[Fix rubocop#12731] Treat csend the same way as send for setter methods

In order to detect code like `if test&.method = 10` we need to find not only
send nodes but also csend nodes.

changelog/fix_assignment_in_condition_safe_nav_setter.md

@@ -0,0 +1 @@
+* [#12731](https://github.com/rubocop/rubocop/pull/12731): Treat `&.` the same way as `.` for setter methods in `Lint/AssignmentInCondition`. ([@jonas054][])

lib/rubocop/cop/lint/assignment_in_condition.rb

@@ -50,7 +50,7 @@ class AssignmentInCondition < Base
         MSG_WITHOUT_SAFE_ASSIGNMENT_ALLOWED =
           'Use `==` if you meant to do a comparison or move the assignment ' \
           'up out of the condition.'
-        ASGN_TYPES = [:begin, *AST::Node::EQUALS_ASSIGNMENTS, :send].freeze
+        ASGN_TYPES = [:begin, *AST::Node::EQUALS_ASSIGNMENTS, :send, :csend].freeze
 
         def on_if(node)
           return if node.condition.block_type?

lib/rubocop/cop/mixin/safe_assignment.rb

@@ -14,7 +14,7 @@ module SafeAssignment
       def_node_matcher :empty_condition?, '(begin)'
 
       # @!method setter_method?(node)
-      def_node_matcher :setter_method?, '[(send ...) setter_method?]'
+      def_node_matcher :setter_method?, '[({send csend} ...) setter_method?]'
 
       # @!method safe_assignment?(node)
       def_node_matcher :safe_assignment?, '(begin {equals_asgn? #setter_method?})'

spec/rubocop/cop/lint/assignment_in_condition_spec.rb

@@ -182,6 +182,19 @@
     RUBY
   end
 
+  it 'registers an offense for assignment methods with safe navigation operator' do
+    expect_offense(<<~RUBY)
+      if test&.method = 10
+                      ^ Use `==` if you meant to do a comparison or wrap the expression in parentheses to indicate you meant to assign in a condition.
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      if (test&.method = 10)
+      end
+    RUBY
+  end
+
   it 'does not blow up for empty if condition' do
     expect_no_offenses(<<~RUBY)
       if ()