LUCENE-9564: add spotless and gjf (automatic code formatter)

build.gradle

@@ -26,6 +26,7 @@ plugins {
   id "de.undercouch.download" version "4.0.2" apply false
   id "net.ltgt.errorprone" version "1.2.1" apply false
   id "com.palantir.docker" version "0.25.0" apply false
+  id 'com.diffplug.spotless' version "5.8.2" apply false
 }
 
 apply from: file('gradle/defaults.gradle')
@@ -145,6 +146,7 @@ apply from: file('gradle/validation/ecj-lint.gradle')
 apply from: file('gradle/validation/gradlew-scripts-tweaked.gradle')
 apply from: file('gradle/validation/validate-log-calls.gradle')
 apply from: file('gradle/validation/check-broken-links.gradle')
+apply from: file('gradle/validation/spotless.gradle')
 
 // Source or data regeneration tasks
 apply from: file('gradle/generation/jflex.gradle')

gradle/help.gradle

@@ -22,6 +22,7 @@ configure(rootProject) {
       ["Workflow", "help/workflow.txt", "Typical workflow commands."],
       ["Ant", "help/ant.txt", "Ant-gradle migration help."],
       ["Tests", "help/tests.txt", "Tests, filtering, beasting, etc."],
+      ["Formatting", "help/formatting.txt", "Code formatting conventions."],
       ["Jvms", "help/jvms.txt", "Using alternative or EA JVM toolchains."],
       ["Deps", "help/dependencies.txt", "Declaring, inspecting and excluding dependencies."],
       ["ForbiddenApis", "help/forbiddenApis.txt", "How to add/apply rules for forbidden APIs."],

gradle/validation/spotless.gradle

@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * LUCENE-9564: This adds automatic (and enforced) code formatting.
+ */
+
+def resources = scriptResources(buildscript)
+
+allprojects { prj ->
+  plugins.withType(JavaPlugin) {
+    prj.apply plugin: 'com.diffplug.spotless'
+
+    spotless {
+      java {
+        licenseHeaderFile file("${resources}/asl-header.txt"), '^(\\s*package)'
+        lineEndings 'UNIX'
+        endWithNewline()
+        googleJavaFormat('1.9')
+
+        switch (project.path) {
+          // Disable for everything else for now.
+          default:
+            target 'non-existing/**'
+            break
+        }
+      }
+    }
+  }
+}
+
+// Add an alias to 'spotlessApply' simply called 'tidy' and add
+// spotlessCheck to check.
+allprojects { prj ->
+  task tidy() {
+    description "Applies formatters and cleanups to sources."
+    group "verification"
+  }
+
+  tasks.matching { task -> task.name == "spotlessApply" }.configureEach { v ->
+    tidy.dependsOn v
+  }
+
+  tasks.matching { task -> task.name == "spotlessCheck" }.configureEach { v ->
+    check.dependsOn v
+  }
+}

gradle/validation/spotless/asl-header.txt

@@ -0,0 +1,16 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */

help/formatting.txt

@@ -0,0 +1,20 @@
+Code formatting
+===============
+
+Starting with (LUCENE-9564) Java code is enforced to comply with
+google-java-format conventions. In theory you shouldn't worry about
+what the convention actually looks like - write the code in any way
+you like and then run:
+
+./gradlew tidy
+
+prior to running your regular precommit checks. This will reformat
+your code so that it complies with the convention and passes gradle
+'check' task.
+
+IMPORTANT: There is *no* way to mark sections of the code as excluded
+from formatting. This is by design and cannot be altered. In vast
+majority of cases the formatter will do a great job of cleaning up the
+code. Occasionally you may want to rewrite the code (introduce a local
+variable orreshape code paths) so that it's easier to read after
+automatic formatting.