Fix false negatives for Lint/UnreachableLoop

changelog/fix_false_negatives_for_lint_unreachable_loop.md

@@ -0,0 +1 @@
+* [#12841](https://github.com/rubocop/rubocop/pull/12841): Fix false negatives for `Lint/UnreachableLoop` when using pattern matching. ([@koic][])

lib/rubocop/cop/lint/unreachable_loop.rb

@@ -160,7 +160,7 @@ def break_statement?(node)
             break_statement && !preceded_by_continue_statement?(break_statement)
           when :if
             check_if(node)
-          when :case
+          when :case, :case_match
             check_case(node)
           else
             false
@@ -178,7 +178,13 @@ def check_case(node)
           return false unless else_branch
           return false unless break_statement?(else_branch)
 
-          node.when_branches.all? { |branch| branch.body && break_statement?(branch.body) }
+          branches = if node.case_type?
+                       node.when_branches
+                     else
+                       node.in_pattern_branches
+                     end
+
+          branches.all? { |branch| branch.body && break_statement?(branch.body) }
         end
 
         def preceded_by_continue_statement?(break_statement)

spec/rubocop/cop/lint/unreachable_loop_spec.rb

@@ -90,6 +90,46 @@
         end
       RUBY
     end
+
+    it 'registers an offense when using `case-in-else` with all break branches' do
+      expect_offense(<<~RUBY)
+        while x > 0
+        ^^^^^^^^^^^ This loop will have at most one iteration.
+          case x
+          in 1
+            break
+          else
+            raise MyError
+          end
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when using `case` match without `else`' do
+      expect_no_offenses(<<~RUBY)
+        while x > 0
+          case x
+          in 1
+            break
+          end
+        end
+      RUBY
+    end
+
+    it 'does not register an offense when using `case-in-else` and not all branches are breaking' do
+      expect_no_offenses(<<~RUBY)
+        while x > 0
+          case x
+          in 1
+            break
+          in 2
+            do_something
+          else
+            raise MyError
+          end
+        end
+      RUBY
+    end
   end
 
   context 'with preceding continue statements' do
@@ -130,6 +170,21 @@
         end
       RUBY
     end
+
+    it 'does not register an offense when using `case-in-else` with all break branches' do
+      expect_no_offenses(<<~RUBY)
+        while x > 0
+          redo if x.odd?
+
+          case x
+          in 1
+            break
+          else
+            raise MyError
+          end
+        end
+      RUBY
+    end
   end
 
   context 'with an enumerator method' do