a9e4d571..abb729e9e9f 100644
--- a/rubocop.gemspec
+++ b/rubocop.gemspec
@@ -35,7 +35,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency('rainbow', '>= 2.2.2', '< 4.0')
   s.add_runtime_dependency('regexp_parser', '>= 1.8', '< 3.0')
   s.add_runtime_dependency('rexml')
-  s.add_runtime_dependency('rubocop-ast', '>= 1.7.0', '< 2.0')
+  s.add_runtime_dependency('rubocop-ast', '>= 1.8.0', '< 2.0')
   s.add_runtime_dependency('ruby-progressbar', '~> 1.7')
   s.add_runtime_dependency('unicode-display_width', '>= 1.4.0', '< 3.0')
 
diff --git a/spec/rubocop/cop/lint/duplicate_branch_spec.rb b/spec/rubocop/cop/lint/duplicate_branch_spec.rb
index ccfbada6158..1137c04ad1b 100644
--- a/spec/rubocop/cop/lint/duplicate_branch_spec.rb
+++ b/spec/rubocop/cop/lint/duplicate_branch_spec.rb
@@ -65,6 +65,36 @@
     end
   end
 
+  shared_examples_for 'literal case-match allowed' do |type, value|
+    context "when returning a #{type} in multiple branches", :ruby27 do
+      it 'allows branches to be duplicated' do
+        expect_no_offenses(<<~RUBY)
+          case foo
+          in x then #{value}
+          in y then #{value}
+          else #{value}
+          end
+        RUBY
+      end
+    end
+  end
+
+  shared_examples_for 'literal case-match disallowed' do |type, value|
+    context "when returning a #{type} in multiple branches", :ruby27 do
+      it 'registers an offense' do
+        expect_offense(<<~RUBY, value: value)
+          case foo
+          in x then #{value}
+          in y then #{value}
+          ^^^^^^^^^^^{value} Duplicate branch body detected.
+          else #{value}
+          ^^^^ Duplicate branch body detected.
+          end
+        RUBY
+      end
+    end
+  end
+
   shared_examples_for 'literal rescue allowed' do |type, value|
     context "when returning a #{type} in multiple branches" do
       it 'allows branches to be duplicated' do
@@ -400,7 +430,7 @@
   context 'with IgnoreConstantBranches: true' do
     let(:cop_config) { { 'IgnoreConstantBranches' => true } }
 
-    %w[if case rescue].each do |keyword|
+    %w[if case case-match rescue].each do |keyword|
       context "with `#{keyword}`" do
         it_behaves_like "literal #{keyword} allowed", 'constant', 'MY_CONST'