From 28d097d48a346826806186a78b17f520c8533c1a Mon Sep 17 00:00:00 2001
From: Noah Kantrowitz <noah@coderanger.net>
Date: Tue, 5 Jun 2018 21:02:41 -0700
Subject: Streamline the map locking process with a resource level flag.

Signed-off-by: Noah Kantrowitz <noah@coderanger.net>
---
 lib/chef/resource.rb       | 22 ++++++++++++++++++++++
 spec/unit/resource_spec.rb | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/lib/chef/resource.rb b/lib/chef/resource.rb
index 05349b80e7..239c4ddc68 100644
--- a/lib/chef/resource.rb
+++ b/lib/chef/resource.rb
@@ -1161,6 +1161,22 @@ class Chef
         end
     end
 
+    # Set or return if this resource is in preview mode.
+    #
+    # This is used in Chef core as part of the process of migrating resources
+    # from a cookbook into core. It should be set to `true` when a cookbook
+    # resource is added to core, and then removed (set to `false`) in the next
+    # major release.
+    #
+    # @param value [nil, Boolean] If nil, get the current value. If not nil, set
+    #   the value of the flag.
+    # @return [Boolean]
+    def self.preview_resource(value=nil)
+        @preview_resource = false unless defined?(@preview_resource)
+        @preview_resource = value unless value.nil?
+        @preview_resource
+    end
+
     #
     # Internal Resource Interface (for Chef)
     #
@@ -1305,6 +1321,12 @@ class Chef
         remove_canonical_dsl
       end
 
+      # If a resource is in preview mode, set allow_cookbook_override on all its
+      # mappings by default.
+      if preview_resource && !options.include?(:allow_cookbook_override)
+        options[:allow_cookbook_override] = true
+      end
+
       result = Chef.resource_handler_map.set(name, self, options, &block)
       Chef::DSL::Resources.add_resource_dsl(name)
       result
diff --git a/spec/unit/resource_spec.rb b/spec/unit/resource_spec.rb
index 67b8f59ff4..7dc2c83c5d 100644
--- a/spec/unit/resource_spec.rb
+++ b/spec/unit/resource_spec.rb
@@ -1144,4 +1144,38 @@ end
       it { is_expected.to eq [:two, :one] }
     end
   end
+
+  describe ".preview_resource" do
+    let(:klass) { Class.new(Chef::Resource) }
+
+    before do
+      allow(Chef::DSL::Resources).to receive(:add_resource_dsl).with(:test_resource)
+    end
+
+    it "defaults to false" do
+      expect(klass.preview_resource).to eq false
+    end
+
+    it "can be set to true" do
+      klass.preview_resource(true)
+      expect(klass.preview_resource).to eq true
+    end
+
+    it "does not affect provides by default" do
+      expect(Chef.resource_handler_map).to receive(:set).with(:test_resource, klass, {canonical: true})
+      klass.resource_name(:test_resource)
+    end
+
+    it "adds allow_cookbook_override when true" do
+      expect(Chef.resource_handler_map).to receive(:set).with(:test_resource, klass, {canonical: true, allow_cookbook_override: true})
+      klass.preview_resource(true)
+      klass.resource_name(:test_resource)
+    end
+
+    it "allows manually overriding back to false" do
+      expect(Chef.resource_handler_map).to receive(:set).with(:test_resource, klass, {allow_cookbook_override: false})
+      klass.preview_resource(true)
+      klass.provides(:test_resource, allow_cookbook_override: false)
+    end
+  end
 end
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