Mimimal checkstyle configuration

This adds a small pile of checkstyle checks that all pass without any changes.
It moves some checks from ForbiddenPatterns that were java only into
checkstyle.

Don't duplicate forbiddenPatterns in checkstyle

buildSrc/src/main/groovy/org/elasticsearch/gradle/precommit/ForbiddenPatternsTask.groovy

@@ -61,10 +61,6 @@ public class ForbiddenPatternsTask extends DefaultTask {
         // add mandatory rules
         patterns.put('nocommit', /nocommit/)
         patterns.put('tab', /\t/)
-        patterns.put('wildcard imports', /^\s*import.*\.\*/)
-        // We don't use Java serialization so we fail if it looks like we're trying to.
-        patterns.put('declares serialVersionUID', /serialVersionUID/)
-        patterns.put('references Serializable', /java\.io\.Serializable/)
 
         inputs.property("excludes", filesFilter.excludes)
         inputs.property("rules", patterns)

buildSrc/src/main/groovy/org/elasticsearch/gradle/precommit/PrecommitTasks.groovy

@@ -30,9 +30,9 @@ class PrecommitTasks {
 
     /** Adds a precommit task, which depends on non-test verification tasks. */
     public static Task create(Project project, boolean includeDependencyLicenses) {
-
         List<Task> precommitTasks = [
             configureForbiddenApis(project),
+            configureCheckstyle(project),
             project.tasks.create('forbiddenPatterns', ForbiddenPatternsTask.class),
             project.tasks.create('licenseHeaders', LicenseHeadersTask.class),
             project.tasks.create('jarHell', JarHellTask.class),
@@ -83,4 +83,25 @@ class PrecommitTasks {
         forbiddenApis.group = "" // clear group, so this does not show up under verification tasks
         return forbiddenApis
     }
+
+    private static Task configureCheckstyle(Project project) {
+        Task checkstyleTask = project.tasks.create('checkstyle')
+        // Apply the checkstyle plugin to create `checkstyleMain` and `checkstyleTest`. It only
+        // creates them if there is main or test code to check and it makes `check` depend
+        // on them. But we want `precommit` to depend on `checkstyle` which depends on them so
+        // we have to swap them.
+        project.pluginManager.apply('checkstyle')
+        project.checkstyle {
+            config = project.resources.text.fromFile(
+                PrecommitTasks.getResource('/checkstyle.xml'), 'UTF-8')
+        }
+        for (String taskName : ['checkstyleMain', 'checkstyleTest']) {
+            Task task = project.tasks.findByName(taskName)
+            if (task != null) {
+                project.tasks['check'].dependsOn.remove(task)
+                checkstyleTask.dependsOn(task)
+            }
+        }
+        return checkstyleTask
+    }
 }

buildSrc/src/main/resources/checkstyle.xml

@@ -0,0 +1,50 @@
+<?xml version="1.0"?>
+<!DOCTYPE module PUBLIC
+          "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
+          "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
+
+<module name="Checker">
+  <property name="charset" value="UTF-8" />
+
+  <module name="TreeWalker">
+    <!-- ~3500 violations
+    <module name="LineLength">
+      <property name="max" value="140"/>
+    </module>
+    -->
+
+    <module name="AvoidStarImport" />
+    <!-- Doesn't pass but we could make it pass pretty quick.
+    <module name="UnusedImports">
+      The next property is optional. If we remove it then imports that are
+      only referenced by Javadoc cause the check to fail.
+      <property name="processJavadoc" value="true" />
+    </module>
+    -->
+
+    <!-- Non-inner classes must be in files that match their names. -->
+    <module name="OuterTypeFilename" />
+    <!-- No line wraps inside of import and package statements. -->
+    <module name="NoLineWrap" />
+    <!-- Each java file has only one outer class -->
+    <module name="OneTopLevelClass" />
+
+    <!-- We don't use Java's builtin serialization and we suppress all warning
+      about it. The flip side of that coin is that we shouldn't _try_ to use
+      it. We can't outright ban it with ForbiddenApis because it complain about
+      every we reference a class that implements Serializable like String or
+      Exception.
+      -->
+    <module name="RegexpSinglelineJava">
+      <property name="format" value="serialVersionUID" />
+      <property name="message" value="Do not declare serialVersionUID." />
+      <property name="ignoreComments" value="true" />
+    </module>
+    <module name="RegexpSinglelineJava">
+      <property name="format" value="java\.io\.Serializable" />
+      <property name="message" value="References java.io.Serializable." />
+      <property name="ignoreComments" value="true" />
+    </module>
+    <!-- end Orwellian suppression of Serializable -->
+  </module>
+</module>