Do not process PlantUML diagrams with Kroki if PlantUML is enabled

lib/banzai/filter/kroki_filter.rb

@@ -14,13 +14,12 @@ module Banzai
       end.join(', ')
 
       def call
-        # QUESTION: should we make Kroki and PlantUML mutually exclusive?
-        # Potentially, Kroki and PlantUML could work side by side.
-        # In fact, if both PlantUML and Kroki are enabled, PlantUML could still render PlantUML diagrams and Kroki could render the other diagrams?
-        # Having said that, since Kroki can render PlantUML diagrams, maybe it will be confusing...
-        #
-        # What about Mermaid? should we keep client side rendering for Mermaid?
-        return doc unless settings.kroki_enabled && doc.at(DIAGRAM_SELECTORS)
+        plantuml_enabled = settings.plantuml_enabled
+        diagram_selectors = ::Gitlab::Kroki::DIAGRAM_TYPES.map do |diagram_type|
+          # if PlantUML is enabled, PlantUML diagrams will be processed by the PlantUML filter.
+          %(pre[lang="#{diagram_type}"] > code) if (plantuml_enabled && diagram_type != 'plantuml') || !plantuml_enabled
+        end.compact.join(', ')
+        return doc unless settings.kroki_enabled && doc.at(diagram_selectors)
 
         diagram_format = "svg"
         doc.css(DIAGRAM_SELECTORS).each do |node|

spec/lib/banzai/filter/kroki_filter_spec.rb

@@ -5,17 +5,37 @@ require 'spec_helper'
 RSpec.describe Banzai::Filter::KrokiFilter do
   include FilterSpecHelper
 
-  it 'replaces nomnoml pre tag with img tag' do
+  it 'replaces nomnoml pre tag with img tag if kroki is enabled' do
     stub_application_setting(kroki_enabled: true, kroki_url: "http://localhost:8000")
     doc = filter("<pre lang='nomnoml'><code>[Pirate|eyeCount: Int|raid();pillage()|\n  [beard]--[parrot]\n  [beard]-:>[foul mouth]\n]</code></pre>")
 
     expect(doc.to_s).to eq '<img src="http://localhost:8000/nomnoml/svg/eNqLDsgsSixJrUmtTHXOL80rsVLwzCupKUrMTNHQtC7IzMlJTE_V0KzhUlCITkpNLEqJ1dWNLkgsKsoviUUSs7KLTssvzVHIzS8tyYjligUAMhEd0g==">'
   end
 
-  it 'does not replace nomnoml pre tag with img tag if disabled' do
+  it 'replaces nomnoml pre tag with img tag if both kroki and plantuml are enabled' do
+    stub_application_setting(kroki_enabled: true,
+                             kroki_url: "http://localhost:8000",
+                             plantuml_enabled: true,
+                             plantuml_url: "http://localhost:8080")
+    doc = filter("<pre lang='nomnoml'><code>[Pirate|eyeCount: Int|raid();pillage()|\n  [beard]--[parrot]\n  [beard]-:>[foul mouth]\n]</code></pre>")
+
+    expect(doc.to_s).to eq '<img src="http://localhost:8000/nomnoml/svg/eNqLDsgsSixJrUmtTHXOL80rsVLwzCupKUrMTNHQtC7IzMlJTE_V0KzhUlCITkpNLEqJ1dWNLkgsKsoviUUSs7KLTssvzVHIzS8tyYjligUAMhEd0g==">'
+  end
+
+  it 'does not replace nomnoml pre tag with img tag if kroki is disabled' do
     stub_application_setting(kroki_enabled: false)
     doc = filter("<pre lang='nomnoml'><code>[Pirate|eyeCount: Int|raid();pillage()|\n  [beard]--[parrot]\n  [beard]-:>[foul mouth]\n]</code></pre>")
 
     expect(doc.to_s).to eq "<pre lang=\"nomnoml\"><code>[Pirate|eyeCount: Int|raid();pillage()|\n  [beard]--[parrot]\n  [beard]-:&gt;[foul mouth]\n]</code></pre>"
   end
+
+  it 'does not replace plantuml pre tag with img tag if both kroki and plantuml are enabled' do
+    stub_application_setting(kroki_enabled: true,
+                             kroki_url: "http://localhost:8000",
+                             plantuml_enabled: true,
+                             plantuml_url: "http://localhost:8080")
+    doc = filter("<pre lang='plantuml'><code>Bob->Alice : hello</code></pre>")
+
+    expect(doc.to_s).to eq '<pre lang="plantuml"><code>Bob-&gt;Alice : hello</code></pre>'
+  end
 end