Prevent warning when let is overridden in an include (#2593)

lib/rspec/core/memoized_helpers.rb

@@ -288,7 +288,26 @@ def let(name, &block)
           raise(
             "#let or #subject called with a reserved name #initialize"
           ) if :initialize == name
-          MemoizedHelpers.module_for(self).__send__(:define_method, name, &block)
+          our_module = MemoizedHelpers.module_for(self)
+
+          # If we have a module clash in our helper module
+          # then we need to remove it to prevent a warning.
+          #
+          # Note we do not check ancestor modules (see: `instance_methods(false)`)
+          # as we can override them.
+          if our_module.instance_methods(false).include?(name)
+            our_module.__send__(:remove_method, name)
+          end
+          our_module.__send__(:define_method, name, &block)
+
+          # If we have a module clash in the example module
+          # then we need to remove it to prevent a warning.
+          #
+          # Note we do not check ancestor modules (see: `instance_methods(false)`)
+          # as we can override them.
+          if instance_methods(false).include?(name)
+            remove_method(name)
+          end
 
           # Apply the memoization. The method has been defined in an ancestor
           # module so we can use `super` here to get the value.

spec/rspec/core/shared_context_spec.rb

@@ -66,6 +66,19 @@
     expect(group.new.foo).to eq('foo')
   end
 
+  it 'supports overriding let without warnings' do
+    shared = Module.new do
+      extend RSpec::SharedContext
+      let(:foo) { 'foo' }
+    end
+    group = RSpec.describe do
+      include shared
+      let(:foo) { 'bar' }
+    end
+
+    expect(group.new.foo).to eq('bar')
+  end
+
   it "supports let when applied to an individual example via metadata" do
     shared = Module.new do
       extend RSpec::SharedContext