[Fix rubocop#8708] Fix bad regexp recognition in `Lint/OutOfRangeRege…

…xpRef` when there are multiple regexps.

changelog/fix_fix_8708_fix_bad_regexp_recognition_in.md

@@ -0,0 +1 @@
+* [#8708](https://github.com/rubocop-hq/rubocop/pull/8708): Fix bad regexp recognition in `Lint/OutOfRangeRegexpRef` when there are multiple regexps. ([@dvandersluis][])

lib/rubocop/cop/lint/out_of_range_regexp_ref.rb

@@ -35,14 +35,13 @@ def on_match_with_lvasgn(node)
           check_regexp(node.children.first)
         end
 
-        def on_send(node)
+        def after_send(node)
           @valid_ref = nil
 
-          if node.receiver&.regexp_type?
-            check_regexp(node.receiver)
-          elsif node.first_argument&.regexp_type? \
-            && REGEXP_ARGUMENT_METHODS.include?(node.method_name)
+          if regexp_first_argument?(node)
             check_regexp(node.first_argument)
+          elsif regexp_receiver?(node)
+            check_regexp(node.receiver)
           end
         end
 
@@ -80,6 +79,19 @@ def check_regexp(node)
                          node.each_capture(named: false).count
                        end
         end
+
+        def regexp_first_argument?(send_node)
+          send_node.first_argument&.regexp_type? \
+            && REGEXP_ARGUMENT_METHODS.include?(send_node.method_name)
+        end
+
+        def regexp_receiver?(send_node)
+          send_node.receiver&.regexp_type?
+        end
+
+        def nth_ref_receiver?(send_node)
+          send_node.receiver&.nth_ref_type?
+        end
       end
     end
   end

spec/rubocop/cop/lint/out_of_range_regexp_ref_spec.rb

@@ -234,6 +234,51 @@
     end
   end
 
+  context 'when both the LHS and RHS use regexp' do
+    it 'only considers the RHS regexp' do
+      expect_no_offenses(<<~RUBY)
+        if "foo bar".gsub(/\s+/, "") =~ /foo(bar)/
+          p $1
+        end
+      RUBY
+
+      expect_offense(<<~RUBY)
+        if "foo bar".gsub(/(\s+)/, "") =~ /foobar/
+          p $1
+            ^^ $1 is out of range (no regexp capture groups detected).
+        end
+      RUBY
+    end
+  end
+
+  context 'when calling a regexp method on a nth-ref node' do
+    it 'does not register an offense when calling gsub on a valid nth-ref' do
+      expect_no_offenses(<<~RUBY)
+        if "some : line " =~ / : (.+)/
+          $1.gsub(/\s{2}/, " ")
+        end
+      RUBY
+    end
+
+    it 'registers an offense when calling gsub on an invalid nth-ref' do
+      expect_offense(<<~RUBY)
+        if "some : line " =~ / : (.+)/
+          $2.gsub(/\s{2}/, " ")
+          ^^ $2 is out of range (1 regexp capture group detected).
+        end
+      RUBY
+    end
+
+    it 'registers an offense if the capturing groups have changed' do
+      expect_offense(<<~RUBY)
+        "some : line " =~ / : (.+)/
+        $1.gsub(/\s{2}/, " ")
+        puts $1
+             ^^ $1 is out of range (no regexp capture groups detected).
+      RUBY
+    end
+  end
+
   %i[gsub gsub! sub sub! scan].each do |method|
     context "matching with #{method}" do
       it 'does not register an offense when in range references are used' do