Merge pull request #2117 from rubocop/2075

Fix a false positive for `RSpec/LetSetup` when `let!` used in outer scope

Author: ydah

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Add new cop `RSpec/LeakyLocalVariable`. ([@lovro-bikic])
 - Bump RuboCop requirement to +1.81. ([@ydah])
+- Fix a false positive for `RSpec/LetSetup` when `let!` used in outer scope. ([@ydah])
 
 ## 3.7.0 (2025-09-01)
 

docs/modules/ROOT/pages/cops_rspec.adoc

@@ -3575,6 +3575,17 @@ before { create(:widget) }
 it 'counts widgets' do
   expect(Widget.count).to eq(1)
 end
+
+# good
+describe 'a widget' do
+  let!(:my_widget) { create(:widget) }
+  context 'when visiting its page' do
+    let!(:my_widget) { create(:widget, name: 'Special') }
+    it 'counts widgets' do
+      expect(Widget.count).to eq(1)
+    end
+  end
+end
 ----
 
 [#references-rspecletsetup]

lib/rubocop/cop/rspec/let_setup.rb

@@ -25,6 +25,18 @@ module RSpec
       #   it 'counts widgets' do
       #     expect(Widget.count).to eq(1)
       #   end
+      #
+      #   # good
+      #   describe 'a widget' do
+      #     let!(:my_widget) { create(:widget) }
+      #     context 'when visiting its page' do
+      #       let!(:my_widget) { create(:widget, name: 'Special') }
+      #       it 'counts widgets' do
+      #         expect(Widget.count).to eq(1)
+      #       end
+      #     end
+      #   end
+      #
       class LetSetup < Base
         MSG = 'Do not use `let!` to setup objects not referenced in tests.'
 
@@ -59,6 +71,8 @@ def on_block(node) # rubocop:disable InternalAffairs/NumblockHandler
 
         def unused_let_bang(node)
           child_let_bang(node) do |method_send, method_name|
+            next if overrides_outer_let_bang?(node, method_name)
+
             yield(method_send) unless method_called?(node, method_name.to_sym)
           end
         end
@@ -68,6 +82,22 @@ def child_let_bang(node, &block)
             let_bang(let, &block)
           end
         end
+
+        def overrides_outer_let_bang?(node, method_name)
+          node.each_ancestor(:block).any? do |ancestor|
+            next unless example_or_shared_group_or_including?(ancestor)
+
+            outer_let_bang?(ancestor, method_name)
+          end
+        end
+
+        def outer_let_bang?(ancestor_node, method_name)
+          RuboCop::RSpec::ExampleGroup.new(ancestor_node).lets.any? do |let|
+            let_bang(let) do |_send, name|
+              name == method_name
+            end
+          end
+        end
       end
     end
   end

spec/rubocop/cop/rspec/let_setup_spec.rb

@@ -137,4 +137,124 @@
       end
     RUBY
   end
+
+  it 'ignores let! that overrides outer scope let!' do
+    expect_no_offenses(<<~RUBY)
+      describe User, type: :model do
+        let!(:user) { create(:user) }
+
+        it 'is valid' do
+          expect(user).to be_valid
+        end
+
+        context 'with no direct usage' do
+          let!(:user) { create(:user, :special) }
+
+          it 'creates something' do
+            expect(SomeModel.count).to eq(2)
+          end
+        end
+      end
+    RUBY
+  end
+
+  it 'ignores let! overriding outer scope across multiple nesting levels' do
+    expect_no_offenses(<<~RUBY)
+      describe User do
+        let!(:user) { create(:user) }
+
+        it 'uses user' do
+          expect(user).to be_valid
+        end
+
+        context 'level 1' do
+          context 'level 2' do
+            let!(:user) { create(:user, :admin) }
+
+            it 'creates admin user' do
+              expect(User.count).to eq(2)
+            end
+          end
+        end
+      end
+    RUBY
+  end
+
+  it 'still flags unused let! when outer scope has different name' do
+    expect_offense(<<~RUBY)
+      describe User do
+        let!(:user) { create(:user) }
+
+        it 'uses user' do
+          expect(user).to be_valid
+        end
+
+        context 'different variable' do
+          let!(:admin) { create(:user, :admin) }
+          ^^^^^^^^^^^^ Do not use `let!` to setup objects not referenced in tests.
+
+          it 'creates admin user' do
+            expect(User.count).to eq(2)
+          end
+        end
+      end
+    RUBY
+  end
+
+  it 'allows let! override when outer let! is used elsewhere' do
+    expect_no_offenses(<<~RUBY)
+      describe User do
+        let!(:user) { create(:user) }
+
+        it 'uses user' do
+          expect(user).to be_valid
+        end
+
+        context 'special case' do
+          let!(:user) { create(:user, :special) }
+
+          it 'setup only' do
+            expect(User.count).to eq(2)
+          end
+        end
+      end
+    RUBY
+  end
+
+  it 'does not consider non-RSpec blocks as outer scope' do
+    expect_offense(<<~RUBY)
+      describe User do
+        [1, 2, 3].each do |i|
+          let!(:user) { create(:user, id: i) }
+          ^^^^^^^^^^^ Do not use `let!` to setup objects not referenced in tests.
+
+          it 'creates user' do
+            expect(User.count).to eq(3)
+          end
+        end
+      end
+    RUBY
+  end
+
+  it 'correctly identifies override through mixed block types' do
+    expect_no_offenses(<<~RUBY)
+      describe User do
+        let!(:user) { create(:user) }
+
+        it 'uses user' do
+          expect(user).to be_valid
+        end
+
+        [true, false].each do |flag|
+          context "when flag is \#{flag}" do
+            let!(:user) { create(:user, flag: flag) }
+
+            it 'setup only' do
+              expect(User.count).to be > 0
+            end
+          end
+        end
+      end
+    RUBY
+  end
 end