Fix RSpec/ScatteredLet to detect let with proc argument

Closes #771

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Add new `Capybara/VisibilityMatcher` cop. ([@aried3r][])
 * Ignore String constants by `RSpec/Describe`. ([@AlexWayfer][])
 * Drop support for ruby 2.3. ([@bquorning][])
+* Fix `RSpec/ScatteredLet` to detect `let` with proc argument. ([@tejasbubane][])
 
 ## 1.38.1 (2020-02-15)
 
@@ -497,3 +498,4 @@ Compatibility release so users can upgrade RuboCop to 0.51.0. No new features.
 [@eitoball]: https://github.com/eitoball
 [@aried3r]: https://github.com/aried3r
 [@AlexWayfer]: https://github.com/AlexWayfer
+[@tejasbubane]: https://github.com/tejasbubane

lib/rubocop/rspec/language/node_pattern.rb

@@ -17,7 +17,11 @@ module NodePattern
 
         def_node_matcher :hook?, Hooks::ALL.block_pattern
 
-        def_node_matcher :let?, Helpers::ALL.block_pattern
+        def_node_matcher :let?, <<-PATTERN
+          {#{Helpers::ALL.block_pattern}
+           (send #{RSPEC} #{Helpers::ALL.node_pattern_union}
+                 _ (block_pass ...))}
+        PATTERN
 
         def_node_matcher :subject?, Subject::ALL.block_pattern
       end

spec/rubocop/cop/rspec/scattered_let_spec.rb

@@ -25,4 +25,15 @@
       end
     RUBY
   end
+
+  it 'flags `let` with proc argument' do
+    expect_offense(<<-RUBY)
+      RSpec.describe User do
+        let(:a) { a }
+        subject { User }
+        let(:user, &args[:build_user])
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Group all let/let! blocks in the example group together.
+      end
+    RUBY
+  end
 end