Don't consider accepting on behalf of valid-but-accepted reviewers to be a validation error

Summary:
Fixes T12757. Here's a simple repro for this:

  - Add a package you own as a reviewer to a revision you're reviewing.
  - Open two windows, select "Accept", don't submit the form.
  - Submit the form in window A.
  - Submit the fomr in window B.

Previously, window B would show an error, because we considered accepting on behalf of the package invalid, as the package had already accepted.

Instead, let repeat-accepts through without complaint.

Some product stuff:

  - We could roadblock users with a more narrow validation error message here instead, like "Package X has already been accepted.", but I think this would be more annoying than helpful.
  - If your accept has no effect (i.e., everything you're accepting for has already accepted) we currently just let it through. I think this is fine -- and a bit tricky to tailor -- but the ideal/consistent beavior is to do a "no effect" warning like "All the reviewers you're accepting for have already accepted.". This is sufficiently finnicky/rare (and probably not terribly useful/desiable in this specific case)that I'm just punting.

Test Plan: Did the flow above, got an "Accept" instead of a validation error.

Reviewers: chad, lvital

Reviewed By: chad, lvital

Subscribers: lvital

Maniphest Tasks: T12757

Differential Revision: https://secure.phabricator.com/D18019

src/applications/differential/xaction/DifferentialRevisionAcceptTransaction.php

@@ -50,7 +50,8 @@ final class DifferentialRevisionAcceptTransaction
 
   protected function getActionOptions(
     PhabricatorUser $viewer,
-    DifferentialRevision $revision) {
+    DifferentialRevision $revision,
+    $include_accepted = false) {
 
     $reviewers = $revision->getReviewers();
 
@@ -98,11 +99,14 @@ final class DifferentialRevisionAcceptTransaction
         }
       }
 
+      if (!$include_accepted) {
         if ($reviewer->isAccepted($diff_phid)) {
           // If a reviewer is already in a full "accepted" state, don't
-        // include that reviewer as an option.
+          // include that reviewer as an option unless we're listing all
+          // reviwers, including reviewers who have already accepted.
           continue;
         }
+      }
 
       $reviewer_phids[$reviewer_phid] = $reviewer_phid;
     }
@@ -185,7 +189,12 @@ final class DifferentialRevisionAcceptTransaction
           'least one reviewer.'));
     }
 
-    list($options) = $this->getActionOptions($actor, $object);
+    // NOTE: We're including reviewers who have already been accepted in this
+    // check. Legitimate users may race one another to accept on behalf of
+    // packages. If we get a form submission which includes a reviewer which
+    // someone has already accepted, that's fine. See T12757.
+
+    list($options) = $this->getActionOptions($actor, $object, true);
     foreach ($value as $phid) {
       if (!isset($options[$phid])) {
         throw new Exception(

src/applications/differential/xaction/DifferentialRevisionReviewTransaction.php

@@ -17,6 +17,16 @@ abstract class DifferentialRevisionReviewTransaction
     $viewer = $this->getActor();
     list($options, $default) = $this->getActionOptions($viewer, $object);
 
+    // Remove reviewers which aren't actionable. In the case of "Accept", we
+    // may allow the transaction to proceed with some reviewers who have
+    // already accepted, to avoid race conditions where two reviewers fill
+    // out the form at the same time and accept on behalf of the same package.
+    // It's okay for these reviewers to survive validation, but they should
+    // not survive beyond this point.
+    $value = array_fuse($value);
+    $value = array_intersect($value, array_keys($options));
+    $value = array_values($value);
+
     sort($default);
     sort($value);