Allow empty strings in -o to result in empty override run listlcg/empty-override-runlist

Previously this was not possible.  Now you can do this:

```
chef-client -o "" ./foo.rb
```

And it will only run foo.rb and not any of the recipes in your
run_list at all.  Node will not be saved at the end.

Useful to one-shot something like keyrotation (which still needs
keys and needs to talk to the chef server API, so this is a
different use case from simple chef-apply).

Signed-off-by: Lamont Granquist <lamont@scriptkiddie.org>

3 files changed, 32 insertions, 9 deletions

diff --git a/lib/chef/application.rb b/lib/chef/application.rb
index a63d8218f4..817cdf051d 100644
--- a/lib/chef/application.rb
+++ b/lib/chef/application.rb
@@ -1,7 +1,7 @@
 #
 # Author:: AJ Christensen (<aj@chef.io>)
 # Author:: Mark Mzyk (mmzyk@chef.io)
-# Copyright:: Copyright 2008-2018, Chef Software Inc.
+# Copyright:: Copyright 2008-2019, Chef Software Inc.
 # License:: Apache License, Version 2.0
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -260,7 +260,6 @@ class Chef
 
       Chef::LocalMode.with_server_connectivity do
         override_runlist = config[:override_runlist]
-        override_runlist ||= [] if specific_recipes.size > 0
         @chef_client = Chef::Client.new(
           @chef_client_json,
           override_runlist: override_runlist,
diff --git a/lib/chef/node.rb b/lib/chef/node.rb
index 9b67f27f14..c945bb640f 100644
--- a/lib/chef/node.rb
+++ b/lib/chef/node.rb
@@ -300,13 +300,37 @@ class Chef
       @primary_runlist
     end
 
-    attr_writer :override_runlist
+    # This boolean can be useful to determine if an override_runlist is set, it can be true
+    # even if the override_runlist is empty.
+    #
+    # (Mutators can set the override_runlist so any non-empty override_runlist is considered set)
+    #
+    # @return [Boolean] if the override run list has been set
+    def override_runlist_set?
+      !!@override_runlist_set || !override_runlist.empty?
+    end
+
+    # Accessor for override_runlist (this cannot set an empty override run list)
+    #
+    # @params args [Array] override run list to set
+    # @return [Chef::RunList] the override run list
     def override_runlist(*args)
-      args.length > 0 ? @override_runlist.reset!(args) : @override_runlist
+      return @override_runlist if args.length == 0
+      @override_runlist_set = true
+      @override_runlist.reset!(args)
+    end
+
+    # Setter for override_runlist which allows setting an empty override run list and marking it to be used
+    #
+    # @params array [Array] override run list to set
+    # @return [Chef::RunList] the override run list
+    def override_runlist=(array)
+      @override_runlist_set = true
+      @override_runlist.reset!(array)
     end
 
     def select_run_list
-      @override_runlist.empty? ? @primary_runlist : @override_runlist
+      override_runlist_set? ? @override_runlist : @primary_runlist
     end
 
     # Returns an Array of roles and recipes, in the order they will be applied.
diff --git a/lib/chef/policy_builder/expand_node_object.rb b/lib/chef/policy_builder/expand_node_object.rb
index dda4a2b4c3..eea5a37edd 100644
--- a/lib/chef/policy_builder/expand_node_object.rb
+++ b/lib/chef/policy_builder/expand_node_object.rb
@@ -214,7 +214,7 @@ class Chef
       # override_runlist was provided. Chef::Client uses this to decide whether
       # to do the final node save at the end of the run or not.
       def temporary_policy?
-        !node.override_runlist.empty?
+        node.override_runlist_set?
       end
 
       ########################################
@@ -222,9 +222,9 @@ class Chef
       ########################################
 
       def setup_run_list_override
-        runlist_override_sanity_check!
-        unless override_runlist.empty?
-          node.override_runlist(*override_runlist)
+        unless override_runlist.nil?
+          runlist_override_sanity_check!
+          node.override_runlist = override_runlist
           Chef::Log.warn "Run List override has been provided."
           Chef::Log.warn "Original Run List: [#{node.primary_runlist}]"
           Chef::Log.warn "Overridden Run List: [#{node.run_list}]"