(PUP-11751) catch :undefined_variable when defaults defined

Now that scope objects raise errors when variables are not found,
interpolation needs to guard against this case when defaults are
defined in a lookup and use the default in case a lookup fails.

Author: tvpartytonight

lib/puppet/pops/lookup/interpolation.rb

@@ -90,14 +90,16 @@ def interpolate_method(method_key)
             lookup_invocation.report_found_in_overrides(root_key, ovr[root_key])
           else
             scope = lookup_invocation.scope
-            val = scope[root_key]
-            if val.nil? && !nil_in_scope?(scope, root_key)
-              defaults = lookup_invocation.default_values
-              if defaults.include?(root_key)
-                lookup_invocation.report_found_in_defaults(root_key, defaults[root_key])
-              else
-                nil
-              end
+            val = nil
+            if (default_val = lookup_invocation.default_values[root_key])
+              catch(:undefined_variable) { val = scope[root_key] }
+            else
+              val = scope[root_key]
+            end
+            if val.nil? && default_val.nil?
+              nil
+            elsif val.nil?
+              lookup_invocation.report_found_in_defaults(root_key, default_val)
             else
               lookup_invocation.report_found(root_key, val)
             end
@@ -125,15 +127,6 @@ def interpolate_method(method_key)
     interpolate_method
   end
 
-  # Because the semantics of Puppet::Parser::Scope#include? differs from Hash#include?
-  def nil_in_scope?(scope, key)
-    if scope.is_a?(Hash)
-      scope.include?(key)
-    else
-      scope.exist?(key)
-    end
-  end
-
   def get_method_and_data(data, allow_methods)
     match = data.match(/^(\w+)\((?:["]([^"]+)["]|[']([^']+)['])\)$/)
     if match

spec/unit/functions/lookup_spec.rb

@@ -2420,7 +2420,6 @@ def uri_test_func(options, context)
         end
 
         it 'defaults are used when data is not found in scope interpolations' do
-          pending('See PUP-11751')
           expect(lookup('mod_a::interpolate_scope_xd', { 'default_values_hash' => defaults })).to eql('-- value scope_xd (from default) --')
         end