(puppetlabsGH-1365) Add resolve_references plan function

This adds support for a `resolve_references` plan function that accepts
a hash of target data, resolves all references in the hash, and returns
the resolved target data.

bolt-modules/boltlib/lib/puppet/functions/resolve_references.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require 'bolt/error'
+
+# Evaulates all _plugin references in a hash and returns the resolved reference data.
+Puppet::Functions.create_function(:resolve_references) do
+  # Resolve references.
+  # @param references A hash of reference data to resolve.
+  # @return A hash of resolved reference data.
+  # @example Resolve a hash of reference data
+  #   $references = {
+  #     "targets" => [
+  #       "_plugin" => "terraform",
+  #       "dir" => "path/to/terraform/project",
+  #       "resource_type" => "aws_instance.web",
+  #       "uri" => "public_ip"
+  #     ]
+  #   }
+  #
+  #   resolve_references($references)
+  dispatch :resolve_references do
+    param 'Hash[String[1], Any]', :references
+    return_type 'Hash[String[1], Any]'
+  end
+
+  def resolve_references(references)
+    unless Puppet[:tasks]
+      raise Puppet::ParseErrorWithIssue
+        .from_issue_and_stack(Bolt::PAL::Issues::PLAN_OPERATION_NOT_SUPPORTED_WHEN_COMPILING, action: 'resolve_references')
+    end
+
+    references = references.merge('name' => 'all') unless references['name']
+    inventory = Puppet.lookup(:bolt_inventory)
+    group = Bolt::Inventory::Group2.new(references, inventory.plugins)
+
+    group.resolve_references(references)
+  end
+end

bolt-modules/boltlib/spec/functions/resolve_references_spec.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'resolve_references' do
+  it 'resolves data' do
+    # TODO
+  end
+end

lib/bolt/inventory/group2.rb

@@ -82,7 +82,6 @@ def resolve_references(data)
           reference?(value) ? resolve_references(resolve_single_reference(value)) : value
         end
       end
-      private :resolve_references
 
       # Iteratively resolves "top-level" references until the result no longer
       # has top-level references. A top-level reference is one which is not