Merge "Add --other-branches option to the /changes/<id>/revisions/<id>/mergeable"

Documentation/rest-api-changes.txt

@@ -1793,6 +1793,34 @@ As response a link:#mergeable-info[MergeableInfo] entity is returned.
   }
 ----
 
+If the `other-branches` parameter is specified, the mergeability will also be
+checked for all other branches.
+
+.Request
+----
+  GET /changes/myProject~master~I8473b95934b5732ac55d26311a706c9c2bde9940/revisions/current/mergeable?other-branches HTTP/1.0
+----
+
+The response will then contain a list of all other branches where this changes
+could merge cleanly.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json;charset=UTF-8
+
+  )]}'
+  {
+    submit_type: "MERGE_IF_NECESSARY",
+    mergeable: true,
+    mergeable_into: [
+        "refs/heads/stable-2.7",
+        "refs/heads/stable-2.8",
+    ]
+  }
+----
+
 [[get-submit-type]]
 === Get Submit Type
 --
@@ -3115,15 +3143,17 @@ to the value descriptions.
 The `MergeableInfo` entity contains information about the mergeability of a
 change.
 
-[options="header",width="50%",cols="1,6"]
+[options="header",width="50%",cols="1,^1,5"]
 |============================
-|Field Name   |Description
-|`submit_type`|
+|Field Name      ||Description
+|`submit_type`   ||
 Submit type used for this change, can be `MERGE_IF_NECESSARY`,
 `FAST_FORWARD_ONLY`, `REBASE_IF_NECESSARY`, `MERGE_ALWAYS` or
 `CHERRY_PICK`.
-|`mergeable`  |
+|`mergeable`     ||
 `true` if this change is cleanly mergeable, `false` otherwise
+|`mergeable_into`|optional|
+A list of other branch names where this change could merge cleanly
 
 [[restore-input]]
 === RestoreInput

gerrit-server/src/main/java/com/google/gerrit/server/change/Mergeable.java

@@ -46,12 +46,15 @@ import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.revwalk.RevCommit;
 import org.eclipse.jgit.revwalk.RevFlag;
 import org.eclipse.jgit.revwalk.RevWalk;
+import org.kohsuke.args4j.Option;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
@@ -61,8 +64,13 @@ public class Mergeable implements RestReadView<RevisionResource> {
   public static class MergeableInfo {
     public SubmitType submitType;
     public boolean mergeable;
+    public List<String> mergeableInto;
   }
 
+  @Option(name = "--other-branches", aliases = {"-o"},
+      usage = "test mergeability for other branches too")
+  private boolean otherBranches;
+
   private final TestSubmitType.Get submitType;
   private final GitRepositoryManager gitManager;
   private final SubmitStrategyFactory submitStrategyFactory;
@@ -113,6 +121,18 @@ public class Mergeable implements RestReadView<RevisionResource> {
         result.mergeable =
             refresh(change, ps, result.submitType, git, refs, ref);
       }
+
+      if (otherBranches) {
+        result.mergeableInto = new ArrayList<>();
+        for (Ref r : refs.values()) {
+          if (r.getName().startsWith(Constants.R_HEADS)
+              && !r.getName().equals(ref.getName())) {
+            if (isMergeable(change, ps, SubmitType.CHERRY_PICK, git, refs, r)) {
+              result.mergeableInto.add(r.getName());
+            }
+          }
+        }
+      }
     } finally {
       git.close();
     }
@@ -136,6 +156,36 @@ public class Mergeable implements RestReadView<RevisionResource> {
       Repository git,
       Map<String, Ref> refs,
       final Ref ref) throws IOException, OrmException {
+
+    final boolean mergeable = isMergeable(change, ps, type, git, refs, ref);
+
+    Change c = db.get().changes().atomicUpdate(
+        change.getId(),
+        new AtomicUpdate<Change>() {
+          @Override
+          public Change update(Change c) {
+            if (c.getStatus().isOpen()
+                && ps.getId().equals(c.currentPatchSetId())) {
+              c.setMergeable(mergeable);
+              c.setLastSha1MergeTested(toRevId(ref));
+              return c;
+            } else {
+              return null;
+            }
+          }
+        });
+    if (c != null) {
+      indexer.index(db.get(), c);
+    }
+    return mergeable;
+  }
+
+  private boolean isMergeable(Change change,
+      final PatchSet ps,
+      SubmitType type,
+      Repository git,
+      Map<String, Ref> refs,
+      final Ref ref) throws IOException, OrmException {
     RevWalk rw = new RevWalk(git) {
       @Override
       protected CodeReviewCommit createCommit(AnyObjectId id) {
@@ -176,25 +226,6 @@ public class Mergeable implements RestReadView<RevisionResource> {
             accepted,
             change.getDest()).dryRun(tip, rev);
       }
-
-      Change c = db.get().changes().atomicUpdate(
-        change.getId(),
-        new AtomicUpdate<Change>() {
-          @Override
-          public Change update(Change c) {
-            if (c.getStatus().isOpen()
-                && ps.getId().equals(c.currentPatchSetId())) {
-              c.setMergeable(mergeable);
-              c.setLastSha1MergeTested(toRevId(ref));
-              return c;
-            } else {
-              return null;
-            }
-          }
-        });
-      if (c != null) {
-        indexer.index(db.get(), c);
-      }
       return mergeable;
     } catch (MergeException | IOException | NoSuchProjectException e) {
       log.error(String.format(