Add a Herald pre-commit field for detecting LFS usage

Summary: Depends on D18825. Ref T7789. See PHI131. Allows installs to selectively disable LFS by adding Herald rules to block commits that use LFS.

Test Plan:
  - Wrote an LFS rule ("When commit uses git lfs, block commit").
  - Pushed an LFS commit: rejected.
  - Pushed a non-lFS commit: success.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T7789

Differential Revision: https://secure.phabricator.com/D18827

src/__phutil_library_map__.php

@@ -821,6 +821,7 @@ phutil_register_library_map(array(
     'DiffusionPreCommitRefRepositoryHeraldField' => 'applications/diffusion/herald/DiffusionPreCommitRefRepositoryHeraldField.php',
     'DiffusionPreCommitRefRepositoryProjectsHeraldField' => 'applications/diffusion/herald/DiffusionPreCommitRefRepositoryProjectsHeraldField.php',
     'DiffusionPreCommitRefTypeHeraldField' => 'applications/diffusion/herald/DiffusionPreCommitRefTypeHeraldField.php',
+    'DiffusionPreCommitUsesGitLFSHeraldField' => 'applications/diffusion/herald/DiffusionPreCommitUsesGitLFSHeraldField.php',
     'DiffusionPullEventGarbageCollector' => 'applications/diffusion/garbagecollector/DiffusionPullEventGarbageCollector.php',
     'DiffusionPushCapability' => 'applications/diffusion/capability/DiffusionPushCapability.php',
     'DiffusionPushEventViewController' => 'applications/diffusion/controller/DiffusionPushEventViewController.php',
@@ -5881,6 +5882,7 @@ phutil_register_library_map(array(
     'DiffusionPreCommitRefRepositoryHeraldField' => 'DiffusionPreCommitRefHeraldField',
     'DiffusionPreCommitRefRepositoryProjectsHeraldField' => 'DiffusionPreCommitRefHeraldField',
     'DiffusionPreCommitRefTypeHeraldField' => 'DiffusionPreCommitRefHeraldField',
+    'DiffusionPreCommitUsesGitLFSHeraldField' => 'DiffusionPreCommitContentHeraldField',
     'DiffusionPullEventGarbageCollector' => 'PhabricatorGarbageCollector',
     'DiffusionPushCapability' => 'PhabricatorPolicyCapability',
     'DiffusionPushEventViewController' => 'DiffusionPushLogController',

src/applications/diffusion/herald/DiffusionPreCommitUsesGitLFSHeraldField.php

@@ -0,0 +1,41 @@
+<?php
+
+final class DiffusionPreCommitUsesGitLFSHeraldField
+  extends DiffusionPreCommitContentHeraldField {
+
+  const FIELDCONST = 'diffusion.pre.commit.git-lfs';
+
+  public function getHeraldFieldName() {
+    return pht('Commit uses Git LFS');
+  }
+
+  public function getFieldGroupKey() {
+    return DiffusionChangeHeraldFieldGroup::FIELDGROUPKEY;
+  }
+
+  public function getHeraldFieldValue($object) {
+    $map = $this->getAdapter()->getDiffContent('+');
+
+    // At the time of writing, all current Git LFS files begin with this
+    // line, verbatim:
+    //
+    //   version https://git-lfs.github.com/spec/v1
+    //
+    // ...but we don't try to match the specific version here, in the hopes
+    // that this might also detect future versions.
+    $pattern = '(^version\s*https://git-lfs.github.com/spec/)i';
+
+    foreach ($map as $path => $content) {
+      if (preg_match($pattern, $content)) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  protected function getHeraldFieldStandardType() {
+    return self::STANDARD_BOOL;
+  }
+
+}