[JENKINS-35098] Disable AutoBrowserHolder by default to improve the changelog rendering performance (jenkinsci#2371)

* [FIXED JENKINS-35098] Deleting AutoBrowserHolder.

* Normalizing form binding scheme for AbstractProject.scm.

* At @oleg-nenashev’s insistence, restoring AutoBrowserHolder, though not using it by default.

* Using SystemProperties at @oleg-nenashev’s recommendation.

Author: jglick

core/src/main/java/hudson/scm/AutoBrowserHolder.java

@@ -37,7 +37,9 @@
  *
  * <p>
  * This class makes such tracking easy by hiding this logic.
+ * @deprecated Disabled by default: JENKINS-35098
  */
+@Deprecated
 final class AutoBrowserHolder {
     private int cacheGeneration;
     private RepositoryBrowser cache;

core/src/main/java/hudson/scm/NullSCM.java

@@ -31,16 +31,19 @@
 import hudson.model.TaskListener;
 import java.io.File;
 import java.io.IOException;
-import net.sf.json.JSONObject;
 import org.jenkinsci.Symbol;
-import org.kohsuke.stapler.StaplerRequest;
+import org.kohsuke.stapler.DataBoundConstructor;
 
 /**
  * No {@link SCM}.
  *
  * @author Kohsuke Kawaguchi
  */
 public class NullSCM extends SCM {
+
+    @DataBoundConstructor
+    public NullSCM() {}
+
     @Override public SCMRevisionState calcRevisionsFromBuild(Run<?, ?> build, FilePath workspace, Launcher launcher, TaskListener listener) throws IOException, InterruptedException {
         return null;
     }
@@ -69,9 +72,5 @@ public DescriptorImpl() {
             return Messages.NullSCM_DisplayName();
         }
 
-        @Override
-        public SCM newInstance(StaplerRequest req, JSONObject formData) throws FormException {
-            return new NullSCM();
-        }
     }
 }

core/src/main/java/hudson/scm/SCM.java

@@ -58,6 +58,7 @@
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import jenkins.model.Jenkins;
+import jenkins.util.SystemProperties;
 import org.kohsuke.stapler.export.Exported;
 import org.kohsuke.stapler.export.ExportedBean;
 
@@ -84,8 +85,13 @@
  */
 @ExportedBean
 public abstract class SCM implements Describable<SCM>, ExtensionPoint {
+
+    /** JENKINS-35098: discouraged */
+    @SuppressWarnings("FieldMayBeFinal")
+    private static boolean useAutoBrowserHolder = SystemProperties.getBoolean(SCM.class.getName() + ".useAutoBrowserHolder");
     /**
      * Stores {@link AutoBrowserHolder}. Lazily created.
+     * @deprecated Unused by default.
      */
     private transient AutoBrowserHolder autoBrowserHolder;
 
@@ -124,17 +130,21 @@ public String getType() {
      * Returns the applicable {@link RepositoryBrowser} for files
      * controlled by this {@link SCM}.
      * @see #guessBrowser
-     * @see SCMDescriptor#isBrowserReusable
      */
+    @SuppressWarnings("deprecation")
     @Exported(name="browser")
     public final @CheckForNull RepositoryBrowser<?> getEffectiveBrowser() {
         RepositoryBrowser<?> b = getBrowser();
         if(b!=null)
             return b;
-        if(autoBrowserHolder==null)
-            autoBrowserHolder = new AutoBrowserHolder(this);
-        return autoBrowserHolder.get();
-
+        if (useAutoBrowserHolder) {
+            if (autoBrowserHolder == null) {
+                autoBrowserHolder = new AutoBrowserHolder(this);
+            }
+            return autoBrowserHolder.get();
+        } else {
+            return guessBrowser();
+        }
     }
 
     /**

core/src/main/java/hudson/scm/SCMDescriptor.java

@@ -53,7 +53,9 @@ public abstract class SCMDescriptor<T extends SCM> extends Descriptor<SCM> {
      * This is used to invalidate cache of {@link SCM#getEffectiveBrowser}. Due to the lack of synchronization and serialization,
      * this field doesn't really count the # of instances created to date,
      * but it's good enough for the cache invalidation.
+     * @deprecated No longer used by default.
      */
+    @Deprecated
     public volatile int generation = 1;
 
     protected SCMDescriptor(Class<T> clazz, Class<? extends RepositoryBrowser> repositoryBrowser) {
@@ -102,7 +104,9 @@ public void load() {
      * @return
      *      true if the two given SCM configurations are similar enough
      *      that they can reuse {@link RepositoryBrowser} between them.
+     * @deprecated No longer used by default. {@link SCM#getKey} could be used to implement similar features if needed.
      */
+    @Deprecated
     public boolean isBrowserReusable(T x, T y) {
         return false;
     }

core/src/main/java/hudson/scm/SCMS.java

@@ -54,14 +54,11 @@ public class SCMS {
      * @param target
      *      The project for which this SCM is configured to.
      */
+    @SuppressWarnings("deprecation")
     public static SCM parseSCM(StaplerRequest req, AbstractProject target) throws FormException, ServletException {
-        String scm = req.getParameter("scm");
-        if(scm==null)   return new NullSCM();
-
-        int scmidx = Integer.parseInt(scm);
-        SCMDescriptor<?> d = SCM._for(target).get(scmidx);
-        d.generation++;
-        return d.newInstance(req, req.getSubmittedForm().getJSONObject("scm"));
+        SCM scm = req.bindJSON(SCM.class, req.getSubmittedForm().getJSONObject("scm"));
+        scm.getDescriptor().generation++;
+        return scm;
     }
 
     /**

core/src/main/resources/lib/hudson/project/config-scm.jelly

@@ -26,14 +26,14 @@ THE SOFTWARE.
 <?jelly escape-by-default='true'?>
 <j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:d="jelly:define" xmlns:l="/lib/layout" xmlns:t="/lib/hudson" xmlns:f="/lib/form">
   <f:section title="${%Source Code Management}">
-    <j:set var="scms" value="${h.getSCMDescriptors(it)}" />
-    <j:forEach var="idx" begin="0" end="${size(scms)-1}">
-      <j:set var="descriptor" value="${scms[idx]}" />
+    <!-- Could use f:descriptorRadioList were it not for scm/scmd compatibility code; pending JENKINS-20959 would not help with performance -->
+    <j:forEach var="descriptor" items="${h.getSCMDescriptors(instance)}" varStatus="loop">
       <j:set var="scmd" value="${descriptor}" /><!-- backward compatibility with <1.238 -->
-      <f:radioBlock name="scm" value="${idx}" title="${scmd.displayName}" checked="${it.scm.descriptor==scmd}">
-        <j:set var="instance" value="${it.scm.descriptor==descriptor ? it.scm : null}"/>
+      <f:radioBlock name="scm" help="${descriptor.helpFile}" value="${loop.index}" title="${descriptor.displayName}" checked="${instance.scm.descriptor == descriptor}">
+        <j:set var="instance" value="${instance.scm.descriptor == descriptor ? it.scm : null}"/>
         <j:set var="scm" value="${instance}" /><!-- backward compatibility with <1.238 -->
-        <st:include from="${scmd}" page="${scmd.configPage}"/>
+        <f:class-entry descriptor="${descriptor}" />
+        <st:include from="${descriptor}" page="${descriptor.configPage}" optional="true"/>
       </f:radioBlock>
     </j:forEach>
   </f:section>