Validate Javadoc as part of the checks.

build.gradle

@@ -20,7 +20,6 @@ editorconfig {
 check.dependsOn(editorconfigCheck)
 
 subprojects {
-
   ext {
     versions = [
       'ace':            '1.3.3',
@@ -48,6 +47,8 @@ subprojects {
 
   apply from: "${rootDir}/gradle/source-layout.gradle"
 
+  check.dependsOn(javadoc)
+
   sourceCompatibility = '1.8'
   targetCompatibility = '1.8'
 
@@ -76,6 +77,17 @@ subprojects {
     options.compilerArgs << '-Werror'
   }
 
+  javadoc {
+    // Can't exclude generated files based on source path
+    // (cf. https://stackoverflow.com/a/47711311).
+    //exclude '**/xtext-gen'
+    source = source.filter(f -> !f.getPath().contains('xtext-gen'))
+
+    options {
+      addBooleanOption 'Xwerror', true
+    }
+  }
+
   publishing {
     publications {
       mavenArtifacts(MavenPublication) {

config/checkstyle/checkstyle.xml

@@ -69,6 +69,7 @@
         <module name="InterfaceIsType"/>
         <module name="InterfaceTypeParameterName"/>
         <module name="JavaNCSS"/>
+        <module name="JavadocMethod"/>
         <module name="JavadocType"/>
         <module name="LambdaParameterName"/>
         <module name="LeftCurly"/>
@@ -92,14 +93,15 @@
         </module>
         <module name="MultipleVariableDeclarations"/>
         <module name="MutableException"/>
-        <module name="NeedBraces"/>
         <module name="NPathComplexity"/>
+        <module name="NeedBraces"/>
         <module name="NoArrayTrailingComma"/>
         <module name="NoClone"/>
         <module name="NoEnumTrailingComma"/>
         <module name="NoFinalizer"/>
         <module name="NoWhitespaceAfter"/>
         <module name="NoWhitespaceBefore"/>
+        <module name="NonEmptyAtclauseDescription"/>
         <module name="OneStatementPerLine">
             <property name="treatTryResourcesAsStatement" value="true"/>
         </module>
@@ -151,8 +153,8 @@
         <module name="ThrowsCount">
             <property name="max" value="2"/>
         </module>
-        <module name="TypecastParenPad"/>
         <module name="TypeName"/>
+        <module name="TypecastParenPad"/>
         <module name="UnnecessaryParentheses"/>
         <module name="UnnecessarySemicolonAfterTypeMemberDeclaration"/>
         <module name="UnnecessarySemicolonInEnumeration"/>