From f5f9076cac93d8536b132def7bc621244bdc0201 Mon Sep 17 00:00:00 2001
From: Marc-Andre Lafortune <github@marc-andre.ca>
Date: Tue, 18 Aug 2020 15:25:03 -0400
Subject: [PATCH]  Add `ConstNode` and some helper methods.

---
 CHANGELOG.md                        |  1 +
 lib/rubocop/ast.rb                  |  1 +
 lib/rubocop/ast/builder.rb          |  1 +
 lib/rubocop/ast/node/const_node.rb  | 63 +++++++++++++++++++++++++++++
 spec/rubocop/ast/const_node_spec.rb | 45 +++++++++++++++++++++
 5 files changed, 111 insertions(+)
 create mode 100644 lib/rubocop/ast/node/const_node.rb
 create mode 100644 spec/rubocop/ast/const_node_spec.rb

diff --git a/CHANGELOG.md b/CHANGELOG.md
index cdfc2d989..a8ad0a9aa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@
 * [#88](https://github.com/rubocop-hq/rubocop-ast/pull/88): Add `RescueNode`. Add `ResbodyNode#exceptions` and `ResbodyNode#branch_index`. ([@fatkodima][])
 * [#89](https://github.com/rubocop-hq/rubocop-ast/pull/89): Support right hand assignment for Ruby 2.8 (3.0) parser. ([@koic][])
 * [#93](https://github.com/rubocop-hq/rubocop-ast/pull/93): Add `Node#{left|right}_sibling{s}` ([@marcandre][])
+* [#99](https://github.com/rubocop-hq/rubocop-ast/pull/99): Add `ConstNode` and some helper methods. ([@marcandre][])
 
 ### Changes
 
diff --git a/lib/rubocop/ast.rb b/lib/rubocop/ast.rb
index 153ada376..49c84a08e 100644
--- a/lib/rubocop/ast.rb
+++ b/lib/rubocop/ast.rb
@@ -29,6 +29,7 @@
 require_relative 'ast/node/case_match_node'
 require_relative 'ast/node/case_node'
 require_relative 'ast/node/class_node'
+require_relative 'ast/node/const_node'
 require_relative 'ast/node/def_node'
 require_relative 'ast/node/defined_node'
 require_relative 'ast/node/ensure_node'
diff --git a/lib/rubocop/ast/builder.rb b/lib/rubocop/ast/builder.rb
index c80c29519..afbd15022 100644
--- a/lib/rubocop/ast/builder.rb
+++ b/lib/rubocop/ast/builder.rb
@@ -27,6 +27,7 @@ class Builder < Parser::Builders::Default
         case_match:   CaseMatchNode,
         case:         CaseNode,
         class:        ClassNode,
+        const:        ConstNode,
         def:          DefNode,
         defined?:     DefinedNode,
         defs:         DefNode,
diff --git a/lib/rubocop/ast/node/const_node.rb b/lib/rubocop/ast/node/const_node.rb
new file mode 100644
index 000000000..12f52e01d
--- /dev/null
+++ b/lib/rubocop/ast/node/const_node.rb
@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module AST
+    # A node extension for `const` nodes.
+    class ConstNode < Node
+      # The `send` node associated with this block.
+      #
+      # @return [Node, nil] the node associated with the scope (e.g. cbase, const, ...)
+      def namespace
+        children[0]
+      end
+
+      # @return [Symbol] the demodulized name of the constant: "::Foo::Bar" => :Bar
+      def short_name
+        children[1]
+      end
+
+      # The body of this block.
+      #
+      # @return [Boolean] if the constant is a Module / Class, according to the standard convention.
+      #                   Note: some classes might have uppercase in which case this method
+      #                         returns false
+      def module_name?
+        short_name.match?(/[[:lower:]]/)
+      end
+      alias class_name? module_name?
+
+      # @return [Boolean] if the constant starts with `::` (aka s(:cbase))
+      def absolute?
+        each_path.first.cbase_type?
+      end
+
+      # @return [Boolean] if the constant does not start with `::` (aka s(:cbase))
+      def relative?
+        !absolute?
+      end
+
+      # Yield nodes for the namespace
+      #
+      #   For `::Foo::Bar::BAZ` => yields:
+      #      s(:cbase), then
+      #      s(:const, :Foo), then
+      #      s(:const, s(:const, :Foo), :Bar)
+      def each_path(&block)
+        return to_enum(__method__) unless block_given?
+
+        descendants = []
+        last = self
+        loop do
+          last = last.children.first
+          break if last.nil?
+
+          descendants << last
+          break unless last.const_type?
+        end
+        descendants.reverse_each(&block)
+
+        self
+      end
+    end
+  end
+end
diff --git a/spec/rubocop/ast/const_node_spec.rb b/spec/rubocop/ast/const_node_spec.rb
new file mode 100644
index 000000000..8a53db0f9
--- /dev/null
+++ b/spec/rubocop/ast/const_node_spec.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::AST::ConstNode do
+  let(:ast) { parse_source(source).ast }
+  let(:const_node) { ast }
+  let(:source) { '::Foo::Bar::BAZ' }
+
+  describe '#namespace' do
+    it { expect(const_node.namespace.source).to eq '::Foo::Bar' }
+  end
+
+  describe '#short_name' do
+    it { expect(const_node.short_name).to eq :BAZ }
+  end
+
+  describe '#module_name?' do
+    it { expect(const_node.module_name?).to eq false }
+
+    context 'with a constant with a lowercase letter' do
+      let(:source) { '::Foo::Bar' }
+
+      it { expect(const_node.module_name?).to eq true }
+    end
+  end
+
+  describe '#absolute?' do
+    it { expect(const_node.absolute?).to eq true }
+
+    context 'with a constant not starting with ::' do
+      let(:source) { 'Foo::Bar::BAZ' }
+
+      it { expect(const_node.absolute?).to eq false }
+    end
+  end
+
+  describe '#each_path' do
+    let(:source) { 'var = ::Foo::Bar::BAZ' }
+    let(:const_node) { ast.children.last }
+
+    it 'yields all parts of the namespace' do
+      expect(const_node.each_path.map(&:type)).to eq %i[cbase const const]
+      expect(const_node.each_path.to_a.last(2).map(&:short_name)).to eq %i[Foo Bar]
+    end
+  end
+end