Log deprecation warning when using built-in JettyLauncher

This patch has two approaches to check if the JettyLauncher is being
used, it checks for any configured filters/servlets (other than the
defaults provided by Jetty) in order to log a warning on startup, and
it checks for non-404 responses to catch other resources loaded after
startup.

No warning is logged for tests.

Fixes #9863

dev/core/src/com/google/gwt/dev/shell/jetty/JettyLauncher.java

@@ -63,11 +63,41 @@
 import java.util.Enumeration;
 import java.util.Iterator;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.stream.Stream;
 
 /**
  * A {@link ServletContainerLauncher} for an embedded Jetty server.
  */
 public class JettyLauncher extends ServletContainerLauncher {
+  private static final AtomicBoolean hasLoggedDeprecationWarning = new AtomicBoolean(false);
+
+  /**
+   * Disable warning about JettyLauncher being deprecated when running tests, as this only is
+   * intended to apply to DevMode - The test runner can be updated at the same time as any other
+   * changes are made to JettyLauncher.
+   */
+  public static void suppressDeprecationWarningForTests() {
+    hasLoggedDeprecationWarning.set(true);
+  }
+
+  /**
+   * Warns, only once, that JettyLauncher is deprecated for removal. Call when it is clear that
+   * the developer is actively deploying code to, or loading resources from, the embedded Jetty
+   * instance.
+   *
+   * @param log existing TreeLogger to append warning to
+   */
+  private static void maybeLogDeprecationWarning(TreeLogger log) {
+    if (hasLoggedDeprecationWarning.compareAndSet(false, true)) {
+      log.log(TreeLogger.Type.WARN, "DevMode will default to -noserver in a future release, and " +
+              "JettyLauncher may be removed or changed. Please consider running your own " +
+              "application server and either passing -noserver to DevMode or migrating to " +
+              "CodeServer. Alternatively, consider implementing your own " +
+              "ServletContainerLauncher to continue running your application server from " +
+              "DevMode.");
+    }
+  }
 
   /**
    * Log jetty requests/responses to TreeLogger.
@@ -93,6 +123,10 @@ public void log(Request request, Response response) {
         // Copied from NCSARequestLog
         status = 404;
       }
+      if (status != 404) {
+        // Ignore 404 errors, log the first other call to the server if we haven't logged yet
+        maybeLogDeprecationWarning(logger);
+      }
       TreeLogger.Type logStatus, logHeaders;
       if (status >= 500) {
         logStatus = TreeLogger.ERROR;
@@ -566,6 +600,15 @@ private WebAppContextWithReload(TreeLogger logger, String webApp,
     protected void doStart() throws Exception {
       setClassLoader(new WebAppClassLoaderExtension());
       super.doStart();
+
+      // After start, warn if a servlet/filter was configured other than those provided by Jetty
+      boolean hasNonJettyFiltersOrServlets = Stream.concat(
+              getServletContext().getServletRegistrations().values().stream(),
+              getServletContext().getFilterRegistrations().values().stream()
+      ).anyMatch(r -> !r.getClassName().startsWith("org.eclipse.jetty"));
+      if (hasNonJettyFiltersOrServlets) {
+        maybeLogDeprecationWarning(logger);
+      }
     }
 
     @Override

user/src/com/google/gwt/junit/JUnitShell.java

@@ -249,6 +249,7 @@ public String[] getDefaultArgs() {
        * ----- Options from DevMode -------
        */
       // Hard code the server.
+      JettyLauncher.suppressDeprecationWarningForTests();
       options.setServletContainerLauncher(shell.new MyJettyLauncher());
       // DISABLE: ArgHandlerStartupURLs
       registerHandler(new ArgHandlerWarDir(options) {