Add Scope#yields?

src/ameba/ast/scope.cr

@@ -4,6 +4,9 @@ module Ameba::AST
   # Represents a context of the local variable visibility.
   # This is where the local variables belong to.
   class Scope
+    # Whether the scope yields.
+    setter yields = false
+
     # Link to local variables
     getter variables = [] of Variable
 
@@ -143,6 +146,14 @@ module Ameba::AST
       end || variable.used_in_macro?
     end
 
+    # Returns `true` if current scope (or any of inner scopes) yields,
+    # `false` otherwise.
+    def yields?(check_inner_scopes = true)
+      return true if @yields
+      return inner_scopes.any?(&.yields?) if check_inner_scopes
+      false
+    end
+
     # Returns `true` if current scope is a def, `false` otherwise.
     def def?
       node.is_a?(Crystal::Def)

src/ameba/ast/visitors/scope_visitor.cr

@@ -64,6 +64,11 @@ module Ameba::AST
       end
     {% end %}
 
+    # :nodoc:
+    def visit(node : Crystal::Yield)
+      @current_scope.yields = true
+    end
+
     # :nodoc:
     def visit(node : Crystal::Def)
       node.name == "->" || on_scope_enter(node)