Ignore a leading thematic break that isn't really frontmatter

lib/perron/resource/separator.rb

@@ -19,12 +19,21 @@ def frontmatter
 
       def parsed(content)
         if content =~ /\A---\s*(.*?)\s*---\s*(.*)/m
-          @frontmatter = YAML.safe_load($1, permitted_classes: [Date, Time]) || {}
-          @content = $2.strip
-        else
-          @frontmatter = {}
-          @content = content
+          parsed_yaml = YAML.safe_load($1, permitted_classes: [Date, Time])
+
+          # A `---` at the start of the body (a thematic break) followed by
+          # another `---` also matches, but parses to a string or an array
+          # rather than a mapping. Only treat it as frontmatter when it is one.
+          if parsed_yaml.nil? || parsed_yaml.is_a?(Hash)
+            @frontmatter = parsed_yaml || {}
+            @content = $2.strip
+
+            return
+          end
         end
+
+        @frontmatter = {}
+        @content = content
       end
     end
   end

test/perron/resource/separator_test.rb

@@ -60,6 +60,30 @@ def test_parses_yaml_list_syntax
     assert_equal ["alice", "bob"], separator.frontmatter.authors
   end
 
+  def test_treats_a_leading_thematic_break_as_content_not_frontmatter
+    content = <<~CONTENT
+      ---
+
+      An intro paragraph.
+
+      ---
+
+      The rest of the post.
+    CONTENT
+    separator = Perron::Resource::Separator.new(content)
+
+    assert_equal content, separator.content
+    assert_empty separator.frontmatter.to_h
+  end
+
+  def test_ignores_a_scalar_between_the_fences
+    content = "---\nJust a sentence, not a mapping\n---\nBody\n"
+    separator = Perron::Resource::Separator.new(content)
+
+    assert_equal content, separator.content
+    assert_empty separator.frontmatter.to_h
+  end
+
   def test_parses_mixed_types_in_frontmatter
     content = <<~CONTENT
       ---