[doc] List all languages in rule doc

Even without rules.

- Relates #4205
- Relates #4105

docs/_data/sidebars/pmd_sidebar.yml

@@ -307,6 +307,15 @@ entries:
         - title: Security
           output: web, pdf
           url: /pmd_rules_vf_security.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Scala Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_scala.html
     - title: null
       output: web, pdf
       subfolders:
@@ -325,6 +334,15 @@ entries:
         - title: Error Prone
           output: web, pdf
           url: /pmd_rules_vm_errorprone.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: WSDL Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_wsdl.html
     - title: null
       output: web, pdf
       subfolders:

pmd-doc/src/main/java/net/sourceforge/pmd/docs/RuleDocGenerator.java

@@ -38,6 +38,7 @@ import net.sourceforge.pmd.RuleSet;
 import net.sourceforge.pmd.RuleSetLoadException;
 import net.sourceforge.pmd.RuleSetLoader;
 import net.sourceforge.pmd.lang.Language;
+import net.sourceforge.pmd.lang.LanguageRegistry;
 import net.sourceforge.pmd.lang.rule.RuleReference;
 import net.sourceforge.pmd.lang.rule.XPathRule;
 import net.sourceforge.pmd.properties.MultiValuePropertyDescriptor;
@@ -99,9 +100,16 @@ public class RuleDocGenerator {
         generateLanguageIndex(sortedRulesets, sortedAdditionalRulesets);
         generateRuleSetIndex(sortedRulesets);
 
+        ensureAllLanguages(sortedRulesets);
         generateSidebar(sortedRulesets);
     }
 
+    private void ensureAllLanguages(Map<Language, List<RuleSet>> sortedRulesets) {
+        for (Language language : LanguageRegistry.findWithRuleSupport()) {
+            sortedRulesets.putIfAbsent(language, Collections.emptyList());
+        }
+    }
+
     private void generateSidebar(Map<Language, List<RuleSet>> sortedRulesets) throws IOException {
         SidebarGenerator generator = new SidebarGenerator(writer, root);
         generator.generateSidebar(sortedRulesets);

pmd-doc/src/test/java/net/sourceforge/pmd/docs/SidebarGeneratorTest.java

@@ -11,9 +11,9 @@ import java.nio.charset.StandardCharsets;
 import java.nio.file.FileSystems;
 import java.util.Arrays;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.TreeMap;
 
 import org.apache.commons.lang3.SystemUtils;
 import org.junit.Before;
@@ -39,11 +39,12 @@ public class SidebarGeneratorTest {
 
     @Test
     public void testSidebar() throws IOException {
-        Map<Language, List<RuleSet>> rulesets = new HashMap<>();
+        Map<Language, List<RuleSet>> rulesets = new TreeMap<>();
         RuleSet ruleSet1 = RulesetsFactoryUtils.defaultFactory().createNewRuleSet("test", "test", "bestpractices.xml", Collections.emptyList(), Collections.emptyList(), Collections.emptyList());
         RuleSet ruleSet2 = RulesetsFactoryUtils.defaultFactory().createNewRuleSet("test2", "test", "codestyle.xml", Collections.emptyList(), Collections.emptyList(), Collections.emptyList());
         rulesets.put(LanguageRegistry.findLanguageByTerseName("java"), Arrays.asList(ruleSet1, ruleSet2));
         rulesets.put(LanguageRegistry.findLanguageByTerseName("ecmascript"), Arrays.asList(ruleSet1));
+        rulesets.put(LanguageRegistry.findLanguageByTerseName("scala"), Collections.emptyList());
 
         SidebarGenerator generator = new SidebarGenerator(writer, FileSystems.getDefault().getPath(".."));
         List<Map<String, Object>> result = generator.generateRuleReferenceSection(rulesets);

pmd-doc/src/test/resources/expected/pmd_sidebar.yml

@@ -6,6 +6,33 @@ entries:
   - title: 3
   - title: Rules
     folderitems:
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Apex Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_apex.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Ecmascript Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_ecmascript.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: HTML Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_html.html
     - title: null
       output: web, pdf
       subfolders:
@@ -18,3 +45,93 @@ entries:
         - title: Sample
           output: web, pdf
           url: /pmd_rules_java_sample.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Java Server Pages Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_jsp.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Maven POM Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_pom.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Modelica Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_modelica.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: PLSQL Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_plsql.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Salesforce VisualForce Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_vf.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: Scala Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_scala.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: VM Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_vm.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: WSDL Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_wsdl.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: XML Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_xml.html
+    - title: null
+      output: web, pdf
+      subfolders:
+      - title: XSL Rules
+        output: web, pdf
+        subfolderitems:
+        - title: Index
+          output: web, pdf
+          url: /pmd_rules_xsl.html

pmd-doc/src/test/resources/net/sourceforge/pmd/docs/sidebar.yml

@@ -1,3 +1,15 @@
+- title: null
+  output: web, pdf
+  subfolders:
+  - title: Ecmascript Rules
+    output: web, pdf
+    subfolderitems:
+    - title: Index
+      output: web, pdf
+      url: /pmd_rules_ecmascript.html
+    - title: test
+      output: web, pdf
+      url: /pmd_rules_ecmascript_bestpractices.html
 - title: null
   output: web, pdf
   subfolders:
@@ -16,12 +28,9 @@
 - title: null
   output: web, pdf
   subfolders:
-  - title: Ecmascript Rules
+  - title: Scala Rules
     output: web, pdf
     subfolderitems:
     - title: Index
       output: web, pdf
-      url: /pmd_rules_ecmascript.html
-    - title: test
-      output: web, pdf
-      url: /pmd_rules_ecmascript_bestpractices.html
+      url: /pmd_rules_scala.html