Support Markdown rendering using multiple projectsrendering-markdown-multiple-projects

This refactors the Markdown pipeline so it supports the rendering of
multiple documents that may belong to different projects. An example of
where this happens is when displaying the event feed of a group. In this
case we retrieve events for all projects in the group. Previously we
would group events per project and render these chunks separately, but
this would result in many SQL queries being executed. By extending the
Markdown pipeline to support this out of the box we can drastically
reduce the number of SQL queries.

To achieve this we introduce a new object to the pipeline:
Banzai::RenderContext. This object simply wraps two other objects: an
optional Project instance, and an optional User instance. On its own
this wouldn't be very helpful, but a RenderContext can also be used to
associate HTML documents with specific Project instances. This work is
done in Banzai::ObjectRenderer and allows us to reuse as many queries
(and results) as possible.

3 files changed, 44 insertions, 14 deletions

diff --git a/lib/banzai/reference_parser/base_parser.rb b/lib/banzai/reference_parser/base_parser.rb
index 279fca8d043..68752f5bb5a 100644
--- a/lib/banzai/reference_parser/base_parser.rb
+++ b/lib/banzai/reference_parser/base_parser.rb
@@ -45,9 +45,13 @@ module Banzai
         @data_attribute ||= "data-#{reference_type.to_s.dasherize}"
       end
 
-      def initialize(project = nil, current_user = nil)
-        @project = project
-        @current_user = current_user
+      # context - An instance of `Banzai::RenderContext`.
+      def initialize(context)
+        @context = context
+      end
+
+      def project_for_node(node)
+        context.project_for_node(node)
       end
 
       # Returns all the nodes containing references that the user can refer to.
@@ -224,7 +228,11 @@ module Banzai
 
       private
 
-      attr_reader :current_user, :project
+      attr_reader :context
+
+      def current_user
+        context.current_user
+      end
 
       # When a feature is disabled or visible only for
       # team members we should not allow team members
diff --git a/lib/banzai/reference_parser/issue_parser.rb b/lib/banzai/reference_parser/issue_parser.rb
index 230827129b6..6bee5ea15b9 100644
--- a/lib/banzai/reference_parser/issue_parser.rb
+++ b/lib/banzai/reference_parser/issue_parser.rb
@@ -5,15 +5,10 @@ module Banzai
 
       def nodes_visible_to_user(user, nodes)
         issues = records_for_nodes(nodes)
-        issues_to_check = issues.values
+        issues_to_check, cross_project_issues = partition_issues(issues, user)
 
-        unless can?(user, :read_cross_project)
-          issues_to_check, cross_project_issues = issues_to_check.partition do |issue|
-            issue.project == project
-          end
-        end
-
-        readable_issues = Ability.issues_readable_by_user(issues_to_check, user).to_set
+        readable_issues =
+          Ability.issues_readable_by_user(issues_to_check, user).to_set
 
         nodes.select do |node|
           issue_in_node = issues[node]
@@ -25,7 +20,7 @@ module Banzai
           # but not the issue.
           if readable_issues.include?(issue_in_node)
             true
-          elsif cross_project_issues&.include?(issue_in_node)
+          elsif cross_project_issues.include?(issue_in_node)
             can_read_reference?(user, issue_in_node)
           else
             false
@@ -33,6 +28,32 @@ module Banzai
         end
       end
 
+      # issues - A Hash mapping HTML nodes to their corresponding Issue
+      #          instances.
+      # user - The current User.
+      def partition_issues(issues, user)
+        return [issues.values, []] if can?(user, :read_cross_project)
+
+        issues_to_check = []
+        cross_project_issues = []
+
+        # We manually partition the data since our input is a Hash and our
+        # output has to be an Array of issues; not an Array of (node, issue)
+        # pairs.
+        issues.each do |node, issue|
+          target =
+            if issue.project == project_for_node(node)
+              issues_to_check
+            else
+              cross_project_issues
+            end
+
+          target << issue
+        end
+
+        [issues_to_check, cross_project_issues]
+      end
+
       def records_for_nodes(nodes)
         @issues_for_nodes ||= grouped_objects_for_nodes(
           nodes,
diff --git a/lib/banzai/reference_parser/user_parser.rb b/lib/banzai/reference_parser/user_parser.rb
index 8932d4f2905..ceb7f1d165c 100644
--- a/lib/banzai/reference_parser/user_parser.rb
+++ b/lib/banzai/reference_parser/user_parser.rb
@@ -58,7 +58,7 @@ module Banzai
       def can_read_project_reference?(node)
         node_id = node.attr('data-project').to_i
 
-        project && project.id == node_id
+        project_for_node(node)&.id == node_id
       end
 
       def nodes_user_can_reference(current_user, nodes)
@@ -71,6 +71,7 @@ module Banzai
         nodes.select do |node|
           project_id = node.attr(project_attr)
           user_id = node.attr(author_attr)
+          project = project_for_node(node)
 
           if project && project_id && project.id == project_id.to_i
             true