Fix #value for a dstr node.

lib/rubocop/ast.rb

@@ -72,6 +72,7 @@
 require_relative 'ast/node/self_class_node'
 require_relative 'ast/node/send_node'
 require_relative 'ast/node/str_node'
+require_relative 'ast/node/dstr_node'
 require_relative 'ast/node/super_node'
 require_relative 'ast/node/symbol_node'
 require_relative 'ast/node/until_node'

lib/rubocop/ast/builder.rb

@@ -42,6 +42,7 @@ class Builder < Parser::Builders::Default
         def:          DefNode,
         defined?:     DefinedNode,
         defs:         DefNode,
+        dstr:         DstrNode,
         ensure:       EnsureNode,
         for:          ForNode,
         forward_args: ForwardArgsNode,
@@ -68,7 +69,6 @@ class Builder < Parser::Builders::Default
         csend:        SendNode,
         send:         SendNode,
         str:          StrNode,
-        dstr:         StrNode,
         xstr:         StrNode,
         sclass:       SelfClassNode,
         super:        SuperNode,

lib/rubocop/ast/node/dstr_node.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module AST
+    # A node extension for `dstr` nodes. This will be used
+    # in place of a plain node when the builder constructs the AST, making
+    # its methods available to all `dstr` nodes within RuboCop.
+    class DstrNode < StrNode
+      def value
+        child_nodes.map do |child|
+          child.respond_to?(:value) ? child.value : child.source
+        end.join
+      end
+    end
+  end
+end

spec/rubocop/ast/dstr_node_spec.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::AST::DstrNode do
+  subject(:dstr_node) { parse_source(source).ast }
+
+  describe '#value' do
+    subject { dstr_node.value }
+
+    context 'with a multiline string' do
+      let(:source) do
+        <<~RUBY
+          'this is a multiline ' \
+          'string'
+        RUBY
+      end
+
+      it { is_expected.to eq('this is a multiline string') }
+    end
+
+    context 'with interpolation' do
+      let(:source) do
+        '"foo #{bar} baz"'
+      end
+
+      it { is_expected.to eq('foo #{bar} baz') }
+    end
+
+    context 'with implicit concatenation' do
+      let(:source) do
+        <<~RUBY
+          'foo ' 'bar ' 'baz'
+        RUBY
+      end
+
+      it { is_expected.to eq('foo bar baz') }
+    end
+  end
+end