Ensure front matter defaults are dot access hashes (#944)

Fixes #704

bridgetown-core/lib/bridgetown-core/front_matter/defaults.rb

@@ -5,6 +5,8 @@ module FrontMatter
     # This class handles custom defaults for front matter settings.
     # It is exposed via the frontmatter_defaults method on the site class.
     class Defaults
+      using Bridgetown::Refinements
+
       # @return [Bridgetown::Site]
       attr_reader :site
 
@@ -16,6 +18,7 @@ def initialize(site)
       def reset
         @glob_cache = {}
         @defaults_cache = {}
+        @sets = nil
       end
 
       def ensure_time!(set)
@@ -175,15 +178,12 @@ def matching_sets(path, collection)
 
       # Returns a list of valid sets
       #
-      # This is not cached to allow plugins to modify the configuration
-      # and have their changes take effect
-      #
       # @return [Array<Hash>]
       def valid_sets
-        sets = site.config["defaults"]
-        return [] unless sets.is_a?(Array)
+        @sets ||= site.config["defaults"].map(&:as_dots)
+        return [] unless @sets.is_a?(Array)
 
-        sets.filter_map do |set|
+        @sets.filter_map do |set|
           if valid?(set)
             massage_scope!(set)
             # TODO: is this trip really necessary?

bridgetown-core/test/test_front_matter_defaults.rb

@@ -137,22 +137,22 @@ class TestFrontMatterDefaults < BridgetownUnitTest
 
   context "A site with front matter defaults with no path" do
     setup do
-      @site = fixture_site(
-        "defaults" => [{
-          "scope"  => {
-            "type" => "pages",
-          },
-          "values" => {
-            "key" => "val",
-          },
-        }]
-      )
-      @site.process
+      @site = fixture_site
+      @site.config.defaults << {
+        scope: {
+          type: "pages",
+        },
+        values: {
+          key: "val",
+        },
+      }
+      @site.read
       @affected = @site.collections.pages.resources
       @not_affected = @site.collections.posts.resources
     end
 
     should "affect only the specified type and all paths" do
+      assert @affected.length > 1
       assert_equal @affected.reject { |page| page.data["key"] == "val" }, []
       assert_equal @not_affected.reject { |page| page.data["key"] == "val" },
                    @not_affected