Do the heavy lifting for git commit hooks

Summary:
Ref T4189. This doesn't add any rules yet, but does all the heavy lifting to figure out what's changed and put it in a consuamble (if somewhat ad-hoc) datastructure, which lists all the ref and tag modifications and all the new commits in a consistent way.

From here, it should be fairly straightforward to add top-level rules (e.g., ff pushes only).

Test Plan: Output is huge, see comments.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4189

Differential Revision: https://secure.phabricator.com/D7687

src/applications/diffusion/engine/DiffusionCommitHookEngine.php

@@ -61,14 +61,128 @@ final class DiffusionCommitHookEngine extends Phobject {
     return $err;
   }
 
+  /**
+   * @task git
+   */
   private function executeGitHook() {
     $updates = $this->parseGitUpdates($this->getStdin());
 
-    // TODO: Do useful things.
+    // TODO: Do cheap checks: non-ff commits, mutating refs without access,
+    // creating or deleting things you can't touch. We can do all non-content
+    // checks here.
+
+    $updates = $this->findGitNewCommits($updates);
+
+    // TODO: Now, do content checks.
 
     return 0;
   }
 
+
+  /**
+   * @task git
+   */
+  private function parseGitUpdates($stdin) {
+    $updates = array();
+
+    $lines = phutil_split_lines($stdin, $retain_endings = false);
+    foreach ($lines as $line) {
+      $parts = explode(' ', $line, 3);
+      if (count($parts) != 3) {
+        throw new Exception(pht('Expected "old new ref", got "%s".', $line));
+      }
+      $update = array(
+        'old' => $parts[0],
+        'old.short' => substr($parts[0], 0, 8),
+        'new' => $parts[1],
+        'new.short' => substr($parts[1], 0, 8),
+        'ref' => $parts[2],
+      );
+
+      if (preg_match('(^refs/heads/)', $update['ref'])) {
+        $update['type'] = 'branch';
+      } else if (preg_match('(^refs/tags/)', $update['ref'])) {
+        $update['type'] = 'tag';
+      } else {
+        $update['type'] = 'unknown';
+      }
+
+      $updates[] = $update;
+    }
+
+    $updates = $this->findGitMergeBases($updates);
+
+    return $updates;
+  }
+
+
+  /**
+   * @task git
+   */
+  private function findGitMergeBases(array $updates) {
+    $empty = str_repeat('0', 40);
+
+    $futures = array();
+    foreach ($updates as $key => $update) {
+      // Updates are in the form:
+      //
+      //   <old hash> <new hash> <ref>
+      //
+      // If the old hash is "00000...", the ref is being created (either a new
+      // branch, or a new tag). If the new hash is "00000...", the ref is being
+      // deleted. If both are nonempty, the ref is being updated. For updates,
+      // we'll figure out the `merge-base` of the old and new objects here. This
+      // lets us reject non-FF changes cheaply; later, we'll figure out exactly
+      // which commits are new.
+
+      if ($update['old'] == $empty) {
+        $updates[$key]['operation'] = 'create';
+      } else if ($update['new'] == $empty) {
+        $updates[$key]['operation'] = 'delete';
+      } else {
+        $updates[$key]['operation'] = 'update';
+        $futures[$key] = $this->getRepository()->getLocalCommandFuture(
+          'merge-base %s %s',
+          $update['old'],
+          $update['new']);
+      }
+    }
+
+    foreach (Futures($futures)->limit(8) as $key => $future) {
+      list($stdout) = $future->resolvex();
+      $updates[$key]['merge-base'] = rtrim($stdout, "\n");
+    }
+
+    return $updates;
+  }
+
+  private function findGitNewCommits(array $updates) {
+    $futures = array();
+    foreach ($updates as $key => $update) {
+      if ($update['type'] == 'delete') {
+        // Deleting a branch or tag can never create any new commits.
+        continue;
+      }
+
+      // NOTE: This piece of magic finds all new commits, by walking backward
+      // from the new value to the value of *any* existing ref in the
+      // repository. Particularly, this will cover the cases of a new branch, a
+      // completely moved tag, etc.
+      $futures[$key] = $this->getRepository()->getLocalCommandFuture(
+        'log --format=%s %s --not --all',
+        '%H',
+        $update['new']);
+    }
+
+    foreach (Futures($futures)->limit(8) as $key => $future) {
+      list($stdout) = $future->resolvex();
+      $commits = phutil_split_lines($stdout, $retain_newlines = false);
+      $updates[$key]['commits'] = $commits;
+    }
+
+    return $updates;
+  }
+
   private function executeSubversionHook() {
 
     // TODO: Do useful things here, too.
@@ -82,24 +196,4 @@ final class DiffusionCommitHookEngine extends Phobject {
 
     return 0;
   }
-
-  private function parseGitUpdates($stdin) {
-    $updates = array();
-
-    $lines = phutil_split_lines($stdin, $retain_endings = false);
-    foreach ($lines as $line) {
-      $parts = explode(' ', $line, 3);
-      if (count($parts) != 3) {
-        throw new Exception(pht('Expected "old new ref", got "%s".', $line));
-      }
-      $updates[] = array(
-        'old' => $parts[0],
-        'new' => $parts[1],
-        'ref' => $parts[2],
-      );
-    }
-
-    return $updates;
-  }
-
 }