Add :follow_links option to not follow links on select pages

lib/docs/filters/core/internal_urls.rb

@@ -3,7 +3,7 @@ require 'set'
 module Docs
   class InternalUrlsFilter < Filter
     def call
-      internal_urls = Set.new
+      internal_urls = Set.new if follow_links?
 
       css('a').each do |link|
         next if skip_link?(link)
@@ -17,13 +17,17 @@ module Docs
         normalize_internal_url(url, subpath)
 
         link['href'] = internal_path_to(url)
-        internal_urls << url.merge!(fragment: nil).to_s
+        internal_urls << url.merge!(fragment: nil).to_s if internal_urls
       end
 
-      result[:internal_urls] = internal_urls.to_a
+      result[:internal_urls] = (internal_urls || []).to_a
       doc
     end
 
+    def follow_links?
+      !(context[:follow_links] && context[:follow_links].call(self) == false)
+    end
+
     def skip_link?(link)
       context[:skip_links] && context[:skip_links].call(link)
     end

test/lib/docs/filters/core/internal_urls_test.rb

@@ -159,6 +159,28 @@ class InternalUrlsFilterTest < MiniTest::Spec
         assert_equal 1, internal_urls.length
       end
     end
+
+    context "when context[:follow_links] is a block" do
+      before do
+        @body = link_to context[:url]
+      end
+
+      it "calls the block with the filter instance" do
+        context[:follow_links] = ->(arg) { @arg = arg; nil }
+        filter.call
+        assert_equal filter, @arg
+      end
+
+      it "is empty when the block returns false" do
+        context[:follow_links] = ->(_) { false }
+        assert_empty internal_urls
+      end
+
+      it "is the default when the block returns true" do
+        context[:follow_links] = ->(_) { true }
+        refute_empty internal_urls
+      end
+    end
   end
 
   context "when the base url is 'example.com'" do