Improve some Spaces behaviors

Summary:
Ref T8449. Try out some more subtle behaviors:

  - Make the "Space" control part of the policy control, so the UI shows "Visible To: [Space][Policy]". I think this helps make the role of spaces more clear. It also makes them easier to implement.
  - Don't show the default space in headers: instead, show nothing.
  - If the user has access to only one space, pretend spaces don't exist (no edit controls, no header stuff).

This might be confusing, but I think most of the time it will all align fairly well with user expectation.

Test Plan:
  - Viewed a list of pastes (saw Space with non-default space, no space with default space, no space with user in only one space).
  - Viewed a paste (saw Space with non-default space, saw no space with default space, saw no space with user in only one space).
  - Edited spaces on objects (control as privileged user, no control as locked user).
  - Created a new paste in a space (got space select as privileged user, no select as locked user).

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8449

Differential Revision: https://secure.phabricator.com/D13229

src/view/form/control/AphrontFormPolicyControl.php

@@ -5,6 +5,7 @@ final class AphrontFormPolicyControl extends AphrontFormControl {
   private $object;
   private $capability;
   private $policies;
+  private $spacePHID;
 
   public function setPolicyObject(PhabricatorPolicyInterface $object) {
     $this->object = $object;
@@ -17,6 +18,15 @@ final class AphrontFormPolicyControl extends AphrontFormControl {
     return $this;
   }
 
+  public function setSpacePHID($space_phid) {
+    $this->spacePHID = $space_phid;
+    return $this;
+  }
+
+  public function getSpacePHID() {
+    return $this->spacePHID;
+  }
+
   public function setCapability($capability) {
     $this->capability = $capability;
 
@@ -187,11 +197,14 @@ final class AphrontFormPolicyControl extends AphrontFormControl {
     $selected_icon = idx($selected, 'icon');
     $selected_name = idx($selected, 'name');
 
+    $spaces_control = $this->buildSpacesControl();
+
     return phutil_tag(
       'div',
       array(
       ),
       array(
+        $spaces_control,
         javelin_tag(
           'a',
           array(
@@ -231,4 +244,48 @@ final class AphrontFormPolicyControl extends AphrontFormControl {
     return 'custom:placeholder';
   }
 
+  private function buildSpacesControl() {
+    if ($this->capability != PhabricatorPolicyCapability::CAN_VIEW) {
+      return null;
+    }
+
+    if (!($this->object instanceof PhabricatorSpacesInterface)) {
+      return null;
+    }
+
+    $viewer = $this->getUser();
+    if (!PhabricatorSpacesNamespaceQuery::getViewerSpacesExist($viewer)) {
+      return null;
+    }
+
+    $space_phid = $this->getSpacePHID();
+    if ($space_phid === null) {
+      $space_phid = $viewer->getDefaultSpacePHID();
+    }
+
+    $select = AphrontFormSelectControl::renderSelectTag(
+      $space_phid,
+      $this->getSpaceOptions(),
+      array(
+        'name' => 'spacePHID',
+      ));
+
+    return $select;
+  }
+
+  protected function getSpaceOptions() {
+    $viewer = $this->getUser();
+    $viewer_spaces = PhabricatorSpacesNamespaceQuery::getViewerSpaces($viewer);
+
+    $map = array();
+    foreach ($viewer_spaces as $space) {
+      $map[$space->getPHID()] = pht(
+        'Space %s: %s',
+        $space->getMonogram(),
+        $space->getNamespaceName());
+    }
+    asort($map);
+
+    return $map;
+  }
 }