[JENKINS-23365] Follow-up API fixes: introduce SCM.getKey(), and add an...

[JENKINS-23365] Follow-up API fixes: introduce SCM.getKey(), and add an SCMRevisionState baseline argument to checkout.
Necessary in order to produce correct changelogs by SCM plugins which actually use SCMRevisionState correctly (unlike git-plugin!).
(cherry picked from commit df9dc4c8)

core/src/main/java/hudson/model/AbstractBuild.java

@@ -43,6 +43,7 @@ import hudson.scm.ChangeLogSet;
 import hudson.scm.ChangeLogSet.Entry;
 import hudson.scm.NullChangeLogParser;
 import hudson.scm.SCM;
+import hudson.scm.SCMRevisionState;
 import hudson.slaves.NodeProperty;
 import hudson.slaves.WorkspaceList;
 import hudson.slaves.WorkspaceList.Lease;
@@ -625,7 +626,7 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
                         SCM scm = project.getScm();
                         for (SCMListener l : SCMListener.all()) {
                             try {
-                                l.onCheckout(build, scm, build.getWorkspace(), listener, changeLogFile, project.pollingBaseline);
+                                l.onCheckout(build, scm, build.getWorkspace(), listener, changeLogFile, build.getAction(SCMRevisionState.class));
                             } catch (Exception e) {
                                 throw new IOException(e);
                             }

core/src/main/java/hudson/model/AbstractProject.java

@@ -159,7 +159,7 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
     /**
      * State returned from {@link SCM#poll(AbstractProject, Launcher, FilePath, TaskListener, SCMRevisionState)}.
      */
-    volatile transient SCMRevisionState pollingBaseline = null;
+    private volatile transient SCMRevisionState pollingBaseline = null;
 
     private transient LazyBuildMixIn<P,R> buildMixIn;
 

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

@@ -48,9 +48,9 @@ public class NullSCM extends SCM {
         return PollingResult.NO_CHANGES;
     }
 
-    @Override public void checkout(Run<?,?> build, Launcher launcher, FilePath remoteDir, TaskListener listener, File changeLogFile) throws IOException, InterruptedException {
-        if (changeLogFile != null) {
-            createEmptyChangeLog(changeLogFile, listener, "log");
+    @Override public void checkout(Run<?,?> build, Launcher launcher, FilePath workspace, TaskListener listener, File changelogFile, SCMRevisionState baseline) throws IOException, InterruptedException {
+        if (changelogFile != null) {
+            createEmptyChangeLog(changelogFile, listener, "log");
         }
     }
 

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

@@ -419,6 +419,20 @@ public abstract class SCM implements Describable<SCM>, ExtensionPoint {
         return false;
     }
 
+    /**
+     * Should create a key by which this SCM configuration might be distinguished from others in the same project.
+     * Should be invariable across builds but otherwise as distinctive as possible.
+     * <p>Could include information such as the relative paths used in {@link #getModuleRoots(FilePath, AbstractBuild)},
+     * and/or configured repository URLs and branch names, and/or labels set for this purpose by the user.
+     * <p>The result may be used for various purposes, but it may be long and/or include URL-unsafe characters,
+     * so to use in a URL path component you may need to first wrap it in {@link Util#getDigestOf(String)} or otherwise encode it.
+     * @return by default, just {@link #getType}
+     * @since 1.568
+     */
+    public @Nonnull String getKey() {
+        return getType();
+    }
+
     /**
      * Obtains a fresh workspace of the module(s) into the specified directory
      * of the specified machine.
@@ -440,14 +454,14 @@ public abstract class SCM implements Describable<SCM>, ExtensionPoint {
      *      When there's no change, this file should contain an empty entry.
      *      See {@link #createEmptyChangeLog(File, TaskListener, String)}.
      *      May be null, in which case no changelog was requested.
-     *
+     * @param  baseline version from the previous build to use for changelog creation, if requested and available
      * @throws InterruptedException
      *      interruption is usually caused by the user aborting the build.
      *      this exception will cause the build to be aborted.
      * @throws AbortException in case of a routine failure
      * @since 1.568
      */
-    public void checkout(@Nonnull Run<?,?> build, @Nonnull Launcher launcher, @Nonnull FilePath workspace, @Nonnull TaskListener listener, @CheckForNull File changelogFile) throws IOException, InterruptedException {
+    public void checkout(@Nonnull Run<?,?> build, @Nonnull Launcher launcher, @Nonnull FilePath workspace, @Nonnull TaskListener listener, @CheckForNull File changelogFile, @CheckForNull SCMRevisionState baseline) throws IOException, InterruptedException {
         if (build instanceof AbstractBuild && listener instanceof BuildListener && Util.isOverridden(SCM.class, getClass(), "checkout", AbstractBuild.class, Launcher.class, FilePath.class, BuildListener.class, File.class)) {
             if (changelogFile == null) {
                 changelogFile = File.createTempFile("changelog", ".xml");
@@ -470,7 +484,8 @@ public abstract class SCM implements Describable<SCM>, ExtensionPoint {
 
     @Deprecated
     public boolean checkout(AbstractBuild<?,?> build, Launcher launcher, FilePath workspace, BuildListener listener, @Nonnull File changelogFile) throws IOException, InterruptedException {
-        checkout((Run) build, launcher, workspace, listener, changelogFile);
+        AbstractBuild<?,?> prev = build.getPreviousBuild();
+        checkout((Run) build, launcher, workspace, listener, changelogFile, prev != null ? prev.getAction(SCMRevisionState.class) : null);
         return true;
     }