Merge branch 'optimize-cross-ref-system-notes-check' into 'master'

Optimize cross ref system notes check

## What does this MR do?

This MR optimizes system note visibility checking by memoizing the visible reference count, reducing the overhead of calling `Note#cross_reference_not_visible_for?`.

## Are there points in the code the reviewer needs to double check?

Note that since a cross reference message contains, "Mentioned in XYZ", we EXPECT that there is at least one reference. That's why using the ref count > 0 works. 

## Why was this MR needed?

The previous implementation relied on `Note#cross_reference_not_visible_for?`, which essentially tries to render all the Markdown references in a system note
and only displays the note if the user can see the referring project. But this duplicated the work that Banzai::NotesRenderer was doing already. This shaves about 0.8 s
from the load time from https://gitlab.com/gitlab-com/operations/issues/42.

## What are the relevant issue numbers?

#19273

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5070

2 files changed, 29 insertions, 18 deletions

diff --git a/lib/banzai/object_renderer.rb b/lib/banzai/object_renderer.rb
index f0e4f28bf12..dc83b87a6c1 100644
--- a/lib/banzai/object_renderer.rb
+++ b/lib/banzai/object_renderer.rb
@@ -31,10 +31,10 @@ module Banzai
       redacted = redact_documents(documents)
 
       objects.each_with_index do |object, index|
-        object.__send__("#{attribute}_html=", redacted.fetch(index))
+        redacted_data = redacted[index]
+        object.__send__("#{attribute}_html=", redacted_data[:document].to_html.html_safe)
+        object.user_visible_reference_count = redacted_data[:visible_reference_count]
       end
-
-      objects
     end
 
     # Renders the attribute of every given object.
@@ -50,9 +50,7 @@ module Banzai
     def redact_documents(documents)
       redactor = Redactor.new(project, user)
 
-      redactor.redact(documents).map do |document|
-        document.to_html.html_safe
-      end
+      redactor.redact(documents)
     end
 
     # Returns a Banzai context for the given object and attribute.
diff --git a/lib/banzai/redactor.rb b/lib/banzai/redactor.rb
index ffd267d5e9a..0df3a72d1c4 100644
--- a/lib/banzai/redactor.rb
+++ b/lib/banzai/redactor.rb
@@ -19,29 +19,36 @@ module Banzai
     #
     # Returns the documents passed as the first argument.
     def redact(documents)
-      nodes = documents.flat_map do |document|
-        Querying.css(document, 'a.gfm[data-reference-type]')
-      end
-
-      redact_nodes(nodes)
+      all_document_nodes = document_nodes(documents)
 
-      documents
+      redact_document_nodes(all_document_nodes)
     end
 
-    # Redacts the given nodes
+    # Redacts the given node documents
     #
-    # nodes - An Array of HTML nodes to redact.
-    def redact_nodes(nodes)
-      visible = nodes_visible_to_user(nodes)
+    # data - An Array of a Hashes mapping an HTML document to nodes to redact.
+    def redact_document_nodes(all_document_nodes)
+      all_nodes = all_document_nodes.map { |x| x[:nodes] }.flatten
+      visible = nodes_visible_to_user(all_nodes)
+      metadata = []
 
-      nodes.each do |node|
-        unless visible.include?(node)
+      all_document_nodes.each do |entry|
+        nodes_for_document = entry[:nodes]
+        doc_data = { document: entry[:document], visible_reference_count: nodes_for_document.count }
+        metadata << doc_data
+
+        nodes_for_document.each do |node|
+          next if visible.include?(node)
+
+          doc_data[:visible_reference_count] -= 1
           # The reference should be replaced by the original text,
           # which is not always the same as the rendered text.
           text = node.attr('data-original') || node.text
           node.replace(text)
         end
       end
+
+      metadata
     end
 
     # Returns the nodes visible to the current user.
@@ -65,5 +72,11 @@ module Banzai
 
       visible
     end
+
+    def document_nodes(documents)
+      documents.map do |document|
+        { document: document, nodes: Querying.css(document, 'a.gfm[data-reference-type]') }
+      end
+    end
   end
 end