Add initial support for rendering javadocs.

build.gradle

@@ -1,3 +1,5 @@
+import java.time.ZonedDateTime
+import java.time.format.DateTimeFormatter
 
 plugins {
   id "base"
@@ -10,6 +12,13 @@ allprojects {
   version = "9.0.0-SNAPSHOT"
 }
 
+ext {
+  def tstamp = ZonedDateTime.now()
+  buildDate = DateTimeFormatter.ofPattern("yyyy-MM-dd").format(tstamp)
+  buildTime = DateTimeFormatter.ofPattern("HH:mm:ss").format(tstamp)
+  buildYear = DateTimeFormatter.ofPattern("yyyy").format(tstamp)
+}
+
 // Include smaller chunks configuring dedicated build areas.
 // Some of these intersect or add additional functionality.
 // The order of inclusion of these files shouldn't matter (but may
@@ -22,6 +31,7 @@ apply from: file('gradle/generate-defaults.gradle')
 // (java, tests)
 apply from: file('gradle/defaults.gradle')
 apply from: file('gradle/defaults-java.gradle')
+apply from: file('gradle/defaults-javadoc.gradle')
 apply from: file('gradle/testing/defaults-tests.gradle')
 apply from: file('gradle/testing/randomization.gradle')
 apply from: file('gradle/testing/fail-on-no-tests.gradle')

gradle/defaults-javadoc.gradle

@@ -0,0 +1,38 @@
+// Configure javadoc defaults.
+
+allprojects {
+  plugins.withType(JavaPlugin) {
+    tasks.matching { it.name == "javadoc" }.all {
+      StandardJavadocDocletOptions opts = (options as StandardJavadocDocletOptions)
+      opts.locale("en_US")
+      opts.charSet = "UTF-8"
+      opts.encoding = "UTF-8"
+      opts.docEncoding = "UTF-8"
+
+      opts.noIndex()
+      opts.memberLevel = JavadocMemberLevel.PROTECTED
+      opts.version = true
+      opts.author = true
+      opts.use = true
+
+      opts.linksOffline(
+          "https://docs.oracle.com/en/java/javase/11/docs/api/",
+          project(":lucene").file("tools/javadoc/java11/").toString())
+
+      opts.tags(
+          "lucene.experimental:a:WARNING: This API is experimental and might change in incompatible ways in the next release.",
+          "lucene.internal:a:NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.",
+          "lucene.spi:t:SPI Name (Note: This is case-insensitive. e.g., if the name is 'htmlStrip', 'htmlstrip' can be used when looking up the service).",
+      )
+
+      opts.addStringOption("-release", "11")
+      opts.addBooleanOption('Xdoclint:all,-accessibility,-missing,-html,-syntax', true)
+
+      def libName = project.path.startsWith(":lucene") ? "Lucene" : "Solr"
+      opts.overview = file("src/main/java/overview.html").toString()
+      opts.docTitle = "${libName} ${project.version} ${project.name} API"
+      opts.windowTitle = "${libName} ${project.version} ${project.name} API"
+      opts.bottom = "<i>Copyright &copy; 2000-${buildYear} Apache Software Foundation. All Rights Reserved.</i>"
+    }
+  }
+}

solr/solr-ref-guide/build.gradle

@@ -119,11 +119,6 @@ ext {
 
     bareBonesDir = file("${buildDir}/bare-bones-html")
 
-    def tstamp = ZonedDateTime.now()
-    buildDate = DateTimeFormatter.ofPattern("yyyy-MM-dd").format(tstamp)
-    buildTime = DateTimeFormatter.ofPattern("HH:mm:ss").format(tstamp)
-    buildYear = DateTimeFormatter.ofPattern("yyyy").format(tstamp)
-
     // Some additional version properties are lazily computed
     // in setupLazyProps (because they need to be computed after evaluation is complete).
     props = [