Basic implementation of prevalidateConfig working.

core/src/main/java/hudson/PluginManager.java

@@ -98,6 +98,12 @@ import java.util.logging.Level;
 import java.util.logging.Logger;
 
 import static hudson.init.InitMilestone.*;
+import hudson.util.VersionNumber;
+import java.util.TreeMap;
+import javax.xml.parsers.SAXParserFactory;
+import org.xml.sax.Attributes;
+import org.xml.sax.SAXException;
+import org.xml.sax.helpers.DefaultHandler;
 
 /**
  * Manages {@link PluginWrapper}s.
@@ -740,7 +746,7 @@ public abstract class PluginManager extends AbstractModelObject implements OnMas
      * If the configuration (typically a job’s {@code config.xml})
      * needs some plugins to be installed (or updated), those jobs
      * will be triggered.
-     * Plugins are dynamically loaded if possible (see {@link hudson.model.UpdateSite.Plugin#deploy(boolean)}).
+     * Plugins are dynamically loaded whenever possible.
      * Requires {@link Jenkins#ADMINISTER}.
      * @param configXml configuration that might be uploaded
      * @return an empty list if all is well, else a list of submitted jobs which must be completed before this configuration can be fully read
@@ -748,11 +754,83 @@ public abstract class PluginManager extends AbstractModelObject implements OnMas
      * @see ItemGroupMixIn#createProjectFromXML
      * @see AbstractItem#updateByXml(javax.xml.transform.Source)
      * @see XStream2
+     * @see hudson.model.UpdateSite.Plugin#deploy(boolean)
+     * @see PluginWrapper#supportsDynamicLoad
+     * @see hudson.model.UpdateCenter.DownloadJob.SuccessButRequiresRestart
      * @since XXX
      */
     public List<Future<UpdateCenter.UpdateCenterJob>> prevalidateConfig(InputStream configXml) throws IOException {
         Jenkins.getInstance().checkPermission(Jenkins.ADMINISTER);
-        return Collections.emptyList(); // XXX
+        List<Future<UpdateCenter.UpdateCenterJob>> jobs = new ArrayList<Future<UpdateCenter.UpdateCenterJob>>();
+        UpdateCenter uc = Jenkins.getInstance().getUpdateCenter();
+        // XXX call uc.updateAllSites() when available? perhaps not, since we should not block on network here
+        for (Map.Entry<String,VersionNumber> requestedPlugin : parseRequestedPlugins(configXml).entrySet()) {
+            PluginWrapper pw = getPlugin(requestedPlugin.getKey());
+            if (pw == null) { // install new
+                UpdateSite.Plugin toInstall = uc.getPlugin(requestedPlugin.getKey());
+                if (toInstall == null) {
+                    LOGGER.log(Level.WARNING, "No such plugin {0} to install", requestedPlugin.getKey());
+                    continue;
+                }
+                if (new VersionNumber(toInstall.version).compareTo(requestedPlugin.getValue()) < 0) {
+                    LOGGER.log(Level.WARNING, "{0} can only be satisfied in @{1}", new Object[] {requestedPlugin, toInstall.version});
+                }
+                if (toInstall.isForNewerHudson()) {
+                    LOGGER.log(Level.WARNING, "{0}@{1} was built for a newer Jenkins", new Object[] {toInstall.name, toInstall.version});
+                }
+                jobs.add(toInstall.deploy(true));
+            } else if (pw.isOlderThan(requestedPlugin.getValue())) { // upgrade
+                UpdateSite.Plugin toInstall = uc.getPlugin(requestedPlugin.getKey());
+                if (toInstall == null) {
+                    LOGGER.log(Level.WARNING, "No such plugin {0} to upgrade", requestedPlugin.getKey());
+                    continue;
+                }
+                if (!pw.isOlderThan(new VersionNumber(toInstall.version))) {
+                    LOGGER.log(Level.WARNING, "{0}@{1} is no newer than what we already have", new Object[] {toInstall.name, toInstall.version});
+                    continue;
+                }
+                if (new VersionNumber(toInstall.version).compareTo(requestedPlugin.getValue()) < 0) {
+                    LOGGER.log(Level.WARNING, "{0} can only be satisfied in @{1}", new Object[] {requestedPlugin, toInstall.version});
+                }
+                if (toInstall.isForNewerHudson()) {
+                    LOGGER.log(Level.WARNING, "{0}@{1} was built for a newer Jenkins", new Object[] {toInstall.name, toInstall.version});
+                }
+                if (!toInstall.isCompatibleWithInstalledVersion()) {
+                    LOGGER.log(Level.WARNING, "{0}@{1} is incompatible with the installed @{2}", new Object[] {toInstall.name, toInstall.version, pw.getVersion()});
+                }
+                jobs.add(toInstall.deploy(true)); // dynamicLoad=true => sure to throw RestartRequiredException, but at least message is nicer
+            } // else already good
+        }
+        return jobs;
+    }
+
+    static Map<String,VersionNumber> parseRequestedPlugins(InputStream configXml) throws IOException {
+        final Map<String,VersionNumber> requestedPlugins = new TreeMap<String,VersionNumber>();
+        try {
+            SAXParserFactory.newInstance().newSAXParser().parse(configXml, new DefaultHandler() {
+                @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
+                    String plugin = attributes.getValue("plugin");
+                    if (plugin == null) {
+                        return;
+                    }
+                    if (!plugin.matches("[^@]+@[^@]+")) {
+                        throw new SAXException("Malformed plugin attribute: " + plugin);
+                    }
+                    int at = plugin.indexOf('@');
+                    String shortName = plugin.substring(0, at);
+                    VersionNumber existing = requestedPlugins.get(shortName);
+                    VersionNumber requested = new VersionNumber(plugin.substring(at + 1));
+                    if (existing == null || existing.compareTo(requested) < 0) {
+                        requestedPlugins.put(shortName, requested);
+                    }
+                }
+            });
+        } catch (IOException x) {
+            throw x;
+        } catch (Exception x) {
+            throw (IOException) new IOException(x.toString()).initCause(x);
+        }
+        return requestedPlugins;
     }
 
     /**