Reduce visibility of "Host" and "Path" Differential fields by default

Summary:
See discussion in T838. These fields expose information which it isn't necessary
or useful to expose in the general case.

  - Disable fields by default, allow them to be enabled in config (these fields
were useful for me at Facebook when I had access to all the machines).
  - Remove 'sourcePath' from Conduit methods other than differential.query.
  - Condition 'sourcePath' field in Conduit on the caller being the revision
author. This is a bit hacky but not so awful.

Test Plan:
  - Verified fields are gone by default and restored by configuration.
  - Verified Conduit no longer returns these fields other than
differential.query.
  - Verified field presence/absence according to authorship in
differential.query.
  - Grepped around in arcanist to make sure we aren't relying on sourcePath.
There's a workflow in "arc merge" that technically might hit it, but I think
it's unreachable, definitely irrelvant (we never use source path as a
distinguisher under git/hg, and can't 'arc merge' in SVN) and it's going away
Real Soon Now anyway.

Reviewers: btrahan, arice

Reviewed By: arice

CC: aran, epriestley

Maniphest Tasks: T838

Differential Revision: https://secure.phabricator.com/D1582

conf/default.conf.php

@@ -597,6 +597,13 @@ return array(
 
   'differential.field-selector' => 'DifferentialDefaultFieldSelector',
 
+  // Differential can show "Host" and "Path" fields on revisions, with
+  // information about the machine and working directory where the change
+  // came from. These fields are disabled by default because they may
+  // occasionally have sensitive information; you can set this to true to
+  // enable them.
+  'differential.show-host-field'  => false,
+
   // If you set this to true, users can "!accept" revisions via email (normally,
   // they can take other actions but can not "!accept"). This action is disabled
   // by default because email authentication can be configured to be very weak,

src/applications/conduit/method/differential/query/ConduitAPI_differential_query_Method.php

@@ -166,7 +166,7 @@ class ConduitAPI_differential_query_Method extends ConduitAPIMethod {
       }
 
       $id = $revision->getID();
-      $results[] = array(
+      $result = array(
         'id'            => $id,
         'phid'          => $revision->getPHID(),
         'title'         => $revision->getTitle(),
@@ -178,7 +178,6 @@ class ConduitAPI_differential_query_Method extends ConduitAPIMethod {
         'statusName'    =>
           ArcanistDifferentialRevisionStatus::getNameForRevisionStatus(
             $revision->getStatus()),
-        'sourcePath'    => $diff->getSourcePath(),
         'branch'        => $diff->getBranch(),
         'summary'       => $revision->getSummary(),
         'testPlan'      => $revision->getTestPlan(),
@@ -188,6 +187,14 @@ class ConduitAPI_differential_query_Method extends ConduitAPIMethod {
         'reviewers'     => array_values($revision->getReviewers()),
         'ccs'           => array_values($revision->getCCPHIDs()),
       );
+
+      // TODO: This is a hacky way to put permissions on this field until we
+      // have first-class support, see T838.
+      if ($revision->getAuthorPHID() == $request->getUser()->getPHID()) {
+        $result['sourcePath'] = $diff->getSourcePath();
+      }
+
+      $results[] = $result;
     }
 
     return $results;

src/applications/differential/field/selector/default/DifferentialDefaultFieldSelector.php

@@ -20,7 +20,7 @@ final class DifferentialDefaultFieldSelector
   extends DifferentialFieldSelector {
 
   public function getFieldSpecifications() {
-    return array(
+    $fields = array(
       new DifferentialTitleFieldSpecification(),
       new DifferentialSummaryFieldSpecification(),
       new DifferentialTestPlanFieldSpecification(),
@@ -34,13 +34,27 @@ final class DifferentialDefaultFieldSelector
       new DifferentialCommitsFieldSpecification(),
       new DifferentialDependenciesFieldSpecification(),
       new DifferentialManiphestTasksFieldSpecification(),
-      new DifferentialHostFieldSpecification(),
-      new DifferentialPathFieldSpecification(),
-      new DifferentialArcanistProjectFieldSpecification(),
-      new DifferentialApplyPatchFieldSpecification(),
-      new DifferentialRevisionIDFieldSpecification(),
-      new DifferentialGitSVNIDFieldSpecification(),
     );
+
+    if (PhabricatorEnv::getEnvConfig('differential.show-host-field')) {
+      $fields = array_merge(
+        $fields,
+        array(
+          new DifferentialHostFieldSpecification(),
+          new DifferentialPathFieldSpecification(),
+        ));
+    }
+
+    $fields = array_merge(
+      $fields,
+      array(
+        new DifferentialArcanistProjectFieldSpecification(),
+        new DifferentialApplyPatchFieldSpecification(),
+        new DifferentialRevisionIDFieldSpecification(),
+        new DifferentialGitSVNIDFieldSpecification(),
+      ));
+
+    return $fields;
   }
 
 }

src/applications/differential/field/selector/default/__init__.php

@@ -26,6 +26,7 @@ phutil_require_module('phabricator', 'applications/differential/field/specificat
 phutil_require_module('phabricator', 'applications/differential/field/specification/testplan');
 phutil_require_module('phabricator', 'applications/differential/field/specification/title');
 phutil_require_module('phabricator', 'applications/differential/field/specification/unit');
+phutil_require_module('phabricator', 'infrastructure/env');
 
 
 phutil_require_source('DifferentialDefaultFieldSelector.php');

src/applications/differential/storage/diff/DifferentialDiff.php

@@ -160,7 +160,6 @@ class DifferentialDiff extends DifferentialDAO {
       'sourceControlBaseRevision' => $this->getSourceControlBaseRevision(),
       'sourceControlPath' => $this->getSourceControlPath(),
       'sourceControlSystem' => $this->getSourceControlSystem(),
-      'sourcePath' => $this->getSourcePath(),
       'branch' => $this->getBranch(),
       'unitStatus' => $this->getUnitStatus(),
       'lintStatus' => $this->getLintStatus(),