fix #29: track hash changes of branches to avoid cheating

Author: nunoplopes

cron.php

@@ -173,8 +173,10 @@ function run_patch_stats() {
         continue;
       try {
         $oldstatus = $patch->getStatus();
+        $oldhash   = $patch->hash;
         $patch->updateStats();
         $newstatus = $patch->getStatus();
+        $newhash   = $patch->hash;
 
         if ($newstatus != $oldstatus) {
           $patch->comments->add(
@@ -187,9 +189,15 @@ function run_patch_stats() {
                    link_patch($patch));
           echo "Patch $patch->id changed status from $oldstatus to ",
                $newstatus, "\n";
-        } else {
-          echo "Patch $patch->id status unchanged\n";
         }
+
+        if ($newhash != $oldhash) {
+          $patch->comments->add(
+            new PatchComment($patch, "New branch hash: $newhash"));
+          echo "Patch $patch->id changed hash from $oldhash to $newhash\n";
+        }
+        echo "Updated patch $patch->id\n";
+
       } catch (ValidationException $ex) {
         error_ta($group, "Patch $patch->id is broken", <<< EOF
 Cron job failed to process patch $patch->id

entities/GitHub/GitHubPatch.php

@@ -97,6 +97,7 @@ public function commits() : array {
       $commit['name']     = $commit['commit']['author']['name'];
       $commit['email']    = $commit['commit']['author']['email'];
       $commit['message']  = $commit['commit']['message'];
+      $commit['hash']     = $commit['sha'];
 
       $authors = [];
       preg_match_all('/^Co-authored-by: ([^<]+) <([^>]+)>$/Sm',
@@ -111,6 +112,14 @@ public function commits() : array {
     return $commits;
   }
 
+  protected function computeBranchHash() : string {
+    $hash = '';
+    foreach ($this->stats()['commits'] as $commit) {
+      $hash = $commit['sha'];
+    }
+    return $hash;
+  }
+
   protected function computeLinesAdded() : int {
     $add = 0;
     foreach ($this->stats()['files'] as $f) {

entities/Patch.php

@@ -72,6 +72,9 @@ abstract class Patch
   /** @ManyToMany(targetEntity="User") */
   public $students;
 
+  /** @Column(length=64) */
+  public string $hash = '';
+
   /** @Column */
   public int $lines_added;
 
@@ -94,16 +97,17 @@ static function factory(ProjGroup $group, string $url, $type,
     $p->type      = (int)$type;
     $p->issue_url = check_url($issue_url);
 
-    $description = trim($description);
-    $p->comments->add(
-      new PatchComment($p, "Patch submitted\n$description", $submitter));
-
     try {
       $p->updateStats();
     } catch (Exception $ex) {
       throw new ValidationException('Patch not found');
     }
 
+    $description = trim($description);
+    $p->comments->add(
+      new PatchComment($p, "Patch submitted; hash: {$p->hash}\n\n$description",
+                       $submitter));
+
     try {
       if (!$description)
         throw new ValidationException("Empty description");
@@ -154,7 +158,7 @@ static function factory(ProjGroup $group, string $url, $type,
                                             "the end\n$msg");
             }
           }
-      }
+        }
 
         check_reasonable_name($commit['name'], $group);
         check_wrapped_commit_text($msg, 72);
@@ -206,6 +210,7 @@ abstract public function isValid() : bool;
   abstract public function branch() : string;
   abstract public function origin() : string;
   abstract public function commits() : array;
+  abstract protected function computeBranchHash() : string;
   abstract protected function computeLinesAdded() : int;
   abstract protected function computeLinesDeleted() : int;
   abstract protected function computeFilesModified() : int;
@@ -214,6 +219,8 @@ abstract public function setPR(PullRequest $pr);
   abstract public function getPR() : ?PullRequest;
 
   public function updateStats() {
+    $this->hash = $this->computeBranchHash();
+
     if ($pr = $this->getPR()) {
       $legal = $this->status == PATCH_PR_OPEN;
       if ($pr->wasMerged()) {