Use active project filter as default field value when creating new tasks

Summary: See T389. If you're looking at tasks in project X, default new tasks
into project X.
Test Plan:
  - Created a new task without associated projects.
  - Created a new task from a filter view with 1 and 2 projects; defaults were
filled in.
  - Submitted task with invalid title, projects were correctly preserved.

Reviewed By: skrul
Reviewers: skrul, hunterbridges, jungejason, tuomaspelkonen, aran
CC: aran, skrul, epriestley
Differential Revision: 757

src/applications/maniphest/controller/taskedit/ManiphestTaskEditController.php

@@ -47,6 +47,11 @@ class ManiphestTaskEditController extends ManiphestController {
       // These allow task creation with defaults.
       if (!$request->isFormPost()) {
         $task->setTitle($request->getStr('title'));
+
+        $default_projects = $request->getStr('projects');
+        if ($default_projects) {
+          $task->setProjectPHIDs(explode(';', $default_projects));
+        }
       }
 
       $file_phids = $request->getArr('files', array());

src/applications/maniphest/controller/tasklist/ManiphestTaskListController.php

@@ -176,12 +176,19 @@ class ManiphestTaskListController extends ManiphestController {
       id(new AphrontFormSubmitControl())
         ->setValue('Filter Tasks'));
 
+    $create_uri = new PhutilURI('/maniphest/task/create/');
+    if ($project_phids) {
+      // If we have project filters selected, use them as defaults for task
+      // creation.
+      $create_uri->setQueryParam('projects', implode(';', $project_phids));
+    }
+
     $filter = new AphrontListFilterView();
     $filter->addButton(
       phutil_render_tag(
         'a',
         array(
-          'href' => '/maniphest/task/create/',
+          'href'  => (string)$create_uri,
           'class' => 'green button',
         ),
         'Create New Task'));

src/applications/maniphest/controller/tasklist/__init__.php

@@ -23,6 +23,7 @@ phutil_require_module('phabricator', 'view/layout/listfilter');
 phutil_require_module('phabricator', 'view/layout/sidenav');
 
 phutil_require_module('phutil', 'markup');
+phutil_require_module('phutil', 'parser/uri');
 phutil_require_module('phutil', 'utils');